Based on ASA physical status, there was a significant difference in SICU length of stay, duration of mechanical ventilation, duration of vasopressor treatment, number of acquired organs with dysfunction, and likelihood of readmission to the SICU. (Image source: Thinkstock)

Based on ASA physical status, there was a significant difference in SICU length of stay, duration of mechanical ventilation, duration of vasopressor treatment, number of acquired organs with dysfunction, and likelihood of readmission to the SICU. (Image source: Thinkstock)

Can we predict the future? Of course! You can go online and find out precisely when and where the next solar eclipse will occur. Science excels at predicting future events characterized by precise systems (e.g., planetary motion) or large overall trends (e.g., global warming). However, predictions are far less accurate in systems characterized by high levels of random variation (e.g., will it rain three weeks from today?). Predictions are important in medicine. We know that decreased smoking saves lives. What is harder is predictions for individual patients: will you live longer if you stop smoking?

The ASA status is known to predict trends such as cardiac risk and mortality with reasonable accuracy.  There are other risk stratification methods, including surgical risk as defined by American College of Cardiology/American Heart Association guidelines, and the simplified Revised Cardiac Index (SRCI). How well do any of these predict the length of SICU stay and postoperative morbidity in individual patients?

Dr. Monica I. Lupei, Anesthesiology Critical Care Medicine Department, University of Minnesota, Minneapolis, Minnesota, and colleagues from the Anesthesiology Critical Care Medicine Department, Northwestern University Feinberg School of Medicine, Chicago, Illinois, the Surgery Department, University of Minnesota School of Medicine, Minneapolis, Minnesota, and the Master of Public Health Program, Department of Family & Community Medicine, University of North Dakota, Grand Forks, North Dakota, retrospectively analyzed 220 patients from one institution who were admitted to the SICU between October 1, 2010, and March 1, 2011.  The authors determined the relationship between ASA physical status and SICU length of stay, mechanical ventilation, vasopressor treatment duration, number of acquired organ dysfunctions, SICU readmission within 7 days, and SICU and 30-day mortality.  The results of their study are published in this month’s issue of Anesthesia & Analgesia in the article “The Association Between ASA Status and Other Risk Stratification Models on Postoperative Intensive Care Unit Outcomes.”

ASA physical status was a risk factor for SICU length of stay, duration of mechanical ventilation, duration of vasopressor treatment, number of acquired organ dysfunctions, and likelihood of readmission to the SICU.  Surgical risk as defined by the ACC/AHA was only associated with increased risk in acquired organ dysfunction. The simplified Revised Cardiac Index was not associated with any SICU outcomes.  No preoperative data was associated with mortality.

The authors should be commended for addressing a challenging area and building predictive models.  At the same time, it is important to acknowledge that this study was retrospective in nature. Retrospective studies necessarily fit some of the random noise to the model parameters. The test of the model requires either prospective evaluation, or a test of exactly the same model in a different population of patients at a different institution.

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