Adjustment of intensive care unit outcomes for severity of illness and comorbidity scores

Comparison of outcomes among intensive care units (ICUs) requires adjustment for patient variables. Severity of illness scores are associated with hospital mortality, but administrative databases rarely include the elements of these scores. However, these databases include the elements of comorbidity scores. The purpose of this study was to compare the value of these scores as adjustment variables in statistical models of hospital mortality and hospital and ICU length of stay after adjustment for other covariates.

We used multivariable regression to study 1808 patients admitted to a 13-bed medical-surgical ICU in a 400-bed tertiary hospital between December 1998 and August 2003.

For all patients, after adjusting for age, sex, major clinical category, source of admission, and socioeconomic determinants of health, we found that Acute Physiology and Chronic Health Evaluation (APACHE) II and comorbidity scores were significantly associated with hospital mortality and that comorbidity but not APACHE II was significantly associated with hospital length of stay. Separate analysis of hospital survivors and nonsurvivors showed that both APACHE II and comorbidity scores were significantly associated with hospital length of stay and APACHE II score was associated with ICU length of stay.

The value of APACHE II and comorbidity scores as adjustment variables depends on the outcome and population of interest.