Parents bring their 4-week-old male infant to the acute care clinic because he has been fo… — USMLE Step 2 CK

Parents bring their $4$ -week-old male infant to the acute care clinic because he has been forcefully vomiting after feeds for the past five days. The nonbilious vomitus frequently shoots across the crib. Despite the recurrent emesis, the infant appears remarkably hungry and demands to feed again immediately. Over the last $48$ hours, his urine output has decreased to only one wet diaper per day. Vital signs show a heart rate of $165\text{/min}$ , blood pressure of $68/38\text{ mm Hg}$ , and respiratory rate of $32\text{/min}$ . Physical examination reveals a lethargic infant with sunken eyes, a depressed anterior fontanelle, and a capillary refill time of $5$ seconds. Abdominal examination is notable for a palpable, firm, olive-shaped mass in the right upper quadrant.

Laboratory studies demonstrate the following:

Laboratory Test	Result	Reference Range
Sodium	$131\text{ mEq/L}$	$135 - 145\text{ mEq/L}$
Potassium	$2.8\text{ mEq/L}$	$3.5 - 5.0\text{ mEq/L}$
Chloride	$85\text{ mEq/L}$	$98 - 106\text{ mEq/L}$
Bicarbonate	$35\text{ mEq/L}$	$22 - 28\text{ mEq/L}$
Blood urea nitrogen	$32\text{ mg/dL}$	$5 - 18\text{ mg/dL}$
Creatinine	$0.7\text{ mg/dL}$	$0.2 - 0.4\text{ mg/dL}$

What is the most appropriate initial step in the management of this patient?

Administration of an intravenous normal saline bolusCevap
B
Immediate surgical consultation for pyloromyotomy
C
Intravenous fluid resuscitation with potassium-enriched half-normal saline
D
Diagnostic evaluation with a right upper quadrant ultrasound
E
Initiation of feeding with an extensively hydrolyzed formula

Cevap

Administration of an intravenous normal saline bolus

The most appropriate initial step in the management of this patient is the administration of an intravenous normal saline bolus. This infant presents with the classic triad of hypertrophic pyloric stenosis: projectile nonbilious vomiting, a palpable olive-shaped abdominal mass, and visible gastric peristalsis (often seen in hungry infants). The profound vomiting of gastric contents (hydrochloric acid) results in a hypochloremic, hypokalemic metabolic alkalosis. This infant is hemodynamically unstable, exhibiting tachycardia, hypotension, lethargy, and a prolonged capillary refill time indicative of hypovolemic shock. According to pediatric advanced life support guidelines, the immediate priority in a patient with decompensated hypovolemic shock is rapid restoration of intravascular volume using an isotonic crystalloid, such as

0.9\%

normal saline. Only after the patient's intravascular volume is restored and urine output is established should maintenance fluids with added potassium be initiated. Pyloromyotomy is the definitive treatment, but it is considered an elective procedure that must be delayed until the patient's acid-base status and electrolyte derangements are fully corrected.

Adım Adım Çözüm

Identify the primary diagnosis based on the clinical presentation and physical exam.

The infant has hypertrophic pyloric stenosis, characterized by projectile nonbilious vomiting, an 'olive-shaped' abdominal mass, and an eagerness to feed.

Recognizing the classic triad of symptoms is essential for guiding subsequent workup and management.

Analyze the laboratory data and vital signs to determine the patient's physiological state.

The patient has severe hypovolemia (tachycardia, hypotension, prolonged capillary refill, elevated BUN/creatinine) and classic hypochloremic, hypokalemic metabolic alkalosis.

Prolonged vomiting of gastric acid leads to depletion of fluid, hydrogen, and chloride ions. The kidneys compensate by excreting potassium to retain hydrogen, worsening the hypokalemia.

Select the most appropriate immediate intervention based on acuity.

The patient requires immediate fluid resuscitation with an isotonic crystalloid solution (normal saline).

In any hemodynamically unstable patient, restoring intravascular volume and organ perfusion takes absolute precedence over definitive surgical treatment or imaging.

Anahtar Kavram

Medical optimization of hypertrophic pyloric stenosis prior to surgery

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