Papers

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

Paul S Myles, head of research, Andrew D M McLeod, specialist registrar, Jennifer O Hunt, clinical trials coordinator, Helen Fletcher, research nurse. 

Department of Anaesthesia and Pain Management, Alfred Hospital, Prahran, Victoria 3181, Australia

Correspondence to: P S Myles p.myles{at}alfred.org.au

Recent evidence shows that postoperative recovery may differ between men and women. ^{1 2} We planned a prospective cohort study to examine the impact of gender on postoperative outcome. This was associated with a trial investigating the effectiveness of several anaesthetic regimens.³

	Participants, methods, and results

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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 ², 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

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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 -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.

	Acknowledgments

We thank the anaesthetists and recovery room nursing staff who cooperated with this study.

Contributors: PSM conceived and designed the study, analysed the data, and wrote the final drafts of the paper. ADMMcL performed a literature review, contributed to data interpretation, and wrote the first draft of the paper. JOH and HF recruited most of the patients in the study, collected all the postoperative data, carried out data entry, and helped to write the paper. PSM is the guarantor.

	Footnotes

Funding: This study was supported by the Abbott/Australian Society of Anaesthetists Research Grant (1996) and a research grant from the Alfred Research Trust (1997).

Competing interests: None declared.

	References

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1.	Gan TJ, Glass PS, Sigl J, Sebel P, Payne F, Rosow C, et al. Women emerge from general anesthesia with propofol/alfentanil/nitrous oxide faster than men. Anesthesiology 1999; 90: 1283-1287[CrossRef][Medline].
2.	Myles PS, Williams DL, Hendrata M, Anderson H, Weeks AM. Patient satisfaction after anaesthesia and surgery: results of a prospective survey of 10,811 patients. Br J Anaesth 2000; 84: 6-10[Abstract/Free Full Text].
3.	Myles PS, Hunt JO, Fletcher H, Smart J, Jackson T. Part I: propofol, thiopental, sevoflurane, and isofluranea randomized, controlled trial of effectiveness. Anesth Analg 2000; 91: 1163-1169[Abstract/Free Full Text].
4.	Myles PS, Hunt JO, Nightingale CE, Fletcher H, Beh T, Tanil D, et al. Development and psychometric testing of a quality of recovery score after general anesthesia and surgery in adults. Anesth Analg 1999; 88: 83-90[Abstract/Free Full Text].
5.	Frye CA, Duncan JE. Progesterone metabolites, effective at the GABAA receptor complex, attenuate pain sensitivity in rats. Brain Res 1994; 643: 194-203[CrossRef][Medline].

(Accepted 18 December 2000)