Intervals For Oscillometric Arterial Pressure Monitoring During Noncardiac Surgery: the ‘2.5-Minute Versus 5-Minute’ Randomized Clinical Trial

Background: Guidelines recommend measuring arterial pressure at least every 5 minutes during surgery. However, it remains unknown whether shortening the measurement interval of intermittent oscillometric arterial pressure monitoring can help reduce intraoperative hypotension. This trial tested the primary hypothesis that oscillometric arterial pressure monitoring at 2.5-minute versus 5-minute intervals reduces intraoperative hypotension in noncardiac surgery patients under general anesthesia. Methods: In this single-center trial, 264 noncardiac surgery patients were randomized to oscillometric arterial pressure measurements with an upper-arm cuff at 2.5-minute or 5-minute intervals during surgery. The primary outcome was the amount of intraoperative hypotension quantified as the time-weighted average mean arterial pressure (MAP) <65 mmHg during surgery. Secondary outcomes included the administered time-weighted cumulative amount of norepinephrine indexed to body weight. Results: Of the 264 patients randomized (132 to each group), the primary outcome analysis included 132 patients in the 2.5-minute group and 131 in the 5-minute group. The median time-weighted average MAP <65 mmHg was 0.00 (0.00, 0.04) mmHg in patients assigned to the 2.5-minute group and 0.00 (0.00, 0.21) mmHg in patients assigned to the 5-minute group (estimated location shift -1.40x10 -5 95% CI: -6.64x10 -5 to 2.93x10 -6 mmHg; P=0.27). Seven patients (5.3%) in the 2.5-minute group had at least one 1-minute episode of a MAP <50 mmHg versus 13 patients (9.9%) in the 5-minute group (P=0.24). The median time-weighted cumulative amount of norepinephrine indexed to body weight patients were given during surgery was 0.05 (0.03, 0.08) µg kg -1 min -1 in the 2.5-minute group and 0.05 (0.02, 0.08) µg kg -1 min -1 in the 5-minute group (P=0.40). Conclusions: In our trial of patients having elective low-to-moderate risk surgery under general anesthesia, arterial pressure was tightly controlled with norepinephrine, and the amount of intraoperative hypotension was low – irrespective of the randomized arterial pressure measurement interval. Although oscillometric arterial pressure monitoring at 2.5-minute intervals – compared to 5-minute intervals – did not reduce the time-weighted average MAP <65 mmHg, we cannot exclude that monitoring at 2.5-minute intervals helps reduce profound hypotension.