April 1, 2009
View Full PaperEffect of Subjective Preoperative Variables on Risk-Adjusted Assessment of Hospital Morbidity and Mortality
Key Result
Inclusion of subjective ASA and FHS variables in risk-adjusted models for colorectal surgery patients (overall morbidity 24.3%, mortality 3.9%) provided small improvements in model quality.
Study Design
Type
Observational (n=28,751)
Multicenter
Yes
Structured PICO
P
Population
28,751 colorectal surgery patients at 170 hospitals participating in the ACS NSQIP during 2006 to 2007.
E
Exposure
Logistic regression models for morbidity and mortality including American Society of Anesthesiologists Physical Status Classification (ASA) and preoperative Functional Health Status (FHS)
C
Comparator
Logistic regression models without inclusion of ASA and FHS
O
Outcome
Hospital quality rankings and model fit/discrimination for morbidity and mortality
Subjective preoperative variables like ASA and FHS make a unique contribution to assessing severity of preoperative risk without significant institutional bias, supporting their use in risk-adjusted surgical quality assessment.
Abstract
In Brief Objective: To examine the influence of American Society of Anesthesiologists Physical Status Classification (ASA) and preoperative Functional Health Status (FHS) variables on risk-adjusted estimates of surgical quality and to assess whether classifications are inflated at some hospitals. Background: ASA and FHS are influential in risk-adjusted comparisons of surgical quality. However, because ASA and FHS are subjective they can be inflated, making patients appear more ill than they actually are, and crediting hospitals for a sicker patient population. Methods: We identified 28,751 colorectal surgery patients at 170 hospitals participating in the American College of Surgeon's National Surgical Quality Improvement Program (ACS NSQIP) during 2006 to 2007. Logistic regression models were developed for morbidity and mortality with and without inclusion of ASA and FHS. Hospital quality rankings from the different models were compared. Results: Morbidity and mortality rates were 24.3% and 3.9%, respectively. Percents of patients in ASA classes I through V were 3.3%, 46.4%, 41.5%, 8.3%, and 0.7% and that were independent or partially or totally dependent were 89.2%, 7.2%, and 3.6%, respectively. Models that included ASA and FHS exhibited slightly better fit (Hosmer-Lemshow statistic) and discrimination (c-statistic) than models without both these variables, though magnitudes of differences were consistent with chance. There was inconsistent evidence for improper assignment of ASA and FHS. Conclusions: The small improvements in model quality when both ASA and FHS are present versus absent, suggest that they make a unique contribution to assessing severity of preoperative risk. With little indication that these subjective variables are subject to an important level of institutional bias, it is appropriate that they be used to assess risk-adjusted surgical quality. Periodic monitoring for inappropriate inflation of ASA status is warranted. American Society of Anesthesiologists Physical Status Classification (ASA) and preoperative Functional Health Status (FHS) are subjective variables which, if there is systematic institutional bias, could unfairly influence the risk-adjustment process in surgical quality assessment. The possibility of such bias was examined by evaluating statistical features of models built with versus without these variables.