Sex difference and intra-operative tidal volume: Insights from the LAS VEGAS study

Abstract

Background: One key element of lung-protective ventilation is the use of a low tidal volume (VT). A sex difference in use of low tidal volume ventilation (LTVV) has been described in critically ill ICU patients.

Objectives: The aim of this study was to determine whether a sex difference in use of LTVV also exists in operating room patients, and if present what factors drive this difference.

Design, patients and setting: This is a posthoc analysis of LAS VEGAS, a 1-week worldwide observational study in adults requiring intra-operative ventilation during general anaesthesia for surgery in 146 hospitals in 29 countries.

Main outcome measures: Women and men were compared with respect to use of LTVV, defined as VT of 8 ml kg-1 or less predicted bodyweight (PBW). A VT was deemed 'default' if the set VT was a round number. A mediation analysis assessed which factors may explain the sex difference in use of LTVV during intra-operative ventilation.

Results: This analysis includes 9864 patients, of whom 5425 (55%) were women. A default VT was often set, both in women and men; mode VT was 500 ml. Median [IQR] VT was higher in women than in men (8.6 [7.7 to 9.6] vs. 7.6 [6.8 to 8.4] ml kg-1 PBW, P < 0.001). Compared with men, women were twice as likely not to receive LTVV [68.8 vs. 36.0%; relative risk ratio 2.1 (95% CI 1.9 to 2.1), P < 0.001]. In the mediation analysis, patients' height and actual body weight (ABW) explained 81 and 18% of the sex difference in use of LTVV, respectively; it was not explained by the use of a default VT.

Conclusion: In this worldwide cohort of patients receiving intra-operative ventilation during general anaesthesia for surgery, women received a higher VT than men during intra-operative ventilation. The risk for a female not to receive LTVV during surgery was double that of males. Height and ABW were the two mediators of the sex difference in use of LTVV.

Trial registration: The study was registered at Clinicaltrials.gov, NCT01601223.

Conflict of interest statement

Conflicts of interest: none.

Copyright © 2021 European Society of Anaesthesiology and Intensive Care. Unauthorized reproduction of this article is prohibited.

Figures

Fig. 1. Cumulative distribution plots for the median values of the ventilatory parameters during the intra-operative period stratified by sex

PBW calculated according to standard formula. P value from the unadjusted mixed-effect linear model with centres as random effect. ABW, actual body weight; PBW, predicted body weight.

Fig. 2. Frequency of use of low tidal volume ventilation in the overall cohort stratified by sex and according to quintiles of height and weight

A low tidal volume was defined as a tidal volume ≤8 ml kg−1. PBW calculated according to standard formula. ABW, actual body weight; PBW, predicted body weight.