Venous and Pulmonary Thromboembolism: An Algorithmic Approach to Diagnosis and Management  Edward C. Rosenow, M.D.  Mayo Clinic Proceedings  Volume 70, Issue 1, Pages 45-49 (February 1995) DOI: 10.4065/70.1.45 Copyright © 1995 Mayo Foundation for Medical Education and Research Terms and Conditions

Fig. 1 Algorithm for assessment of patients with possible venous thromboembolism (VTE). (1) Physicians must maintain a high clinical suspicion for VTE in those patients at moderate to high risk (see Table 1). Clinicians should develop a perspective for determining the degree of clinical suspicion—high (H/S), intermediate (I/S), or low (L/S)—because the degree of suspicion generally correlates with results of a ventilation-perfusion (V/Q) scan and other tests and closely identifies the incidence of pulmonary embolism (PE). (2) If the patient is hemodynamically unstable, one cannot allow time (an estimated 2 to 6 hours, even with experienced personnel) for completion of all appropriate studies before initiation of some type of therapy. Unless the patient has an absolute contra-indication (Cl) to heparin anticoagulation (AlC), it should be begun before all other studies are initiated. For an accurate baseline, arterial blood gases (ABG) should be determined with the patient breathing room air. If electromechanical dissociation—and thus the likelihood of massive PE—is present, heroic measures should be considered. Esophageal echocardiography is a rapid, relatively noninvasive bedside test that can detect central massive emboli. (3) If the degree of clinical suspicion for PE is intermediate or high and heparin A/C is not contraindicated, A/C should be initiated before studies are done in hemodynamically stable patients. (4) A chest roentgenogram (CXR), electrocardiogram (ECG), and complete blood cell count (CBC) should be done on all patients with clinically suspected VTE, primarily to rule out other causes. An ECG shows abnormalities in almost 80% of patients with acute PE but is rarely diagnostic for right heart strain. (5) ABG with the patient breathing room air should be determined as a baseline. A widened alveolar-arterial oxygen pressure difference [P(A-a)02] and an arterial carbon dioxide tension (Paco2)of less than 36 torr are found in at least 90% of patients with acute PE, an arterial oxygen tension of less than 80 torr in 76%, a Paco2 of less than 36 torr in 74%, and an increased P(A-a)02 gradient in 95%. The reverse—a normal P(A-a)02 gradient and a Paco2 of 36 torr or more—rules out (r/o) acute PE but not deep venous thrombosis (DVT).6 (6) Results of the V/Q scan have four interpretations only: “normal,” “low probability” (LP), “intermediate probability” (IP) (nondiagnostic), and “high probability” (HP) for PE. (6.1) A normal perfusion scan rules out clinically important PE in 99% or more. Although many clinicians do not accept intermediate-or low-probability V/Q results, they are included here because the extensive Prospective Pulmonary Embolism Diagnosis study7 included these interpretations. (6.2) Most low-probability scans are seen in patients with chronic obstructive pulmonary disease, including those with minimal symptoms of asthma. If clinical suspicion is low, the incidence of PE is 4%—not sufficiently high for treatment; patients should be observed. With intermediate or high clinical suspicion, pulmonary angiography (PA) or leg studies should be done. (6.3) With nondiagnostic V/Q scans (intermediate probability of PE) and low clinical suspicion, only 16% have acute PE. In such patients, impedance plethysmography (IPG) or duplex ultrasonography (DUS) should be done. With “positive” (Pos) (abnormal) findings, treatment should be instituted. With normal findings (Neg), observe or do serial IPG. The risks of PE become higher with intermediate or high clinical suspicion; IPG or DUS (if not already done) or PA should be performed in such patients. (6.4) A high-probability V/Q scan (found in only 41% of patients with acute PE) is accepted as evidence of acute PE in more than 90%, and no further studies are done unless the patient has had a previous PE and no follow-up V/Q scan has been done for comparison. The incidence declines to 75% in such situations.7 Percentages of confirmed PE based on index of clinical suspicion are noted, with 96% positive PA for patients with high clinical suspicion, high-probability V/Q scan, and no previous PE. In patients with intermediate or high clinical suspicion for PE and no previous PE, A/C should be initiated unless contraindications exist. With a high-probability V/Q scan but low clinical suspicion, only 56% will actually have PE; serial IPG or PA should be done. (7) A positive IPG or DUS implies a thrombus in the deep venous system of the lower extremity above the calf and almost certainly warrants A/C even if the patient does not have a PE. With experienced technicians, false-positive IPG for technical reasons is rare and occurs because of congestive heart failure, arteriosclerosis obliterans, neoplasm compressing a vessel in the pelvis, or hypotension. Forty percent of patients with PE will have normal findings on lPG, DUS, or venography. In patients with intermediate or high clinical suspicion for PE and normal IPG results, V/Q scanning (if not already done) or PA should be performed. If clinical suspicion is low for PE, serial IPG during a period of 5 to 14 days is indicated. Within this group, 5 to 10% will have findings that convert to abnormal because of the nature of the setting. In such patients, A/C should be initiated. Pulmonary infiltrates on the CXR reduce the sensitivity and specificity of the V/Q scan. Mayo Clinic Proceedings 1995 70, 45-49DOI: (10.4065/70.1.45) Copyright © 1995 Mayo Foundation for Medical Education and Research Terms and Conditions