Detecting low brain oxygen levels in patients undergoing non-cardiac surgery to assess its association with post-operative delirium

The following will be assessed once the final participant has finished the study (as these measurements require the total number of patients):
1. Proportion of patients enrolled in whom we acquired interpretable regional oxygen saturation (rScO2) data (%) is assessed: 100 X total number recruited with interpretable data / total number recruited
2. Proportion of patients enrolled in whom we acquired delirium data (%) is assessed: 100 X total number recruited with delirium data / total number recruited

For each cohort of surgical patients, and the cohort as a whole, use descriptive statistics (proportion (%), or mean and standard deviation, or median and interquartile range – according to parametric or non-parametric distribution respectively):
1. Incidence of cerebral desaturation using three previously utilised definitions (as below). Cerebral saturation is assessed using a cerebral oximetry machine, recorded continuously during surgery and for 1 hour after surgery.
1.1. Any occurrence of a decrease of 10% from baseline
1.2. Any occurrence of a decrease of 20% from baseline
1.3. Any occurrence of an absolute value of regional oxygen saturation (rScO2) <50%
2. Average duration of relative desaturation - time with rScO2 ≤ 60%
3. Incidence of systemic hypotension using three common definitions (as below). Systolic hypotension is assessed using blood pressure readings taken during surgery. Baseline values will be obtained from the pre-operative clinic; however, if this is not possible then the pre-induction blood pressure will be used as a baseline.
3.1. Any occurrence of systolic blood pressure (BP) ≤20% of baseline
3.2. Any occurrence of systolic BP ≤30% of baseline
3.3. Any occurrence of systolic BP ≤40% of baseline
4. Average duration of systemic hypotension - time with mean arterial pressure (MAP) ≤20% of baseline
5. Incidence of hypoxaemia using three definitions (as below). Hypoxaemia will be assessed using saturation probe readings during surgery.
5.1. Any occurrence of blood oxygen saturation (SpO2) ≤ 88%
5.2. Any occurrence of SpO2 ≤ 90%
5.3. Any occurrence of SpO2 ≤ 92%
6. Average duration of hypoxaemia - time with SpO2 ≤ 90%
7. Utilisation of vasopressor drugs (α-agonists) - we will record either a vasopressor infusion or bolus is given during surgery, and if any are given during the recovery. Time administered, drug, dose and the Mean Arterial Pressure (obtained from the anaesthetic machine) will be recorded by the clinician
8. Baseline rScO2 values
9. The incidence of delirium during the postoperative in-patient stay (up to day 7), assessed using 4AT (clinic test for delirium)
10. For the cohort as a whole, compare the difference in variables listed above (1 to 8) between those who developed postoperative delirium and those who did not, using appropriate statistical test: Chi-squared for proportions, unpaired test-t for continuous parametrically-distributed variables, Mann-Whitney U test for continuous non-parametrically-distributed variables.