NEW YORK (Reuters Health) – In patients undergoing non-cardiac surgery under general anesthesia, intraoperative mean arterial pressure (MAP) of less than 55 mm Hg is associated with increased risk of postoperative delirium within 30 days of surgery, according to a new study.

And the longer hypotension lasted, the greater the odds of delirium, Dr. Matthias Eikermann of Montefiore Medical Center, in New York City, and colleagues report in Anesthesia and Analgesia.

“Anesthesiologists should pay more attention to avoid the use of deep anesthesia whenever possible, since anesthetic agents (such as propofol or sevoflurane) decrease the arterial blood pressure in a dose-dependent fashion,” Dr. Eikermann told Reuters Health by email

He noted that anesthesiologists measure a patient’s blood pressure every three to five minutes, “but may not consider a moderately low blood pressure as a risk factor” for  delirium.

The study involved more than 316,000 adults who underwent non-cardiac surgery at one of two U.S. medical centers between 2005 and 2017.

Duration of intraoperative hypotension, if any, was categorized as short (less than 15 minutes) or prolonged (15 minutes or longer).

A MAP of less than 55 mm Hg occurred in 44% of patients, with short duration in 42% and prolonged duration in 2.6%. The overall incidence of postoperative delirium was 0.7%.

Short durations of MAP<55 mm Hg were associated with 22% higher odds of postoperative delirium after adjusting for confounders (P<0.001), while longer durations were tied to a 57% increase (P<0.001). The odds rose 6% for every 10 cumulative minutes of intraoperative hypotension (P=0.006).

Surgeries lasting longer than three hours were also associated with significantly higher odds of postoperative delirium compared with shorter ones.

The authors speculate that the arterial hypotension seen in their study “may have led to a critical decrease in cerebral blood flow in vulnerable patients, which in turn may have led to delirium.”

If the relationship between hypotension and delirium is confirmed by further research, they write, “rigorous blood pressure control and even hypotension early warning systems currently in development might be anticipated to prevent postoperative delirium.”

Dr. Eikermann noted that some delirium risk factors, such as “co-morbid illness, high acuity of medical illness, and diminished activities of daily living prior to admission, may not be easily modified.”

Still, he added, preoperative preventive measures include “judicious use of sedatives,” such as benzodiazepines, and avoiding prolonged (more than 6 hours) of preoperative fluid fasting.

During surgery, Dr. Eikermann said, it would be helpful to use opioid-sparing approaches such as regional analgesia. In addition, “Some studies indicate that EEG monitoring of the depth of anesthesia may also be helpful in the prevention of postoperative delirium.”

Dr. Andrew Shaw, chair of the Department of Intensive Care and Resuscitation at the Cleveland Clinic, in Ohio, told Reuters Health by email. “This study provides very convincing circumstantial evidence of an association between low blood pressure in the OR and postoperative delirium.”

As to the authors’ suggestion that their results could be explained by reduced blood flow to the brain, he noted, “a MAP of 55 mmHg is below the lower limit of most people’s cerebral autoregulation threshold. There is very little doubt that intraoperative hypotension is to be avoided if at all possible.”

“We don’t know if intraoperative drops in BP are due to a single cause, or multiple reasons, but it is likely the latter,” Dr. Shaw continued. “This underscores the need for technology that can best estimate the likely cause (such as hypovolemia, vasodilation, or poor contractility of the heart) or a combination of these.”

SOURCE: https://bit.ly/3D0U3tx Anesthesia and Analgesia, online September 13, 2021.

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