Journal of Pediatric Critical Care

P - ISSN : 2349-6592    |    E - ISSN : 2455-7099

Critical Thinking
Year : 2014 | Volume : 1 | Issue : 4 | Page : 324-328



Director Pediatric critical care and pulmonology BLK Superspeciality hospital.New Delhi

Correspondence Address:

Praveen Khilnani
Director Pediatric critical care and pulmonology BLK Superspeciality hospital.New Delhi

Received:1-Nov-2014/Accepted:8-Nov-2014 /Published online:15-Nov-2014

Source of Funding:None Conflict of Interest:None


Question 1:
Which of the following effects is least likely to be mediated by atrial natriuretic peptide on the kidneys?

A) A direct increase in efferent arteriolar resistance with a net increase in glomerular filtration
B) Direct natriuresis resulting from inhibition of sodium transport in the medullary collecting duct
C) Indirect natriuresis resulting from inhibition of aldosterone release from the zona glomerulosa of the adrenal gland
D) A direct decrease in afferent arteriolar resistance resulting in an increase in renal blood flow E) An indirect increase in efferent arteriolar resistance via activation of the renin-angiotensin system

Question 2:
A 14-year-old boy sustains significant blunt abdominal trauma when hit by a motor vehicle while riding his bicycle. Following adequate resuscitation with multiple blood products and crystalloid, he has significant abdominal distension and oliguria with increasing serum potassium on serial measurements. Which of the following is the least likely to be a cause of hyperkalemia?

A) Decreased glomerular filtering of potassium due to an overall decrease in the glomerular filtration rate
B) Hypoxemic injury to the renal tubule and impaired potassium excretion
C) Activation of the renin-angiotensin-aldosterone axis with increased tubular reabsorption of potassium
D) Metabolic acidosis with cellular exchange of intracellular potassium for hydrogen ion
E) Increased potassium load from tissue catabolism

Question 3:
A 9-month-old boy presents with difficulty breathing. His mother states that he has been treated for croup twice already with similar symptoms. He has had 2 days of upper respiratory tract infection symptoms and now has expiratory stridor on examination. Which of the following is correct?

A) Croup (viral laryngotracheobronchitis) is typically characterized by expiratory stridor
B) Intrathoracic airway obstruction is typically worse during inspiration
C) Extrathoracic airway obstruction is typically worse during inspiration
D) Croup (viral laryngotracheobronchitis) is typically characterized by intrathoracic airway obstruction

Question 4:
A 12-year-old boy with acute respiratory distress syndrome is being mechanically ventilated in synchronized intermittent mandatory ventilation pressure control/pressure support mode with peak inspiratory pressures of 28 mm Hg, positive endexpiratory pressure of 12 mm Hg, FIO2 of 0.60, and rate of 15/min. Arterial blood gas analysis shows PaCO2 of 60 mm Hg, and PaO2 of 60 mm Hg. His respiratory quotient is 0.8, core body temperature is 37°C (98.5°F), and barometric pressure is 747 mm Hg. What is this patient’’s PAO2-PaO2 difference?

A) 285 mm Hg
B) 300 mm Hg
C) 345 mm Hg
D) 360 mm Hg
E) Cannot be determined

Question 5:
A patient with acute respiratory distress syndrome has been managed with high-frequency oscillatory ventilation for the past 2 hours. A blood gas study shows pH of 7.48, PaCO2 of 30 mm Hg, PaO2 of 70 mm Hg, bicarbonate level of 22 mEq/L, and oxygen saturation of 97% on a FIO2 of 60%. Which of the following is the most appropriate intervention?

A) Wean the mean airway pressure.
B) Increase the delta P.
C) Decrease the frequency.
D) Increase the mean airway pressure.
E) Increase the frequency.

Question 6:
A patient is admitted following an elective posterior spinal fusion. Besides kyphoscoliosis, the only pertinent history is sulfamethoxazole/trimethoprim allergy. In the operating room, he received packed red blood cells, 3 U; platelets, 4 U; and crystalloid fluid, 6 L, with only 2.4 L of urine output. He is admitted to the pediatric ICU on mechanical ventilation due to persistent hypoxemia. His admission chest radiograph shows diffuse pulmonary edema, so he is given a dose of furosemide. In the next 30 minutes he develops tachycardia, bronchospasm, and diffuse flushing. Which of the following is the most likely cause of his decompensation?

