VALUE OF CEM CO2 IN THE NEGATIVE DIAGNOSI S OF ACUTE PULMONARY EMBOLUS IN CASES OF CHRONIC BRONCHOPNEUMOPATHIC OBSTRUCTIONS

The aim of this prospective study was to analyse the contribution of t he measurement of alveolar arterial gradients of CO2 during forced exp iration in the diagnosis of pulmonary emboli occurring in chronic airf low obstruction (COPD) as a result of smoking. The study was carried o ut on 178 patients: Group 1: 54 subjects without emboli (14 controls, 33 COPD and 7 patients with chest pain); Group 2: 72 patients with pro ved emboli (49 non COPD, 23 COPD); Group 3: 52 patients COPD presentin g with varied non-embolic broncho-pulmonary pathology (pneumonia, bron chospasm, pulmonary oedema, bronchial neoplasm). The diagnosis of pulm onary emboli was confirmed by scintigraphy in patients with non COPD o r angiography (in patients with COPD). The maximal fraction of CO2 was measured using a capnologue during a forced expiration which was long and prolonged until residual volume was achieved. The PaCO2 was measu red simultaneously by an analysis of arterial blood gases. The D index was calculated according to the formula [(PaCO2 - PEM CO2)/PaCO2] x 1 00. The D index was significantly lower in Group 1 (3.42+/-3,8% p <0,0 001) than in Group 2 (20.8+/-10%) and Group 3 (27.6+/-11.7%) (not sign ificant between Groups 2 and 3). in patients with COPD the specificity and sensitivity and the predicted positive and negative value were 10 0% for a D limit of 7%. In COPD patients these values were respectivel y 82, 95, 75 and 96% for a D limit of 7%; on the other hand for a D be low 5% the values were 60, 100, 64 and 100% respectively. In conclusio n a gradient below 5% was a useful negative argument against the diagn osis of pulmonary emboli in COPD patients and enabled invasive examina tions to be avoided.