Demographic changes over a 12-year period in intensive care

Introduction

We describe the demographic characteristics of patients admitted to the ICU of a large general hospital over the past 12 years and the severity of their condition on admission, examining the relationships between these changes and trends in mortality and length of stay (LOS).

Methods

All patients admitted to the ICU from 1 January 1996 to 31 December 2007 were included in this retrospective study. We captured data on age, sex, admission category, APACHE II predicted mortality, duration of ICU stay, and hospital mortality. Statistical analysis was conducted with SPSS version 15.0 using logistical regression models. To investigate trends in mortality independent of demographic changes in the ICU population, expected deaths based on the age–sex mortality experience across the whole 12-year period were calculated for each year. Expected mortality rates based on APACHE II probability of death scores were also calculated for each year.

Results

In total 7,158 patients were included in this study. There was no significant trend in median age across the 12 years studied; however, there has been a steady increase in the proportion of ICU patients over the age of 80. In 1996, 6% were over 80 years old and by 2008 it was 12.5%. There was no significant trend in the sex distribution of ICU patients (60:40 male to female). The LOS for medical and emergency surgical patients is similar, with an average of 6 days. However, the LOS of elective surgical patients has increased from around 3 to 4 days. The median APACHE II probability of death for ICU patients increased over the period, the significant linear trend (P = 0.001, logistic regression) showing an increase of almost 1% per year. The hospital mortality over the study period was 20%. During this period mortality rates rose in correlation with predicted mortality, before starting a downward trend in 2003 to eventually fall below APACHE II predicted levels in 2007.

Conclusion

The average age of ICU admissions is not significantly increasing over time. However, the proportion of patients aged over 80 has almost doubled to 12.5%. The severity of illness has increased and this is seen across all categories of admission, but seems to be due particularly to an increase in the subgroup of over 80 year olds. There has been no consistent change in mortality rates over the 12-year period.