Avoiding intraoperative hypotension might serve as a measure of clinician skill. We, therefore, estimated the range of hypotension in patients of nurse anesthetists, and whether observed differences were associated with a composite of serious complications.
First, we developed a multivariable model to predict the amount of hypotension, defined as minutes of mean arterial pressure (MAP) <65 mm Hg, for noncardiac surgical cases from baseline characteristics excluding nurse anesthetist. Second, we compared observed and predicted amounts of hypotension for each case and summarized “excess” amounts across providers. Third, we estimated the extent to which hypotension on an individual case level was independently associated with a composite of serious complications. Finally, we assessed the range of actual and excess minutes of MAP <65 mm Hg on a provider level, and the extent to which these pressure exposures were associated with complications.
We considered 110,391 hours of anesthesia by 99 nurse anesthetists. A total of 69% of 25,702 included cases had at least 1 minute of MAP <65 mm Hg, with a median (quartiles) of 4 (0–15) minutes on the case level. We were unable to explain much variance of intraoperative hypotension from baseline patient characteristics. However, cases in the highest 2 quartiles (>10 and >24 min/case more than predicted) were an estimated 27% (95% confidence interval [CI], 1.1–1.4) and 31% (95% CI, 1.2–1.5) more likely to experience complications compared to those with 0 excess minutes (both P < .001). There was little variation of the average excess minutes <65 mm Hg across the nurse anesthetists, with median (quartiles) of 1.6 (1.2–1.9) min/h. There was no association in confounder-adjusted models on the nurse anesthetist level between average excess hypotension and complications, either for continuous exposure (P = .09) or as quintiles (P = .30).
Hypotension is associated with complications on a case basis. But the average amount of hypotension for nurse anesthetists over hundreds of cases differed only slightly and was insufficient to explain meaningful differences in complications. Avoiding hypotension is a worthy clinical goal, but does not appear to be a useful metric of performance because the range of average amounts per clinician is not meaningfully associated with patient outcomes, at least among nurse anesthetists in 1 tertiary center.