Journal of Pediatric Critical Care

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

Critical Thinking
Year : 2016 | Volume : 3 | Issue : 4 | Page : 127-131

PICU Quiz (Pediatric Cardiac issues)

Praveen Khilnani

BLK Superspeciality Hospital, New Delhi & Mediclinic City Hospital, Dubai

Correspondence Address:

author
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Received: 05-Nov-16/Accepted: 15-Nov-16/Published online: 22-Nov-16

Source of Funding:None Conflict of Interest:None

DOI:10.21304/2016.0304.00155

1. A patient has poor perfusion postoperatively following repair of an AV canal-type ventricular septal defect. Which of the following conditions is NOT likely the cause?
A. Hypovolemia
B. Mitral regurgitation
C. Pulmonary hypertension
D. Residual right ventricular outflow tract obstruction
E. Low cardiac output syndrome secondary to cardiopulmonary bypass

2. Which of the following statements about pressure volume loops of compensated systolic heart failure is true?

A. Stroke volume is decreased.
B. End diastolic pressure is decreased.
C. Ventricular contractility is usually preserved.
D. Slope of the end systolic pressure volume relation (ESPVR) is reduced.
E. The passive diastolic pressure volume curve is shifted up and to the left.

3. Which of the following statements about pressure volume loops of compensated diastolic heart failure is true?
A. End diastolic pressure is decreased.
B. Stroke volume is usually unchanged.
C. Ventricular compliance is increased.
D. Slope of the end systolic pressure volume relation (ESPVR) is reduced.
E. The passive diastolic pressure volume curve is shifted up and to the left.

4. The half-life of milrinone is characterized by which of the following?
A. Duration of 2 to 3 minutes
B. Prolonged by hemofiltration
C. Age dependence
D. Unaffected by renal failure

5. Which of the following statements about IV loading with amiodarone is true?
A. Total loading dose should not exceed 50 mg /kg.
B. A slow IV bolus over 30 minutes usually does not cause hypotension.
C. Its associated hypotensive effects are due to its β-adrenergic blocking effects.
D. Administration in an acute setting may cause acute respiratory distress syndrome.

6. The neonatal myocardium is characterized as being:
A. more responsive to increases in preload.
B. more tolerant of increases in afterload.
C. more compliant than that of an older child.
D. less tolerant to changes in pulmonary vascular resistance.

7. Which of the following conditions is NOT considered a clinical consequence of cardiopulmonary bypass in a newborn or infant?
A. Generalized capillary leak and increased interstitial fluid
B. Myocardial edema and decreased diastolic and systolic function
C. Decreased alveolar-arterial oxygen (A-a) gradient
D. Multiple-organ dysfunction
E. Delayed sternal closure

8. A 2.2-kg, 4-day-old neonate born at 36 weeks’ gestation who has borderline-small structures on the left side of the heart is unstable after repair of critical coarctation and perimembranous ventricular septal defect. Systolic blood pressure is in the mid to low 50s. The following are being administered: dopamine 15 μg /kg /min, epinephrine 0.12 μg /kg /min, and milrinone 0.5 μg /kg /min. Physical examination reveals weak peripheral pulses, prolonged capillary refill, and cool extremities. Pressures are 17 mm Hg in the right atrium and 20 mm Hg in the left atrium. Five fluid boluses have been given with only minimal response in blood pressure. The patient’s heart rate is in normal sinus rhythm at 168 beats/min. Arterial blood gas analysis shows excellent gas exchange but increasing metabolic acidosis. The patient’s lactic acid level is 5.8 mg /dL. What is the next most appropriate step to achieve the greatest improvement in cardiac output?
A. Give a bolus of albumin.
B. Discontinue the milrinone.
C. Increase the epinephrine to 0.15 μg /kg /min.
D. Start vasopressin at 0.05 mu/kg /min.
E. Request that the surgeon open the chest.

