Patients whose mean arterial blood pressure decreases during bypass surgery may be at increased risk for early postoperative cognitive problems, according to an article posted online June 11 by the Archives of Neurology.

"Many patients who undergo a coronary artery bypass graft (CABG) operation have pre-existing vascular disease, and a subset have pre-existing cognitive dysfunction," the authors wrote as background information. "Although recent prospective controlled trials have suggested that CABG may not cause long-term cognitive dysfunction, there may be a subset of patients who experience short-term cognitive problems."

Rebecca F. Gottesman, MD, of the Johns Hopkins University School of Medicine, Baltimore, and colleagues assessed 15 patients age 57 to 81 years undergoing bypass surgery who were believed to be at high risk for postoperative stroke. All 15 patients were given cognitive tests before and 3 to 5 days after surgery.

Blood pressure was taken before and during surgery; mean arterial blood pressure (MAP) was measured (MAP, diastolic pressure plus one-third times the difference between systolic blood pressure and diastolic blood pressure).Thirteen patients also underwent magnetic resonance imaging of the brain following surgery.

All participants had a decrease in mean arterial pressure during surgery compared with before surgery. Patients whose MAP decreased by 27 mm Hg or more had an average decrease in score on the Mini-Mental State Examination, a cognitive test, of 1.4 points (maximum, 30 points). After one individual was excluded from analysis, patients who had a pressure decrease of less than 27 mm Hg increased their scores by an average of 1 point. Individuals with high MAP before surgery also were more likely to have a decreased cognitive score.

Of the 13 individuals who underwent MRI after surgery, 6 had findings consistent with acute stroke. Because the number of participants was small, it was difficult to analyze this information, the authors noted. However, patients with a drop in pressure greater than 27 mm Hg were 2.7 times more likely to have such a lesion than patients whose pressure decreased by a smaller amount.

"Our preliminary data from a small group of subjects suggest that a substantial decrease in mean arterial pressure from a patient's baseline may be a risk factor for short-term cognitive dysfunction," the authors concluded. "This may be in part because of an increased risk for radiographic stroke. Future prospective studies are needed to further define the relationship between change in blood pressure and postoperative stroke as well as change in blood pressure and postoperative cognitive performance."