Our third aim was to determine the incidence of intraoperative CDEs during arthroscopic shoulder surgery with the patient in the BCP. Incidence of CDEs varied widely among the 7 studies reviewed (Table 3). Minimum incidence of intraoperative CDE was 0% in a cohort of 30 patients,1 and maximum incidence was 80% in a study of 61 patients,12 all of whom underwent elective arthroscopic shoulder surgery in the BCP. Although there was wide variability in CDE incidence, the studies were consistent with respect to their definition of a CDE. Most authors used a decrease in regional cerebral tissue oxygen saturation of 20% or more from baseline, or an absolute value up to 55%, to define a CDE. None of the 7 studies reviewed reported a clinically significant adverse neurocognitive event.
Discussion
Of concern, there have been several surveys, case reports, and small case series of previously healthy patients who had no known risk factors, underwent arthroscopic shoulder surgery in the BCP, and developed unanticipated postoperative neurologic complications.4-6,14 Beach-chair positioning during surgical procedures has been implicated as a contributing factor leading to cerebral hypoperfusion with potential for cerebral ischemia.1,12,23 These changes in cerebral perfusion pressure are thought to be the major determinant of poor neurologic outcomes. Such reports have exposed the potential need for heightened vigilance, alternative anesthesia techniques, and improved monitoring, though the exact etiology of the central nervous system injuries in this patient population is incompletely understood and is likely multifactorial. Therefore, in this study we wanted to determine the incidence of postoperative neurocognitive deficits and review all reported cases of neurocognitive complications in patients who have undergone arthroscopic shoulder surgery in the BCP. In addition, we wanted to define the incidence of intraoperative CDEs and investigate their relationship with postoperative neurocognitive complications.
According to our review, the incidence of postoperative neurocognitive complications after surgery in the BCP is 0.004% (1/24,701). However, this finding is based only on what has been reported; the true incidence is not known. It is also important to note that the incidence of neurocognitive deficits after many other types of surgery is not known and that surgery itself may be a risk factor for postoperative neurocognitive deficits.24 In their retrospective review of 15,014 patients who underwent arthroscopic shoulder surgery in the BCP at a single institution over an 11-year period, Rohrbaugh and colleagues18 found an overall postoperative complication rate of 0.37% and a 0.0067% incidence of neurocognitive deficits. One patient in the series was given a diagnosis of ischemic stroke on the basis of neurologic deficits that occurred 24 hours after surgery. Yadeau and colleagues20 found no postoperative neurocognitive complications in a mixed prospective-retrospective study of 4169 patients—3000 identified retrospectively, 1169 prospectively—who underwent arthroscopic shoulder surgery in the BCP at an ambulatory surgery center. Pin-on and colleagues19 reported on a series of 5177 orthopedic and neurosurgical patients who underwent surgery in the BCP. In those who had arthroscopic shoulder surgery, intraoperative systolic blood pressures obtained from an arterial line referenced to heart level decreased a mean (SD) of 14.4% (12.7%), whereas in those whose pressures were obtained from a noninvasive blood pressure cuff referenced to heart level decreased 19.3% (12.6%). However, the authors reported no incidence of postoperative stroke or neurologic deficits.
Although uncommon, perioperative cerebral ischemic accidents are potentially devastating for patients, their families, and the health care professionals involved. These events have tremendous economic, social, professional, and medicolegal implications, with perioperative stroke being particularly morbid. Perioperative stroke has a mortality rate of 60%, versus 15% to 46% for stroke in general.25,26 In 2005, Pohl and Cullen6 published a landmark article on a series of 4 relatively healthy middle-aged patients who were at low risk for stroke but had catastrophic neurocognitive complications (including 1 death) after arthroscopic shoulder surgery in the BCP. Bhatti and Enneking3 described a case of acute postoperative vision loss and ophthalmoplegia attributed to intraoperative hypotension leading to ischemia in a patient who underwent an elective shoulder arthroscopic procedure in the BCP. These reports prompted multiple investigations into the physiologic hemodynamic changes associated with surgery in the BCP and the treatment strategies used to improve patient safety.
In the normal physiologic state, the sympathetic nervous system is activated when a person assumes the seated position. The result is increased systemic vascular resistance and heart rate alterations to maintain cardiac output and mean arterial pressure. In anesthetized patients, this response is blunted by the vasodilatory effects of intravenous and volatile anesthetics. Multiple studies have demonstrated substantial hemodynamic changes in both awake and anesthetized patients during the maneuver from the supine position to the seated position1,27,28; these changes include diminished cardiac index, stroke volume, and arterial pressure.17 The data underscore the need for attentiveness and accurate monitoring of cerebral perfusion when the transition is made from the supine position to the BCP, particularly in the early phase of surgery and in high-risk patients.