Effect of volatile anaesthetics and nitrous oxide-fentanyl anaesthesia on bleeding time.

Fifty-one patients were divided randomly into four groups: halothane in oxygen; fentanyl plus nitrous oxide in oxygen; enflurane in oxygen; or isoflurane in oxygen. Standardized bleeding time was measured using a Simplate II bleeding device before and at least 40 min after the induction of anaesthesia. Arterial pressure was maintained at +/- 20% of control values and temperature was kept at 35-37 degrees C. The bleeding time was prolonged by 33% in the halothane group (P less than 0.01) and by 20% in the nitrous oxide-fentanyl group (n.s.). There was essentially no change in bleeding time in the groups receiving enflurane or isoflurane, although there was considerable variability within each group, which did not seem to be related to differences in sex, age, type of surgery, concentration of agent used or surgical procedure.