# # Pediatric Critical Care Review Hasan Pappas

86. Closing capacity is the sum of residual volume and closing volume. An increase in closing capacity leads to a situation where lung volume is so much reduced below functional residual capacity that small alveoli and airways in the dependent regions of the lungs are closed. Which of the following conditions is least likely to lead to elevation of closing capacity: A. Infancy B. Bronchiolitis C. Cystic fibrosis D. Asthma E. Pulmonary edema Click here for answer 87. In conditions associated with increased closing capacity, the most appropriate therapeutic intervention includes: A. Increase residual volume B. Control pulmonary secretions and use of bronchodilators C. Use of CPAP D. Use of PEEP when on mechanical ventilation Click here for answer 88. The Ventilation/Perfusion (V/Q) ratio remains stable as one moves from the base of the lung up to the third rib, but then as one moves towards the apex, the V/Q ratio changes exponentially because: A. Blood flow falls more rapidly than ventilation with distance up the lung B. Ventilation increases more rapidly down the lungs than perfusion C. Both ventilation and perfusion increase exponentially down the lungs D. Ventilation decreases linearly but perfusion exponentially down the lungs Click here for answer 89. Regarding the compliance and resistance of the ventilatory circuits and their interaction with the patient, which of the following statements is most accurate: A. If the compliance of the ventilator circuit and the patient are equal, adequate delivery of tidal volume to the patient is assured B. Large circuit compliance leads to delay in the delivery of an assisted breath C. Use of rigid short tubing aggravates loss of tidal volume D. Distribution of volume delivered by a positive pressure ventilator between the ventilator circuit and the patient is determined entirely by the patient’s respiratory compliance and resistance Click here for answer 90. Modifications of ventilator circuiting for pediatric mechanical ventilators, in order to substantially reduce the ventilator system compliance, include all of the following except: A. Small diameter circuit tubing B. Rigid tubing with inspiratory circuit as short as possible C. Decreasing humidifier size D. Positioning of exhalation valve away from the airway opening E. Maintaining humidifier fluid level Click here for answer 91. The most common clinical application of hyperbaric O2 therapy is: A. Carbon monoxide poisoning B. Decompression sickness C. Gas embolism D. Radiation necrosis E. Crush injury Click here for answer 92. Use of hyperbaric O2 therapy for carbon monoxide poisoning is probably the most common application of this technology. All of the following statements regarding this application are true except: A. The beneficial effect of hyperbaric O2 therapy is directly related to the associated increase in PaO2 B. The half-life of carbon monoxide as measured by carboxy-hemoglobin is decreased to 53 minutes at 3 atmospheric pressure C. Hyperbaric O2 therapy helps reverse binding of carbon monoxide to cytochrome a3 D. Hyperbaric O2 therapy is indicated in patients who suffer unconsciousness or display signs of CNS depression Click here for answer 93. The least likely complication of hyperbaric oxygen therapy is: A. Tympanic membrane perforation B. Pneumomediastinum C. Fire and ignition accidents D. Significant central nervous system toxicity at 2.5 atm pressure Click here for answer 94. Helium is a low density gas that, when used in combination with O2, has proven particularly useful. All of the following statements are true except: A. The use of helium/O2 mixture is not feasible in patients requiring higher than 0.4 FiO2 B. Helium/O2 mixture may improve gas exchange and decrease peak inspiratory pressure in asthmatics requiring ventilatory support C. In children with large airway obstruction helium/O2 mixture improves alveolar O2 component D. Helium/O2 mixture decreases work of breathing E. Helium/O2 mixture can not be used in patients whose airway has been instrumented Click here for answer 95. A 6 kg infant with pneumonia is being ventilated with conventional mechanical ventilation at a rate of 35 bpm on an FiO2 of 0.6. The peak inspiratory pressure is 32 cm H2O and positive end-expiratory pressure is 6cm H2O. The inspiratory time is set at 0.5 seconds and the flow of gas through the ventilator circuit is set at 8 liters/min. The approximate tidal volume is: A. 11 ml/kg B. 5 ml/kg C. 7 ml/kg D. 9 ml/kg E. None of the above Click here for answer 96. Most of gas exchange during mechanical ventilation with a normal I:E ratio occurs during: A. Inspiration B. The inspiratory plateau C. Exhalation D. Gas exchange is uniform throughout the respiratory cycle Click here for answer 97. Time-limited, constant-flow ventilators are one category of ventilators that are sometimes used in the Pediatric ICU. True statements pertaining to this category of ventilators include all of the following except: A. Use is restricted to the asynchronous mode B. Tidal volume can only be estimated C. Inspiratory flow limits of these ventilators do not provide adequate flow for patients weighing in excess of 15 kg D. The peak inspiratory pressure relief valve is housed in the inspiratory circuit in these ventilators Click here for answer 98. In the assist-control mode of mechanical ventilation: A. A pre-set tidal volume is delivered in response to every patient-initiated effort B. The patient must perform inspiratory work to open the inspiratory valve and initiate each tidal volume C. Ventilator trigger sensitivity and peak inspiratory flow are controlled by the operator D. Ventilator peak inspiratory flow and trigger sensitivity affect work of breathing E. All of the above Click here for answer 99. Intermittent mandatory ventilation allows spontaneous breathing between positive pressure breaths with a pre-set tidal volume and frequency. Which one of the following statements least accurately describes intermittent mandatory ventilation: A. To minimize work of breathing, the inspiratory gas flow in continuous flow circuit should not exceed the patient’s own peak inspiratory flow rate B. A flow-by system avoids problems associated with continuous flow and demand flow systems in terms of work of breathing C. Intermittent mandatory ventilation is likely to be associated with more stable hemodynamics compared to continuous mandatory ventilation D. Intermittent mandatory ventilation is more likely to be associated with improved V/Q matching compared to continuous mandatory ventilation E. The need for frequent administration of sedatives and/or muscle relaxants seems to be decreased by using intermittent mandatory ventilation compared to continuous mandatory ventilation Click here for answer 100. In describing pressure support ventilation, which one of the following options is least accurate: A. The ventilator retains control of the cycle length as well as the depth and flow characteristics B. It has been shown to abolish diaphragmatic muscle fatigue in patients who fail conventional weaning attempts C. Pressure support ventilation helps compensate for work of breathing due to the inspiratory demand valve and endotracheal tube impedance D. Patient effort, length of pressure support and the respiratory system impedance determine the tidal volume Click here for answer 101. Inverse-ratio ventilation is performed using: A. Pressure-limited breaths with decelerating inspiratory flow rates and adjustment of inspiratory time to the desired level B. Volume-limited breaths with low inspiratory flow rates to achieve the desired inspiratory time C. Volume-limited breaths with normal inspiratory flow rate and prolonged inspiratory pause to maintain a prolonged inspiratory phase D. All of the above Click here for answer 102. During pressure-control inverse-ratio ventilation, tidal volume is a function of: A. Respiratory system compliance and resistance B. The pre-set pressure limit C. The ratio of inspiratory time to total duty cycle D. Frequency E. All of the above Click here for answer 103. Positive pressure ventilatory support in the setting of respiratory failure is aimed at elevating the functional residual capacity or mean lung volume through the application of continuous positive airway pressure (CPAP) or positive end expiratory pressure (PEEP). Appropriate statements pertaining to this application include all of the following except: A. Application of appropriate levels of PEEP/CPAP can decrease work of breathing B. High levels of PEEP have the potential to increase work of breathing C. The decrease in oxygen delivery associated with high levels of PEEP is often resistant to fluid resuscitation and inotropic support D. In the absence of pulmonary artery catheter, PEEP should be gradually increased to maintain an A-a gradient < 250 torr with adequate perfusion E. As a general rule, a pulmonary artery catheter is recommended to monitor cardiac output when PEEP of > 15 cm is used Click here for answer 104. When deciding to discharge a patient home who is ventilator dependent, the least important factor to consider is: A. Presence of an established tracheostomy with healed stoma B. PaO2 > 60 torr with FiO2 < 0.3 and PaCO2 < 50 torr using home ventilatory settings C. No need for PEEP D. The underlying disease E. Stabile ventilatory settings for one month Click here for answer 105. Adverse hemodynamic effects of PEEP are related to: A. Decreased venous return B. Ventricular interdependence C. Increased RV afterload D. Reflex neurohormonal factors leading to ventricular dysfunction E. All of the above Click here for answer 106. Barotrauma is a recognized complication of mechanical ventilatory support and has a number of clinical manifestations. Which of the following is always considered clinically significant: A. Pulmonary interstitial emphysema B. Pneumomediastinum C. Subcutaneous emphysema D. Pneumoperitoneum E. None of the above Click here for answer 107. Tension pneumothorax is a life-threatening complication of trauma or positive pressure ventilation that