Intraoperative Hypotension: How Do We Fare in Lower Risk Surgeries and How Can We Improve?

Wael Saasouh, MD

Intraoperative hypotension has been shown to negatively influence patient outcomes based on large trials from major academic centers. During the session, “A Pragmatic Discussion on Intraoperative Hypotension” on Saturday, April 15 at the IARS 2023 Annual Meeting, experts on this topic shared the results of similar work in the community setting where a significant share of anesthetic care occurs. More importantly, the results of this work seem to point to valuable opportunities to mitigate intraoperative hypotension, and suggest that anesthesia clinicians may have a lot more influence and control on outcomes than previously thought.

Intraoperative hypotension (IOH) is a relatively older topic of discussion that is resurfacing with more emphasis. Hypotension during surgery, while sometimes considered expected, and even labeled “normal,” has serious ramifications for postoperative recovery and the risk for major adverse events. This discussion has been more recently revitalized with newer hemodynamic monitors that allow more continuous monitoring and less invasively than traditional methods. These monitors are the product of an industrial race and would naturally spark an element of healthy competition in the field, all to the benefit of the clinician who has increasingly impressive gadgets and the patient who is being more protected against dangerous sequelae of IOH.

The session started with speaker Richard Dutton, MD, MBA, Adjunct Professor of Anesthesiology at Texas A&M College of Medicine and Chief Quality Officer at US Anesthesia Partners. Dr. Dutton began with a review of published literature highlighting the relationship between drops in intraoperative mean arterial pressure (MAP) and adverse outcomes after noncardiac surgery, and the increased likelihood of renal and cardiac complications with increasing duration of IOH. The data is clear on two aspects: longer duration of IOH and lower absolute decreases in blood pressure (severity of IOH) are both detrimental, especially when combined. Published literature seems to converge around a MAP threshold of 60-70 mmHg (or a systolic blood pressure threshold of 100 mmHg) per the Perioperative Quality Initiative (POQI) Consensus Statement, below which myocardial injury would be more likely.

Currently, published literature tends to be the result of studies conducted at major academic centers. In an effort to extend the knowledge into the community setting, a collaborative was formed by NorthStar Anesthesia (NSA), US Anesthesia Partners (USAP), and Edwards Lifesciences, with statistical support from Mathematica and in collaboration with the American Society of Anesthesiologists (ASA). The running thought was that IOH was common in community practice, especially during longer surgical procedures, higher risk patients (older, sicker), and at hospitals as opposed to ambulatory surgery centers. The objectives were to assess the incidence of IOH in the community setting and describe its variation according to data obtained from NSA and USAP de-identified electronic records.

Wael Saasouh, MD, Regional Director of Research for NSA, Assistant Professor at Wayne State University, and Associate Professor at Michigan State University described the collaborative and shared the results of the conducted analyses. These results are currently pending publication. Multiple definitions for IOH exist, and the one highlighted in this effort was a MAP of 65 mmHg or less over a total cumulative duration of at least 15 minutes. This definition has been put forth according to the “Intraoperative Hypotension Among Non-Emergent Noncardiac Surgical Cases” measure (also known as the “ePreop31 measure”) and adopted by the Centers for Medicare & Medicaid Services (CMS) Merit-Based Incentive Payment System (MIPS) and the ASA. The data was collected from 45 centers around the US over two years (2020-2021). The IOH measure inclusion and exclusion criteria can be reviewed in the original publication. In the relatively low risk sample of non-emergent cases studied by this collaborative, the results were not intuitive. Two thirds of the cases that satisfied the IOH definition were under 65 years of age, nearly half were low risk for anesthesia, around 60% were surgeries lasting up to 2 hours, and 13% of cases were performed at ambulatory surgery centers. The overall incidence of IOH was 29%, quite similar to that reported in prior academic center publications. In a sub-analysis of the ambulatory cases, 75% were under 65 years of age, 80% were low risk for anesthesia, and almost 80% were surgeries lasting up to 2 hours. Keeping in mind that these cases are generally considered lower risk than the average surgery performed at a major academic center, a deeper dive into the details revealed that individual providers may be driving at least part of the results, making this a potential target for quality improvement initiatives. While the study did not include patient outcomes, the authors plan to investigate outcomes in future work.

Josh Lumbley, MD, Chief Quality Officer at NSA, discussed the aspect of the study relating to quality improvement. Namely that, after accounting for most variables, IOH seems to be driven to a decent extent by individual variability among anesthesia providers. This data comes from the calculated ”observed-to-expected” IOH ratio which identifies clinicians outside the average incidence of IOH in the study population. This picks up on clinicians who experience more IOH than expected, but also those with less IOH than expected. This presents the opportunity to learn and adapt techniques from the latter group to lower the incidence of IOH more globally. Of note, “expected incidence of IOH” was based on a logistic regression model that accounts for case mix, age, gender, BMI, and ASA physical status of the surgical patient, as well as the surgical duration of the procedure. The somewhat surprising result was that clinicians with more IOH than would be expected did not seem to have particularly older, sicker, or more at-risk patients. In fact, that group of clinicians seemed to be caring for somewhat younger, more female, lower ASA status patients, mostly undergoing surgery at an ambulatory surgery center. This counter-intuitive result, generally attributed to clinician tolerance of lower blood pressures in certain perceived healthier populations, points to evidence that individual clinician behavior may, in fact, be an excellent target for quality improvement initiatives that would greatly benefit surgical patients.

Anna Christensen, PhD, Director of Health Research, Strategy, and Analytics at Mathematica, then gave a glimpse of the future direction in IOH research based on this work. While Phase I of this project described incidence of IOH in the community setting and identified potential drivers, Phase II is expected to link these incidences with patient outcomes, thus better identifying the impact of mitigation and treatment initiatives. The group also plans to further refine the risk-adjustment model for clinician influence on IOH and focus on specific surgical procedures and patient characteristics. One aspect of IOH that is currently being studied is the variation of blood pressure during a surgical procedure and whether patterns could be recognized and acted upon. An example would be to identify anesthetic-related hypotension and differentiate it from surgery-related hypotension.

Two papers based on this work are currently being reviewed for journal publication and expected to be published later this year.