Sex differences in intensive care unit admissions in Australia and New Zealand

Introduction: Fewer women than men are admitted to intensive care units (ICUs) worldwide. Objectives: To quantify the relative contribution of each major diagnostic category to the overall sex balance in ICU admissions in Australia and New Zealand, and to describe changes in the sex balance over time and with patient age. Methods: Retrospective cross-sectional study of Australian and New Zealand ICU admissions recorded in the Australian and New Zealand Intensive Care Society Adult Patient Database between 2005 and 2018. Multivariate logistic regression for the likelihood of female admission considered key explanatory variables: diagnostic category, patient age, admission year, geographic region, hospital type, and planned versus unplanned ICU admission. Results: Overall, 42.3% of 1 616 856 Australian and New Zealand ICU patients were women (99% CI, 42.2-42.4%). 247 988 more men than women were admitted to an ICU during the 14-year study period. There was a sex imbalance in most diagnostic categories: less than 48% women in 15 of 23 diagnostic categories, and greater than 52% women in four diagnostic categories (P < 0.001). Admissions following cardiovascular surgery accounted for over half of the total sex imbalance. The percentage of ICU patients who are women increased linearly from 40.8% in 2005 to 43.6% in 2018 (R² = 93.1%; P < 0.001). Compared with admission in 2005, the adjusted odds ratio for female admission in 2018 was 1.03 (99% CI, 1.01-1.06). Conclusion: There is a significant sex imbalance in ICU admissions in Australia and New Zealand, widespread across the diagnostic categories. Cardiovascular admissions contribute most to the observed preponderance of men. The proportion of female ICU patients is steadily increasing.