A) Inadvertent administration of an aminoglycoside for postoperative wound prophylaxis
B) Allergic reaction to furosemide
C) Transfusion reaction
D) Worsening pulmonary edema from transfusionrelated acute lung injury
E) Aspiration pneumonia

Question 7:
A 2-year-old, acyanotic infant with tetralogy of Fallot undergoes elective repair with ventricular septal defect closure and right ventricle-topulmonary artery conduit placement, but a restrictive patent foramen ovale is not addressed. Four hours after being admitted postoperatively, she develops tachycardia with hypotension despite a central venous pressure of 20 mm Hg and hypoxemia. Her arterial blood gas analysis shows pH of 7.28, PaCO2 of 55 mm Hg, PaO2 of 50 mm Hg, bicarbonate level of 23 mEq/L, and base excess of ––0.1 mEq/L. The most appropriate next maneuver is:

A) Sedation with fentanyl, 2 µg/kg
B) Opening her sternotomy incision
C) Initiation of cooling and administration of amiodarone
D) Giving 5% albumin solution, 20 mL rapid IV push
E) Hyperventilation with 100% oxygen

Question 8:
A 6-month-old infant is admitted to the pediatric ICU with the confirmed diagnosis of Klebsiella pneumoniae meningitis. Antibiogram profile shows the organism to be an extended-spectrum betalactamase- positive strain that is sensitive to extendedspectrum penicillins, second-generation and thirdgeneration cephalosporins, and aminoglycosides. The most appropriate long-term course of antibiotic therapy would include:
A) Gentamicin
B) Ceftazidime
C) Clindamycin
D) Cefuroxime

Question 9:
An obtunded, 2-year-old boy presents to the emergency department with a BP of 70/20 mm Hg, HR of 200/min, and temperature of 40.1°C (104.1°F). He has the ecchymotic lesions pictured in the Figure on his trunk and extremities. Which of the following statements is incorrect?
A) Absence of meningitis (>20 WBCs/µL in cerebrospinal fluid) is associated with a poorer outcome.
B) Carriage of the organism in the nasopharynx is common.
C) Presence of petechiae for less than 12 hours prior to admission is associated with a favorable outcome.
D) Prior infections with influenza A or B have been associated with increased susceptibility to this organism.
E) Association of thrombocytopenia is common.

Question 10:
A child with acute respiratory distress syndrome is receiving mechanical ventilation with the following settings: mode, pressure-regulated; volume control, 8 mL/kg; plateau pressure, 30 cm H2O; mean airway pressure, 20 cm H2O; positive end-expiratory pressure, 10 cm H2O; FIO2, 0.5; rate, 22/min; inspiratory time, 0.7 seconds. The associated arterial blood gas measurements are pH, 7.36; PaO2, 106 mm Hg; PaCO2, 45 mm Hg; bicarbonate, 25 mEq/L. Which of the following will most adversely affect the oxygenation index?
A) Need to increase mean airway pressure to 25 cm H2O to generate the same blood gas data
B) Drop in PaO2 to 80 mm Hg with no changes in ventilator settings
C) Need to increase the ventilator rate to 30/min to generate the same blood gas data
D) Need to increase FIO2 to 0.60 to generate the same blood gas data
E) Increase in PaCO2 with no changes in ventilator settings

QUIZ Answers and explanantions
1. Answer E
Rationale: Atrial natriuretic peptide directly decreases the afferent arteriolar resistance and inhibits the activity of the renin-angiotensin axis, thereby indirectly resulting in decreased afferent arteriolar resistance and an increase in renal blood flow. Increased efferent arteriolar resistance is a direct effect of atrial natriuretic peptide that somewhat counteracts the increase in renal blood flow, but results in increased glomerular pressures and increased glomerular filtration rate. Natriuresis is accomplished directly by the action of atrial natriuretic peptide on sodium reabsorption in the medullary collecting duct, and indirectly by the inhibition of aldosterone release from the adrenal gland.

