Surgery to the shoulder may be performed with patients seated upright in a position known as the "Beach Chair Position (BCP)." This position has certain advantages compared to alternative surgical positions (e.g. side lying) in some situations. However, it has been found that surgery in the BCP can temporarily decrease the amount of oxygen in the brain as a result of the combined effects of gravity and anaesthesia. This can result in complications following surgery such as some memory loss and confusion. Rarely, more serious complications have been reported in the past including death and stroke.

Due to these reported complications the use of "cerebral oximetry" during shoulder surgery in the BCP has become more common. Before and during surgery, a monitor placed on the patients forehead measures the amount of oxygen present in the brain to help control this to an acceptable level. A number of monitors are now commercially available. Two monitors are commonly discussed in the literature; the INVOS™ 5100 and the FORE-SIGHT® machines. However, the actual relationship between the supply of oxygen to the brain during surgery and the chance of later developing problems with memory and thinking (known as "post operative cognitive decline" - POCD) is not clear. It is also not known if one monitor is more accurate than another at predicting these complications.

Therefore, the main aim of this study is to examine the relationship between cerebral oxygen levels during shoulder surgery and the incidence of POCD (i.e. problems with memory and thinking). A second aim is to compare the INVOS™ 5100 and FORE-SIGHT® monitors ability to measure cerebral oxygen and cerebral desaturation events (CDEs) as well as the importance of other key clinical variables (e.g. blood pressure, nausea, body fat etc).

PURPOSE OF THE INVESTIGATION The purpose of this investigation is to generate evidence about cerebral oxygenation during shoulder surgery and the incidence of POCD. Currently, evidence relating to POCD following surgery is conflicting and relates mostly to outcomes following cardiac surgery. There is a strong need to explore this relationship in the specific context of shoulder surgery in the BCP.

INTERVENTION GROUPS This study will involve a single prospective cohort. Patients who meet the selection criteria will be recruited to the study following voluntary informed consent . Cerebral oxygenation will be measured by application of cerebral oximeters to each patients forehead.

AIM OF THE STUDY This study has three aims; (i) To examine the relationship between cerebral desaturation during shoulder surgery in the BCP, and the incidence of POCD.

(ii) To determine the variation in cerebral oxygenation recorded using randomised (for superior/inferior) simultaneous application of the INVOS™ and FORE-SIGHT® oximeters, during shoulder surgery in the beach chair position.

(iii) Assess the relationships between cerebral oxygen desaturation during shoulder surgery in the BCP and variables including mean arterial pressure, incidence of nausea/vomiting, duration of hospital stay, BMI, hypertension and adverse events.

RESEARCH QUESTION There are three research questions correlating with the three research aims; (i) Is cerebral desaturation during shoulder surgery associated with POCD? (ii) Do the FORE-SIGHT® and INVOS™ 5100 devices vary in their measurement of cerebral oxygenation during shoulder surgery in the BCP? (iii) Is there a relationship between cerebral desaturation events during shoulder surgery in the BCP and variables including mean arterial blood pressure, post-operative nausea/vomiting, length of hospital stay, BMI, hypertension and any adverse events?

NULL HYPOTHESES The three null hypotheses are; (i) Cerebral desaturation as measured using cerebral oximetry is not related to POCD after shoulder surgery in the BCP.

(ii) There is no significant difference between the INVOS™ 5100 and the FORE-SIGHT® monitors assessment of cerebral oxygenation during shoulder surgery in the BCP.

(iii) There is no relationship between cerebral desaturation events during shoulder surgery in the BCP and variables including mean arterial blood pressure, the frequency of post-operative nausea/vomiting, length of hospital stay, BMI, hypertension and any adverse events.

PRIMARY HYPOTHESES The primary research hypotheses are; (i) Cerebral desaturation events during surgery in the BCP will be related to POCD.

(ii) The INVOS™ 5100 and the FORE-SIGHT® monitors will show no significant difference in their ability to measure cerebral oxygenation.

(iii) Cerebral desaturation events experienced during shoulder surgery in the BCP are related to a drop in mean arterial blood pressure, an increased likelihood of post-operative nausea and vomiting, greater length of hospital stay, a higher BMI, hypertension and greater frequency of adverse events.

Inclusion Criteria:

• Receiving treatment primarily by, but not restricted to, one of the Primary investigators for a shoulder condition that requires surgery in the BCP.
• Over 18 years of age
• Able to read and speak English

Exclusion Criteria:

• Under 18 years of age
• Pregnant women
• Pre-operative Mini-Mental State Examination (MMSE) < 24
• Pre-existing cerebrovascular disease as reported by the assessing medical consultant and recorded in patient charts
• Orthostatic hypotension
• American Society of Anaesthesiologists (ASA) physical status III, IV and V*
• History of drug and/or alcohol abuse
• Neurological disease (e.g. previous stroke)
• Significant mood and anxiety disorders as determined by treating consultant.
• Any other condition, which in the opinion of the investigators, would render the patient unsuitable for participation in the study

Deidentified cerebral oximeter data acquisition files will be made available to the equipment manufacturers (Medtronic, CASMED) at the conclusion of the study.