Agreements Between Transcutaneous and Arterial Monitoring of Oxygen and Carbon Dioxide After Non-cardiac Surgery

Study method The data collection will start 1st of February 2021 and will be finished by 30th of April 2021. Patients will be set up with TCM equipment and an Empatica at the PACU. They will be observed for 2 hours. If an intervention is started before 2 hours and not completed, recordings will continue until 5 minutes after the intervention is completed for a maximum of 1 hour (3 hours maximal observation). The sensor will be placed on the patient's antebrachium. Patients will be set up with TCM equipment as soon as possible after arrival at PACU. Every clinical procedure entailing changes in circulatory and/or respiratory support or medication (appendix 1) will be observed and noted in a timetable (ap-pendix 2). Perfusion index (PI) and a full DASAIM score (Danish Association of Anesthesiology and Intensive Care Medicine) will be noted every 15 minutes. Every ABG analysis of PaO2, PaCO2 and lactate conducted during the observational period will be noted.

Age, sex, BMI (Body Mass Index), ASA-score (American Society of Anesthesiologists physical sta-tus classification), comorbidity (Charlson Comorbidity Index - CCI), baseline laboratory data (hemo-globin and creatinine) and name of surgical procedure will be obtained for each patient. REDCap (Research Electronic Data Capture) will be used as a data management system for the project. The study is a part of the Wireless Assessment of Respiratory and circulatory Distress (WARD) project.

Study materials All patients will be monitored with a TCM-5 Flex monitor connected to a Sensor 84 (Radiometer Medical Aps, Brønshøj, Denmark). The sensor consists of a Stow-Severinghaus-type TcPCO2 electrode combined with a Clark-type TcPO2 electrode, with values per second for TcPO2, TcPCO2 in kPa and heat effect measured in units of mW. The sensor temperature will automatically be heated to 43.5℃ and calibrated. The sensor membrane will be changed every 28th day. There will be a 20-minute stabilization period from patient setup to valid data capturing. The use of sensors and monitors will be according to the manufacturer's instructions.

As a supplement, patients will be wearing an Empatica, as a measurement for the activity of the autonomic nervous system. The Empatica tracks activity, heartrate, blood volume pulse, skin temper-ature and skin conductance. The Empatica E4 consist of a PPG sensor and an EDA sensor. Data from the E4 will be processed in further studies and is not a part of the statistical analysis in this protocol.

Statistics The primary analysis is changes in TCM readings, and the association between clinical procedures, tested using paired statistics comparing both average (mean) TcPO2 and TcPCO2 during 5 minutes before an intervention versus 5 minutes after an intervention. Depending on the data distribution, either t-test or Wilcoxon test will be used.