Variation of results of the SMR using APACHE II, APACHE III and SAPS II

Introduction

The Standardized Mortality Ratio (SMR) has been designed as a measurement of the clinical performance in the intensive care units (ICUs), because it compares the actual mortality rate with the predicted mortality for each group of patients in the ICU. However, due to the existence of many scoring systems, an approach that allows one to settle which scoring system better shows the real performance of the ICU when it is used in the SMR does not exist. Therefore, we defined as our objective to establish a comparison between the results of the SMR using three different scoring systems (APACHE II, APACHE III, SAPS II).

Methods

We determined the severity of disease or injury of the patients admitted to the ICU, using APACHE II, APACHE III, and SAPS II. We also determined the crude mortality for each interval of patients. Then we calculated the real mortality of each interval and we obtained the SMR using the risk of mortality assessed by APACHE II, APACHE III and SAPS II, divided by the crude mortality. Finally, we elaborated the curves of risk of death using the results of each scoring system.

Results

In a prospective study, we collected data from 161 patients admitted in the ICU during 4 months (1 May 2002–30 August 2002). We included in our study 157 patients, with an average age of 55 years. Seventy-two per cent (n = 113) of the patients included in our study were men, and 28% (n = 44) were women. Most of the patients came from the Emergency Room: 51% from Maximum Urgency, and 20.4% from the Emergency Operation Room. We obtained a crude mortality of 28%. The averages of the scores were: APACHE II, 15; APACHE III, 44.7; SAPS II, 35.6. The tendencies of SMR using APACHE II, APACHE III and SAPS II were compared. The tendencies obtained from SMR using APACHE II and APACHE III showed a bigger dispersion of the results, especially in the intervals of more severity when they were compared with the tendency of SMR using SAPS II. From the three scoring systems used, APACHE II showed higher values of SMR than those from APACHE III and SAPS II, which demonstrate the inconsistency of the SMR when we use different scoring systems to determine it.

Conclusion

Inconsistency exists in the SMR when we use the different scoring systems, especially when we analyze the higher scores. We should carry out larger studies to define which scoring system is the one that provides better information about the clinical performance of ICU, when it is used in the SMR.

Table 1

Table 2

Table 3