SET 1:
Q: 1 A term male becomes tachypneic 30 minutes after birth. Preductal SpO₂ is 96% and postductal is 86%. No murmur. Which physiologic change most directly explains the gradient? What is the single best explanation for the differential saturation?
A. Decreased endogenous prostaglandin production causing PFO closure
B. Increased pulmonary venous return promoting left-to-right PDA shunt
C. Persistent elevated PVR maintaining right-to-left PDA shunt
D. Sudden drop in SVR increasing ductal flow into the descending aorta
E. Closure of the ductus venosus increasing preload to the right heart
Answer:
C
Rationale: In early transition, if PVR remains high, right-to-left shunting across the PDA causes lower postductal saturation. PFO behavior doesn’t explain upper–lower gradient; SVR rises (not drops) after cord clamping; ductus venosus changes don’t create differential sats.
Q: 2 A fetus with suspected HLHS is referred at 30 weeks. Which prenatal Doppler pattern predicts ductal-dependent systemic flow after birth? Which finding is most predictive of postnatal ductal dependence?
A. Antegrade flow across the transverse aortic arch
B. Retrograde flow in the transverse aortic arch
C. High MCA pulsatility index
D. Low umbilical artery pulsatility index
E. Increased flow through the ductus venosus into the IVC
Answer:
B
Rationale: Retrograde arch flow signals severely limited LV output and ductal-dependent systemic circulation postnatally. Antegrade arch flow suggests the LV can support systemic output; brain-sparing changes (MCA PI) are secondary, not diagnostic.
Q: 3 A neonate with HLHS on PGE has worsening acidosis after increasing FiO₂. Pre-/post-ductal sats are now 98/98. Lactate rises. What is the most appropriate next step?
A. Further increase FiO₂ to maximize arterial O₂ content
B. Add inhaled nitric oxide
C. Decrease FiO₂ and allow mild hypercapnia to raise PVR
D. Start milrinone to increase systemic blood flow
E. Immediate balloon atrial septostomy
Answer:
C
Rationale: In single ventricle parallel circulation, excessive pulmonary blood flow (“steal”) compromises systemic perfusion; raising PVR (less O₂, mild hypercapnia) rebalances Qp:Qs. iNO and higher FiO₂ further lower PVR (worse). BAS is for restrictive atrial septum, not suggested here.
Q: 4 A cyanotic 2-day-old with weak femoral pulses is at a community ED. Preductal SpO₂ 95%, postductal 80%. First action before transport?
A. 20 mL/kg normal saline
B. Start prostaglandin E1 infusion
C. Give furosemide
D. Immediate intubation with 100% O₂
E. Synchronized cardioversion
Answer:
B
Rationale: Differential cyanosis suggests ductal-dependent systemic flow (e.g., coarctation). PGE1 to maintain/reopen PDA is time-critical prior to transport; hyperoxia can worsen systemic output in some lesions; other options are not definitive first steps.
Q: 5 A 6-month-old with cardiomyopathy presents with rising PaCO₂ (38→58 mmHg in 1 hr), increasing work of breathing, and fatigue. What is the best next step?
A. Continue noninvasive ventilation and observe
B. Trial of diuretics and recheck gas in 2 hours
C. Intubate and institute mechanical ventilation
D. Start bicarbonate for acidosis
E. Begin neuromuscular blockade without intubation
Answer:
C
Rationale: Impending respiratory failure with rapidly rising PaCO₂ and fatigue is a relative indication for controlled intubation/mechanical ventilation in critically ill children. Delays worsen decompensation.
