Platelet aggregation is impaired during anaesthesia with sevoflurane but not with isoflurane

Purpose: Halothane suppresses platelet aggregation in vitro and ex vivo, and prolongs bleeding time. In a previous in vitro study we demonstrated that sevoflurane had a more suppressive effect on platelet aggregation than did halothane. The present study investigated whether the clinical use of sevoflurane affected platelet aggregation ex vivo. Methods: Thirty-eight patients undergoing minor elective surgery were divided randomly into sevoflurane and isoflurane groups, Anaesthesia was induced with thiopentone iv, and was maintained with sevoflurane or isoflurane with nitrous oxide, Blood was collected to measure platelet aggregation induced by adenosine diphosphate (ADP) and epinephrine. The first (control) blood collection was performed in the operating room before induction of anaesthesia, and the second 5-10 min after tracheal intubation but before the start of surgery when the end-expiratory sevoflurane or isoflurane concentrations had stabilised at 1-1.5 times the minimum alveolar concentration (MAC) and mean arterial pressures were between 80-120% of preanaesthetic values. Results: In all samples obtained during sevoflurane anaesthesia (r = 15), ADP and epinephrine could not induce secondary aggregation, although they did induce primary aggregation. In contrast, in the isoflurane group, both primary and secondary aggregation were observed in 14 out of 15 patients, and secondary aggregation was abolished in only one of the samples obtained during anaesthesia. Conclusion: Sevoflurane, but not isoflurane, alters platelet aggregation in the clinical situation, possibly by suppression of thromboxane A(2) formation.