Patients whose mean arterial blood pressure drops during bypass surgery may be at risk for early difficulties in thinking, learning and memory, according to a new article.
"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."
Reference: Arch Neurol. 2007;64(8):(doi:10.1001/archneur.64.8.noc70028)
This study was funded by GlaxoSmithKline.
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In Patients with Hypertension, Wider Swings in Blood Pressure Linked to Higher Risk of Death
Newswise — San Francisco, CA. (June 23, 2011) – For patients with hypertension undergoing heart surgery, large variations in blood pressure before, during, and after the operation are associated with an increased risk of death, reports the July issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS).
Although preliminary, the findings raise the possibility that anesthesiologists and surgeons may want to exercise tighter control over blood pressure during heart surgery in patients with hypertension. The study was led by Dr. Solomon Aronson of Duke University Medical Center, Durham, N.C.
Blood Pressure Variability Linked to One-Month Mortality RiskThe researchers analyzed data on 1,512 patients with hypertension (high blood pressure) undergoing cardiac surgery, drawn from a previous study. Most of the patients were undergoing coronary artery bypass graft (CABG) surgery for blocked coronary arteries.
Data on variations in blood pressure during surgery and in the pre- and postoperative period were analyzed in relation to the risk of death after surgery. One month after surgery, 3.2 percent of patients had died.
The results suggested that patients who spent more time with their systolic blood pressure outside a certain range were at increased risk of death. Systolic blood pressure is the first, or higher, number in the blood pressure reading. A systolic blood pressure of less than 120 millimeters of mercury (mm Hg) is considered normal.
The risk of death was higher for patients who spent more time with blood pressure outside the range of 75 to 135 mm Hg during surgery, and 85 to 145 mm Hg before and after surgery. For each systolic blood pressure swing of greater than 60 mm Hg, the risk of death was increased by 16 percent. Put another way, the risk of death increased by three percent for each minute spent outside a range of 105 to 130 mm Hg.
The impact of blood pressure variability was greater for patients at higher risk of death. For this group, the 30-day risk of death was 61 percent for those with wide swings in blood pressure versus 40 percent without such variability. For low-risk patients, the absolute difference was much smaller: 0.5 versus 0.2 percent.
More than two-thirds of patients undergoing cardiac surgery have hypertension, which is a major risk factor for death and other adverse outcomes. However, it's not a simple matter to establish the optimal blood pressure before, during, and after surgery. Because patients with hypertension have problems with blood pressure regulation, the range of "acceptable" blood pressures may be narrower than in patients with normal blood pressure.
The study provides new evidence linking wide variations in blood pressure to an increased risk of death after heart surgery in patients with hypertension. It's too early to draw any conclusions about proper blood pressure control, however—further studies will be needed to confirm the findings and to determine the reasons for the increased risk.
In an accompanying editorial, Dr. Martin J. London discusses the study implications, emphasizing the highly complex nature of the data and the difficulty of reaching definitive conclusions. Until such studies are available, Dr. London plans to continue following the "sage advice" of a respected mentor who advised letting the blood pressure drop…"but maybe not so much or so often."
Read the current issue of Anesthesia & Analgesia
About the IARS The International Anesthesia Research Society is a nonpolitical, not-for-profit medical society founded in 1922 to advance and support scientific research and education related to anesthesia, and to improve patient care through basic research. The IARS contributes nearly $1 million annually to fund anesthesia research; sponsors an annual forum for anesthesiology leaders to share information and ideas; maintains a worldwide membership of more 15,000 physicians, physician residents, and others with doctoral degrees, as well as health professionals in anesthesia-related practice; sponsors the SmartTots initiative in conjunction with the FDA; and publishes the journal Anesthesia & Analgesia. Additional information about the society and the journal may be found at the IARS website.
About Anesthesia & AnalgesiaAnesthesia & Analgesia was founded in 1922 and was issued bi-monthly until 1980, when it became a monthly publication. A&A is the leading journal for anesthesia clinicians and researchers and includes more than 500 articles annually in all areas related to anesthesia and analgesia, such as cardiovascular anesthesiology, patient safety, anesthetic pharmacology, and pain management. The journal is published on behalf of the IARS by Lippincott Williams & Wilkins (LWW), a division of Wolters Kluwer Health.