Mortality prediction in a vertebral compression fracture population: The ASA Physical Status score versus the Charlson Comorbidity Index

Abstract

Background Morbidity and mortality scores are useful to control for medical comorbidities in study populations where either effects of an illness or benefits of a treatment are examined. Our study examined if a direct relationship existed between the American Society of Anesthesiologists Physical Status (ASA) score and the Charlson Comorbidity Index (CCI) in an osteoporosis population where patients had sustained a vertebral compression fracture. Methods A retrospective chart review of patients with osteoporotic compression fractures treated by the same orthopedic surgeon between June 2000 and June 2004 was performed. The primary endpoint was death by the close of the study period (September 2006). A board certified Anesthesiologist blindly assigned all of the ASA scores as well as the Charlson Scores independently in a blinded manner. All patients were assumed to be undergoing surgery as they were assigned. A statistical relationship was examined between ASA and CCI scores through a cross table analysis with chi-squared testing as both scoring systems were considered categorical. A Pearson correlation was completed to examine the quality of a linear relationship between the categorical variable ASA compared to the continuous variable Charlson. A value of p < 0.05 was considered significant. Results Ninety patients elected conservative therapy with oral analgesics and an orthosis, while 94 patients elected for kyphoplasty. The CCI by log rank testing was not significant (p = 0.2027) for the surgery population; however, the test resulted in a highly significant value (p=0.0161) in non-operative population. The ASA Score was correlated with significance to mortality (p = 0.0150) for the surgery population, while the test was not significant (p=0.1439) in non-operative population. Treating both ASA and CCI scores as categorical variables, a relationship between them was examined and found to be highly significant (p = 0.000001) meaning patients with low ASA scores were likely to have low CCI scores. Conclusion The ASA score was predictive of mortality in a surgical population, while CCI was highly predictive of mortality in a non-surgical population. There is great agreement between the CCI score and the ASA score, reflecting that anesthesiologists subjectively consider the same elements of the patient's medical history when assigning ASA scores as the CCI objectively uses. This was a Level III Study.