AUTHOR: Michael Vlessides
Continuous noninvasive blood pressure monitoring helps limit hypotension during noncardiac surgery. Researchers at the Cleveland Clinic concluded that a novel device halved the amount of hypotension below a mean arterial pressure (MAP) threshold of 65 mm Hg.
“There is increasing evidence that low blood pressure during noncardiac surgery is associated with serious complications, especially myocardial injury and acute kidney injury, but also 30-day mortality,” said Gausan R. Bajracharya, MD, a resident at the Cleveland Clinic’s Anesthesiology Institute, in Ohio.
“Blood pressure is usually measured oscillometrically, typically at five-minute intervals, with only selected patients benefiting from continuous monitoring with invasive arterial lines,” he said. “But continuous monitoring might help anesthesiologists recognize hypotension early, and facilitate prompt and effective treatment.”
Set Threshold Evaluated
The investigators enrolled 320 patients presenting at the institution between August 2016 and August 2017, and complete data were available for 316. The patients were 45 years of age or older, undergoing moderate- to high-risk noncardiac surgery lasting more than two hours. They were randomly assigned to undergo continuous hemodynamic monitoring (n=158) using the ClearSight device (Edwards Lifesciences) or intermittent oscillometric blood pressure measurement (n=158).
The trial’s primary end point was time-weighted average MAP below a threshold of 65 mm Hg, which was compared between the two groups using the Wilcoxon rank sum test and Hodges-Lehmann estimation of location shift.
The study found that patients in the continuous blood pressure monitoring group had significantly lower time-weighted average MAP under 65 mm Hg (0.05 mm Hg; 95% CI, 0.00-0.22 mm Hg) compared with standard intermittent blood pressure monitoring (0.11 mm Hg; 95% CI, 0.00-0.54 mm Hg) (P=0.039). The median time spent below 65 mm Hg was halved with continuous monitoring, decreasing from four minutes in patients monitored intermittently to two minutes in those monitored continuously.
These results, the investigators said, demonstrate that continuous blood pressure monitoring during noncardiac surgery halved the magnitude of hypotension below the 65 mm Hg threshold.
“MAC hours of volatile anesthetic were nearly the same in the two groups,” Dr. Bajracharya said. “However, the timing of anesthetic a dministration might have differed.”
Despite the strength of the findings, some of Dr. Bajracharya’s audience questioned the clinical relevance of the hypotension measurement used in the trial. “Were these clinically significant episodes of hypotension?” asked Bobbie Jean Sweitzer, MD, a professor of anesthesiology at Northwestern University Feinberg School of Medicine, in Chicago. “You’ve used time-weighted averages over the length of the entire anesthetic. But did you look at individual hypotensive episodes in terms of how long they lasted or how significant the decreases in blood pressure were?”
“Blood pressure is a complex signal and there are many ways to characterize hypotension,” commented study co-investigator Kamal Maheshwari, MD. “We therefore evaluated hypotension using multiple different metrics, like minutes spent under a threshold and the area under the curve below a threshold. Each metric confirmed our primary finding that continuous blood pressure monitoring roughly halved the amount of hypotension.”