requires immediate intervention. True statements regarding tension pneumothorax include all of the following except: A. Tension pneumothorax occurs when a communication exists between the pleural space and either the alveoli or the atmosphere, so that air enters the pleural space during inspiration but is unable to exit during exhalation B. Tension pneumothorax occurs when intrapleural pressure continues to remain subatmospheric C. Obstruction of venous return occurs D. Treatment is by closed chest thoracotomy tube Click here for answer 108. Features of veno-venous extra-corporeal life support include all of the following except: A. It depends on patient’s native heart for O2 delivery to tissue B. Usually requires lower extracorporeal flow C. It reduces the risk of embolization with an intact heart D. It maintains well oxygenated pulmonary blood flow E. It requires the right ventricle to work unremittingly in the face of pulmonary hypertension Click here for answer A. Veno-arterial extra-corporeal life support B. Veno-venous extra-corporeal life support C. Both D. Neither 109. ____ Maintain(s) pulmonary blood flow with oxygenated blood ____ Assist(s) systemic circulation ____ Decrease(s) pulmonary artery pressure Click here for answer 110. Which of the following equations best describes the O2 saturation that is obtained using the pulse oximetry? A. = HbO2 / HbO2 + Hb + HbCO + Hb met B. = HbO2 / Hb C. = HbO2 / HbO2 + Hb D. = HbO2 + Hb / HbO2 Click here for answer 111. You have made a diagnosis of nitrite poisoning and decide to administer methylene blue intravenously at a dose of 1 mg/kg over few minutes. As the nurse is injecting the methylene blue, you notice that the saturation on pulse oximetry decreases precipitously from 99% to 85%. The most likely explanation and the appropriate course of action is: A. Shock with hypotension; stop the medication B. Formation of carboxyhemoglobin C. Methylene blue is misinterpreted by the pulse oximeter as reduced hemoglobin resulting in a low saturation; this should resolve in two minutes without any intervention D. None of the above Click here for answer A. Carboxy hemoglobin B. Hemoglobin C. Oxyhemoglobin 112. ____ High level of this compound leads to a low fractional saturation but relatively high functional saturation. Click here for answer 113. Which of the following is least likely to interfere with an accurate reading of saturation on pulse oximetry? A. High levels of HbCO B. High levels of met Hb C. An external light source such as a surgical lamp, bilirubin lamps or fluorescent lights D. Hyperbilirubinemia E. Shock with low perfusion states Click here for answer 114. Which of the following clinical conditions is not associated with a low mixed venous oxygen saturation: A. Low Hb B. Low arterial oxygen saturation C. Low cardiac output D. Increased O2 delivery E. Increased O2 consumption Click here for answer 115. Which of the following clinical conditions is not associated with a high mixed venous oxygen saturation: A. Increased O2 delivery B. Decreased O2 extraction by the tissue C. Severe mitral regurgitation D. A wedged pulmonary artery catheter E. Increased O2 consumption Click here for answer 116. The above figure represents the capnogram obtained from a patient on SIMV mode of mechanical ventilation and a ventilator with a demand valve mechanism. The best course of action would be: A. Substitute the neuromuscular blockade agent used with a non-depolarizing agent B. Calm the patient and reassure him C. Add a bronchodilator and intravenous corticosteroid D. Add 20 cm H2O of pressure support E. None of the above, as this represents a normal variation of capnography Click here for answer 117. Which one of the clinical conditions listed below is not expected to be associated with a sudden decline in end tidal CO2: A. Cardiac standstill B. Air embolism C. Obstruction of the endotracheal tube D. Leakage in the circuit or discontinuation of the ventilator suddenly E. Hypoventilation Click here for answer 118. You are preparing to draw an arterial blood gas sample from a patient in the Pediatric ICU. In discussing with your medical students, the technical errors associated with this process, which one of the following statements would you not make: A. A gas bubble in the syringe will falsely elevate PaCO2 B. The major blood gas error associated with excess heparin in the sample is a drop in PaCO2 C. When a sample that is obtained from a patient breathing room air is interfaced with a bubble, the PaO2 obtained will be close to 150 torr D. In a patient on high FiO2 with normal lungs, the presence of an air bubble in the syringe may spuriously lower PaO2 Click here for answer 119. Alterations in blood gas values occur if the sample is not immediately analyzed leading to spurious results; generally this effect is most noticeable in patients with: A. Hyponatremia and hypercalcemia B. Leukopenia C. Neutropenia D. Leukocytosis and reticulocytopenia E. Reticulocytosis with high band forms Click here for answer 120. Which one of the following drugs leads to a high anion gap metabolic acidosis: A. Acetazolamide B. Aldactone C. Arginine HCL D. Aspirin E. Cholestyramine and Sulfamylon Click here for answer 121. Which of the following is not a characteristic feature of posterior choanal atresia: A. Clinical symptoms have been noted to persist after surgical correction in some infants B. Most cases are unilateral C. Has a familiar occurrence D. Other associated anomalies are extremely uncommon Click here for answer 122. Nasal encephalocele is a recognized cause of nasal obstruction in children. Which one of the following statements does not accurately describe this condition: A. Usually communicates with the subarachnoid space B. May be seen as a nasofrontal or a nasoethmoidal mass C. The mass is soft, compressible and may be pulsatile, but biopsy is contraindicated D. Nasal obstruction does not occur when the mass is located at the base of skull Click here for answer 123. Nasopharyngeal angiofibromas A. May extend to the nasal passages and cause obstruction B. Tend to cause symptoms typically at puberty C. Rhinorrhea and epistaxis are common symptoms D. Treatment is radiation therapy or surgery E. All of the above Click here for answer A. Infant B. Adult C. Both D. Neither 124. ____ Vocal cords are concave and at an angle to the trachea ____ The main bronchi branch from the trachea at equal angles ____ The glottis is located at C6 ____ The tracheal length from glottis to bifurcation is 11 cm Click here for answer 125. The true statement regarding the pediatric airway is: A. The lateral diameter of the newborn glottis is 10 mm B. At birth, the trachea is approximately 10 cm in length C. At 4-6 months, the epiglottis loses contact with the soft palate and becomes more erect D. The glottis assumes the adult location at the level of the 6th cervical vertebra by 6 years of age Click here for answer 126. During spontaneous respirations, the major contribution to total respiratory resistance is by: A. Nasal airway and mouth B. Glottis C. Trachea D. Bronchi Click here for answer 127. A child with an airway that has a diameter of 8 mm develops a respiratory infection with airway inflammation and circumferential edema which leads to a 1 mm uniform reduction in the size of the airway; this will decrease the cross-sectional area of the airway by: A. 34% B. 44% C. 56% D. 64% E. 74% Click here for answer 128. Laryngospasm is induced by reflexes in the nose, oropharynx, epiglottis and vocal cords and may be seen in response to mucous, saliva, emesis or blood. It necessitates immediate interventions which may include: A. Positive pressure ventilation by a mask B. Removal of the offending agent C. Elevation of the mandible D. Use of a muscle relaxant E. All of the above Click here for answer 129. In children younger than 2-1/2 years with chronic stridor, the most common etiology is: A. Infection of the larynx and surrounding structures B. Congenital anomalies of the larynx C. Foreign body aspiration D. Trauma Click here for answer 130. Laryngomalacia is characterized by all of the following except: A. It is the most common congenital laryngeal anomaly B. Aryepiglottic folds fall into the glottis on inspiration C. Voice is hoarse leading to abnormal cry D. Resolves by 18-24 months E. Tracheostomy may be required if the problem interferes with feeding and growth Click here for answer 131. All of the following congenital abnormalities lead to abnormal cry and hoarseness of voice except: A. Laryngocele B. Laryngeal web C. Laryngomalacia D. Laryngeal cyst E. Laryngotracheoesophageal cleft Click here for answer A. Laryngomalacia B. Airway hemangioma C. Both D. Neither 132. ____ Symptoms usually occur before six months of age ____ Treatment is conservative, since most cases resolve by two years of age Click here for answer 133. Syndromes associated with difficult airway management due to micrognathia is/are: A. Hallermann-Streiff Syndrome (Occulomandibulodyscephaly) B. Mobius Syndrome C. Noonan’s Syndrome D. DiGeorge Syndrome E. All of the above Click here for answer 134. Post-operative complications associated with cleft lip/palate repair include: A. Edema leading to nasopharyngeal obstruction B. Nasopharyngeal blockage from secretions C. Laryngospasm from excessive secretion and bloody drainage D. All of the above Click here for answer 135. Macroglossia with a short neck combine to produce a difficult airway in which of the following clinical disorders: A. Hurler’s Syndrome B. Scheie’s Syndrome C. Both D. Neither Click here for answer 136. A difficult airway due to a short and rigid neck is seen in: A. Hurler’s and Marqio’s mucopolysaccharidoses B. Klippel-Feil Syndrome C. Myositis ossificans D. Ankylosing spondylitis E. All of the above Click here for answer 137. A 2-1/2 year old white male who has a 2-day history of an upper respiratory tract infection and fever, is now having mild stridor and dysphagia. His immunizations are up to date. You suspect retropharyngeal abscess. Which one of the following statements is incorrect regarding this patient: