CORR Insights®: What Is the Risk of Intraoperative Cerebral Oxygen Desaturation in Patients Undergoing Shoulder Surgery in the Beach Chair Position?

Where Are We Now? Although intraoperative cerebral desaturation is a known complication of shoulder surgery in the beach chair position [6], what we know of it comes mainly from small, single-center studies [1-3, 5]. Estimates of its incidence, risk factors, and downstream neurologic effects have varied widely [7]. Although the underlying pathophysiology has not been fully elucidated, it is thought to be the result of hemodynamic fluctuations that occur as the patient is transitioned from supine to an upright position [10]. Whereas normal baroreceptor firing can compensate for these positional changes in a nonanesthetized patient, the vasodilatory effects of intravenous and inhaled anesthetic agents may dampen this autonomic response and result in cerebral hypoperfusion [6]. If sustained over time, decreased cerebral perfusion can lead to catastrophic neurocognitive complications, as described in multiple case reports [8]. In this prospective study, Thanaboriboon et al. [11] investigated the risk of intraoperative cerebral desaturation during arthroscopic rotator cuff repair in the beach chair position. The authors found that 43% of these instances had at least one cerebral desaturation event that typically lasted a median of 19 minutes and occurred within 20 minutes of the time at which maximum head elevation was reached. Female sex was identified as a risk factor for developing cerebral desaturation intraoperatively. No association was found between intraoperative cerebral desaturation and either intraoperative hypotension or postoperative cognitive decline. Based on these discoveries, orthopaedic surgeons performing beach chair shoulder surgery may consider a graduated transition from supine to an upright position as well as enhanced cerebral perfusion management during the initial phase of the operative procedure, particularly in female patients who may be more susceptible to cerebral desaturation. Where Do We Need To Go? Prior studies [4, 6, 8] generally have defined intraoperative cerebral desaturation as a decrease in regional cerebral tissue oxygen saturation (rSO2) that exceeds a particular threshold compared to baseline values. However, the definition of baseline rSO2 as well as the quantitative drop in rSO2 that qualifies as a cerebral desaturation event has varied widely between studies. These methodologic inconsistencies have resulted in estimates of incidence that ranged from 0% to 57% in a recent systematic review [7]. Until a consensus definition of cerebral desaturation can be reached, it will be difficult for physicians and surgeons to reconcile disparate study findings and accurately assess the scale of the cerebral desaturation problem in the setting of beach chair shoulder surgery. In addition to defining the epidemiology, we must strive to better understand the short- and long-term sequelae of intraoperative cerebral desaturation. Although a previous study reported a deleterious impact of cerebral desaturation on postoperative neurocognitive testing [1], several high-quality studies have found no difference in neurocognitive scores between patients who experienced a cerebral desaturation event and those who did not [2, 4, 5]. Further study is needed to determine the degree and duration of cerebral desaturation that is required to produce neurocognitive decline, with the primary goal of minimizing the rare but devastating complications such as stroke that may occur in the perioperative period. Targeted research efforts should focus on elucidating the complex relationship between intraoperative blood pressure control and cerebral perfusion. Maintaining an open line of communication between the orthopaedic surgeon and anesthesiologist or anesthetist is particularly important in this regard. Intraoperative hypotension creates the potential for cerebral hypoperfusion, whereas elevated blood pressure can obscure the surgical view in arthroscopic shoulder procedures and increase blood loss in open shoulder procedures. Data presented in this study by Thanaboriboon et al. [11] and other previous studies [9] suggest that the first 20 minutes after upright positioning may be the most important phase of the operation from the standpoint of cerebral perfusion. Future studies should be specifically geared toward improving blood pressure management protocols during this time period to minimize the risk of cerebral desaturation events without compromising surgical outcomes. How Do We Get There? Interdisciplinary collaboration between orthopaedic shoulder surgeons and anesthesia providers should be initiated to precisely define what constitutes an intraoperative cerebral desaturation event. Such collaborative efforts could be beneficial for quality control monitoring and single-center prospective investigation at the institutional level. However, the formation of a multicenter working group focused on intraoperative cerebral desaturation would be ideal to establish consensus statements that could be applied more broadly. Prospective observational studies that enroll patients undergoing shoulder surgery in the beach chair position could utilize intraoperative rSO2 monitoring to record cerebral saturation values in real time throughout the course of the surgical procedure. Specific variables of interest would include the timing and duration of any desaturation events as well as the magnitude of decrease in rSO2 with respect to baseline values, both of which could be treated as continuous variables in regression models to determine their association with any adverse neurologic outcomes that occur postoperatively. Testing modalities such as computerized neurocognitive assessment tools may also be helpful to reveal more subtle abnormalities that are not detected by the conventional testing instruments (Mini Mental State Examination, Montreal Cognitive Assessment). Moreover, prospective observational studies could track intraoperative blood pressures throughout the surgical procedure, measuring the rSO2 at various timepoints while assessing the quality of arthroscopic visualization at those same timepoints. These data could be used to establish a “safe zone” of blood pressure in which adequate cerebral perfusion is maintained without substantially impeding surgical performance. Such a “safe zone” would be dependent on a host of factors including the patient’s baseline preoperative blood pressure, the beach chair position angle, and the stage of the surgical procedure. For example, beach chair positioning at 60 degrees may require a higher blood pressure to maintain cerebral perfusion than a beach chair position angle of 45 degrees. Likewise, a lower blood pressure may be required during the placement of suture anchors near the end of a rotator cuff repair compared to the diagnostic shoulder arthroscopy performed at the beginning. As orthopaedic surgeons, we must resist the temptation to dismiss intraoperative cerebral desaturation as a nonsurgical issue that falls outside our scope of musculoskeletal practice. It is imperative that we share the burden of scholarly investigation with our anesthesiology colleagues in order to achieve a comprehensive understanding of this problem and propose strategies to help ameliorate it.