Preoperative Identification of Patient-Dependent Blood Pressure Targets Associated With Low Risk of Intraoperative Hypotension During Noncardiac Surgery

Abstract

BACKGROUND: Intraoperative hypotension (IOH) is strongly linked to organ system injuries and postoperative death. Blood pressure itself is a powerful predictor of IOH; however, it is unclear which pressures carry the lowest risk and may be leveraged to prevent subsequent hypotension. Our objective was to develop a model that predicts, before surgery and according to a patient's unique characteristics, which intraoperative mean arterial pressures (MAPs) between 65 and 100 mm Hg have a low risk of IOH, defined as an MAP <65 mm Hg, and may serve as testable hemodynamic targets to prevent IOH. METHODS: Adult, noncardiac surgeries under general anesthesia at 2 tertiary care hospitals of the University of Pittsburgh Medical Center were divided into training and validation cohorts, then assigned into smaller subgroups according to preoperative risk factors. Primary outcome was hypotension risk, defined for each intraoperative MAP value from 65 to 100 mm Hg as the proportion of a value's total measurements followed by at least 1 MAP <65 mm Hg within 5 or 10 minutes, and calculated for all values in each subgroup. Five models depicting MAPassociated IOH risk were compared according to best fit across subgroups with proportions whose confidence interval was <0.05. For the best fitting model, (1) performance was validated, (2) low-risk MAP targets were identified according to applied benchmarks, and (3) preoperative risk factors were evaluated as predictors of model parameters. RESULTS: A total of 166,091 surgeries were included, with 121,032 and 45,059 surgeries containing 5.4 million and 1.9 million MAP measurements included in the training and validation sets, respectively. Thirty-six subgroups with at least 21 eligible proportions (confidence interval <0.05) were identified, representing 92% and 94% of available MAP measurements, respectively. The exponential with theta constant model demonstrated the best fit (weighted sum of squared error 0.0005), and the mean squared error of hypotension risk per MAP did not exceed 0.01% in validation testing. MAP targets ranged between 69 and 90 mm Hg depending on the subgroup and benchmark used. Increased age, higher American Society of Anesthesiologists physical status, and female sexindependently predicted (P < .05) hypotension risk curves with less rapid decay and higher plateaus. CONCLUSIONS: We demonstrate that IOH risk specific to a given MAP is patient-dependent, but predictable before surgery. Our model can identify intraoperative MAP targets before surgery predicted to reduce a patient's exposure to IOH, potentially allowing clinicians to develop more personalized approaches for managing hemodynamics. (Anesth Analg 2023;136:194-203) KEY POINTS• Question: Blood pressures commonly maintained during noncardiac surgery possess inherently different risks of intraoperative hypotension (IOH); can those with the lowest risks be predicted before surgery to reduce exposure to intraoperative hypotension? • Findings: Using 7.3 million intraoperative blood pressure measurements fro...

In Response

“…Supplemental Digital Content 5, Table 4, shows the distribution of the number of blood pressure readings following each MAP value studied. 2 There was no difference in monitoring, on average, between the highest and lowest MAPs, demonstrating risk differences between them was not secondary to more and less frequent monitoring, respectively.…”

“…Figure 3A shows, however, models with 5- and 10-minute periods similarly distinguish risk between MAPs, supporting our use of the shorter, 5-minute period. 2 Risk is greater for each MAP in the 10-minute interval because there is simply more time to capture hypotension compared to the model using a shorter 5-minute interval. Importantly, we evaluated frequency and duration of blood pressure monitoring in the period used to calculate hypotension risk in separate experiments, not just one or the other.…”

“…Aghi et al 1 raise an important point of clarification related to our recently published models describing the relationship between intraoperative mean arterial pressure (MAP) values between 65 and 100 mm Hg and their associated risk of hypotension defined by MAP <65 mm Hg. 2 Risk exponentially increases as MAP decreases from 100 to 65 mm Hg. The precise manner in which risk changes is dependent on individual patient characteristics before surgery and can be used to identify and test more personalized blood pressure targets predicted to reduce hypotension exposure.…”

Toward a Better Understanding of a Model Identifying Blood Pressure Targets Associated With Low Risk of Intraoperative Hypotension

“…We read with immense interest the article by Schnetz et al, 1 which aimed to create a model to predict preoperatively which intraoperative mean arterial pressures (MAPs) have a low risk of developing intraoperative hypotension (IOH), based on the patient’s unique characteristics in those receiving general anesthesia for noncardiac surgery. Although we concede that the study is a much-needed step toward developing patient-specific targets to allow individualized anesthesia, this study has a few areas worthy of further discussion.…”

“…Hypotension in the intraoperative period has shown to be a major risk factor associated with end organ damage and mortality that is fortunately alterable. 2 The study by Schnetz et al 1 is commendable in its contribution to help identify patient-specific targets of intraoperative MAPs, in an attempt to avoid adverse outcomes after surgery under general anesthesia. Its relatively large sample size, selection of the best fit model, and validation using a dataset make it a strong study, the results of which would be invaluable for future studies on individualized hemodynamic control during general anesthesia.…”