A. Age of the patient is somewhat atypical B. Inspiratory radiograph films are more informative than expiratory films C. A chest radiograph should be obtained to evaluate mediastinal extension D. The retropharyngeal space extends from the base of the skull to the level of the 2nd thoracic vertebra E. The usual organisms are staphylococci, group A streptococci and anaerobes Click here for answer 138. A 3-year-old is admitted to the Pediatric ICU with a diagnosis of bacterial tracheitis. True statements regarding this condition include all of the following except: A. Diagnosis is confirmed by thick purulent secretions suctioned from the trachea or the presence of a pseudomembrane, or ulcerations intratracheally B. Intermittent tracheal suctioning should be avoided C. Intubation may be required in cases of severe airway obstruction D. Repeated bronchoscopy aids secretion removal and assessment of disease progression E. Extubation criteria include lack of fever, presence of air leak around the tube, signs of healing at bronchoscopy and a decreased need for suctioning Click here for answer 139. A 2-1/2 year old with viral croup required intubation for increasing CO2 and acidemia three days ago. Extubation is recommended when: A. An air leak around the tube can be heard with coughing B. An air leak around the tube can be heard with a positive pressure insufflation of < 40 cm H20 C. The amount of endotracheal secretions has diminished D. All of the above Click here for answer 140. With regard to orofacial trauma caused by external forces, all of the following statements are true except: A. Nasotracheal intubation should be avoided with midfacial fractures B. Provided the cervical spine is stable, hemorrhage at the base of the tongue should be managed by having the patient in the prone or lateral position with the head down to allow drainage of blood C. A skateboard-associated injury to the neck usually involves an area of soft tissue and an underlying skeletal injury D. The amount of subcutaneous emphysema of the neck correlates with the severity of airway injury Click here for answer 141. In children with acquired subglottic stenosis, the most common etiology is: A. Endotracheal intubation B. External neck trauma C. Burns D. High tracheostomy sites E. Tumors Click here for answer 142. Among the risk factors for the development of subglottic stenosis is the duration of mechanical ventilation. The acceptable time for the duration of intubation is: A. 2 days B. 4 days C. 7 days D. 10 days E. None of the above Click here for answer 143. With regard to thermal and chemical injuries to the head and neck region, all of the following statements are true except: A. If there are flame burns of the face or singed facial hairs, the temperature is high enough to result in a respiratory burn B. Thermal injury usually affects the nasopharynx and larynx C. A child with a history of caustic ingestion requires examination of the larynx D. Helium-O2 has not been shown to be effective in the management of post-extubation stridor in burn victims Click here for answer 144. Papillomas are the most common airway tumors in children with symptoms usually appearing before age 7. True statements about papillomas include all of the following except: A. Most commonly located on vocal cords B. Initial symptoms involve a change in voice such as stridor C. Often these children have personality changes D. The natural history is life-long recurrence E. The goal of therapy is to remove most of the lesions to prevent spreading, while preserving airway anatomy Click here for answer 145. The predominant pathophysiologic abnormality leading to hypoxemia in bronchiolitis due to respiratory syncytial virus infection is: A. Ventilation/perfusion mismatch B. Right-to-left intrapulmonary shunting C. Hypoventilation with relative alveolar hypoxemia D. Diffusion barrier E. All of the above Click here for answer 146. A 5-month-old with severe respiratory syncytial virus bronchiolitis is noted to be slightly edematous with puffiness of the periorbital area and low urine output. Past medical history is unremarkable for prematurity or other perinatal disorders. It is also negative for any liver or kidney diseases. Physical examination does not reveal evidence of hepatomegaly or pronounced component of the second heart sound. Laboratory data shows that serum electrolytes are within normal limits. The most likely explanation for this finding is: A. Hypoalbuminemia B. Hyponatremia with low urine Na+ C. Congestive heart failure due to cor pulmonale D. High anti-diuretic hormone levels with hyperaldosteronism E. None of the above Click here for answer 147. Evaluation of urine for the patient in the previous question will most likely show: A. Low urine Na+ B. High urine Na+ C. Normal urine Na+ D. Any of the above Click here for answer 148. In acute asthma, which one of the following demonstrates the most severe decrease: A. Maximum mid-expiratory flow rate B. Mean expiratory forced reserve C. Functional vital capacity D. Forced expiratory volume 1.0 (FEV1.0) Click here for answer 149. After treatment of an acute attack of asthma, which of the following is least likely to improve: A. Maximum mid-expiratory flow rate B. Mean expiratory forced reserve C. Functional vital capacity D. Forced expiratory volume 1.0 (FEV1.0) Click here for answer 150. Which one of the following parameters is least likely to decrease during an acute attack of asthma: A. Inspiratory capacity B. Vital capacity C. Expiratory reserve volume D. Maximum expiratory flow rate E. Residual volume Click here for answer 151. Pathophysiologic changes that occur in an acute episode of asthma include all of the following except: A. Hypocapnia is caused by alveolar hyperventilation secondary to activation of pulmonary reflexes B. Hypocapnia correlates with the degree of airway obstruction C. The degree of hyperoxia correlates well with the degree of airway obstruction as measured by FEV1.0 D. Elevated PaCO2 occurs when (FEV1.0) falls below 20% predicted E. Elevated PaCO2 is not seen if peak expiratory flow rate is > 25% predicted Click here for answer 152. True statements regarding an acute asthmatic attack include: A. Left ventricular afterload is advantageously lowered by the significantly negative intrathoracic pressure with inspiration B. A decrease in pulsus paradoxus always indicates an improvement in the patient’s clinical condition C. Hypocapnia seen in the early stages of an attack correlates with the degree of airway obstruction D. Pulsus paradoxus is due to a combination of increased left ventricular afterload and ventricular interdependence during inspiration E. None of the above Click here for answer 153. Hypoxemia during status asthmaticus results from: A. Ventilation/perfusion mismatch B. Increased O2 requirement C. Increased interstitial lung fluid D. All of the above Click here for answer 154. FEV1.0 is an important parameter in the evaluation of a patient in status asthmaticus because of all of the following, except: A. FEV1.0 correlates with PaO2 B. FEV1.0 inversely correlates with PaCO2 C. PaCO2 elevation occurs when FEV1.0 falls below 20% predicted D. Pulsus paradoxus is present in all patients with an FEV1.0 less than 20% predicted Click here for answer 155. At an FEV1.0 < 20% predicted: A. PaCO2 rises B. Hypoxemia occurs C. Pulsus paradoxus is present in all patients D. All of the above Click here for answer 156. A 3-year-old boy developed acute airway obstruction possibly secondary to pneumococcal epiglottitis at home. An emergency cricothyrotomy was performed using a 16-gauge angiocath, which was connected to a size 3.0 endotracheal tube adapter. Oxygen is delivered at a rate of 4 liters/min from an E-cylinder. The pressure gauge reading on the E-cylinder is at 1100 PSI. The transport team leader asks you, “How much time do we have before we run out of O2?” (The cylinder factor for the E-cylinder is 0.3 liters / PSI) Your answer should be: A. 8.2 minutes B. 82 minutes C. 820 minutes D. 8 hours E. Cannot be determined with the information provided Click here for answer 157. Which one of the combinations of values below best describes ventilation/perfusion ratio in the normal lung in the upright posture: Apices Bases A. > 1 > 1 B. > 1 < 1 C. < 1 > 1 D. < 1 < 1 E. 1 1 Click here for answer 158. Which of the following would be the most compelling indication for tracheostomy in a fire victim: A. Full thickness facial burns B. Apnea C. Proximal laryngeal damage D. Severe pulmonary edema E. Circumferential full-thickness burns of the neck Click here for answer 159. Which of the following statements is true regarding the growth and development of lung units in infants: A. The lungs of newborn infants lack true alveoli B. Terminal bronchioles grow and bifurcate to give rise to respiratory bronchioles during infancy C. Interalveolar Pores of Kohn are well developed in the neonate D. Alveoli form via septation of saccules E. The number of secondary acini increases during the first year of life Click here for answer 160. A patient with pneumonia is breathing an FiO2 of 0.4. The PaCO2 on arterial blood gases is 40 torr, and the PaO2 is 100. The patient’s temperature is 37oC and the barometric pressure is 747. Assuming that the respiratory quotient is 0.8, what is the alveolar-arterial O2 gradient in this patient: A. 30 B. 130 C. 180 D. 430 E. 140 Click here for answer 161. Which of the following ______ type is primarily responsible for the production of tumor necrosis factor: A. Platelets B. Macrophages C. B-lymphocytes D. T-lymphocytes E. Neutrophils Click here for answer 162. A 10-year-old girl was involved in a motor vehicle collision, and is noted to have moderate respiratory distress. A chest radiograph shows a large left-sided pneumothorax. BP is normal. After a chest tube is inserted and is functioning properly, a persistent large air leak is noted. A repeat chest radiograph shows that there is still persistent pneumothorax. The patient’s condition remains stable. The most appropriate next step in the management of this patient is: A. Insert a second