Sex differences in speed of emergence and quality of recovery after anaesthesia: cohort study

Participants, methods, and results

After obtaining ethics committee approval and informed consent, we studied 463 adult patients undergoing elective inpatient surgery. An observer experienced in postoperative review followed up all patients daily until the third postoperative day. The primary end point was quality of recovery, as measured by a quality of recovery score consisting of nine (range 0-18) items.4 Secondary end points included recovery times and the incidence of complications (postoperative nausea and vomiting, headache, backache, and sore throat).

Data were analysed using t tests or generalised linear models (to adjust for the covariates of patients' age, American Society of Anesthesiologists status, and extent and duration of surgery). Associations were described using χ², risk ratios, and 95% confidence intervals. Cox proportional hazards was used to adjust for the covariates to identify the effect of gender on the pattern of recovery.

The men (n=241) and women (n=222) in our study were similar in terms of age, American Society of Anesthesiologists physical status, and type, duration, and extent of surgery. Women were more likely to have a history of postoperative nausea and vomiting (42 (19%) women v 18 (7.4%) men, P<0.001) and to have received prophylactic antiemetic agents (102 (46%) women v 70 (29%) men, P<0.001).

Women emerged significantly more quickly than men (table), and overall quality of recovery was worse (quality of recovery score averaged over time: women 15.7 (95% confidence interval 15.6 to 16.0); men 16.3 (16.2 to 16.5); P=0.024). Women had a slower return to baseline health status, as determined by their quality of recovery score (hazard ratio 0.75 (0.59 to 0.95), P=0.005), and were more likely to have postoperative complications (table). All these findings were similar when analysed separately for each anaesthetic regimen and type of surgery (results not shown).

Comment

We found that women emerged more quickly than men from general anaesthesia but had a 25% slower rate of return to their preoperative health status. They also reported complications more often than did men. These complications are traditionally termed “minor” but are common after surgery, and more rapid emergence may not translate to earlier discharge from the recovery room if the patient's condition has to be stabilised. This may explain the lack of difference between groups for eligibility for discharge from the recovery room.

Underlying physiological differences partly account for variation in the effects of anaesthesia. Sex hormones can cause functional changes in the γ-aminobutyric acid receptor, the site of action of most intravenous anaesthetic drugs.5 Our study confirms that women emerge faster when propofol has been used,1 and it extends the findings to include anaesthesia with volatile agents such as isoflurane and sevoflurane. Postoperative nausea and vomiting in women has been related to the phase of the menstrual cycle, and women have a higher incidence of migraine and tension headaches generally (a risk factor for postoperative headache). Postoperative backache may be attributed to immobility of the lumbar spine during surgery, and there are anatomical differences between men and women.

The higher incidence of some complications among women may be attributable to greater willingness to report them. However, participants in this study were directly questioned about nausea, headache, backache, and sore throat rather than being obliged to mention them without prompting. This makes it more likely that the differences in outcome between the sexes, which have previously received limited attention, are genuine and important.