9. A 5-month-old female infant undergoes uneventful repair of a large perimembranous ventricular septal defect and returns to the ICU on a dopamine infusion of 5 μg /kg /min. Six hours postoperatively, junctional ectopic tachycardia (JET) develops, with a heart rate of 135 beats/min. Despite cooling and sedation, the patient remains in JET, with a heart rate of 140 beats/min. She is mildly hypotensive, with cool extremities and decreased urine output. What is the next most appropriate step to improve cardiac output?
A. Increase the dopamine from 5 to 10 μg /kg /min.
B. Initiate atrial (AAI) pacing at 145 beats/min.
C. Administer epinephrine.
D. Administer amiodarone 2.5 to 5 mg /kg over 30 minutes, followed by an amiodarone drip.


10. A 2-week-old female infant underwent repair of classic hypoplastic left heart syndrome (HLHS) with the Norwood Sano procedure 9 days ago. Up to now, the postoperative course has been uneventful. She is noted to have a decreased PaO2 to 24 mm Hg over the past few hours despite increases in her FiO2 from 0.3 to 0.6. Chest radiographs show no pulmonary disease; her systolic blood pressure is maintained in the 80 mm Hg range with dopamine 7 μg /kg /min; and an echocardiogram shows decent right ventricular function, with minimal tricuspid regurgitation and no residual coarctation. Lactic acid is 4 mg /dL. What is the next most appropriate step in management?
A. Administer epinephrine to further increase the blood pressure.
B. Administer nitric oxide to treat pulmonary hypertension.
C. Take the patient to the cardiac catheterization lab to assess the shunt.
D. Open the chest to allow for allow for myocardial swelling.

Answers
1.Answer: D         Residual right ventricular outflow tract obstruction
Rationale: All of the above conditions may cause low cardiac output postoperatively; however, residual right ventricular outflow obstruction would be the least likely unless tetralogy of Fallot repair accompanied the AV canal repair.
Factors implicated in the development of myocardial dysfunction following cardiopulmonary bypass (CPB) include the inflammatory response associated with CPB, myocardial ischemia from aortic cross-clamping, hypothermia, reperfusion injury, inadequate myocardial protection, and ventriculotomy (when performed).
Residual or undiagnosed structural lesions can also result in low cardiac output after CPB (eg, mitral regurgitation after AV canal repair).
Pulmonary vascular resistance may be elevated following CPB. Factors such as pulmonary vascular endothelial dysfunction, microemboli, pulmonary leukosequestration, excess thromboxane production, atelectasis, hypoxic pulmonary vasoconstriction, and adrenergic stimulation may contribute to the development of postoperative pulmonary hypertension. Other factors that predispose patients to postoperative pulmonary vascular reactivity include preoperative pulmonary hypertension and left-to-right shunts and the duration of CPB.
References:
1. Nichols DG, ed. Rogers’ Textbook of Pediatric Intensive Care. 4th ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2008:1161–1168.

2.Answer: D        Slope of the end systolic pressure volume relation (ESPVR) is reduced.
Rationale: Cardiac function can be evaluated experimentally by plotting ventricular pressure against ventricular volume throughout the cardiac cycle. Pressure-volume (PV) loops can be generated under different physiologic conditions.
With systolic heart failure, the slope of the ESPVR is reduced, indicating decreased contractility. Stroke volume can be maintained by increasing preload, but end diastolic pressure is increased. The PV loop for compensated systolic heart failure is shown below.
Reproduced from Sidebotham D, McKee A, Gillham M, et al, eds. Cardiothoracic Critical Care. Philadelphia, PA: Butterworth-Heinemann; 2007:8. With permission from Elsevier.
References:
1. Sidebotham D, McKee A, Gillham M, et al, eds. Cardiothoracic Critical Care. Philadelphia, PA: Butterworth-Heinemann; 2007:8.