2. Answer C
Rationale: Activation of the renin-angiotensin-aldosterone axis may occur due to decreased renal blood flow or reduced tubular effluent flow; however, the activity of aldosterone in the intact kidney is to reabsorb sodium ion at the expense of potassium ion, thereby resulting in hypokalemia. The most common causes of hyperkalemia in acute renal failure are as follows:
•• Reduction in the glomerular filtration rate, thereby limiting the glomerular filtration of potassium ion
•• Decreased secretion of potassium due to direct injury to the renal tubular cells (acute tubular necrosis)
•• Metabolic acidosis due to azotemia or lactic acid, resulting in the exchange of intracellular potassium ion for extracellular hydrogen ion
•• Increased tissue catabolism or tissue necrosis with the resultant release of potassium ion •
• Exogenous administration of potassium ion, such as may occur with transfusion of multiple blood products

3. Answer C
Rationale: Intrathoracic airway (ie, distal trachea, bronchi, bronchioles) obstruction is typically worse during expiration. Therefore, tracheobronchomalacia and bronchiolitis are characterized by expiratory stridor and wheezing, respectively. In contrast, extrathoracic airway (ie, larynx, proximal trachea) obstruction is typically worse during inspiration. Croup is therefore characterized by inspiratory stridor.

4. Answer A
Rationale: PAO2 is calculated using the alveolar gas equation (PB, barometric pressure; PH2O, water vapor pressure; RQ, respiratory quotient): PAO2 = FIO2 (PB –– PH2O) –– PaCO2/RQ The water vapor pressure (PH2O) at a temperature of 37°C (98.5°F) is 47 mm Hg. Therefore, PaO2 =0.60 (747 –– 47) - 60/0.8 = 420 –– 75 = 345 mm Hg The PAO2 –– PaO2 difference is then 345 mm Hg –– 60 mm Hg, or 285 mm Hg.

5. Answer E
Rationale: High-frequency oscillatory ventilation (HFOV) has become an increasingly utilized tool in the management of severe hypoxemic respiratory failure. A modest number of variables are under control of the practitioner that allow support for oxygenation and/ or ventilation. The blood gas analysis demonstrates a respiratory alkalosis (pH will decrease by 0.08 for every 10 mm Hg change in PaCO2 from a normal value). As a result, the patient is currently being overventilated, and an alteration that results in decreased ventilation is indicated. It is important to recall that ventilation is inversely proportional to the frequency (Hz). Therefore, to decrease ventilation, one would increase the frequency. Increasing the delta P would increase the ventilation further. Changing the mean airway pressure (MAP) would have little influence on ventilation. The patient continues to have a marginally accepted PaO2 (70 mm Hg) while on an FIO2 of 60%; therefore, it is premature to consider weaning the MAP at this time. Since the patient has only been managed for 2 hours and the PaO2 remains acceptable, increasing the MAP is not indicated at this time. High-frequency oscillatory ventilation is used predominantly for hypoxemic respiratory failure and persistent, severe air leaks. Its effect on ventilation is often unpredictable.

Two parameters regulate oxygenation:

•• FIO2 •
•• MAP: increase MAP to increase PaO2 Two parameters regulate ventilation:
••• Delta P or amplitude: increase delta P to increase carbon dioxide.
••• Frequency: increase frequency to DECREASE ventilation/carbon dioxide.
••• Remember that frequency goes in the direction you want your carbon dioxide to go.

CvO2 = (13.5 × 1.36 × 0.56) + (0.003 × 30) = 10.37 mL/dL Recall that respiratory quotient (RQ) is the ratio of VCO2 to VO2 such that, VO2 = VCO2/RQ or here: VO2 = 236 mL/min/0.76 = 310 mL/min As a result: cardiac output = 310 mL/min/([17.52 –– 10.37 mL/dL]) × 100 = 4.3 L/min Fick principle is frequently used to measure cardiac output using oxygen content differences in systemic and pulmonary circulations:

•• Cardiac Output = Oxygen Uptake/(Arterial Oxygen –– Venous Oxygen)

Remember conversion of units is crucial here: CaO2 and CvO2 are most commonly calculated as mL/dL, so to convert to L/min, the product must be multiplied by 100 (number of dL in L).

