A 62-year-old man is evaluated for sudden-onset shortness of breath and right-sided pleuri… — USMLE Step 2 CK

A 62-year-old man is evaluated for sudden-onset shortness of breath and right-sided pleuritic chest pain. He was admitted 6 days ago for an emergent exploratory laparotomy due to a small bowel obstruction. Following the surgery, he was started on subcutaneous unfractionated heparin for deep vein thrombosis prophylaxis.

On physical examination, his temperature is $37.8^\circ\text{C}$ ( $100.0^\circ\text{F}$ ), heart rate is $118/\text{min}$ , blood pressure is $122/78\text{ mmHg}$ , respiratory rate is $24/\text{min}$ , and oxygen saturation is $91\%$ on room air. The lungs are clear to auscultation bilaterally. The right calf is edematous, erythematous, and tender to palpation. The abdominal incision is clean and intact.

Laboratory results are as follows:

Parameter	Admission	Current
Hemoglobin	$13.5\text{ g/dL}$	$12.4\text{ g/dL}$
Leukocyte count	$10,500/\text{mm}^3$	$8,500/\text{mm}^3$
Platelet count	$250,000/\text{mm}^3$	$75,000/\text{mm}^3$
Creatinine	$1.0\text{ mg/dL}$	$1.1\text{ mg/dL}$

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

Discontinue unfractionated heparin and initiate a direct thrombin inhibitorCevap
B
Administer intravenous furosemide and inhaled bronchodilators
C
Arrange for an emergent exploratory laparotomy to evaluate for bowel ischemia
D
Order a computed tomography scan of the abdomen and pelvis to evaluate for a postoperative abscess
E
Initiate broad-spectrum intravenous antibiotics for presumed hospital-acquired pneumonia

Cevap

Discontinue unfractionated heparin and initiate a direct thrombin inhibitor

The correct action is to discontinue unfractionated heparin and initiate a direct thrombin inhibitor. This patient is presenting with a classic case of Heparin-Induced Thrombocytopenia (HIT), which is characterized by the '4Ts': significant Thrombocytopenia (typically a >50% drop from baseline), Timing (onset 5-10 days after heparin exposure), Thrombosis (new arterial or venous clots, such as his DVT and PE), and the absence of oTher clear causes. HIT is caused by IgG autoantibodies targeting the heparin-platelet factor 4 (PF4) complex. This immune complex activates platelets, leading to massive platelet consumption and a paradoxical, highly prothrombotic state. The most critical initial step in management is the immediate cessation of all heparin products (including low-molecular-weight heparin, which cross-reacts) and the initiation of a non-heparin anticoagulant, such as a direct thrombin inhibitor (e.g., argatroban, bivalirudin) or fondaparinux, to prevent further fatal thromboses.

Adım Adım Çözüm

Analyze the acute clinical presentation.

The patient exhibits tachycardia, hypoxia, pleuritic chest pain, and unilateral calf swelling.

These findings are highly suspicious for a new deep vein thrombosis (DVT) complicated by a pulmonary embolism (PE).

Evaluate the laboratory trends in the context of the patient's medication history.

The platelet count has dropped by 70% (from 250,000 to 75,000) exactly 6 days after the initiation of unfractionated heparin.

A >50% drop in platelets occurring 5-10 days after heparin exposure is the hallmark laboratory finding of Heparin-Induced Thrombocytopenia (HIT).

Calculate the 4T score for HIT probability.

Thrombocytopenia (>50% drop), Timing (day 6), Thrombosis (new DVT/PE), and oTher causes ruled out yields a high probability 4T score.

A high probability score mandates immediate empirical treatment before confirmatory laboratory tests (like serotonin release assay) return.

Determine the definitive management step.

Stop all heparin products immediately and start a non-heparin anticoagulant (such as argatroban or bivalirudin).

Continuing heparin fuels the antibody-mediated platelet activation, worsening the prothrombotic state.

Anahtar Kavram

Diagnosis and management of Heparin-Induced Thrombocytopenia (HIT)

Tahmini Süre:1m 30s

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