In-hospital vs. 30-day mortality in the critically ill - a 2-year Swedish intensive care cohort analysis

Standardised mortality ratio (SMR) is a common quality indicator in critical care and is the ratio between observed mortality and expected mortality. Typically, in-hospital mortality is used to derive SMR, but the use of a time-fixed, more objective, end-point has been advocated. This study aimed to determine the relationship between in-hospital mortality and 30-day mortality on a comprehensive Swedish intensive care cohort.

A retrospective study on patients >15 years old, from the Swedish Intensive Care Register (SIR), where intensive care unit (ICU) admissions in 2009-2010 were matched with the corresponding hospital admissions in the Swedish Hospital Discharge Register. Recalibrated SAPS (Simplified Acute Physiology Score) 3 models were developed to predict and compare in-hospital and 30-day mortality. SMR based on in-hospital mortality and on 30-day mortality were compared between ICUs and between groups with different case-mixes, discharge destinations and length of hospital stays.

Sixty-five ICUs with 48861 patients, of which 35610 were SAPS 3 scored, were included. Thirty-day mortality (17%) was higher than in-hospital mortality (14%). The SMR based on 30-day mortality and that based on in-hospital mortality differed significantly in 7/53 ICUs, for patients with sepsis, for elective surgery-admissions and in groups categorised according to discharge destination and hospital length of stay.

Choice of mortality end-point influences SMR. The extent of the influence depends on hospital-, ICU- and patient cohort characteristics as well as inter-hospital transfer rates, as all these factors influence the difference between SMR based on 30-day mortality and SMR based on in-hospital mortality.