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Shoulder and elbow surgeon, Mohit Gilotra, MD, assistant professor of orthopaedics at the University of Maryland School of Medicine, co-led a study aimed to determine patient-specific risk factors for cerebral desaturation events (CDEs), and assess for any neurologic decline that may occur as a result while in the beach chair position (BCP).

The BCP, which is required for shoulder replacement surgery and is often a preferred protocol, involves patients’ heads being elevated above their hearts, and poses a risk for CDEs, which are strongly correlated with rare events such as ischemic stroke, visual impairment and cranial nerve. The risk for CDEs is increased when patients are placed under general anesthesia while having a BCP procedure, with one study demonstrating that interoperative CDEs occurred in as many as 56% of these patients1. However, Dr. Golitra’s study determined that placing patients in the BCP is in fact effective in reducing CDE occurrence.

Only four percent of the study’s participants experienced a CDE, and only 4.3 percent of those underwent general anesthesia. This rate is dramatically less than expected and not attributable to a healthier study sample. It is inferred that the study’s protocol, though hoping to definitively isolate risk factors for CDE, had the effect of protecting patients from CDE; indeed, in the cognitive function tests administered to patients before and after the study, no subclinical neurologic declines were detected.

The following is a brief summary of the protocol the surgical and anesthesiology teams used for their study, which produced improved outcomes for BCP shoulder surgery patients.

Preparing for Patients at Increased for CDE

Looking at 100 consecutive patients undergoing arthroscopy or shoulder replacement in the BCP, the study stratified them into low-risk and high-risk groups based on BMI, Framingham risk criteria for stroke and history of cardiovascular disease. Forty-five participants were deemed to be at high risk, and the four CDEs observed in the study were all in this group. The only protocol difference between the two groups is that patients in the high-risk group received minimal anesthesia whenever possible; regional anesthesia and sedation were used unless their BMIs indicated that general anesthesia was preferable to prevent airway obstruction. All of the study’s four CDEs occurred in patients who underwent general anesthesia.

Normotensive Anesthesia for All Patients

The anesthesiologists involved in the study were responsible for maintaining mean arterial pressure (MAP) within a certain goal range through the depth of anesthesia and by the administration of ephedrine and/or phenylephrine. When an interoperative CDE was detected, it was recorded and treated immediately by increasing oxygen, medically increasing blood pressure or by decreasing ventilation.

Slow Head Positioning for All Patients

Because previous studies have shown that CDEs most commonly occur when a patient’s head is being elevated or immediately after it is upright, the protocol used in the study involved a two-stage head positioning. Patients’ baseline heart rate, MAP and cerebral oxygenation were measured before receiving anesthesia in the supine position. These measures were taken again after anesthesia, and then once again once the patient’s head was raised to 35 degrees. Following a wait of three minutes, patients’ heads were raised to the final 70-degree positioning, whereupon vitals were measured once again and every five minutes thereafter.

Noninvasive cerebral oximetry in the form of near-infrared spectroscopy (NIRS) was used to monitor the frontal cortex for the occurrence of CDEs. In accordance with similar studies, CDEs were defined by a greater than 20 percent drop from the cerebral oxygenation baseline or below a 55 percent oxygenation threshold.

Study Takeaways

The stratification of patients into low-risk and high-risk groups was substantiated by the study, which found that CDE risk factors in BCP surgery included undergoing general anesthesia with a Framingham score greater or equal to 10 or a BMI of 35 or over. Cardiovascular disease, however, played less of a role than was expected, and none of the patients who had a CDE in the study had CVA.

Despite four percent of the study population experiencing a CDE, none of them experienced an adverse neurologic event or cognitive decline, which may have been prevented through the use of NIRS monitoring and immediate CDE correction.

It is unknown to what extent risk stratification/minimal anesthesia for high-risk patients, slow positioning or normotensive anesthesia each contributed to the study’s low CDE rate. However, because other studies and even common sense suggest that sudden upright positioning and hypointensive anesthesia can reduce cerebral perfusion, it would not be ethical to isolate these parts of the protocol with future studies with control groups.

Because of the protocol for beach chair position shoulder surgery used at the University of Maryland Medical Center, patients have a reduced risk for cerebral desaturation events. Moreover, if patients do experience an interoperative CDE during BCP shoulder surgery, it can be detected and corrected immediately to reduce the chance of cognitive damage.

University of Maryland orthopaedic surgeons are board certified, fellowship-trained, and Shock Trauma credentialed, and Dr. Gilotra is fellowship-trained in advanced shoulder and elbow reconstruction. As part of an academic medical center, our orthopaedic surgeons are heavily involved in research and teaching, in addition to clinical care.

To refer a patient, call 410-448-6400 or visit umortho.org for more information.

Schedule Grand Rounds for your hospital with UM shoulder surgeons.

1 Koh JL, Levin SD, Chehab EL, Murphy GS. Neer award 2012: cerebral oxygenation in the beach chair position: a prospective study on the effect of general anesthesia compared with regional anesthesia and sedation. J Shoulder Elbow Surg. 2013;22:1325-1331.

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