A 72-year-old man is evaluated in the emergency department for severe, sudden-onset abdomi… — USMLE Step 2 CK

A 72-year-old man is evaluated in the emergency department for severe, sudden-onset abdominal pain that began $4$ hours ago. His medical history is significant for a large anterior wall myocardial infarction $4$ weeks ago, hypertension, and hyperlipidemia. He has not adhered to his prescribed medication regimen since discharge. The patient was initially writhing in agony, but over the past hour, he has become progressively lethargic. His temperature is $38.2^\circ\text{C}$ ( $100.8^\circ\text{F}$ ), pulse is $135/\text{min}$ and irregularly irregular, blood pressure is $78/50\text{ mmHg}$ , and respirations are $28/\text{min}$ . Physical examination reveals a mottled appearance of the lower extremities. The abdomen is moderately distended and diffusely rigid, with marked involuntary guarding and rebound tenderness in all four quadrants. Bowel sounds are absent. Laboratory studies show:

Leukocyte count: $26,000/\text{mm}^3$
Hemoglobin: $14.2\text{ g/dL}$
Bicarbonate: $12\text{ mEq/L}$
Lactate: $7.8\text{ mmol/L}$

An electrocardiogram shows atrial fibrillation with a rapid ventricular response and deep Q waves in the anterior leads. Which of the following is the most appropriate next step in management?

Immediate exploratory laparotomyAnswer
B
CT angiography of the abdomen and pelvis
C
Nasogastric intubation, intravenous fluids, and broad-spectrum antibiotics
D
Transthoracic echocardiography
E
Diagnostic laparoscopy

Answer

Immediate exploratory laparotomy is required due to the presence of peritonitis and hemodynamic instability in the setting of acute mesenteric ischemia.

The correct answer is immediate exploratory laparotomy. This patient's presentation of sudden-onset abdominal pain in the setting of atrial fibrillation and a recent anterior myocardial infarction is highly suspicious for acute mesenteric ischemia caused by a superior mesenteric artery embolus. While early mesenteric ischemia classically presents with 'pain out of proportion to physical exam findings,' this patient has progressed to transmural bowel infarction, resulting in a rigid abdomen, generalized peritonitis, and septic shock (hypotension, tachycardia, severe lactic acidosis). In any patient with suspected ischemic bowel, the development of peritonitis or hemodynamic instability mandates immediate exploratory laparotomy to resect the necrotic bowel and perform abdominal washout. Delaying surgery for imaging in this critical state is contraindicated.

Step-by-Step Solution

Identify the underlying diagnosis based on the clinical presentation and risk factors.

The patient has sudden, severe abdominal pain, a high lactate level, and major risk factors for an arterial embolus (recent anterior MI predisposing to left ventricular thrombus, and atrial fibrillation). This strongly points to acute mesenteric ischemia (AMI), likely a superior mesenteric artery (SMA) embolus.

Recognizing the etiology is crucial, but determining the disease stage dictates the immediate action.

Assess the patient's hemodynamic status and physical examination findings.

The patient is in shock (BP 78/50 mmHg, HR 135/min, lethargy, mottled extremities) and has frank peritonitis (rigid abdomen, involuntary guarding, rebound tenderness).

These findings indicate that the ischemia has progressed to transmural bowel infarction and perforation, leading to septic shock.

Determine the appropriate management pathway based on the clinical severity.

Although CT angiography is the standard diagnostic test for early AMI, the presence of peritonitis and hemodynamic instability is an absolute indication for immediate exploratory laparotomy.

Unstable patients with a surgical abdomen must go directly to the operating room; delaying for imaging or attempting conservative measures increases mortality.

Key Concept

Management algorithm for Acute Mesenteric Ischemia (AMI)

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