An 81-year-old woman is brought to the emergency department from a skilled nursing facilit… — USMLE Step 2 CK

An $81$ -year-old woman is brought to the emergency department from a skilled nursing facility due to the sudden onset of severe, unrelenting abdominal pain that began $4$ hours ago. The facility staff reports that she has become progressively lethargic and confused over the past hour. Her past medical history is significant for heart failure with preserved ejection fraction, hypertension, and paroxysmal non-valvular atrial fibrillation. She has not taken her prescribed apixaban for the last three weeks due to an insurance coverage issue.

Her temperature is $38.4^\circ\text{C}$ ( $101.1^\circ\text{F}$ ), pulse is $132/\text{min}$ and irregularly irregular, blood pressure is $82/48\text{ mmHg}$ , and respirations are $26/\text{min}$ . Pulse oximetry shows $94\%$ on ambient air. She is diaphoretic and writhing in bed. Cardiopulmonary examination reveals an irregular heartbeat with no murmurs, and the lungs are clear to auscultation. The abdomen is rigid and distended. There is diffuse, severe tenderness to palpation with marked involuntary guarding and rebound tenderness in all four quadrants. Bowel sounds are absent. Digital rectal examination yields grossly normal-appearing stool that is positive for occult blood.

Laboratory studies are as follows:

Parameter	Result	Reference Range
Leukocyte count	$24,500/\text{mm}^3$	$4,500-11,000/\text{mm}^3$
Hemoglobin	$11.2\text{ g/dL}$	$12.0-15.5\text{ g/dL}$
Platelet count	$190,000/\text{mm}^3$	$150,000-400,000/\text{mm}^3$
Serum sodium	$138\text{ mEq/L}$	$136-145\text{ mEq/L}$
Serum potassium	$5.1\text{ mEq/L}$	$3.5-5.0\text{ mEq/L}$
Serum chloride	$104\text{ mEq/L}$	$95-105\text{ mEq/L}$
Serum bicarbonate	$10\text{ mEq/L}$	$22-28\text{ mEq/L}$
Blood urea nitrogen	$42\text{ mg/dL}$	$8-20\text{ mg/dL}$
Serum creatinine	$1.8\text{ mg/dL}$	$0.6-1.2\text{ mg/dL}$
Serum lactate	$8.4\text{ mmol/L}$	$0.5-2.2\text{ mmol/L}$

Arterial blood gas analysis on room air shows a pH of $7.18$ and a $\text{pCO}_2$ of $28\text{ mmHg}$ .

Which of the following is the most appropriate next step in the management of this patient?

A
Computed tomography angiography of the abdomen and pelvis
Immediate exploratory laparotomyAnswer
C
Intravenous unfractionated heparin infusion and intensive care observation
D
Mesenteric digital subtraction angiography with catheter-directed thrombolysis
E
Intravenous administration of broad-spectrum antibiotics and placement of a nasogastric tube

Answer

Immediate exploratory laparotomy is the correct management due to the presence of hemodynamic instability and overt peritonitis indicating transmural bowel infarction.

This patient presents with classic signs of acute mesenteric ischemia (AMI) resulting from an arterial embolus secondary to unanticoagulated atrial fibrillation. The sudden onset of unrelenting pain, profoundly elevated lactate, leukocytosis, and anion gap metabolic acidosis strongly support this diagnosis. Most critically, her physical examination demonstrates a rigid abdomen with marked rebound tenderness and involuntary guarding. These findings, combined with hemodynamic instability (hypotension, tachycardia), indicate that the affected bowel segment has progressed to transmural infarction and necrosis, leading to peritonitis. In any patient with an acute surgical abdomen and hemodynamic compromise, the definitive and immediate next step is exploratory laparotomy to resect the nonviable bowel and prevent further systemic toxicity. Delaying surgery for imaging or attempting purely medical management in this context is associated with near-universal mortality.

Step-by-Step Solution

Identify the underlying pathology based on the patient's history and symptoms.

The patient has a history of atrial fibrillation, is off anticoagulation, and presents with sudden, severe abdominal pain, pinpointing an embolic acute mesenteric ischemia.

Sudden pain out of proportion to exam findings in a patient with risk factors for arterial thromboembolism is classic for superior mesenteric artery (SMA) occlusion.

Assess the severity and stage of the ischemia.

The presence of hypotension, profound leukocytosis, severe lactic acidosis, and a rigid abdomen with rebound tenderness indicates advanced disease.

These findings signify that the ischemia has progressed to transmural bowel infarction, leading to loss of mucosal integrity, bacterial translocation, peritonitis, and septic shock.

Determine the definitive intervention based on the patient's clinical stability.

Immediate exploratory laparotomy must be performed.

When an acute surgical abdomen (peritonitis) or hemodynamic instability is present, imaging studies (like CT angiography) must be bypassed to prevent deadly delays in surgically resecting the necrotic bowel.

Key Concept

Patients with acute mesenteric ischemia who exhibit signs of peritonitis (e.g., rigid abdomen, rebound tenderness) or hemodynamic instability require immediate exploratory laparotomy, bypassing diagnostic imaging.

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