Hypertension and the Perioperative Period

Perioperative Blood Pressure Changes

The most typical alterations in BP that occur throughout the perioperative period have been evaluated in detail. Acute BP elevations, occasionally reaching severe levels (i.e., ≥180/110 mm Hg), can occur before surgery in response to a number of transient factors (e.g., anxiety, pain, white coat effect, medication withdrawal). Several observational studies have demonstrated that uncontrolled hypertension ranks among the most common causes for surgical or procedural postponement. Intubation and the induction of anesthesia can also induce rapid elevations in both BP and heart rate, responses that are often exaggerated in hypertensive patients. Conversely, anesthesia (intravenous, spinal, or inhaled volatile agents) is most often a cause of hypotension during surgery itself as a result of reduced sympathetic tone, pain control, sedation, and direct hemodynamic actions. Other possible causes of low BP during surgery include blood loss, upright patient position, mechanical ventilation, infection/anaphylaxis or intraoperative CV events (e.g., reduced cardiac output). It is also generally accepted that patients with hypertension are at increased risk for excessive BP variability during the intraoperative period. This has been defined as increases and/or decreases in mean arterial pressure by 20% or more from baseline levels and has been associated with worse perioperative CV outcomes. Finally, acute elevations in BP predominate during the postoperative period.

Perioperative high BP may occur for two general reasons. Patients may present with an acute worsening of underlying chronic hypertension or it may be a new isolated response to one or more transient factors. Anxiety, pain, drug/medication withdrawal (e.g., alpha 2-agonists, beta-blockers, and alcohol), and stress-induced sympathetic nervous system activation can acutely increase BP and heart rate. Postoperative hypertension may be further worsened or induced by hypothermia, hypoxemia, inadequate ventilation with subsequent hypercarbia, or bladder distention. Intraoperative intravenous fluid administration, especially in patients with chronic kidney disease and/or postoperative renal dysfunction, is also commonly responsible. The initial step in the management of postoperative hypertension is to identify and remedy the factor(s) responsible. Treatment of persistent severe elevations in BP (≥180 mm Hg systolic and/or ≥100 mm Hg diastolic) with intravenous or oral antihypertensive agents is thereafter commonly recommended based upon expert opinions and the precautionary principle. However, there are few outcome data supporting the CV benefits of acute perioperative BP-lowering or outlining the optimal therapeutic approach (i.e., BP targets, most effective medications).

Clinical Guidelines and Perioperative Hypertension

Studies that have assessed the effect of hypertension on operative outcomes have been largely limited to patients with chronic hypertension and not those with acute BP elevations in response to transient conditions. The overall evidence supports that chronic hypertension plays a relatively minor role in the risk for CV complications in surgical candidates. In previous versions of the American College of Cardiology (ACC) and the AHA guidelines published in 2007, hypertension was deemed a “minor clinical predictor” of adverse outcomes only when reaching severe levels (systolic BP ≥180 mm Hg and/or diastolic BP ≥110 mm Hg). It was recommended that acute treatment of severe hypertension and/or delay of surgery to control BP should be considered on a case-by-case basis. However, lower stages of hypertension (140 to 179/90 to 109 mm Hg) were not deemed independent predictors of CV complications by their analyses of the pooled results from observational studies. Mild hypertension was therefore not considered in the calculation of global perioperative CV risk, nor was it a factor that required treatment or delay of surgery under most clinical scenarios.

The more recent ACC/AHA guidelines published in 2014 do not specifically discuss the surgical risks associated with high BP. Hypertension is only listed as a single factor among many parameters to calculate global preoperative CV risk in one of the three calculators promulgated for clinical usage (National Surgical Quality Improvement Program). The simpler and likely more often used tool, the Revised Cardiac Risk Index (RCRI), does not include hypertension ( Box 44.1 ). There is also no discussion about the consideration to treat or delay surgery to control severe hypertension (i.e., BP ≥ 180/110 mm Hg). As such, we believe it is reasonable to continue to follow the approach previously outlined in 2007 because there have been no new practice-changing studies published regarding the importance of hypertension or outcome trials challenging the validity of the prior precautionary recommendations.

