To determine the effect of intensive care unit (ICU) length of stay (LOS) on hospital mortality and non-home discharge for patients undergoing cardiac surgery over a 16-year period in Australia and New Zealand.

A retrospective, multicenter cohort study covering the period January 1, 2004 to December 31, 2019.

One hundred one hospitals in Australia and New Zealand that submitted data to the Australia New Zealand Intensive Care Society Adult Patient Database.

Adult patients (aged >18) who underwent coronary artery bypass grafting, valve surgery, or combined valve + coronary artery surgery.

None.

The authors analyzed 252,948 cardiac surgical patients from 101 hospitals, with a median age of 68.3 years (IQR 60-75.5), of whom 74.2% (187,632 of 252,948) were male patients. A U-shaped relationship was observed between ICU LOS and hospital mortality, with significantly elevated mortality at short (<20 hours) and long (>5 days) ICU LOS, which persisted after adjustment for illness severity and across clinically important subgroups (odds ratio for mortality with ICU LOS >5 days = 3.21, 95% CI 2.88-3.58, p < 0.001).

Prolonged duration of ICU LOS after cardiac surgery is associated with increased hospital mortality in a U-shaped relationship. An ICU LOS >5 days should be considered a meaningful definition for prolonged ICU stay after cardiac surgery.