Accuracy of a composite score using daily SAPS II and LOD scores for predicting hospital mortality in ICU patients hospitalized for more than 72 h

In most databases used to build general severity scores the median duration of intensive care unit (ICU) stay is less than 3 days. Consequently, these scores are not the most appropriate tools for measuring prognosis in studi es dealing with ICU patients hospitalized for more than 72 h. Purpose: To develop a new prognostic model based on a general severity scor e (SAPS II), an organ dysfunction score (LOD) and evolution of both scores during the first 3 days of ICU stay. Design: Prospective multicenter study. Setting: Twenty-eight intensive care units (ICUs) in France. Patients: A training data-set was created with four ICUs during an 18-month period (893 patients). Seventy percent of the patients were medical (628) aged 66 years. The median SAPS II was 38. The ICU and hospital mortality ra tes were 22.7% and 30%, respectively. Forty-seven percent (420 patients) we re transferred from hospital wards. In this population, the calibration (Ho smer-Lemeshow chi-square. 37.4, P = 0.001) and the discrimination [area und er the ROC curves: 0.744 (95% CI: 0.714-0.773)] of the original SAPS II wer e relatively poor. A validation data set was created with a random panel of 24 French ICUs during March 1999 (312 patients). Measurements and main results: The LOD and SAPS II scores were calculated d uring the first (SAPS1, LOD1), second (SAPS2, LOD2), and third (SAPS3, LOD3 ) calendar days. The LOD and SAPS scores alterations were assigned the valu e "1" when scores increased with time and "0" otherwise. A multivariable lo gistic regression model was used to select variables measured during the fi rst three calendar days, and independently associated with death. Selected variables were: SAPS II at admission [OR: 1.04 (95% CI: 1.027-1.053) per po int], LOD [OR: 1.16 (95% CI: 1.085-1.253) per point], transfer from ward [O R: 1.74 (95% CI: 1.25-2.42)], as well as SAPS3-SAPS2 alterations [OR: 1.516 (95% CI: 1.04-2.22)], and LOD3-LOD2 alterations [OR: 2.00 (95% CI: 1.29-3. 11)]. The final model has good calibration and discrimination properties in the training data set [area under the ROC curve: 0.794 (95% CI: 0.766-0.82 0), Hosmer-Lemeshow C statistic: 5.56, P = 0.7]. In the validation data set , the model maintained good accuracy [area under the ROC curve: 0.826 (95% CI: 0.780-0.867), Hosmer-Lemeshow C statistic: 7.14, P = 0.5]. Conclusions: The new model using SAPS II and LOD and their evolution during the first calendar days has good discrimination and calibration properties . We propose its use for benchmarking and evaluating the over-risk of death associated with ICU-acquired nosocomial infections.