A 14-day-old female neonate, born at 26 weeks gestation, is evaluated in the neonatal inte… — USMLE Step 2 CK

A $14$ -day-old female neonate, born at $26$ weeks gestation, is evaluated in the neonatal intensive care unit for worsening respiratory distress. She was initially treated with surfactant for respiratory distress syndrome and successfully extubated to noninvasive positive pressure ventilation on day $3$ of life. Over the past $24$ hours, she has required an increasing fraction of inspired oxygen ( $FiO_2$ ) and has experienced three episodes of apnea. Her temperature is $36.9^\circ\text{C}$ ( $98.4^\circ\text{F}$ ), heart rate is $178/\text{min}$ , and blood pressure is $50/20\text{ mmHg}$ . Physical examination reveals bounding palmar and pedal pulses and a hyperactive precordium. A continuous, machinery-like murmur is heard loudest at the left infraclavicular region. Lung auscultation reveals bilateral crackles. An echocardiogram confirms a left-to-right shunt through a vascular structure connecting the descending aorta and the left pulmonary artery. The medical team decides to initiate targeted pharmacologic therapy to close this structure. Which of the following is a well-recognized potential adverse effect of the most appropriate medication for this indication?

Decreased urine outputAnswer
B
Apnea
C
Hypokalemia
D
First-degree atrioventricular block
E
Rebound pulmonary hypertension

Answer

Decreased urine output

The correct answer is decreased urine output. This premature neonate's presentation of bounding pulses, widened pulse pressure, a continuous machinery-like murmur, and pulmonary edema (manifesting as worsening respiratory distress and increasing oxygen requirements) is classic for a symptomatic patent ductus arteriosus (PDA). The echocardiogram confirms the diagnosis by visualizing the connection between the descending aorta and the left pulmonary artery. The initial pharmacologic management to close a PDA involves administering a cyclooxygenase (COX) inhibitor, such as indomethacin or ibuprofen. COX inhibitors work by decreasing the synthesis of prostaglandins, which removes the vasodilatory effect on the ductus arteriosus, allowing it to constrict and close. However, prostaglandins also play a critical physiologic role in maintaining renal blood flow by dilating the afferent arteriole. Therefore, systemic COX inhibition frequently leads to renal vasoconstriction, manifesting as transient oliguria (decreased urine output) and elevated serum creatinine. Other notable adverse effects of indomethacin in neonates include gastrointestinal bleeding, necrotizing enterocolitis, and platelet dysfunction.

Step-by-Step Solution

Diagnose the patient's underlying condition based on the clinical presentation and echocardiogram findings.

The patient has a symptomatic patent ductus arteriosus (PDA).

The bounding pulses, wide pulse pressure (

50/20\text{ mmHg}

), continuous machinery murmur, and echocardiogram demonstrating a connection between the descending aorta and left pulmonary artery are diagnostic of a PDA.

Identify the most appropriate targeted pharmacologic therapy to address the underlying condition.

A cyclooxygenase (COX) inhibitor, such as indomethacin or ibuprofen.

COX inhibitors decrease prostaglandin synthesis, removing the vasodilatory effect on the ductus arteriosus and promoting its closure.

Identify the well-recognized adverse effects of the indicated medication.

Decreased urine output (oliguria), transient acute kidney injury, and gastrointestinal bleeding.

Prostaglandins normally dilate the afferent renal arteriole. Inhibiting their synthesis leads to renal vasoconstriction and decreased renal perfusion.

Key Concept

Pharmacologic closure of a patent ductus arteriosus (PDA) in a premature neonate is achieved with cyclooxygenase (COX) inhibitors (e.g., indomethacin, ibuprofen), which commonly cause transient renal vasoconstriction and decreased urine output.

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