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Blood pressure drop during bypass surgery associated with increased risk of cognitive decline

June 12, 2007

Patients whose mean arterial blood pressure drops during bypass surgery may be at risk for early difficulties in thinking, learning and memory, according to an article posted online today that will appear in the August 2007 print issue of Archives of Neurology, one of the JAMA/Archives journals.

"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 write as background information in the article. "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, M.D., of the Johns Hopkins University School of Medicine, Baltimore, and colleagues assessed 15 patients age 57 to 81 years undergoing CABG operations who were believed to be at high risk for having a stroke following surgery. All 15 patients were given cognitive (thinking, learning and memory) tests before and three to five days after surgery. Their blood pressure was taken before and during the operation and the mean arterial blood pressure (MAP) was measured. The MAP is calculated as the diastolic (bottom number) blood pressure plus one-third times the difference between the systolic (top number) blood pressure and the diastolic blood pressure and provides an estimate of the pressure that perfuses the various organs in the body. Thirteen of the patients also underwent magnetic resonance imaging (MRI) of the brain following surgery.

All of the participants had a decrease in MAP during surgery compared with their MAP before surgery. Those whose MAP decreased by 27 millimeters of mercury or more had an average decrease in score on the Mini-Mental State Examination, one of the cognitive tests, of 1.4 points (out of a maximum of 30 points). After one individual was excluded from the analysis, those who had a MAP decrease of less than 27 millimeters of mercury increased their scores by an average of one point. Individuals with high MAP before surgery also were more likely to have a decreased cognitive score.

Six of the 13 individuals who underwent MRI had findings in the brain consistent with acute stroke. Because the number of participants was small, it was difficult to analyze this information, the authors note. However, patients with a drop in MAP greater than 27 millimeters of mercury were 2.7 times as likely to have such a lesion as those whose MAP decreased by a smaller amount.

"Our preliminary data from a small group of subjects suggest that a substantial decrease in MAP from a patient's baseline may be a risk factor for short-term cognitive dysfunction," the authors conclude. "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."

JAMA and Archives Journals