AtlantaLow intraoperative blood pressure is associated with a significantly greater number of negative outcomes after surgery, according to preliminary results of an ongoing investigation. Researchers at the University of Michigan Medical School, Ann Arbor, said the study showed that patients whose systolic blood pressure drops below 90 mm Hg are more likely to die than are their counterparts whose systolic blood pressure remains above this level; however, additional analysis is required to determine whether hypotension is an independent predictor and to evaluate other predictors of adverse outcomes.

"Several years ago, Terri Monk showed that patients who are kept at a deep level of anesthesia during surgery experience higher mortality [ Anesth Analg 2005;100:4-10]," commented Michael O'Reilly, MD, MS, Associate Professor of Anesthesiology at the University of Michigan Medical School. "But if you look closely at the data, it also turned out that these individuals had low intraoperative blood pressure."

Using data compiled as part of the National Surgical Quality Improvement Program (NSQIP), in addition to data from the University of Michigan computerized anesthesia records, Dr. O'Reilly and his co-investigators were able to examine physiologic and other variables associated with anesthesia care and correlate them with the outcomes recorded in the NSQIP database. "I decided to look at the blood pressures and see if they're correlated with outcomes," he said.

Dr. O'Reilly and his colleagues studied the computerized anesthesia records of 2,383 patients who were also included in the NSQIP database. The anesthesia database was scanned for systolic blood pressure values between 70 and 90 mm Hg; cases were considered positive when the low values lasted for more than five minutes or were recorded during three consecutive measurements in patients wearing a noninvasive blood pressure cuff. Co-investigators with Dr. O'Reilly were Kevin K. Tremper, PhD, MD, Amy Shanks, MS, Sachin Kheterpal, MD, and Darrell A. Campbell Jr, MD.

The investigators also searched the database for patients with tachycardia (defined as a heart rate of >110 or >120 bpm) of at least 10 minutes' duration. The association between intraoperative low blood pressure, tachycardia and outcomes (as reported in the NSQIP database) was then examined.

As Dr. O'Reilly reported at the 2005 annual meeting of the American Society of Anesthesiologists, 24.7% of patients with a systolic blood pressure 80 mm Hg had at least one negative outcome, compared with 13.9% of those who did not have low blood pressure (P=0.0001). Patients with systolic blood pressure measurements <90 mm Hg were more likely to develop septic shock or infections away from the site of surgery. In addition, a clear relationship was found between blood pressure measurements 90 mm Hg and 30-day mortality (Table 1).

Similarly, patients whose intraoperative heart rate exceeded 110 bpm were more likely to die within 30 days and experience septic shock than were those who did not have tachycardia (Table 2).

Despite these results, Dr. O'Reilly was quick to point out that the study is in its early stages. "We're not done with the analysis yet; this is very preliminary," he said in an interview with Anesthesiology News. "The trick is, we have to risk-adjust the data. It may turn out that the patients with low blood pressure didn't do well because they have sick hearts to begin with."

"But I bet that's not the case," he added. "I bet when we risk-adjust the data, it's going to turn out that the low blood pressure was responsible for the negative outcomes and death."

Co-moderator Lucinda L. Everett, MD, saw the potential for such data to ultimately help anesthesiologists. "Hypotension is not uncommon in anesthetized patients," she commented.

"In general, anesthesiologists are probably more aggressive in treating hypotension either if the hypotension is severe or if the patient has underlying coronary or cerebrovascular disease," she continued. "If further analysis shows that hypotension is an independent predictor of adverse outcomes and perhaps better defines threshold blood pressure values, it would help to guide our practice." Dr. Everett is Chief of Pediatric Anesthesia at Massachusetts General Hospital, Boston, and President of the Society for Ambulatory Anesthesia.

Based on a poster presentation (Abstract A-648) at the 2005 annual meeting of the American Society of Anesthesiologists and interviews with Michael O'Reilly, MD, MS, and Lucinda L. Everett, MD.