chest tube B. Perform an immediate thoracotomy C. Repeat a chest radiograph in eight (8) hours D. Initiate jet ventilation E. Perform a bronchoscopy Click here for answer 163. When ketamine is administered by the intramuscular route, a larger dose is necessary to induce general anesthesia, compared to the intravenous route. The most likely explanation for this is: A. Up-regulation of drug receptors B. Tachyphylaxis C. Slower absorption D. Incomplete absorption E. Tissue metabolism Click here for answer 164. Recovery after alveolar injury is characterized by which of the following processes: A. Serum factors enter the alveoli and delay the healing process B. Polymorphonuclear leukocytes clear the alveolar debris C. Alveolar Type I cells divide and multiply to reconstitute the alveolar surface D. The surface is first reconstituted by alveolar Type II cells that, in turn, evolve into alveolar Type I cells E. The pericytes multiply and evolve into alveolar Type I cells Click here for answer 165. Which of the following is the earliest evidence of inspiratory muscle fatigue after discontinuation of mechanical ventilation: A. An increase in respiratory rate B. An increase in PaCO2 C. Alternation of abdominal and thoracic breathing every few breaths D. Primary thoracic inspirator effort when supine E. Abdomen moving inward during inspiration Click here for answer 166. Which of the following statements is correct regarding the physiology of hemeproteins within the hemoglobin or myoglobin: A. CO2 increases the affinity of hemoglobin for O2 B. O2 has a stronger affinity for hemoglobin than myoglobin C. CO2 combines with non-oxygenated hemoglobin to form carbaminohemoglobin D. 2,3 Diphosphoglycerate increase hemoglobin affinity for O2 by competing with hydrogen ion for binding sites E. O2 and hydrogen ions bind to the same sites on hemoglobin Click here for answer 167. An 18-day-old infant male underwent insertion of an aorticopulmonary shunt estimated to be 5 mm in diameter for pulmonary atresia. Post-operatively it is noted that he has a large left-to-right shunt and continues to receive conventional mechanical ventilation. Which of the following interventions is most likely to reduce the left-to-right shunt flow: A. Hydralazine IV B. Nitroprusside IV C. Increase arterial pH D. Increase FiO2 E. Increase PEEP Click here for answer 168. Which of the following is the major precursor of arachidonic acid: A. Glutamic acid B. Leucine C. Isoleucine D. Linoleic acid E. Valine Click here for answer 169. A child with pneumonia and respiratory failure is receiving conventional mechanical ventilation. Minute ventilation (MV) is 2 L/min and the PEEP is set at 5 cmH2O. Hemoglobin is 9 gm% and arterial blood gases show that arterial O2 saturation is 85%. Cardiac output is estimated to be 2.0 L/min. O2 transport from lungs to tissues will be most improved by which of the following: A. Increasing MV to 3 L/min B. Increasing PEEP to 10 cmH2O C. Increasing Hemoglobin to 14 gm% D. Increasing O2 saturation to 95% E. Increasing cardiac output to 2.4 L/min Click here for answer 170. Stimulation of juxtacapillary receptors (J receptors) produces: A. Rapid shallow breathing B. Bronchodilation C. Hypotension D. Cough E. Tachycardia Click here for answer 171. Which of the following types of cells is most likely to manifest injury at the onset of acute respiratory distress syndrome (ARDS): A. Clara cells B. Pulmonary macrophages C. Pulmonary endothelial cells D. Type I epithelial pneumocytes E. Type II epithelial pneumocytes Click here for answer 172. Rebreathing during the use of Mapleson D breathing circuit during anesthesia can be minimized by: A. Increasing fresh gas flow B. Decreasing fresh gas flow C. A short expiratory flow D. Fast respiratory rate E. None of the above Click here for answer 173. Barotrauma is a recognized complication of positive pressure ventilation. Which of the following ventilatory strategies is expected to be associated with the least risk of barotrauma: A. A tidal volume (TV) of 5 ml/kg and a PEEP of 10 cmH2O B. A TV of 7 ml/kg and a PEEP of 15 cmH2O C. A plateau pressure < 35 cmH2O with a decelerating waveform D. Peak airway pressure of 50 cmH2O with a square waveform inspiratory flow E. A TV of 10 ml/kg and a mean inspiratory flow of 60 L/min Click here for answer 174. Regional lung over-distention at end-inspiration rarely occurs during mechanical ventilation in which of the following settings: A. Diffuse idiopathic pulmonary fibrosis B. Acute Respiratory Distress Syndrome (ARDS) C. Acute exacerbation of Chronic Obstructive Pulmonary Disease (COPD) D. Auto-PEEP of 15 cmH2O without bronchospasm (emphysema) E. Acute bronchospasm with hyperinflation Click here for answer 175. When a patient is receiving conventional positive pressure ventilation at a specific fixed tidal volume, which of the following fixed end-points will result as conditions change: A. A uniform expansion of all lung units based on the plateau pressure B. A constant plateau pressure in spite of changing respiratory rate C. A constant end-inspiratory lung volume in spite of varying airway resistance D. A constant increase in intrathoracic pressure in spite of changes in lung compliance E. None of the above Click here for answer 176. A 1-year-old boy with ARDS is on pressure limited ventilation with an inspiratory time of 1 second, SIMV 20 bpm, PIP 30 cmH2O, and PEEP 8 cmH2O. The chest radiograph has shown significant improvement over the past 24 hours, and the FiO2 has been weaned from 0.7 to 0.45. Failure to decrease the inspiratory time may result in all of the following except: A. Decreased venous return B. Decreased physiologic dead space C. Auto-PEEP D. Pneumomediastinum Click here for answer 177. Nitric oxide is synthesized from which of the following: A. Arginine B. Glutamic acid C. Leucine D. Isoleucine E. Linoleic acid Click here for answer 178. A 1-day-old newborn underwent insertion of an aorticopulmonary shunt measuring 5 mm in diameter for an underlying cyanotic congenital heart disease. He has been admitted to the intensive care unit for post-operative care and is on conventional positive pressure ventilation. A large left to right shunt is noted while he is on the ventilator. Which of the following is most likely to reduce the left to right shunt blood flow: A. Hydralazine B. Increasing FiO2 C. Administration of inhaled nitric oxide D. Increasing PEEP on the ventilator E. Increasing arterial pH Click here for answer 179. A 9-month-old infant who was on mechanical ventilation for pneumonia and respiratory failure was extubated this morning. Which of the following is the earliest evidence of inspiratory muscle fatigue after discontinuation of mechanical ventilation: A. Alternation of abdominal and thoracic breathing every few breaths B. Primary thoracic inspiratory efforts when supine C. An increase in respiratory rate D. An increase in arterial CO2 E. Abdomen moving inward during inspiration Click here for answer 180. What is the toxic byproduct of the combination of nitric oxide with oxygen: A. Nitric oxide B. Nitric dioxide C. Nitrous oxide D. Hemoglobin E. All of the above Click here for answer 181. A Helium-Oxygen mixture (HeliOx) has been shown to be of benefit in which of the following clinical situations: A. Croup B. Chronic Obstructive Pulmonary Disease (COPD) C. Asthma D. Fixed upper airway narrowing E. All of the above Click here for answer 182. Marked hypertrophy of smooth muscles in the bronchial arteries and bronchial tree is present in a lung biopsy specimen from a 19-month-old infant. Which of the following is the most likely underlying lung disease in this patient: A. Primary pulmonary hypertension B. Chronic asthma C. Bronchopulmonary dysplasia (BPD) D. Dysmotile cilia syndrome E. Tracheobronchomegaly Click here for answer 183. Respiratory failure characterized by hypercapnia, but a normal PAO2 – PaO2 difference would most likely occur in which of the following conditions: A. Pneumonia with a lobar pattern B. Acute Respiratory Distress Syndrome (ARDS) C. Upper airway obstruction D. Pulmonary edema is association with severe head injury E. Severe status asthmaticus Click here for answer 184. Which of the following is equivalent to intrapleural pressure at rest: A. Airway pressure and the surface tension of the pleura B. Pressure exerted by the weight of the lung at vertical levels C. Airway pressure minus alveolar pressure D. The surface tension of the alveoli E. The net pressure resulting from the elastic recoil of the lung and chest wall Click here for answer 185. Bronchogenic cyst is most likely to occur in which of the following locations: A. Subpleural region B. Middle mediastinum C. Upper lobe D. Anterior mediastinum E. Lingula Click here for answer 186. Which of the following is the most important factor responsible for the hysteresis of the pressure-volume curve of the normal lung in vivo: A. Elastin and collagen properties B. The Laplace relationship C. Airway compliance D. Frequency dependence of compliance E. Air/Surface interface Click here for answer 187. Which of the following results in increased mechanical efficiency of the diaphragm: A. Increasing the curvature of the dome of the diaphragm B. Shortening of the muscle fibers C. Increasing end-expiratory lung volume above the relaxed volume of the rib cage and the abdomen D. Completely relaxing the abdomen E. Inspiration against a resistive load Click here for answer 188. Which of the following distributions of cell types in bronchoalveolar lavage fluid is more consistent with ARDS: Alveolar Macrophages Lymphocytes PMN’s A. 25% 4% 70% B. 25% 2% 4% C. 85% 2% 12% D. 85% 12% 2% E. 92% 5% 2% Click here for answer 189. A 16-year-old adolescent female with cystic fibrosis is admitted to the pediatric ICU with hemoptysis of sufficient severity to require several blood transfusion therapies. Of the following, which procedure would be most appropriate at this time: A. Perfusion lung scan B. Bronchial arteriography C. Pulmonary arteriography D. MRI of the chest E. CT scan of the chest Click here for answer 190. From