Subclassification Predicts Peripheral Revascularization Risk

BY MARK S. LESNEY

A modification of the American Society of Anesthesiology classification for risk stratification for routine preoperative anesthesia evaluation allowed ASA III patients--representing 80% of vascular patients--to be unbundled into two distinct subgroups, according to Dr. Hasan H. Dosluoglu. This proposed modification could potentially lead to a more appropriate perioperative risk assessment.

"The ASA classification system is not practical in patients undergoing revascularization, since the majority of them will be classified as ASA III. And although modifications have been attempted to better identify subgroups, none has been adopted," said Dr. Dosluoglu in an interview about his study that was presented at the Vascular Annual Meeting.

The proposed subclassification involves creating two new subgroups--ASA IIIA and ASA IIIB--representing the perioperative functional status of patients greater than 4 METS (metabolic equivalent levels) or less than 4 METS, respectively, according to Dr. Dosluoglu and his colleagues from the VA Western New York Healthcare System, SUNY at Buffalo, New York.

Estimated energy requirements are described in METS, which are used to express aerobic demands for specific activities. Typically, perioperative cardiac and long-term risk is increased in those who can not meet a 4-METS demand, which basically involves taking care of self, walking a block or two at 2-3 miles/hr, and climbing a flight of stairs.

The researchers reviewed all charts of the 482 patients (99% male) who underwent revascularization for disabling claudication or critical limb ischemia between June 2001 and October 2006 at their institution. Demographics, comorbidities, operative/interventional details, postoperative complications, and outcomes (myocardial infarction/stroke and death) were analyzed.

Using standard assessment, 35 patients were assigned to ASA II (7%), 371 to ASA III (77%), and 76 patients to ASA IV (16%). The ASA III patients were further assigned into the METS-defined subcategories: ASA IIIA (218 patients, or 45% of total patients) and ASA IIIB (153 patients, or 32%). Compared with the ASA IIIA patients, the ASA IIIB subgroup had significantly higher age, albumin levels, incidence of coronary artery disease (CAD), diabetes mellitus, cerebrovascular accident, renal insufficiency (creatinine greater than 1.5 mg/dL), critical limb ischemia, and length of stay. In addition, there were significantly more MIs and deaths in IIIB patients. Survival rates between the two subgroups were significantly different, with IIIA patients closer to the ASA II patients, and ASA IIIB patients closer to the ASA IV patients, Dr. Dosluoglu said.

Overall, multivariate analysis using Cox regression showed that albumin less than 3 g/dL, critical limb ischemia, coronary artery disease, and renal insufficiency correlated with poor survival.

"Functional status assessment is an integral part of routine preoperative anesthesia evaluation, and we found this to be very reliable in predicting not only postoperative morbidity and mortality, but overall survival in ASA III patients undergoing peripheral vascularization," Dr. Dosluoglu said. "The simple modification creating the ASA IIIA and IIIB subgroups allows these patients to be separated into two distinct subgroups, which will potentially lead to a more appropriate perioperative risk assessment in [the] future," he concluded. A key contributor to the work reported by Dr. Dosluoglu was Nader D. Nader, MD, PhD, associate professor of anesthesiology at the department of anethesia, SUNY at Buffalo.

When asked to comment on this article, Dr. Craig. Donaldson, chairman, department of surgery, MetroWest Medical Center, Framingham, Mass., stated: "This suggestion makes intuitive sense, and would refine our ability to more precisely match each patient with the most beneficial and least harmful therapeutic plan for his disease. Objective measurement of "functional status" is the key to this stratification scheme, and the details of methodology will be important to clarify.".