6. Answer B
Rationale: Recall that furosemide is a member of the sulfa family of drugs (similar to cotrimoxazole). The timing of the reaction (within 30 minutes of drug administration) is typical for allergic reactions. The symptomatology is consistent with acute release of histamine from triggered mast cells causing flushing, vasodilation (hence the tachycardia), and bronchospasm. Transfusion-related acute lung injury can manifest with pulmonary edema and persistent hypoxemia, though this is rarely associated with the allergic manifestations described in this case. Acute transfusion reactions can present with these manifestations, but the timing is much more proximate to the timing of the blood product transfusion. There would be no reason that an aminoglycoside should trigger an allergic reaction in a sulfa-allergic patient.

7. Answer E
Rationale: It is imperative to familiarize oneself with anticipated postoperative complications following specific repairs of congenital heart lesions. Bleeding with tamponade and arrhythmias can potentially complicate every postoperative course. In the setting of acyanotic (socalled ““pink””) tetralogy, the pulmonary vasculature is under both increased pressure and flow due to the ventricular septal defect-like physiology with little obstructive physiology. These patients are at risk for acute pulmonary hypertensive crises (PHCs) characterized by acute hypotension with concurrent elevation in the central venous pressure (and pulmonary artery pressure, if being monitored). Several causes can trigger an acute PHC, including hypovolemia, agitation, hypoxia, and/or hypercapnia. In this case, the patient’’s arterial blood gas analysis shows a respiratory acidosis, which can profoundly effect pulmonary vascular resistance by increasing it. The quickest maneuver one can perform in this setting that may be of substantial benefit is to reverse this with hyperventilation. Also, the addition of 100% oxygen is a potent vasodilator, which may acutely aid in decreasing pulmonary vascular resistance. Opening the chest may be indicated ultimately, but would not be the first thing to attempt. Fluid administration to increase right ventricular preload will help with PHC, but this too will take time to obtain and intravenously push. Junctional ectopic tachycardia can be a frequent complication following repairs of congenital lesions associated with right ventricular hypertrophy. Sedation, cooling, and amiodarone can control the rate of junctional ectopic tachycardia; however, this diagnosis and therapy will take additional inquiry of the electrocardiographic strips and time. While all these maneuvers may be necessary and/or indicated, the first response should be immediate reversal of the respiratory acidosis and provision of 100% oxygen, which can be achieved almost immediately.

8. Answer A
Rationale: Appropriate antibiotic coverage is critical to successful treatment of acute bacterial meningitis. Gram-negative meningitis may require an antibiotic course as long as 3 weeks. Antibiotic resistance has become a real issue in both community and hospital clinical settings. The Klebsiella strain described in this scenario is noted to be extended-spectrum betalactamase positive. Although its antibiogram shows sensitivity to beta-lactam antibiotics, it is at high risk for becoming a resistant strain. Aminoglycosides are not affected by beta-lactamases. Clindamycin is not appropriate for gram-negative infections.

9. Answer C
Rationale: Neisseria meningitidis sepsis can produce rapidly developing septic shock. The pictured patient had classic purpura fulminans caused by N meningitidis. This organism is usually endemic and is commonly carried in the nasopharynx. Infection is more common in males and following influenza infections.

10 Answer B
Rationale: Oxygenation Index = FIO2 × mean airway pressure (MAP)/PaO2 has been used to assess risk of ventilatorassociated injury associated with barotraumas and oxygen toxicity and to identify appropriate candidates for extracorporeal life support. Baseline oxygenation index above (0.5 x 20 x 100)/106= 9.4
a. (0.5 x 25 x 100)/106 = 11.8
b. (0.5 x 20 x 100)/80 = 12.5
c. (0.5 x 20 x 100)/106 = 9.4
d. (0.6 x 20 x 100)/106 = 11.3
e. (0.5 x 20 x 100)/106 = 9.4