birth until 6 years of age, functional residual capacity (FRC) increases as a function of total lung capacity because: A. Airway resistance increases B. Chest wall compliance decreases C. The time constant for expiratory flow increases D. A child spends progressively more time in the erect posture E. Laryngeal adductors become active during expiration Click here for answer 191. Therapy with a helium-oxygen mixture (HeO2) can be used in children with severe subglottic stenosis because: A. HeO2 is a bronchodilator B. HeO2 is less dense than air C. HeO2 is less viscous than air D. Flow through large airways is dependent on gas viscosity E. Flow through large airways is always transitional Click here for answer 192. Which of the following is the most prominent histologic feature of bronchopulmonary dysplasia (BPD): A. Disrupted airway branching pattern B. Decreased number of alveoli C. Deficient bronchial cartilage D. Eosinophilic infiltration of alveolar septa E. Capillary hyperplasia Click here for answer 193. An infant with BPD is on oxygen. The current fraction of inspired oxygen that maintains a PaO2 of 55 mmHg and a barometric pressure (BP) of 7650 mmHg is 0.27. The infant is being transferred to another hospital via a plane flying at a high altitude which results in a reduction in the BP to 623 mmHg. What FiO2 will be required to maintain the same PaO2 assuming a constant respiratory quotient (RQ) of 0.8, a constant PaCO2 of 40 mmHg, and a body temperature of 37o C: A. 0.24 B. 0.27 C. 0.30 D. 0.33 E. 0.37 Click here for answer 194. The function of surfactant associated with protein C is: A. To stimulate surfactant synthesis B. To facilitate formation of surfactant films at air, liquid interface C. To regulate surfactant release D. To inhibit enzymes that inactivate surfactant E. Not related to normal surfactant function Click here for answer 195. Type I pulmonary pneumocytes are best described as: A. Cells involved in surfactant synthesis B. Cells involved in neurohumoral release and synthesis C. Cells involved in glycoprotein synthesis D. Cells that function as stem cells for Type II alveolar cells E. Cells that minimize the barrier to gas exchange Click here for answer 196. Forced vital capacity (FVC) is useful as an index of pulmonary impairment because: A. It shows the least decline in the supine position B. It is affected only in obstructive lung diseases C. It has a high intra-subject reproducibility D. It has a large standard deviation E. It remains stable with increasing height Click here for answer 197. Which of the following is used to calculate Work of Breathing: A. Pressure – volume curve B. Flow – volume curve C. Pressure – flow curve D. Volume – time curve E. Flow – time curve Click here for answer 198. A 14-year-old male is admitted to the Pediatric ICU for heroin overdose. Alveolar carbon dioxide is 85 mmHg at a barometric pressure of 760 mmHg and water vapor pressure is 47 mmHg. Upon arrival and while breathing room air, his alveolar-arterial oxygen tension difference was 10 mmHg. Assuming that the fraction of inspired oxygen of room air is 0.21 and the respiratory quotient (RQ) is 0.8, the patient’s arterial oxygen tension would be: A. 23 mmHg B. 33 mmHg C. 43 mmHg D. 53 mmHg E. 63 mmHg Click here for answer 199. A medication is being administered to a patient at intervals equivalent to its half-life. How many half-lives will it take for the plasma concentration of the medication to reach 97% of the final steady-state levels: A. One half-life B. Two half-lives C. Three half-liveS D. Four half-lives E. Five half-lives Click here for answer 200. If the patient in Question #199 above, requires extracorporeal life support (ECLS), what would be the effect of this modality of therapy on the half-life of the medication: A. Increase B. Decrease C. Remain the same D. Volume of distribution decreases dramatically Click here for answer Answers 86-87. E, B Pulmonary edema is more likely to lead to a decrease in functional residual capacity rather than an increase in closing capacity. Elimination of secretions and use of effective bronchodilators are useful strategies to improve closing capacity. 88. A Because blood flow falls more dramatically than ventilation from the base of the lung towards the apex of the lung, the ventilation perfusion ratio increases exponentially as one moves up the lung. (West JB. Ventilation/Blood Flow and Gas Exchange, 3rd Edition; Oxford, Blackwell Scientific, 1977; pp 30) 89-90. B, D A significant portion of the tidal volume dissipates when the compliance of the ventilatory circuit is high. Patient’s compliance and resistance also affects the actual delivered tidal volume. The exhalation valve is usually kept close to the airway opening in order to minimize the circuit volume. (Rogers MC. Textbook of Pediatric Intensive Care, 2nd Edition, 1992; pp 147-150) 91-93. A, B, D In clinical medicine, carbon monoxide poisoning is probably the most common application of hyperbaric O2 therapy. The half-life of carbon monoxide is actually decreased to 23 minutes at 3.0 atmospheric pressure, as opposed to 180 minutes with 100% oxygen at the normal atmospheric pressure. Sixty to ninety minutes of hyperbaric oxygen at 2 to 2.5 atmospheric pressure seems to be safe, without significant CNS toxicity, although other side effects mentioned in the question are possible. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition, 1992; pp 156-157) 94. E With turbulent airflow, the resistance to airflow is proportionate to density (as opposed to viscosity with laminar flow). Because helium is a less dense gas than nitrogen, it has a beneficial role in patients with upper airway obstruction such as croup. More recently, the helium-O2 mixture has also been shown to improve gas exchange in patients with acute asthma with or without ventilatory support. Helium-O2 mixture minimizes work of breathing by altering the resistance to airflow. In patients, breathing > 40% O2, the gas mixture becomes too dense to be beneficial. Helium-O2 mixture is most beneficial at 80:20 or 70:30 ratios. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; p 157) 95. A The flow through the ventilator circuit is set at 8 liters/min. Therefore, 8,000 ¸ 60 ´ 0.5 = 66 ¸ 6 = 11 ml/kg. 96. C Most of gas exchange takes place during exhalation. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition, 1992; pp 156-159) 97-99. D, A, A The inspiratory pressure relief valve is housed in the expiratory limb of the circuit in these ventilators. Actually, in order to minimize work of breathing, the inspiratory gas flow in the continuous flow circuit should meet the patient’s inspiratory flow rate demand. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition, 1992; pp 156-159) 100. A In the pressure support mode of ventilation, the length of the cycle as well as depth and flow characteristics, are determined by the patient. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition, 1992; pp 156-159) 101-102. D, E All three options are methods of providing an inverse ratio ventilation, which has been used successfully to improve oxygenation and ventilation at a reduced peak inspiratory pressure. During inverse ratio ventilation, the tidal volume is a function of multiple factors, some of which are enumerated in the question. (Tharralt RS, et al. Chest, 1988; 94:755) 103. C The decrease in oxygen delivery associated with elevation of PEEP is usually responsive to adequate fluid resuscitation and inotropic support, unless one is using extremely high levels of PEEP. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; pp 297-300) 104. D (Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; pp 184) 105. E All of these factors are operative when it comes to the adverse hemodynamic effects of PEEP. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 186) 106. E Unless they progress to a tension pneumothorax or a tension pneumoperitoneum, none of these manifestations of barotrauma mentioned are usually clinically significant (i.e., do not require immediate intervention). (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 186-188) 107. B During tension pneumothorax, the intrapleural pressure is consistently higher than the atmospheric pressure. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; pp 307-309) 108. B Veno-venous extra-corporeal life support (VV-ECLS) usually requires a higher rate of flow because of the recirculation of the previously oxygenated blood. This is true when the pulmonary bed is totally non-functional. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; pp 317-318) 109. B, A, A Veno-venous extra-corporeal life support (VV-ECLS) maintains pulmonary blood flow with oxygenated blood, but it does not assist the systemic circulation. On the other hand, veno-arterial extra-corporeal life support (VA-ECLS) does assist the systemic circulation and it also tends to decrease the pulmonary artery pressure. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; pp 317-318) 110. C The oxygen saturation that is obtained using pulse oximetry is called a functional saturation, and the pulse oximetry obtains the ratio of oxyhemoglobin divided by the total hemoglobin. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; pp 333-336) 111. C Methylene blue absorbs light maximally at 668nm. The pulse oximeter interprets this extra absorbance as reduced hemoglobin, and therefore a lower oxygen saturation is obtained. The oxygen saturation obtained by the pulse oximetry could drop dramatically within 30 seconds of an intravenous administration of methylene blue, and it remains reduced for approximately 2 minutes. (Scheller M. Anesthesiology, 1986; 65:550) 112. A Carboxyhemoglobin and Met-hemoglobin produce these findings. (Barker SJ. Anesthesiology, 1987; 66:677) 113. D With an increase in Met-hemoglobin concentration, the saturation on the pulse oximeter decreases and plateaus at approximately 85%. Met hemoglobin absorbs light significantly at both 660 nm and 940 nm wave lengths, thereby confusing the pulse oximeter photo detector into believing that both oxyhemoglobin and reduced hemoglobin are increased. This results in increases in both the denominator and numerator. As this happens the microprocessor driven algorithm of the red absorbance and infrared absorbance approaches unity and this gives rise to a saturation of approximately 85% on the calibration curve. Hyperbilirubinemia does not interfere with reading of the pulse oximetry. (Barker SJ, et al. Anesthesiology, 1988; 68:279) 114-115. D, E In the presence of normal oxygen extraction and utilization by the tissue, an increase in oxygen delivery will not result in decreased mixed-venous oxygen saturation. Increased oxygen consumption leads to a decrease in mixed venous oxygen saturation, and not vice versa. