0071643192.pdf

Pulmonary Embolism

By far the most common source of PE is thrombus in the lower extremity deep

venous system. Risk factors are therefore identical to DVT (see Table 2.27).

Other possible emboli include fat, amniotic fluid, and tumor.

PATHOPHYSIOLOGY

■ Thrombus formed in venous system →embolizes to lung →acute obstruc-

tion of the pulmonary arterial system and pulmonary ischemia/infarction.

■ Large emboli →obstruction of right ventricular outflow and circulatory

collapse.

SYMPTOMS

■ Nonspecific

■ Shortness of breath: Most common complaint

■ Chest pain: Classically pleuritic (but not always)

■ Cough and/or hemoptysis

■ Syncope and acute cardiovascular collapse may occur.

EXAM

■ Tachypnea: Most common finding

■ Tachycardia

■ Clear lungs (but may hear rales/wheezes)

■ Hypoxia

■ Fever (<102°F)

■ Evidence of acute R heart failure, hypotension: If massive

DIAGNOSIS

Diagnosis should be suspected in any patient presenting with dyspnea and/or

chest pain, especially in the presence of risk factors.

Multiple tools are available to risk stratify patients for PE; diagnostic evalua-

tion should be based on individual risk assessment. Recent studies suggest

that the Wells clinical prediction rule is a useful risk stratification tool (see

Table 2.31).

■ ECG:Abnormal in most, but not diagnostic

■ Tachycardia and nonspecific ST-T changes most common.

■ Anyevidence of R heart strain: Classic is S wave in lead I, Q wave in

lead III and T-wave inversion in lead III (S 1 Q 3 T 3 pattern)

■ ABG:May demonstrate respiratory alkalosis, hypoxemia, and a widened

A-a gradient; a normal ABG does not excludePE

■ CXR:Abnormal in most, but nonspecific (eg, effusion, atelectasis)

■ Hampton’s hump =pleural-based, wedge-shaped density indicating

infarcted lung.

■ Westermark’s sign =↓vessel markings distal to embolus (oligemia)

(rarelyseen).

■ D-dimer:Described in the section “Deep Venous Thrombosis,” page 132.

■ Test virtually excludes PE in a low-risk (low clinical suspicion) patient.

■ CT angiography (see Figure 2.22): Study of choice where available

■ High sensitivity and specificity

■ Preferred over V/Q scan in pregnancy due to lowerfetal radiation

exposure

CARDIOVASCULAR EMERGENCIES

Symptoms in PE are sudden

onset only half the time!

Most common ECG in PE =

tachycardia and nonspecific

ST-T changes.

Classic ECG finding =S 1 Q 3 T 3.

A-a gradient at sea level:

150—(PO 2 +PCO 2 /0.8)

Normal A-a gradient =

Age/4 +4.

A negative D-dimer virtually

excludes PE in a low clinical

suspicion patient.