Evaluate the Performance of the Dexcom G7 Continuous Glucose Monitoring (CGM) System in Critically Ill Patients Undergoing Major Abdominal Surgery and Solid Organ Transplantation Which Require Blood Glucose Monitoring for Intensive Insulin Therapy.

Main objective: The goal is to to determine the accuracy of Dexcom G7 Continuous glucose monitor system in critically ill patients, undergoing major abdominal surgery and solid organ transplantation, in the intensive care unit. On admission to the intensive care unit or at the end of surgery, two Dexcom G7 sensors are placed in the infraclavicular position. Sensor number 1 will be blinded and will only be active when paired with the receiver, without the ability to monitor glucose levels. Sensor number 2 is used for continuous glucose monitoring and can be used to adjust the insulin dose. Patients will wear the continuous glucose monitoring sensor for a maximum of 10 days, including the time spent in the intensive care unit and the immediate care unit. The study will not interfere with any usual care clinical workflows. Calibration is only performed on an unblinded sensor. The reference method for calibration is the glucose from the blood glucose meter. Calibrate on the first day of monitoring: 4 times a day after approximately 6 hours, or if the blood glucose reading from the blood glucose meter is not within the estimated error range of the continuous glucose monitor (difference greater than 1,5mmol/L). Calibration on days 2 and 3 of monitoring: once in the morning, or when the meter's glucose reading is not within the estimated error range of the continuous glucose monitoring (difference greater than 1,5mmol/L) On subsequent days when the blood glucose meter reading is not within the estimated error range of continuous glucose monitoring (difference greater than 1,5mmol/L). Hypothesis: * Ho: No difference in mean absolute relative difference (MARD) between calibrated and non-calibrated sensors. * Ha: Calibrated sensors have lower mean absolute relative difference (δ = 4%, SD = 5%). Further objectives: To evaluate further aspects regarding the Dexcom G7 continuous glucose monitor system's performance in the intensive care unit (ICU), particularly in terms of sensitivity and specificity to detect hypo- and hyperglycaemic events, data availability, device deficiencies and safety. To identify predictive factors of the accuracy of the Dexcom G7 continuous glucose monitor system in critically ill patients in the ICU.