Physicians who have the opportunity to read the article “Association between Preoperative Blood Pressures and Postoperative Adverse Events” in this issue of Anesthesiology, written by a superb team from Vanderbilt University (Nashville, Tennessee) led by Dr. Walco under the senior authorship of Dr. Freundlich  may at first give pause. Why did the editors of Anesthesiology decide to accept for publication a single-center, retrospective, observational study that documents a rather modest U-shaped association between preoperative blood pressures and postoperative morbidity and mortality among adults undergoing noncardiac surgery?

Adding to such doubt, readers may note that the authors transparently concede both that they lacked an a priori declaration of what would constitute a minimal clinically significant difference and further that the documented association was prone to alteration by a modestly significant hypothetical unmeasured confounder. Putting a quantitative light on the issue of confounding, the authors report e-values for the primary associations of 1.17 and 1.28, respectively. In the context of many measured confounders demonstrating adjusted effect sizes higher than this (see table 2 in the referenced article), this raises concerns that a single unmeasured confounder with these hypothetical risk ratios would have made the observed associations between preoperative systolic and diastolic blood pressures and postoperative morbidity disappear entirely as could a credible combination of even weaker confounders along with the presence of relatively modest outcome misclassifications.  It should also be noted that in a series of admirably extensive sensitivity analyses, the authors found that while preoperative systolic blood pressure derangements were associated with the total ordinal (i.e., additive) number of adverse morbid events (from among acute kidney injury, myocardial infarction, stroke, and mortality) as well as with the binary composite outcome of any such event occurring, systolic blood pressure (SBP) was only associated with acute kidney injury (and not with the occurrence of myocardial infarction, stroke, or mortality) when these outcomes were considered as individual, separate outcomes.

Moreover, the stated motivation for the study’s design rests on the questionable supposition that day-of-surgery blood pressure measurements are somehow categorically different from other contexts of blood pressure readings, a notion that my own research team has questioned in previous manuscripts.  Doubts about what lessons we should glean from the study are thus understandable.

However, with an appreciation informed through the lens of history, I would argue to readers of Anesthesiology that, on the contrary, Walco et al. present us with a valuable analysis and that their findings contain enduring and important observations that have the potential to tangibly advance our specialty. Given these acknowledged weaknesses, how exactly does the current manuscript contribute to the literature, and what lessons should we take away that are relevant to our day-to-day practice of anesthesiology?

When Harvey Cushing first introduced the measurement of arterial blood pressures into the operating room, he opened a legacy of inquiry that continues through the current manuscript. In 1920, and standing on Cushing’s metaphorical shoulders, the famed anesthesiologist and founder of the International Anesthesia Research Society (San Francisco, California), Elmer McKesson, broke new ground with his insistence on recording quantitative blood pressures rather than relying merely on qualitative assessments of so-called “pulse quality,” a change that had been made possible with the introduction of a new device known as the sphygmomanometer. 

In more than a century since such foundational work, physicians have naturally sought to bring a normative understanding to the systemic blood pressure. That is, we anesthesiologists do not simply want to know what the blood pressure is, but rather we want to know what it should be—and of equal importance for our day-to-day practice, what should it not be during our preoperative evaluations as we assess our patients’ fitness for, and likelihood of, safe passage through the fraught period of a pending surgery and anesthetic. Now, with well more than 1 million blood pressure–related references indexed in PubMed, it is clear that inquiries related to blood pressures continue apace throughout all corners of medical practice.

Yet for all that, the answer to what the blood pressure should be has perhaps been quite obvious—at least in the sense of an abstract principle—for over two millennia preceding Drs. Cushing, McKesson, and Walco. In the fourth century BCE, the ancient Greek philosopher Aristotle tells us in his doctrine of the golden mean that “…excess and deficiency belong to badness, whereas intermediacy belongs to excellence… [T]he bad go bad every which way… [E]xcellence both finds and chooses the intermediate…”  Aristotle was certainly not alone in this thinking, as sometime during that same millennium (give or take seven centuries), the author of Ecclesiastes counsels us, “Do not be overrighteous, nor be overwise… Be not overly wicked, nor be a fool… It is good that you should take hold from this and from that.”  For sages in both of these ancient traditions, the notion that one should take the middle course between extremes was advice to live by.

