Access Type

Open Access Dissertation

Date of Award

January 2014

Degree Type


Degree Name




First Advisor

Steven Cala



The Effect of Body Position on Changes in Cerebral Blood Flow, Cognition, and Motor Function in Patients Undergoing Shoulder Surgery: Lateral versus Beach Chair Position Under General Anesthesia



December 2013

Advisor: Dr. Steven Cala

Major: Physiology

Degree: Doctor of Philosophy

This study aims to determine if there are alterations in cerebral perfusion in patients undergoing general anesthesia in the sitting position. With the reporting of 15 catastrophic cerebral vascular accidents recently being published during shoulder surgery in the sitting position, an increase of 90 times from previously reported data, there has become a clear need for immediate research in this area. A peri-operative stroke has a 60% incidence of morbidity versus 15-46% for strokes in general. This is a devastating outcome for families, physicians and all involved. Current literature points to the sitting position as being a significant risk factor for decreasing cerebral perfusion. Surgeons utilize this position for ease of surgery and may request deliberate hypotension to decrease bleeding and increase visualization at the surgical site. It is unclear whether deliberate hypotension, inadvertent hypotension, air embolus, spinal cord stretching, or neck vessel stretching are key factors involved. An area of concern is that the blood pressure recorded in the arm of the patient in the sitting position is significantly less than that in the brain, this in addition to the decrease in cardiac output while sitting, and vasodilation of the general anesthetics all create the perfect storm to offset normal autoregulatory responses.

Interestingly, the brain is the least monitored organ under anesthesia. It is evident that this practice requires re-evaluation. With the invent of numerous non-invasive cerebral perfusion devices being cited in the literature as very useful in monitoring cerebral perfusion, it is important that we utilize this technology to provide safe patient care and improved outcomes. Devices such as the Cerebral Oximeter and non-invasive cardiac output monitorcan provide relevant information and may aid in preventing these catastrophic events. It is our goal to implement these monitors in patients undergoing general anesthesia in the sitting and lateral decubitus position to evaluate their effectiveness in alerting the anesthesia provider to decreases in cerebral perfusion and improving patient outcomes. Secondly, with the concomitant use of these two devices, we may be better able to understand the physiological role of cerebral perfusion in the sitting position and gain insight as to the cause of the cerebral vascular events and patients at risk. In addition, the S-100 lab test is a peripheral marker of glial injury and has been shown to correlate well with brain injury. It is our belief that this lab test is underutilized and may be very beneficial in these cases. Research shows elevation of this marker two days post operatively is indicative of a shorter life expectancy regardless of any known cerebral complications. Lastly, although MRI's and CT Scans can detect brain abnormalities, they cannot assess brain function. Neuro-cognitive testing on the other hand has been shown to reliably evaluate brain function and will be implemented at three different times in this study to correlate with monitoring and lab data obtained peri-operatively..

Methods: 100 patients age 18-65 years old will be included in the study. They will receive a general anesthetic in the beach chair or lateral decubitus position for shoulder surgery. Baseline neurocognitive testing will be done along with cardiac output, cerebral oxygenation, and s-100 lab values. A standard anesthetic protocol will be followed for all patients. Continuous monitoring of CO and cerebral oximetry will be utilized throughout each case. Post-operatively the S-100 lab will be repeated and again at 24 hours followed by neurocognitive testing. The final neuro-cognitive test will be completed at the 6 week post operative follow up visit.

The goal of this study is to determine whether conducting shoulder surgery in the beach chair position causes neurocognitive changes in patients when compared with those undergoing surgery in the lateral decubitus position.

Specific aims

1. To determine whether the regional oxygen saturation in the brain is diminished during shoulder surgery in the beach chair position using near infrared spectroscopy.

2. To determine whether there is a significant change in cardiac output and MAP in the beach chair position versus the lateral decubitus position using a non invasive cardiac output monitor.

3. To determine if there are neurocognitive injuries associated with sitting and lateral positions by examining the S-100 Beta levels and neurocognitive evaluations of patients before and after surgery.

We hypothesize that cerebral perfusion is decreased in patients undergoing surgery in the sitting position due to a combination of decreased cardiac output, vasodilation and higher lower limits of cerebral autoregulation. We believe this decrease in cerebral perfusion will be seen by the cerebral oximeter. We also predict that the S-100 B lab test will be sensitive enough to pick up significant changes in cerebral perfusion.

Included in

Physiology Commons