Is intensive care unit mortality a valid survival outcome measure related to critical illness?

Abstract

Rationale: Use of death as an outcome of intensive care unit (ICU) admission may be biased by differential discharge decisions.

Objective: To determine the validity of ICU survival status as an outcome measure of all cause case-fatality.

Methods: A retrospective cohort of first admissions among adults to four ICUs in North Brisbane, Australia was assembled. Death in ICU (censored at discharge or 30 days) was compared with 30-day overall case-fatality.

Results: The 30-day overall case-fatality was 8.1% (2436/29,939). One thousand six hundred and thirty-one deaths occurred within the ICU stay and 576 subsequent during hospital post-ICU discharge within 30-days; ICU and hospital case-fatality rates were 5.4% and 7.4%, respectively. An additional 229 patients died after hospital separation within 30 days of ICU admission of which 110 (48.0%) were transferred to another acute care hospital, 80 (34.9%) discharged home, and 39 (17.0%) transferred to an aged care/chronic care/rehabilitation facility. Patients who died after ICU discharge were older, had higher APACHE III scores, were more likely to be elective surgical patients, and were less likely to be out of state residents or managed in a tertiary referral hospital. Limiting determination of case-fatality to ICU information alone would correctly detect 95% (780/821) of all-cause mortality at day 3, 90% (1093/1213) at day 5, 75% (1524/2019) at day 15, 72% (1592/2244) at day 21, and 67% (1631/2436) at day 30 of follow-up.

Conclusions: Use of ICU case-fatality significantly underestimates the true burden and biases assessment of determinants of critical illness-related mortality in our region.

Keywords: Bias; Case fatality; Critical care medicine; Epidemiology; Risk factor.