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 210-211) 116. D This capnogram reveals irregularity in the pattern of the exhalation of the CO2 which most likely reflects irregularity in the pattern of breathing of this patient. Adding 20 cm H2O of pressure support will decrease the work of breathing by overcoming the work that is necessary to open the demand valve mechanism that is operating in this ventilator. It will also help to overcome some of the resistance of the endotracheal tube. (Carlon G, et al. Crit Care Med, 1988; 16:550) 117. E Hypoventilation is likely to lead to a gradual increase in the level of end tidal CO2. All other clinical conditions indicated in the question lead to a sudden decline in end tidal CO2 levels. (Carlon G, et al. Crit Care Med, 1988; 16:550) 118. A The presence of a gas bubble in a syringe will usually affect the PaO2. The effect on the PaO2 will depend on the amount of oxygen that is inspired by the patient. In patients on room air, this will lead to a false elevation of PaO2 (atmospheric PO2 is usually higher than alveolar PO2). On the other hand, in patients who are receiving a high fraction of inspired oxygen and have normal lungs, the presence of an air bubble in a syringe may spuriously lower the PaO2. Excess heparin does lead to a drop in PaCO2 but usually there are no changes in the pH level because it is neutralized by the acidity of heparin. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; pp 353-359) 119. E Reticulocytes and band forms are highly metabolic immature cells that are most likely to lead to a change in the blood gas results. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; pp 355-359) 120. D Aspirin, especially with overdose, is likely to lead to high anion gap metabolic acidosis. All other drugs do not. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; p 361) 121. D Other abnormalities of the central nervous system, esophagus, and cardiovascular system have been reported in association with choanal atresia. Therefore, evaluation for possible other anomalies should be done in patients with posterior choanal atresia. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 231-233) 122. D Nasal obstruction is usually seen when the mass is located at the base of the brain. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 231-233) 123. E All are features of angiofibroma. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 231-233) 124. A, A, B, B Vocal cords in infants are concave, and the anterior attachment to the trachea are lower and the glottis is located higher in the neck compared to an adult. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 231-233) 125. C At 4-6 months of age, the epiglottis loses contact with the soft palate and assumes a more erect posture, and this allows oral (mouth) breathing. The lateral diameter of the newborn glottis is only about 4-5 mm and at birth the trachea is approximately 5-7 cm in length. The glottis assumes the adult location at C6 by about 12 years of age. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 231-233) 126. A 127. B p R2 = 16 p when the diameter is 8 mm which gives rise to a radius of 4 mm. With a uniform 1 mm reduction in the size of the airway, this will decrease the diameter from 8 mm to 6 mm, and decrease the radius from 4 mm to 3 mm. Now p R2 = 9 p, 9 ¸ 16 = 54%, which means that the diameter of the airway has been decreased by 44%. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 231-233) 128. E All of these are measures that may be needed to intervene with laryngospasm. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 233-234) 129. B Congenital anomalies are the most common cause of chronic stridor in children less than 2 years of age. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 235-238) 130. C (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 235-238) 131. C Laryngotracheomalacia is characterized by normal voice. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; p 236) 132. C, C Both laryngomalacia and airway or subglottic hemangioma usually present with symptoms before 6 months of age. In both cases, the treatment is conservative, since in most cases, the problem resolves spontaneously by the end of the 2nd birthday. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 235-238) 133. E All of these conditions pose difficult airway management. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 235-238) 134. D All of these are complications that may be noted in the post-operative period following repair of cleft lip and cleft palate. Occasionally bronchospasm is also seen. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 235-238) 135. C Both these conditions are characterized by macroglossia with a short neck, which combine to produce a difficult airway. Both of these conditions belong to the mucopolysaccharidoses. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; p 241) 136. E (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; p 241) 137. A The typical age for this condition is less than 3 years. It is important to obtain inspiratory radiographs to evaluate the thickness of the retropharyngeal soft tissue. Measurement of this soft tissue is important in the diagnosis of the retropharyngeal abscess. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; p 242) 138. B In fact, frequent tracheal suctioning is necessary in these patients to prevent airway obstruction because the infection/inflammation induce an increase in airway secretions. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 242-245) 139. D These are the indications for extubation in a patient with a viral croup. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 244-246) 140. D The amount of subcutaneous emphysema of the neck area does not correlate with the severity of airway injury. Nasotracheal intubation should be avoided in patients with midfacial fractures, and also in patients suspected of having a fracture of the base of the skull. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 245-248) 141. A 70-80% of subglottic stenosis occur following endotracheal intubation. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 245-248) 142. E The accepted duration of time for intubation to prevent subglottic stenosis is unknown. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 245-248) 143. D A helium-oxygen mixture in various combinations has been shown to be effective in the management of post-extubation stridor and burn victims with significant stridor. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; p 245) 144. D Most of these airway papillomas resolve by the teenage years. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; p 252) 145. A Therefore these patients respond to relatively low concentrations of inspired oxygen. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 258-260) 146. D High antidiuretic hormone levels in association with elevation of renin has been reported in patients with bronchiolitis. (Gozal D, et al. Pediatric Research, 1990; 27:204-209) 147. C High ADH in association with high aldosterone levels has been reported in patients with respiratory syncytial virus bronchiolitis. Because of this combination of hormonal abnormalities, there is a decrease in urine output associated with a normal urine sodium concentration. (Gozal D, et al. Pediatric Research, 1990; 27:204-209) 148-151. A, A, E, B Maximum mid-expiratory flow rate is one of the flow volume parameters that demonstrates the most severe decrease during an attack of asthma. This is also the parameter that is the last to improve following treatment for acute asthma. Patients with asthma, particularly those that are in status asthmaticus, have an increased residual volume. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 264-270) 152-153. D, D Transmural pressure = intraluminal pressure – extraluminal pressure. With higher negative inspiratory pressure, as seen with status asthmaticus, there is an increase in afterload during inspiration with a subsequent decrease in left ventricular output which is followed by a sharp increase in left ventricular output during subsequent expiration. This leads to the phenomenon of pulsus paradoxus (PP). A decrease in PP may indicate an improvement in the patient’s condition (i.e., a smaller fall in pleural) but it may also indicate the patient’s fatigue and worsening clinical condition. Another factor that contributes to PP is ventricular interdependence which can be exaggerated by the pulmonary hypertension as it may be seen with severe status asthmaticus. The hypoxia that is seen during status asthmaticus is due to V/Q mismatch, excessive O2 requirement secondary to increased metabolic demand and a degree of interstitial edema. