Deliberate Hypotension for Hip Arthroplasty

For >4 decades, investigators have debated the potential advantages and disadvantages of deliberate hypotension during anesthesia for total hip arthroplasty.1 Available data from randomized clinical trials suggest that deliberate hypotension may reduce intraoperative blood loss,2 although past studies conflict regarding the impact of such techniques on the need for postoperative transfusion.2,3 Moreover, because most available trials predate modern transfusion approaches,4 little definitive evidence exists regarding the potential benefits of deliberate intraoperative hypotension for patients undergoing hip arthroplasty in current practice. One key gap in knowledge related to the safety of hypotensive anesthesia for hip arthroplasty concerns the potential for such techniques to produce adverse neurologic consequences such as stroke. To date, available trials2,3 have not observed large differences in the rate of such outcomes among patients undergoing hypotensive anesthesia versus other regimens for hip arthroplasty, yet these studies have varied markedly in their approaches to assess such outcomes and have been underpowered to detect differences in the rate of rare events such as postoperative stroke, which may occur in approximately 2 of every 1000 patient undergoing hip arthroplasty.5 In this context, Bombardieri et al.6 present new work in this issue of Anesthesia & Analgesia related to the potential effects of hypotensive anesthetic techniques on cerebral perfusion; and although the data that they present do not offer definitive evidence regarding the risks or benefits of hypotensive techniques for hip arthroplasty, they offer insights that may help to guide practitioners’ decisions regarding the use or avoidance of such techniques and to inform future investigations in this area. Bombardieri et al. studied 52 patients without known prior cerebrovascular disease undergoing hypotensive epidural anesthesia, a technique initially described by Sharrock and Salvati7 that uses extensive epidural blockade and continuous epinephrine infusion guided by invasive hemodynamic monitoring. Bombardieri et al. used transcranial Doppler ultrasound to measure changes in cerebral blood flow velocity that accompanied the intraoperative reductions of blood pressure to an average mean arterial blood pressure value of approximately 50 mm Hg compared with an average baseline value (measured after the initiation of sedation but before epidural blockade) of 84 mm Hg. Although the authors found only small changes in the average change in cerebral blood flow velocity of the patients in their sample, the extent of change varied markedly from patient to patient. For example, at the first measurement taken under hypotensive anesthesia, the change in mean cerebral blood flow velocity ranged from a relative decrease of 44% from baseline to a relative increase of 87% with no clear correlation observed between mean arterial blood pressure and mean cerebral blood flow velocity. Over the course of the hypotensive episode, nearly one-fourth of their sample experienced relative decreases in cerebral blood flow velocity of 20% or more. On a basic level, the article highlights the caution that needs to be exercised in drawing inferences for individual patients from population averages. An old joke is relevant here. Three statisticians go duck hunting. The first one shoots and misses a foot too high. The second one misses a foot too low. The third declares: “We got it!” In an analogous sense, the observation of Bombardieri et al. that cerebral blood flow velocity hardly changed at all on average is true in a statistical sense, yet it also obscures the article’s more ambiguous, and more useful, finding that changes in cerebral blood flow varied widely across their sample with a substantial minority of patients experiencing potentially worrisome decreases. Placing emphasis on the heterogeneity of the authors’ findings can help move us away from binary questions about whether hypotensive epidural anesthesia is “safe” or “unsafe” in some general sense and instead encourage us to think quantitatively about the specific risks and benefits that this type of anesthesia might hold for an individual patient. Importantly, the observational, nonrandomized design of the present study precludes causal inferences regarding the effect of hypotensive epidural anesthesia on cerebral blood flow. These data highlight the need for further investigations to quantify the risk of meaningful reductions in cerebral blood flow with hypotensive anesthesia compared with other techniques and the relative importance of such reductions to neurologic outcomes that may be influenced by cerebral blood flow and other factors such as baseline comorbidities and cerebral metabolic rate. Although it is encouraging that the authors note that no patients in the present cohort experienced an adverse neurologic event, postoperative cognitive or neurologic outcomes were not formally assessed; moreover, given the low incidence of postoperative stroke, the relatively small samples of this and prior studies8 preclude quantification of the risks of this technique for neurologic end outcomes. Moreover, the present work does not speak to how the risks of this approach might vary when applied outside the single center in which this study occurred. All the patients in the present cohort experienced short operative times and received care from anesthesia providers who had substantial experience with this technique. Neither the present work nor the past literature that the authors cite3,7,8 speak to what risks and benefits this technique might carry if applied in a different context with longer surgical times or less experienced providers. In the end, providers and researchers should think carefully about what potential benefits might be gained in terms of concrete patient outcomes in deciding where to go next with techniques such as hypotensive epidural anesthesia. Although the present study raises concern for potential adverse effects that need to be taken seriously, adequately powered randomized trials are still needed to better define the extent and magnitude of these risks. Absent these, the present work may serve as a note of caution to practitioners and patients who are considering such techniques and as a call to advocates of hypotensive anesthesia to work to more clearly quantify the potential risks and benefits of these techniques for patient outcomes. DISCLOSURES Name: Ignacio J. Badiola, MD. Contribution: This author wrote the first draft of the manuscript and made critical revisions to the paper. Attestation: Ignacio J. Badiola approved the final version of the manuscript. Name: Jiabin Liu, MD, PhD Contribution: This author made critical revisions to the paper. Attestation: Jiabin Liu approved the final version of the manuscript. Name: Mark D. Neuman, MD, MSc. Contribution: This author made critical revisions to the paper. Attestation: Mark D. Neuman approved the final version of the manuscript. This manuscript was handled by: Gregory Crosby, MD.