Mark Wefers Bettink

Monitoring of mitochondrial oxygen tension in the operating theatre 8 151 Statistical analyses were performed using Graphpad Prism 8 and IBM Statistics SPSS 26. Mitochondrial oxygen tension measurements with a signal quality under 20% were not included. As the O2C measures several times a minute the data was averaged over 60 seconds to allow fluctuation in the minutes range. Descriptive statistics were used to describe demographic parameters. Continuous variables are described as mean and standard deviation (SD)). Results A total of 24 neurosurgery patients were included in the study, 4 patients were withdrawn. One patient was excluded from further analysis because of insufficient signal quality, one patient had forgotten to apply the ALA patch before surgery, in one patient the operation was rescheduled due to the intervention of an emergency operation, in one case the positioning during surgery changed from back to prone position after inclusion. In 2 of the remaining 20 patients the O2C data is missing because of the unavailability of the monitor. Surgical and patient characteristics are summarized in table 1. On average, the ALA patch was applied 17 ± 3.3 hours before surgery. After the measuring surface was well shielded from light, sufficient signal quality was measured at the beginning of surgery. Incidentally, signal quality was below 20% which led to exclusion of one or more data points in 6 out of 20 patient and a total of 3.5% of the mitoPO 2 data points.