Distinct determinants of long-term and short-term survival in critical illness

To identify the determinants of short-term and long-term survival in adult patients admitted to intensive care units (ICUs).

This population-based, observational cohort study included all eleven adult ICUs in the Winnipeg Health Region of Manitoba, Canada, analyzing initial ICU admissions during the period 1999-2010 of all Manitobans ≥17 years old. Analysis included Kaplan-Meier survival curves and multivariable regression models of 30-day mortality and post-90-day survival among those who survived to day 90. We used likelihood ratios to compare the predictive power of clusters of variables in these models.

After 33,324 initial ICU admissions, mortality rates within 30 and 90 days were 15.9 and 19.5 %, respectively. The survival curve demonstrated an early phase with a high rate of death, followed by a markedly lower death rate that was only clearly established after several months. 30-day mortality was predominantly determined by characteristics of the acute illness; with its relative contribution set at 1.00, the next largest contributors were age (0.19) and comorbidity (0.16). In contrast, post-90-day mortality was mainly determined by age (relative contribution 1.00) and comorbidity (0.95); the next largest contributor was characteristics of acute illness (0.28).

We observed two phases of survival related to critical illness. Short-term mortality was mainly determined by the acute illness, but its effect decayed relatively rapidly. Mortality beyond 3 months, among those who survived to that point, was mainly determined by age and comorbidity. Recognition of these findings is relevant to discussions with patients and surrogates about achievable goals of care.