Pulmonary embolism associated with elective surgery, detected by ventilation-perfusion scintigraphy

The frequency of clinical and sub-clinical postoperative pulmonary embolism, demonstrated by combined pulmonary ventilation-perfusion scanning, and the prophylactic effect of low-dose heparin, were assessed in a randomised double-blind study in 43 patients aged over 40 years. Pulmonary embolism was demonstrated using combined ventilation-perfusion scanning in 4 out of 43 patients (9%). The incidence was 1 out of 19 patients in the heparin-treated group and 3 out of 24 patients in the placebo group. This difference was not significant. If post-operative perfusion scanning alone had been utilised for diagnosing pulmonary embolism, the frequency of pulmonary emboli would have been 33%, with 21% in the heparin group and 46% in the placebo group. This difference is not significant. It is concluded that perfusion scanning over-estimates the frequency of post-operative pulmonary embolism. The use of the more specific combined ventilation-perfusion scanning shows that asymptomatic postoperative pulmonary embolism does occur, but that the frequency is considerably lower than indicated by perfusion scanning alone. Combined ventilations-perfusion scanning must be performed in studies assessing the effects of various treatment regimes on the frequency of pulmonary embolism postoperatively. The small number of patients included in the study do not permit any conclusions concerning any prophylactic effect of low-dose heparin against pulmonary embolism.