Note that hypertension is frequently associated with and/or is a cause of other CV diseases (e.g., diabetes mellitus, ischemic heart disease, heart failure) that are more potent risk factors for perioperative complications. As such, an elevated BP should cue clinicians to more thoroughly evaluate patients for other higher risk parameters ( Box 44.1 ). The identification of hypertension during preoperative risk assessment also offers a valuable clinical opportunity for a more complete evaluation of the patient’s overall long-term CV risk. Lifestyle modifications (e.g., diet and exercise) and control of CV risk factors in addition to hypertension (e.g., hyperlipidemia) should be initiated as clinically indicated irrespective of the upcoming surgery. On the other hand, clinical trial evidence does not support performing coronary revascularizations (e.g., angioplasty/stent or bypass surgery) with the sole intention of preventing surgical complications, even among patients with significant cardiac ischemia. Rather, CV diseases (e.g., coronary heart disease, heart failure) should be managed per published guidelines with the goal of reducing life-limiting symptoms (e.g., angina) and improving long-term CV risk. Clinicians need to consider that any coronary revascularization will involve a significant delay in surgery from 1 to 12 months depending upon the procedure and subsequent duration of dual antiplatelet therapy. Guidelines recommend that the risks versus benefits of proceeding with surgery versus delaying the procedure to control hypertension or treat underlying CV diseases need to be carefully evaluated on a case-by-case basis.

Hypertension and Perioperative Cardiovascular Risk

In 1953 Smithwick and Thompson reported that hypertensive patients undergoing sympathectomy had six times the rate of mortality as compared with normotensive patients. Several studies have confirmed that hypertensive patients are at elevated risk for postsurgical CV complications, including the Department of Veterans Affairs National Surgical Quality Improvement Program involving more than 83,000 patients. However, the overall published findings during the past few decades have been mixed in regards to the risks as a result of high BP or benefits of perioperative antihypertensive medications (in particular beta-blockers). For example, in 1977 Goldman et al reported that hypertension was not a significant risk factor among 1001 patients. These observations were confirmed in 1979 among 676 surgical patients as preoperative BP did not correlate with adverse events. Lette et al also demonstrated that numerous clinical parameters, including hypertension, did not predict adverse surgical outcomes; whereas the amount of jeopardized myocardium during stress perfusion testing successfully identified higher risk patients. On the other hand, Rose studied 18,380 general surgery patients and showed that patients with postoperative hypertension had greater rates of unplanned critical care admissions (2.6% versus 0.2%) and excess mortality (1.9% versus 0.3%). It is also important to note that several studies have shown that rather than hypertension per se, the CV risks and complications related to surgery may be more strongly associated with excessive BP variability (both low and high BP outside an “optimal” range) during the perioperative period.

The risks of hypertension in the absence of other higher risk conditions ( Box 44.1 ), as well as the efficacy of lowering of BP on perioperative morbidity and mortality, remain unclear. This is because most published studies have evaluated the impact of hypertension in the setting of multiple other risk factors, in the presence of underlying CV disease or abnormal stress test results, and/or the assessed benefits of a specific class of antihypertensive agent (e.g., beta-blockers). To date, there are few studies that have investigated CV risk associated with mild-to-moderate hypertension (140 to 179/90 to 109 mm Hg) measured in the immediate preoperative setting. Additionally, the little published evidence does not demonstrate that CV outcomes are improved by delaying surgery to control BP among stable patients with mild or even more severe hypertension (i.e., diastolic ≥ 110 mm Hg). The safety and efficacy of an acute treatment strategy for perioperative BP control (i.e., intravenous medications without surgical delay) versus a delayed therapeutic approach (i.e., outpatient management before surgery) among individuals presenting with severe hypertension has rarely been evaluated. Thus far, the available published evidence does not support any clear CV benefits of the latter more cautious approach of delaying surgery to assure satisfactory preoperative BP control as an outpatient.

There are several additional methodological issues to further consider when reviewing the literature regarding hypertension and perioperative risk. Fleisher criticized the statistical design of studies, stating that the majority of studies were underpowered to appropriately evaluate the primary endpoints of myocardial infarction and death, and was particularly critical of trials that used surrogate markers. For example, some studies use electrocardiographic changes to suggest ischemia as a surrogate for myocardial infarction and death, but suppressing myocardial ischemia alone does not necessarily correlate with a reduced incidence of myocardial infarction or death. The methodology of perioperative BP studies may be inherently flawed or limited because the perioperative environment that influences BP cannot be replicated during follow-up. Lastly, proper measurement of consecutive, resting, seated BPs may not have been obtained, or may have been impossible to obtain, during the preoperative evaluation.

In summary, the overall evidence as reported by several reviews, a meta-analysis of 30 observational studies (odds ratio of 1.35 for cardiac complications), and by the analysis performed in the 2007 AHA guidelines is that mild-moderate hypertension (i.e., BP < 180/110 mm Hg) is not a “clinically-relevant” independent risk factor for perioperative CV complications. In the absence of other higher risk parameters, this degree of hypertension does not require clinical attention or treatment before surgery. Conversely, the evidence that BP levels 180/110 or higher mm Hg cause perioperative CV events is mixed ; thus explaining the current clinical equipoise regarding the therapeutic approach to patients with more severe hypertension among guidelines.