Now, thanks to Walco et al. and undergirded by hard data from Vanderbilt University’s operating rooms, we can see in graphic form that the golden mean of both Aristotle and Ecclesiastes indeed retains its wisdom for anesthesiologists of today (see Supplemental Digital Content 9 of the original article, illustrating the relationship between the preoperative SBP and postoperative morbidity and mortality). I hope that readers will forgive my noting the coincidence that these data that harken back to the wisdom of ancient Greece were fittingly collated just around the corner from a modern-day, full-scale reconstruction of the Parthenon in Nashville, Tennessee!

Indeed, what Walco et al. have reminded us is that balance is important. Thanks to their series of analyses, they demonstrate that across a broad set of surgeries among patients with a range of baseline health statuses, a preoperative systolic blood pressure in the low 140 mmHg’s and a diastolic blood pressure in the mid 80 mmHg’s is approximately where our preoperative golden mean is centered. But how will this insight affect our current practice? I believe there are two major lessons we should take away from this article.

The effects of preoperative blood pressure derangements in raising our patients’ risk of perioperative morbidity are generally modest, but they are unlikely to be zero, and such risks increase as we move progressively above or below the 140s/80s. Despite suggestions from several guidelines referenced in their manuscript that it may be wise to postpone elective surgery for SBP greater than 180 mmHg or diastolic blood pressure greater than 110 mmHg, the authors of the current manuscript rightly question such guidance as poorly grounded in evidence.

Specifically, such artificial discontinuities at which case cancellation is warranted should not be seen in the spirit of Ecclesiastes—i.e., as some sort of biblical mandate from on high—but should be more appropriately conceived through the lens of Aristotelian virtue ethics. That is, in the face of severe preoperative blood pressure derangements, the anesthesiologist should feel empowered, in collaboration and in conversation with surgical colleagues and in shared decision-making with the patient, to weigh the benefits and dangers of proceeding versus delaying surgery in the context of the myriad individualized complexities that we all face as part and parcel of our daily medical practice. In essence, lesson one is that in situations such as these, we should strive to act like physicians.

The second lesson I believe we should take away is this: the magnitude of perioperative risk incurred due to most preoperative blood pressure abnormalities pales in comparison to the magnitude of the long-term, longitudinal risk faced by our numerous patients with the condition of poorly controlled hypertension. In quantitative terms, a patient in the current study with an SBP a full 30 points higher than the suggested ideal preoperative SBP would have a relative odds of a higher number of postoperative adverse events somewhere between 1.02 and 1.44 (see table 2 in the referenced article). In comparison, a hypertensive patient who managed to achieve the same 30-mmHg longitudinal drop in SBP—admittedly no small challenge—would see a reduction in his or her relative risk of developing cardiovascular disease of approximately 54% (95% CI, 37 to 66%).

With this comparison in mind, it is incumbent upon anesthesiologists to remind ourselves in our daily practice that among U.S. adults with known hypertension, approximately 56% remain poorly controlled, while 22% of hypertensives are unaware of their diagnosis.  The message suggested by Walco et al. in their discussion as well as by my own research group is that patients in whom we suspect undertreated hypertension—regardless of their perioperative care—should be counseled to pursue postoperative longitudinal treatment of this common, deadly, and modifiable condition. If such a single change in practice were implemented universally, it might conceivably turn exposure to an anesthesiologist into a positive risk factor for longer life. 

Such counseling was indeed included among the anesthesiology-specific Merit-based Incentive Payment System quality metrics as recently as 2017, before it was removed without explanation. Perhaps future versions of our specialty-specific Merit-based Incentive Payment System measures will again include counseling patients regarding the relationship of high blood pressure to both their short- and long-term morbidity. Such a change would help incentivize us in our efforts to maximize our patients’ future well-being. Perhaps it is fitting that lesson two turns out to be precisely the same as lesson one: when deciding what to do in light of our patients’ preoperative blood pressures, we should always strive to act like physicians, communicating to both our patients and colleagues the critical long-term and modest short-term relevance of this physical finding to the health of those entrusted to our care. Thanks to the work of Walco et al., we now have an expanded base of evidence to help guide us in such conversations.