A large international study that is drawing mixed reviews suggests that managing a patient's mean arterial pressure (MAP) during surgery through medication reduces the risk of a stroke or cardiac arrest within the next month.
The study, which was published in the Annals of Internal Medicine this week, suggests that pulling blood pressure or maintaining medication for hypertensive and hypotensive patients can help maintain MAP. However, critics say the study overemphasized the role of blood pressure in surgical outcomes and failed to account for many other factors.
"This is not saying that hemodynamics perioperatively don't matter; they unequivocally matter," said P. J. Devereaux, MD, PhD, a cardiologist and epidemiologist at the Population Health Research Institute in Hamilton, Ontario, Canada, who is the senior author of the study.
The study compared two strategies for managing blood pressure: one designed to maintain an MAP of at least 60 mm Hg during surgery, and the other designed to maintain an MAP of at least 80 mm Hg. Going into the study, Devereaux and colleagues had expected that a cutoff of 80 mm Hg would lead to fewer adverse cardiac outcomes than the other approach. But they found no such differences.
For roughly half the participants (n = 3742), the goal was to avoid hypotension, meaning that anesthesiologists worked to maintain an MAP of at least 80 mm Hg during the procedure. Per study protocol, these patients stopped taking any blood pressure control medications on the day of surgery and over the 2 following days. During this period, patients received a blood pressure medication only if their systolic pressure was 130 mm Hg or higher. After the pause in medications, patients resumed their usual practice.
For the remaining patients (n = 3748), the goal was to avoid hypertension. In this group, the target MAP was at least 60 mm Hg during surgery, and participants continued taking blood pressure medications with no pause.
Patients were aged 45 years or older and had taken at least one medication to control blood pressure for at least 30 days over the 6 weeks prior to inpatient noncardiac surgery. The average age of the patients was 70 years, and 44% of participants were women.
Patients whose MAP is lower than 60 mm HG generally are hypotensive and may not be able to supply enough blood to their organs. The MAP that indicates hypertension is less clear, but an MAP greater than 100 mm Hg usually indicates high blood pressure and extra stress on the heart and arteries.
No difference was observed between the two groups in cardiac events such as stroke or cardiac arrest 30 days after surgery. Almost 14% of participants in the hypotension-avoidance group experienced an event, and the same percentage was observed in the hypertension-avoidance group. One percent of the participants in both study arms died within 30 days following surgery.
Devereaux said this study shows that either strategy is safe for most patients.
"You're safe with a mean arterial pressure of 60 mm Hg or greater," he said.
Concern About Clinical Implications
Martin London, MD, professor emeritus of anesthesiology at the University of California, San Francisco, said the study raises more questions than it was able to answer, given the intricacies of the body's response to surgery.
"It's very problematic to know what to take away from this study" for both internists and anesthesiologists, London said. "An incredibly complex milieu of variables" plays into surgery outcomes.
Blood pressure is only one predictor of outcomes following surgery. Hemoglobin volume in a patient's blood is important for ensuring that organs are perfused properly, so focusing on blood pressure control alone could lead to an overly simplistic view of how to mitigate post-surgery risk, according to London. And the body may mount a strong inflammatory response to surgery, which could also lead to unwanted outcomes after surgery,
However, London did applaud the researchers' attempt to answer a critical question about how best to optimize surgical outcomes for patients who take blood pressure medications.
Earlier research from Devereux's group examined patients who began taking a new blood pressure medication just prior to surgery, which was associated with an increased risk of stroke or death afterward. This study, by contrast, focused on blood pressure medications that people were already taking routinely.
A limitation of the study, as pointed out in an accompanying editorial, is that many participants in both study arms did not follow the protocol; some people took medications when they should not have, and other people skipped the medications that were due. Devereaux acknowledged the limitation but said that a subgroup analysis of patients who fully adhered to the protocol showed similar results as the overall study findings, giving him confidence in the results.
Devereaux also said they didn't analyze management of MAP targets by anesthesiologists. Strategies might have included the administration of IV fluids or vasopressors or use of intraaortic balloon pumps. On-site anesthesiologists made such choices in real time, and the study protocol did not include recording these decisions or analyzing their effects.
Landon has disclosed no relevant financial relationships. Devereaux has relationships with Abbott, Roche, Trimedic, Boehringer Ingelheim, Trimedic, Bayer, Cloud DX, and Philips Healthcare.
Marcus Banks is a freelance journalist.
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Cite this: The MAP to Better Post-Surgery Outcomes - Medscape - Apr 27, 2023.