A 2-hour-old male neonate, born at 39 weeks gestation to a mother with poorly controlled p… — USMLE Step 2 CK

A $2$ -hour-old male neonate, born at $39$ weeks gestation to a mother with poorly controlled pregestational diabetes mellitus, is evaluated in the nursery for persistent cyanosis. The pregnancy was otherwise uncomplicated. Vital signs show a heart rate of $160$ /min, respiratory rate of $65$ /min, and blood pressure of $65/40$ mm Hg in the right arm and $68/42$ mm Hg in the left leg. Pulse oximetry reveals an oxygen saturation of $72\%$ on room air. Administration of $100\%$ oxygen via headbox for $15$ minutes fails to increase the oxygen saturation above $75\%$ . Physical examination shows a deeply cyanotic infant with mild intercostal retractions. Cardiac auscultation reveals a normal first heart sound, a loud and single $S_2$ , and no murmurs. The lungs are clear to auscultation bilaterally. Which of the following is the most appropriate next step in management?

A
Intravenous administration of ampicillin and gentamicin
Initiation of a continuous prostaglandin $E_1$ infusionCevap
C
Endotracheal intubation and administration of exogenous surfactant
D
Immediate transfer to the operating room for an arterial switch procedure
E
Continued observation with supportive care and supplemental oxygen

Cevap

The most appropriate next step is the initiation of a continuous prostaglandin

E_1

infusion.

This neonate presents with severe cyanosis that does not improve with

100\%

oxygen (a failed hyperoxia test) and a loud, single

S_2

without a murmur. This clinical picture is classic for transposition of the great arteries (TGA), the most common cyanotic congenital heart defect in neonates, which also carries a strong association with maternal pregestational diabetes. In TGA, the aorta arises from the right ventricle and the pulmonary artery from the left ventricle, creating two parallel and completely separate circulations. Survival heavily depends on the mixing of oxygenated and deoxygenated blood via an atrial septal defect, ventricular septal defect, or a patent ductus arteriosus (PDA). Therefore, the immediate, life-saving next step is to initiate a continuous prostaglandin

E_1

infusion to keep the ductus arteriosus open, allowing mixing of the circulations until a balloon atrial septostomy or definitive surgical correction can be performed.

Adım Adım Çözüm

Analyze the maternal history and initial presentation.

The patient is a term neonate born to a mother with pregestational diabetes, presenting with profound cyanosis shortly after birth.

Maternal pregestational diabetes is a major risk factor for specific congenital anomalies, notably transposition of the great arteries (TGA) and hypertrophic cardiomyopathy.

Interpret the hyperoxia test results and physical examination findings.

The failure of oxygen saturation to improve with

100\%

oxygen indicates a fixed right-to-left shunt (a cardiac etiology) rather than a pulmonary issue. A loud, single

S_2

without a murmur is highly characteristic of TGA due to the anterior displacement of the aorta.

Differentiating between pulmonary and cardiac causes of cyanosis is critical. A failed hyperoxia test confirms a cyanotic congenital heart defect.

Determine the most appropriate initial management for the suspected diagnosis.

The patient has a ductal-dependent cardiac lesion requiring immediate medical stabilization with a prostaglandin

E_1

infusion.

Prostaglandin

E_1

maintains the patency of the ductus arteriosus. This is essential to allow the mixing of oxygenated and deoxygenated blood between the two parallel circulations in TGA, preventing rapid decompensation before surgical intervention.

Anahtar Kavram

Transposition of the Great Arteries (TGA) presentation and acute management

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

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