3.Answer: E         The passive diastolic pressure volume curve is shifted up and to the left.
Rationale: With diastolic heart failure, the passive diastolic pressure volume (PV) curve is shifted up and to the left, indicating increased chamber stiffness (decreased ventricular compliance). The ESPVR is unchanged and stroke volume is preserved, but end diastolic pressure is increased. The PV loop for compensated diastolic heart failure is shown below. Reproduced from Sidebotham D, McKee A, Gillham M, et al, eds. Cardiothoracic Critical Care. Philadelphia, PA: Butterworth-Heinemann; 2007:8. With permission from Elsevier.
References:
1. Sidebotham D, McKee A, Gillham M, et al, eds. Cardiothoracic Critical Care. Philadelphia, PA: Butterworth-Heinemann; 2007:8.

4.Answer: C       dependence
Rationale: Milrinone is predominantly cleared by renal excretion. Its half-life is much longer than other vasoactive infusions used in the ICU and is age dependent, ranging from more than 3 hours in infants to less than 1 hour in children. Since milrinone is renally excreted, the dose must be adjusted with renal insufficiency. Half-life is even more prolonged by hemofiltration, up to 20 hours.
References:
1. Slonim AD, Pollack MM, Bell MJ, et al, eds. Pediatric Critical Care Medicine. Philadelphia, PA: Lippincott, Williams, & Wilkins; 2006:666.

5.Answer: B         A slow IV bolus over 30 minutes usually does not cause hypotension.
Rationale: The hypotensive effects of amiodarone are due to its α-blocking effects. Rapid IV administration can cause hypotension due to the Tween 80 solvent in which the amiodarone is mixed. IV infusion of 2.5 to 5.0 mg /kg of amiodarone over 30 minutes is generally well tolerated and usually does not cause significant hypotension. The usual maximum loading dose is 15 mg /kg.
One concern regarding acute side effects is a possible relationship between amiodarone and acute respiratory distress syndrome (ARDS). This association has been observed in critically ill patients and in adults following cardiac and thoracic surgery. These studies, however, are retrospective and observational, and the association has not been definitively confirmed. Given the clear benefits of amiodarone in patients who undergo cardiac surgery and the lack of a definitive association between amiodarone and ARDS, it is reasonable to continue its use for the treatment and prevention of perioperative arrhythmia.
References:
1. Sidebotham D, McKee A, Gillham M, et al, eds. Cardiothoracic Critical Care. Philadelphia, PA: Butterworth-Heinemann; 2007:45.

6.Answer: D         less tolerant to changes in pulmonary vascular resistance.
Rationale: Postoperative care of the critically ill neonate after cardiac surgery requires an understanding of the special structural and functional features of immature organs, particularly the immature myocardium and the transitional circulation. The neonate may be more likely to maintain blood pressure in a state of impending shock. Thus, systemic blood pressure is not always a reliable indicator of the adequacy of preload or satisfactory oxygen delivery. The neonatal myocardium is less compliant than that of the older child, is less tolerant of increases in afterload, and is less responsive to increases in preload. Pulmonary vascular resistance may be elevated or labile in neonates. Pulmonary hypertensive events are a potential risk and are poorly tolerated by the neonatal myocardium.
References:
1. Allen HD, Driscoll DJ, Shaddy RE, et al, eds. Moss and Adams’ Heart Disease in Infants, Children, and Adolescents. 7th ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2008:449.

7.Answer: C         Decreased alveolar-arterial oxygen (A-a) gradient
Rationale: Postoperative effects of cardiopulmonary bypass are the result of interaction of blood components with the extracorporeal circuit and result in activation of the inflammatory cascade, resulting in a systemic inflammatory response. The clinical consequences may include increased interstitial fluid, generalized capillary leak, and multiple-organ dysfunction. Pulmonary effects include an increase in total lung water with an associated decrease in lung compliance. These changes result in an increase in A-a gradient. The myocardium becomes edematous, which results in impaired systolic and diastolic function. Cardiac output in neonates often decreases 20% to 30% in the 6 to 12 hours following surgery, which contributes to decreased renal function and oliguria. In sicker patients, sternal closure may be delayed to allow more physical space for myocardial and mediastinal edema and less risk for cardiorespiratory compromise. Other organ dysfunction may also occur, including hepatic congestion, ascites, bowel edema with prolonged ileus, and coagulopathy.
References:
1. Jonas RA. Comprehensive Surgical Management of Congenital Heart Disease. London: Hodder Arnold; 2004:74.

