The value of measuring intravascular platelet aggregates in the prediction of postoperative pulmonary dysfunction

A modified Swank screen filter technique was used to investigate, first, whether intravascular platelet aggregates (IPA) could be detected in patients immediately after surgery and then, the relationship between IPA levels and postoperative pulmonary function. The test, as modified, achieved an excellent reproducibility (r = 0.95) and a close correlation with the number of aggregates identified in samples of femoral vein blood by subsequent scanning electron microscopy (r = 0.93). In 20 patients IPA levels were measured 30 min and 3 h after surgery and pulmonary function (arterial PO2, physiological dead space and alveolar/arterial PO2 gradient) was evaluated preoperatively and on days 1 and 7 postoperatively. Patients with elevated IPA levels suffered a greater mean fall in arterial PO2 at 7 days (1.8 kPa) than did patients with normal IPA levels (0.6 kPa) (P less than 0.05). This was explained by a marked increase in the pulmonary arteriovenous shunt as indicated by the alveolar/arterial PO2 gradient (2.3 kPa v. 0.4 kPa, P less than 0.01). Those patients with increased pulmonary shunting and arterial hypoxia 1 week after surgery also had a greater fall in the platelet count on the first postoperative day. The screen filtration technique is a reproducible test which measures IPA accurately and may be used to predict pulmonary function 1 week later. This suggests that treatment to inhibit IPA may reduce postoperative pulmonary dysfunction.