Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (590 page)

   Meconium ileus during early infancy; causes 20–30% of cases of neonatal intestinal obstruction; present at birth in 8% of these children. Almost all of them will develop the clinical picture of CF.

PULMONARY EMBOLISM

   Definition

Pulmonary embolism (PE) refers to the occlusion of the pulmonary artery or one of its branches by a blood clot, tumor, air, or fat that developed elsewhere in the body. The classic symptoms of PE are hemoptysis, dyspnea, and chest pain. PE can be classified as acute or chronic. In acute PE, patients develop symptoms and signs immediately after obstruction of pulmonary vessels. In chronic PE, patients slowly develop progressive dyspnea over a period of years due to pulmonary hypertension. The incidence of PE appears to be significantly higher in blacks than whites. Mortality rates for PE for blacks have been 50% higher than whites followed by people of other races (Asians) and Native Americans. The risk is increased in pregnancy and during the postpartum period. Other risk factors include venous stasis, various hypercoagulable states, immobilization, surgery, trauma, oral contraceptives, estrogen replacement, CHF, advanced age, and malignancy.

   Who Should Be Suspected?

PE should be suspected in a patient with sudden onset of dyspnea, deterioration of existing dyspnea, or the onset of pleuritic chest pain without another apparent cause. Other signs to look for include chest wall tenderness, back pain, shoulder pain, upper abdominal pain, hemoptysis, painful respiration, and new onset of wheezing. PE is a frequent consideration in emergency departments. Rule-out criteria where the prevalence is low including patient age <50 years, heart rate <100 bpm, oxyhemoglobin saturation >95%. There is no hemoptysis, estrogen use, prior deep venous thrombosis or PE, unilateral leg swelling, surgery, or trauma requiring hospitalization within last 4 weeks.

   Diagnostic Findings

   Pulmonary angiography: The “gold standard” in the diagnosis of PE. CT pulmonary angiography (CT-PA) is being used increasingly as a diagnostic modality in patients suspected of PE, and its accuracy appears to vary widely from institution to institution. This may be due to differences in the experience of the person interpreting images and image quality. Clinicians should consider their institution’s experience and the pretest probability of PE when deciding whether to use CT-PA or to pursue additional testing.

   Chest x-rays: May be normal; suggestive findings include elevated diaphragm, pleural effusion, dilation of the pulmonary artery, abrupt vessel cut off, and atelectasis. Seventy percent of the patients with acute PE will have ECG abnormalities, most commonly nonspecific ST-segment and T-wave changes.

   Majority of the routine laboratory tests are nonspecific for the diagnosis of PE, although they may suggest another diagnosis. A hypercoagulation workup should be performed if no obvious cause of embolic disease is apparent, that includes antithrombin III deficiency, protein C and protein S deficiency, lupus anticoagulant, cardiolipin antibodies, and homocysteine

   ABG and pulse oximetry: Have a limited role in the diagnosis. ABGs usually reveal hypoxemia, hypocapnia, and respiratory alkalosis. Room air pulse oximetry readings of <95% at the time of diagnosis are at increased risk of in-hospital complications.

   Core laboratory: BNP or NT-proBNP levels of higher in patients with PE and appear to correlate with increased risk of complications and prolonged hospitalizations in these patients. Thirty percent to 50% of patients have also have elevated troponin I or T, and they are not useful for diagnosis. Leukocytosis, increased ESR, and elevated LDH or AST with normal serum bilirubin are commonly observed.

   
D
-Dimer assays: Diagnosis of PE has been studied extensively. These assays have good sensitivity (95%) and negative predictive value but poor specificity (40–68%) and positive predictive value.
D
-Dimer levels of <500 ng/mL are sufficient to exclude PE in patients with a low or moderate pretest probability of PE.