8.Answer: E         Request that the surgeon open the chest.
Rationale: The patient has severe ventricular dysfunction. Patients who require persistent or escalating doses of epinephrine may benefit from surgical opening of the sternum to allow room for expansion of the dilated and poorly functioning myocardium.
Increasing the epinephrine dose or adding vasopressin may increase blood pressure temporarily by increasing vasoconstriction. However, afterload will be increased, which may inhibit forward blood flow in the sick heart, further decreasing cardiac output and worsening cardiac function. Neonatal myocardium tolerates afterload stress poorly, especially when already sick. Milrinone is an inodilator that may help decrease afterload and improve cardiac performance. Discontinuing milrinone in this setting is not likely to be beneficial. While an albumin bolus may temporarily improve blood pressure, the left atrial pressure is already high at 20 mm Hg. Excessive fluid may cause further impairment in cardiac function due to overdistention of the left side of the heart.
In this situation, opening the sternum is likely to result in the most significant improvement in cardiac output. Other therapies that might be considered include steroids, triiodothyronine (T3) infusion, and mechanical support such as extracorporeal membrane oxygenation.
References:
1. Jonas RA. Comprehensive Surgical Management of Congenital Heart Disease. London: Hodder Arnold; 2004:74.

9..Answer: B         Initiate atrial (AAI) pacing at 145 beats /min.
Rationale: Postoperative tachydysrhythmias can be very difficult to treat, particularly when cardiac output is compromised. Junctional ectopic tachycardia (JET) commonly occurs following cardiac surgery. Cardiac output decreases due to the loss of atrioventricular (AV) synchrony and resultant decreased diastolic filling. Limiting inotropic support is theoretically helpful in automatic tachydysrhythmias like JET; however, this may not be feasible postoperatively when pressors are needed for depressed cardiac function. When the JET rate is modest, atrial pacing above the JET rate will restore AV synchrony, increase diastolic filling, and thus improve blood pressure by increasing cardiac output and stroke volume. Amiodarone is the drug of choice for JET but may cause further hypotension and would typically be given if a trial of pacing is ineffective. It is typically used when the JET rate is too fast to allow a reasonable rate for overdrive pacing. When conventional management fails in patients with refractory arrhythmias and persistently compromised cardiac output, mechanical support such as extracorporeal membrane oxygenation may be beneficial until the dysrhythmia resolves.
References:
1. Jonas RA. Comprehensive Surgical Management of Congenital Heart Disease. London: Hodder Arnold; 2004:77.

10.Answer: C         Take the patient to the cardiac catheterization lab to assess the shunt.
Rationale: In patients with single ventricle physiology, PaO2 and oxygen saturation depend on the relative amount of blood going to the lungs (Qp) compared with the amount going to the body (QS). Oxygen saturation is low and blood pressure is adequate, so the patient is under circulated. In a patient with under circulation, Qp < Qs, and either pulmonary vascular resistance (PVR) is high or the shunt is small, kinked, or thrombosed. Acute treatment includes lowering PVR (hyperventilation, alkalosis, sedation/paralysis), increasing cardiac output (using inotropes), and increasing hematocrit. However, the priority must be to define the problem. In this example, the patient has significantly diminished pulmonary blood flow with lactic acidosis. A clot in the Sano shunt or a mechanical obstruction must be ruled out by cardiac catheterization. This patient was found to have a kink in the Sano shunt that required stenting.
Reference:
1. Nichols DG, ed. Rogers’ Textbook of Pediatric Intensive Care. 4th ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2008:1173–1177.