APACHE IV is a successful scoring system assessing severity of illness and prognosis of ICU patients . It has been evaluated and validated in our patients for mortality outcome . The objective of this study was to validate the APACHE IV benchmark for patients admitted with severe sepsis and septic shock to the ICU and to compare the performance of the APACHE IV system with APACHE II.
In a cohort study at a tertiary-care medical-surgical ICU with a total of 35 acute-care beds, we included all ICU patients with the diagnosis of severe sepsis and septic shock between 1 January 2007 and 29 February 2008 from a prospectively collected ICU database. Observed mortality rates were compared with predicted mortality rates for both the APACHE II and APACHE IV scoring systems, and standardized mortality ratios (SMR) were determined. The mortality percentages were predicted using the APACHE IV system and were compared with the observed data. The chi-square test is used to calculate statistical significance for categorical data.
One hundred and seventy-two patients were included in the study with an average age of 48.9 years, 53% of patients were males and 47% were females with observed mortality of 33.1%. The average APACHE II score was 20.7 with predicted mortality of 39.9% and SMR 0.83 (95% CI = 0.63 to 1.06, P = 0.15) compared with an average APACHE IV score of 73.1 with predicted mortality of 32.2% and SMR of 0.99 (95% CI = 0.78 to 1.32, P = 0.82) (Figure 1). The hospital mortality calibration curve for APACHE IV shows good calibration, with the line of perfect fit agreement lying within the 95% CI for all the risk ranges. P values of more than 0.05 in all risk ranges confirm adequate calibration. Although the curve shows that observed mortality differs from expected in the ranges of 20 to 40%, there is no statistical significance for its deviations from perfect fit (Figure 2).
The present study demonstrates that the APACHE IV system performs acceptably in our patients with severe sepsis and septic shock and can be utilized as a performance assessment tool in our population.