The influence of length of stay in the ICU on power of discrimination of a multipurpose severity score (SAPS) |
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| Authors: | A Sicignano C Carozzi D Giudici G Merli S Arlati M Pulici |
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| Institution: | (1) Istituto di Anestesia e Rianimazione, Ospedale Maggiore Policlinico IRCCS, Via F. Sforza, 35, 20122 Milano, Italy;(2) Servizio Anestesia e Rianimazione, Ospedale Civile, Legnano, Italy;(3) Cattedra di Anestesiologia e Rianimazione, Università degli Studi di Milano, Ospedale S. Raffaele IRCCS, Milano, Italy;(4) Servizio di Anestesia e Rianimazione, Ospedale Predabissi, Melegnano, Italy;(5) Servizio Anestesia e Rianimazione, Ospedale Niguarda, Milano, Italy |
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| Abstract: | Objective To assess how the power of discrimination of a multipurpose severity score (Simplified Acute Physiology Score; SAPS) changes in relation to the length of stay (LOS) in the intensive care unit (ICU).Design In order to compute the SAPS probability, a model derived from logistic regression was developed in a cohort of 8059 patients. Measures of calibration (goodness-of-fit statistics) and discrimination receiver operating characteristic (ROC) curve and relative area under the curve (AUC)] were adopted in a developmental set (5389 patients) and a validation set (2670 patients), both randomly selected. Once the logit was developed and the model validated, the whole database (8059 patients) was again assembled. To evaluate the accuracy of first-day SAPS probability over time, area under the ROC curve was computed for each of the initial 10 days of ICU care and for day 15.Setting 24 Italian ICUs.Patients A total of 8059 patients out of 10065 consecutive admissions over a period of 3 years (1990–1992) were included in this study. Patients whose SAPS was not correctly compiled (n=687), patients younger than 18 years (n=442), and patients whose LOS was less than 24 h (n=877) were excluded from this analysis.Interventions None.Measurements and results The logistic model gave good results in terms of calibration and discrimination, both in the developmental set (goodness-of-fit:X
2=9.24,p=0.32; AUC=0.79±0.01) and in the validation set (goodness-of-fit:X
2=8.95,p=0.537; AUC=0.78±0.01). The AUC for the whole database showed a loss in discrimination closely related to LOS: 0.79±0.01 at a day 1 and 0.59±0.02 at day 15.Conclusion The logistic model that we developed meets high standards for discrimination and calibration. However, SAPS loses its discriminative power over time; accuracy of prediction is maintained at an acceptable level only in patients who stay in the ICU no longer than 5 days. The stay in the ICU represents a complex variable, which is not predictable, that influences the performance of SAPS on the first day.ARCHIDIA (Archivio Diagnostico): A complete list of study participants appears in theAppendix |
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| Keywords: | Severity of illness index Intensive care units Length of stay Hospital mortality |
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