A male infant is delivered at 39 weeks gestation to a 28-year-old primigravida via emergen… — USMLE Step 2 CK

A male infant is delivered at $39$ weeks gestation to a 28-year-old primigravida via emergency cesarean delivery due to a prolonged fetal heart rate deceleration. At birth, the infant is apneic, cyanotic, and limp. Positive pressure ventilation is initiated, and the infant is subsequently intubated. Apgar scores are 1, 3, and 5 at 1, 5, and 10 minutes of life, respectively. An umbilical cord arterial blood gas reveals a pH of $6.95$ and a base deficit of $17 \text{ mEq/L}$ . At 45 minutes of life, the infant is breathing spontaneously via continuous positive airway pressure (CPAP). Physical examination reveals a lethargic infant with profound hypotonia, an absent Moro reflex, and a weak suck. Vital signs show a heart rate of $145\text{/min}$ , respiratory rate of $40\text{/min}$ , and blood pressure of $60/40\text{ mmHg}$ . Which of the following is the most appropriate next step in the management of this patient?

Initiate whole-body therapeutic hypothermiaAnswer
B
Administer intravenous sodium bicarbonate
C
Obtain an urgent non-contrast computed tomography scan of the head
D
Administer intravenous vancomycin and cefotaxime
E
Measure serum thyroid-stimulating hormone and free T4 levels

Answer

Initiate whole-body therapeutic hypothermia

The correct answer identifies that this infant meets all criteria for therapeutic hypothermia (targeted temperature management) due to Hypoxic-Ischemic Encephalopathy (HIE). The criteria include: gestational age

\geq 36

weeks, evidence of a significant perinatal hypoxic event (cord pH

< 7.0

, base deficit

\geq 16 \text{ mEq/L}

, or Apgar score

< 5

at 10 minutes), and a clinical neurological exam showing moderate to severe encephalopathy (lethargy, hypotonia, abnormal reflexes). Therapeutic hypothermia must be initiated within the first 6 hours of life. It acts by reducing cerebral metabolism, suppressing the release of excitatory neurotransmitters, and limiting apoptosis, thereby decreasing the rates of cerebral palsy and mortality.

Step-by-Step Solution

Analyze the perinatal history and umbilical cord blood gas.

The infant experienced a severe hypoxic-ischemic event, evidenced by a prolonged deceleration, an Apgar score of 5 at 10 minutes, a cord pH of

6.95

, and a base deficit of

17 \text{ mEq/L}

Establishing the presence of severe perinatal asphyxia is the first prerequisite for specific neuroprotective interventions.

Evaluate the infant's current neurological status.

The infant exhibits lethargy, profound hypotonia, an absent Moro reflex, and a weak suck, which are all clinical signs of moderate to severe encephalopathy.

Specific interventions for asphyxia are only indicated if the infant demonstrates subsequent clinical signs of brain injury.

Determine the most appropriate time-sensitive intervention.

Whole-body therapeutic hypothermia must be initiated immediately.

In term or near-term infants (

\geq 36

weeks gestation) with Hypoxic-Ischemic Encephalopathy (HIE), cooling the body temperature to

33.5^\circ\text{C}

within the first 6 hours of life is the standard of care to significantly reduce mortality and long-term neurodevelopmental disability.

Key Concept

Criteria and timely initiation of therapeutic hypothermia for Neonatal Hypoxic-Ischemic Encephalopathy (HIE).

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