Assessing Cerebral Blood Flow Autoregulation During Surgery in the Head-up Position

Neurologic injury under general anesthesia in the beach chair position is believed to result from cerebral hypoperfusion.1 We hypothesize that brain hypoperfusion in this circumstance is caused by blood pressure monitoring that does not reflect of cerebral perfusion pressure. Maintenance of arterial blood pressure above an individual's lower limit of cerebral blood flow autoregulation would prevent this devastating complication. Near infrared spectroscopy can be used to continuously monitor autoregulation with the cerebral oximetry index (COx), a moving linear correlation coefficient between cortical tissue oxygen saturation and arterial pressure. We hypothesize that subjects in the beach chair position have impaired cerebral blood flow autoregulation compared with subjects undergoing surgery in the lateral decubitus supine position. We will test this hypothesis by comparing CBF autoregulation data, including the percentage of time patients undergoing elective surgery have abnormal autoregulation, in the beach chair position versus supine position. We will establish the range of arterial pressure required to maintain autoregulation in the two groups. Cerebral autoregulation results will be assessed for a relationship with postoperative neurocognitive dysfunction and with serum glial fibrillary acid protein levels, a biomarker of brain injury.

The specific aims of this study are:

• To compare the average cerebral oximetry index and the percentage of time with abnormal COx between subjects in the head up or supine position during surgery under general anesthesia.
• To compare the range of arterial blood pressure required for a normal cerebral oximetry index between subjects anesthetized in the head up or supine position.
• To assess the association between impaired cerebral blood flow autoregulation and postoperative neurocognitive decline 1 month after surgery and perioperative elevation of serum glial fibrillary acid protein.

Monitoring autoregulation non-invasively with COx has the potential to improve patient safety by delineating individualized limits of safe ABP for patients at risk of neurologic injury.

Inclusion criteria

• Patients 18 years old or older undergoing shoulder arthroscopy in the beach chair position or lateral decubitus position without elevation of the head.

Exclusion criteria

• Women of child bearing potential require a negative urine HCG test to be enrolled. Patients unable to attend postoperative cognitive testing sessions will be excluded from the study as will those with known allergy to adhesive tape.