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 268-270) 154. A The degree of hypoxemia does not correlate with the degree of airway obstruction as assessed by the reduction in FEV1. (McFaden ER, et al. New Engl J of Med, 1968; 278:1029) 155. D As the FEV1 drops below 20% predicted, PCO2 rises, hypoxemia occurs and pulsus paradoxus is present in almost all of these patients. (McFaden ER, et al. New Engl J of Med, 1968; 278:1029) 156. B 0.3 liters = 1 PSI c liters 1100 PSI therefore: c = 1100 x 0.3 = 330 liters = 82.5 min 1 4 liters/min 157. B Both perfusion and ventilation (V/Q) increase as one moves from the apex of the lungs towards the base of the lung. However, perfusion increases more than ventilation. Therefore, apical regions are underperfused with a V/Q of approximately 3, while basal regions of the lungs are underventilated in relation to perfusion with a V/Q of approximately 0.6. (West JB. Ventilation / Blood Flow and Gas Exchange, 3rd Edition. Oxford, Blackwell Scientific, 1977; pp 30-31) 158. C The major indication for tracheostomy in early burn management is upper airway obstruction which may be due to edema, a foreign body or laryngeal trauma such that an endotracheal tube cannot be passed. (Carvajal HF, Parks DM. Burns in Children, Pediatric Burn Management, Yearbook Medical Publishers, Inc., 1988; pp 167-168) 159. D In the human, there are five (5) stages of lung development: 1) Embryonal (Day 26 – Day 52): characterized by development of trachea and major bronchi 2) Pseudoglandular (Day 52 – Week 16): characterized by development of remaining tracheobronchial tree 3) Canalicular (Week 17 – Week 28): characterized by development of vascular bed and framework of acinus 4) Saccular (Week 29 – Week 36): characterized by increased complexity of saccules 5) Alveolar (Week 26 – Term): characterized by development of alveoli The lungs emerge as a bud from the pharynx at Day 26 following conception. This bud elongates, separates from the esophagus, and continues to divide to form the main bronchi. Extensive subdivision in the pseudoglandular stage leads to formation of the conducting airway, the most peripheral of which are the terminal bronchioles which give rise to respiratory bronchioles and alveolar ducts during the Canalicular stage. During this later stage, the acinus is formed. An acinus is the gas exchange unit associated with a single terminal bronchiole and will eventually contain three orders of respiratory bronchioles: alveolar ducts, alveolar sacs, and alveoli. The Saccular stage was formerly thought to be the last stage of lung development prior to birth. However, because alveoli form before birth, the termination of this period is now arbitrarily set at 35-36 weeks gestation. At the beginning of this phase (28 weeks gestation) the terminal structures are call saccules. They are cylindrical structures with a smooth wall. They become subdivided by ridges call secondary crests. Further subdivision between crests result in small spaces termed subsaccules. Exactly when these subsaccules can be termed alveoli is a matter of debate. The range of timing is between 29-36 weeks gestation. Most of post-natal formation of alveoli occurs over the first 1-1/2 years of life. Pores of Kohn are not established until several years after birth. (Langston C, Kida K, Reed M, et al. Human lung growth in late gestation and in the neonate. Am Rev Resp Dis, 1984; 129:607) 160. B PaO2 = PiO2 - PaCO2 RQ = (747 – 47) x 0.4 - 40 0.8 = 280 - 50 = 230 Alveolar arterial O2 gradient = PAO2 - PaO2 = 230 - 100 = 130 (Kandra TG, Rosenthal M. The pathophysiology of respiratory failure. International Anesthesiology, 1993; Vol. 31(2), pp 119-121) 161. B (Jodka PG, Heard SO. Management of the septic patient in the operating room. International Anesthesiology, 2000; Vol. 35(4), pp 1-10) 162. E Bronchopleural fistulae (BPF) can result from blunt trauma, barotrauma or inflammatory diseases of the lung. Patients with BPF can present acutely due to pulmonary flooding or tension pneumothorax, or subacutely with an insidious clinical course. A persistent air leak without evidence of technical problem in the pleural drainage apparatus also indicates a BPF. Several techniques can be employed using bronchoscopy to localize the proximal endobronchial site of the fistulous tract. Occasionally, air bubbles can be seen emanating from the segmental bronchus. Washing the suspected segment with saline and coughing may accentuate the bubbling. Techniques for obliteration of the fistula bronchoscopically have also been described. (McManigle JE, et al. Bronchoscopy in the management of bronchopleural fistula. Chest, 1990; Vol. 97, pp 1235-1238) 163. C After a delay of 2-8 minutes, intramuscular ketamine (4-8 mg/kg/BW) produces anesthesia for 20-40 minute. Over 90-92% of ketamine is absorbed after an intramuscular injection. (White PF, Way WL, Trevor AJ. Ketamine – its pharmacology and therapeutic uses. Anesthesiology, 1982; Vol. 56, p 119) 164. D The cellular proliferative phase, after alveolar injury, is characterized by Type II cellular hyperplasia, which appears to be a reparative process. These cuboidal cells may virtually cover the entire alveolar surface. They will later transform into the thin, Type I alveolar epithelial cells. (Royall JA, Matalon S. Pulmonary edema and ARDS, In: Fuhrman BP, Zimmerman JJ. Pediatric Critical Care, Mosby Yearbook 1992, pp 445-456) 165. A Tachypnea is the earliest sign of respiratory muscle fatigue. As a compensation for the decrease in efficient tidal volume, the respiratory rate increases in an attempt to maintain minute ventilation. (Nunn JF. Applied Respiratory Physiology, 3rd Edition. Boston: Butterworth, 1987, p 109) 166. C CO2 binds with deoxyhemoglobin (deoxyHb) to form carbaminohemoglobin, which is one of the forms in which CO2 is transported in the blood. However only 10% of CO2 in blood is transported in this form. Myoglobin approaches full saturation at a PO2 of 15-30 mmHg which is the level pertaining to voluntary muscle. The bulk of its oxygen may be released only at very low O2 tension. 2,3 DPG decreases the affinity of O2 for hemoglobin, and thus, facilitates release of O2 to tissues and so does carbon dioxide. This latter phenomenon is also known as the Bohr effect. O2 binds to one of the six coordination bonds of the iron atom. Hydrogen binds to the imidazole ring of Histidine on the globin chains of the hemoglobin molecule. (Nunn JF. Applied Respiratory Physiology, 4th Edition. Boston: Butterworth/Heinemann, 1993; pp 273-275. Guyton AC. Textbook of Medical Physiology, 8th Edition. WB Saunders Co., 1991; pp 440-442) 167. E Increasing PEEP will diminish left-to-right shunting by increasing the pulmonary vascular resistance. All other measures stated in the question would increase left-to-right shunt flow. (Meliones JN, et al. Respiratory Support in Infants & Children. Mosby, 1995; p 352) 168. D Linoleic acid is the primary precursor of arachidonic acid. (Abman S, Stenmark K. Am J Physiology, 1992; Vol 262: L214) 169. C O2 delivery (DO2) = Cardiac output (CO) x Arterial O2 Content (CaO2) CaO2 = Hb (gm%) x 1.34 x O2 Sat + PaO2 x 0.003 In this case, increasing the hemoglobin from 9 gm% to 14 gm% will increase O2 delivery the most. (Fahey JT, Lister G. “Oxygen demand, delivery and consumption.” Fuhrman BP, Zimmerman JJ. Pediatric Critical Care, 2nd Edition; Mosby, 1998; pp 235-240) 170. A 171. C Pulmonary capillary endothelial damage is one of the earliest changes in ARDS. Capillary congestion with intraluminal aggregation of platelets, fibrin, and neutrophils. Pulmonary capillary endothelial cells undergo swelling and focal necrosis with destruction of mitochondria, endoplasmic reticulum and ribosomes during the first few hours of ARDS. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 297-298) 172. A The Mapleson D breathing circuit (shown in the diagram below) can be described as a T-piece with an expiratory limb. The fresh gas inlet is located near the patient, and the expiratory pressure release valve (PRV) is near the reservoir bag. The PRV opens as pressure increases during expiration and a portion of the expired gas along with fresh gas is released into the atmosphere. During the next inspiration, the patient receives a combination of fresh gas and the exhaled gas. The content of this inspired gas is determined by: 1) Rate of fresh gas flow: A fresh gas flow > 2 times the minute ventilation prevents rebreathing 2) Patient’s tidal volume: the amount of rebreathing increases as the tidal volume increases 3) Duration of expiration: a short expiratory pause provides inadequate time to flush the alveolar gas (occurs with faster respiratory rate); this allows rebreathing (Barash PG, Cullen BF, Stoelting RK. Clinical anesthesia, 2nd Edition; pp 654) 173. C When peak airway pressure is allowed to increase to a level beyond that which is necessary to maximally distend the lungs, barotrauma and lung injury result. Since regional differences in lung resistance and compliance often co-exist, maintaining a constant tidal volume may overdistend areas of the lung that are aerated if the remainder of the lung is collapsed. Similarly maintaining a constant inspiratory flow pattern when regional differences in lung units exist will selectively increase distention of lung units with lower resistance. (Haake R, et al. Barotrauma: pathophysiology, risk factors and prevention. Chest, 1987; Vol. 1:608) 174. D Pulmonary conditions associated with decreased compliance such as pulmonary fibrosis and ARDS or increased airway resistance such as bronchial asthma and COPD have the potential for being homogenous. This homogeneity can result in regional over-distention during positive pressure ventilation. Hyperinflation secondary to airway narrowing or collapse such as seen with auto-PEEP increases end-expiratory lung volume but does not result in lung expansion of the hyperinflated lung units until airway pressure exceeds the level of auto-PEEP. Although the work of breathing during spontaneous breathing is increased by auto-PEEP, end-inspiratory lung volumes do not increase. (Bone RC, Stober G. Mechanical ventilation in respiratory failure. Med Clin Noth Am, 1983; Vol. 67:599) 175. D Changes in intrathoracic pressure correlate highly with changes in lung volume. Changes in intrathoracic pressure are independent of lung compliance. An increase in respiratory rate with lung conditions associated with increased expiratory airway resistance will result in dynamic hyperinflation because there is inadequate time for exhalation. Examples are COPD, asthma, and other causes of intrathoracic airway obstruction. Thus, over-distention is possible with a fixed tidal breath or tidal volume. Since regional lung compliance, even in healthy individuals, is different under all conditions, uniform expansion of all lung units by positive pressure ventilation at any setting probably never occurs. (Marini JJ. Ventilatory management in severe airflow obstruction found in Pinsky MR, Dhainaut JFA, Ed. Pathophysiologic Foundations of Critical Care, 1993; pp 453-471) 176. B (Marini JJ. Ventilatory management in severe airflow obstruction found in Pinsky MR, Dhainaut JFA, Ed. Pathophysiologic Foundations of Critical Care, 1993; pp 453-471) 177. A Nitric oxide is synthesized from the amino acid arginine by the action of the enzyme nitric oxide synthetase. (Nichols DG, et al. Critical Heart Disease in Infants and Children. Mosby, 1995; pp 36, 78, 111, 206) 178. D Systemic to pulmonary shunt is often created in neonates and infants with an underlying cardiac defect in order to improve pulmonary blood flow and oxygenation. Examples are the (modified) Blalock-Taussig shunt that connects the subclavian artery to the pulmonary artery using a synthetic material, and the aortic to pulmonary window which usually connects the ascending aorta to the pulmonary artery. Conditions that lead to a reduction in pulmonary artery pressure and pulmonary vascular resistance would increase the flow across the shunt with an increase in left to right shunt. Examples include: Alkalosis, vasodilators such as hydralazine and nitroprusside, an increase in the concentration of inspired oxygen, and selective pulmonary vasodilators such as nitric oxide. Interventions that lead to an increase in pulmonary vascular resistance such as increasing PEEP would lead to a reduction in pulmonary blood flow and a reduction in the left to right shunt. (Nichols DG, et al. Critical Heart Disease in Infants and Children. Mosby, 1995; pp 460) 179. B Tachypnea in this infant would be the earliest evidence of inspiratory muscle fatigue. (Nichols DG, et al. Critical Heart Disease in Infants and Children. Mosby, 1995; pp 319-332) 180. C Nitric dioxide is the toxic by-product. The rate of formation of this toxic product is dependent on the duration of contact between oxygen and nitric oxide. (Nichols DG, et al. Critical Heart Disease in Infants and Children. Mosby, 1995; pp 36, 78, 111, 206) 181. E (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 157, 245-246) 182. C Histological features of infants with bronchopulmonary dysplasia (BPD) include squamous metaplasia of the airway epithelium (large and small airways), increased peribronchial smooth muscle with fibrosis, submucosal edema and inflammation with hypertrophy of submucosal glands. In the parenchyma, there are areas of fibrosis with atelectasis alternating with areas of hyperinflation which, on gross examination of the lungs has a cobblestone appearance. In more long-standing cases, there is diminution in alveolarization and surface area. The decrease in the number of alveoli, probably reflect the onset of the insult with subsequent failure of the ability to regenerate new alveoli. This is associated with increased number of small pulmonary arteries, which may contribute to pulmonary hypertension. The pulmonary arterial tree shows proliferation of the intima, smooth muscle hypertrophy, distal extension of smooth muscles, and adventitial thickening. (Abman SH, Groothius JR. Pathophysiology and treatment of BPD. Pediatr Clin North Am, 1994; 41(2), pp 277-291) 183. C Upper airway obstruction usually does not lead to an alveolar-arterial oxygen gradient. On rare occasions, when upper airway obstruction is complicated by post-obstruction pulmonary edema, this is possible. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 231-296) 184. E The lungs have a tendency to collapse, while the chest wall has a tendency to move outward. Thus the elastic forces of the lung and the chest wall are in opposite directions. These two opposing forces are linked by the pleural surfaces and the nest pressure is the intrapleural pressure. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 145) 185. B Bronchogenic cyst accounts for 5% of mediastinal masses. It is found in five major locations: right paratracheal region (20%); carinal region (51%); hilar region (9%); paraesophageal (14%); and pericardial/retrosternal. (Taussig LM. Pediatric Respiratory Medicine, 1999; p 1118) 186. E Hysteresis refers to the failure of a system to follow identical paths of response during application and during withdrawal of a force. In the lungs, this is due mainly to surface properties and alveolar recruitment-derecruitment. In the chest wall, this is due to muscle and ligaments, both of which exhibit hysteresis. (Taussig LM. Pediatric Respiratory Medicine, 1999; pp 100-101) 187. A Increasing the length of muscle fibers (to a limited extent) would increase the force of contraction and thus the efficiency of the diaphragm. The diaphragm is most efficient at the lung volume that corresponds to the functional residual capacity (FRC) and thus increasing the end-expiratory lung volume above this does not improve the efficiency of the diaphragm. Increasing the radius of curvature increases the efficiency of the diaphragm. The diaphragm of an infant has less radius of curator than that of an adult, and is less efficient. (Fuhrman BP, Zimmerman JJ. Pediatric Critical Care, 2nd Edition; pp 407) 188. A BAL in ARDS is characterized by predominance of PMNs, of 10 > 85%. (Reynolds HY. Am Rev Resp Dis, 1987; Vol. 135, pp 250-263) 189. B Massive hemoptysis is relatively uncommon in cystic fibrosis patients. It occurs in 10% of adolescents and adult patients with cystic fibrosis. Massive hemoptysis usually occurs from the bronchial circulation due to the higher systemic pressure compared to the pulmonary circulation. Often an untreated exacerbation of the disease is a triggering factor, but sometimes there is no clear cause. If hemoptysis persists, bronchial artery embolization is warranted; this requires bronchial arteriography. (Sweeney N, Fellows K. Bronchial artery embolization for severe hemoptysis in cystic fibrosis. Chest, 1990; pp 1322-1326) 190. B In infants, the continuous muscle tone of the thorax is important to maintain functional residual capacity (FRC), because the chest wall is very compliant and lacks the rigidity necessary to oppose the elastic recoil of the lung, which tends to lower FRC. With age, as chest wall compliance decreases and the chest wall becomes more rigid and capable to oppose the elastic recoil of the lungs, FRC increases. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; p 112-128) 191. B A helium-oxygen mixture is less dense that a nitrogen-oxygen (air) mixture. With turbulent flow (seen with upper airway obstruction such as subglottic stenosis), resistance to air flow is proportionate to density. A helium-oxygen mixture is useful in reducing the resistance to flow and work of breathing. ((Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; pp 275-276) 192. B Refer to the answer for Question #182 on the previous page. 193. D PAO2 = (BP – Vapor Pressure) X FiO2 – PaCO2 / RQ Since PaCO2 and RQ are assumed to remain constant, they will remain the same under both situations: (760 – 47) X 0.27 = 192.51 In order to keep the PaO2 the same, and therefore compensate for the same degree of Alveolar-arterial oxygen gradient as the atmospheric pressure decreases, the alveolar oxygen tension must remain the same (i.e., 192.51). Therefore, (632 - 47) X Unknown fraction of inspired oxygen = 192.51 FiO2 = 192.51 / 632-47 = 192.51 / 585 = 0.3290 (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 116-117) 194. B The function of this protein is to promote formation of a surfactant layer. It is, therefore, essential for effective reduction of the surface tension induced by surfactant. (Fuhrman BP, Zimmerman JJ. Pediatric Critical Care, 2nd Edition; pp 382-383) 195. E Type I alveolar cells are less in number than Type II alveolar cells (which synthesize surfactant), but they cover a much larger area of the lung. Their primary function is to reduce the barrier to gas exchange. (Fuhrman BP, Zimmerman JJ. Pediatric Critical Care, 2nd Edition; pp 445-446) 196. C Forced vital capacity (FVC) is easily measured during spirometry. Data obtained from a specific patient can be compared with those from subjects who have the same height, weight and age. FVC is highly reproducible and has a narrow range of normal values. It is affected in both obstructive and restrictive lung diseases. FVC may decline in the sup8ine position by up to 20% in normal subjects and up to 38% in patients with underlying neuromuscular diseases. (Civeta JM, et al. Critical Care, 2nd Edition; pp 565-566) 197. A Work = Force x Distance. When it comes to the respiratory system, “work” is defined as the pressure that is generated by the respiratory muscle to move a particular volume of gas. (Rogers MC, et al. Textbook of Pediatric Intensive Care, 2nd Edition; pp 129-130) 198. B Alveolar O2 tension = (Barometric Pressure – Vapor Pressure) x FiO2 – PaCO2 / RQ (760 – 47) x 0.21 – 85 / 0.8 713 x 0.21 – 106.25 = 43.38 PAO2 - PaO2 = 10 Therefore: PaO2 = 43 – 10 = 33 mmHg (Rogers MC, et al. Textbook of Pediatric Intensive Care, 3rd Edition; p 90) 199-200. E, A The half-life (t½) of a drug is function of clearance (CL) and volume of distribution (Vd) according to the following formula: T½ = 0.693 x Vd / CL Thus half-life is affected not only by elimination, but also by volume of distribution. For instance, during ECLS, most of the increase in the half-life is due to an increase in the volume of distribution, rather than a change in drug clearance. A drug’s half-life can also be used to determine the time it takes for the drug to reach a steady-state concentration, a state in which the amount of drug administered equals the amount cleared by the body. After 3 half-lives 87% of steady-state concentration is achieved After 4 half-lives 93% of steady-state concentration is achieved After 5 half-lives 97% of steady-state concentration is achieved (Fuhrman BP, Zimmerman JJ. Pediatric Critical Care, 2nd Edition; p 1281. Behrman BE, et al. Nelson Textbook of Pediatrics, 15th Edition; p 294)