Upon arrival in the surgical ICU a subcutaneous glucose sensor (Guardian RT® CGMS) will be placed by one of the investigators after informed consent has been obtained. Insertion will be in the lower lateral abdomen using the insertion device provided with the Guardian RT® system. For patients for whom lower abdominal insertion is impossible, e.g. those with open abdomens, a site will be chosen in the proximal thigh or proximal arm based on the estimated thickness of the subcutaneous fat. The sensor transmits a signal wirelessly to a receiver/monitor. This receiver/monitor will be maintained in the patient's room. The meter will be calibrated based on an arterial or capillary blood glucose obtained within one hour of sensor insertion per pre-existing SICU routine care. The meter will then be recalibrated every 12 hours based on blood glucose measurements obtained per existing SICU routine. The existing protocol in the SICU is measurement of a blood glucose every hour while on an insulin infusion until stable then every 2 hours thereafter. For patients requiring only sub-cutaneous insulin blood glucose is measured at a minimum of every 4 hours. If necessary the sensor will be replaced a maximum of three times within 12 hours before placement will be considered a failure. Capillary or arterial blood glucose will be measured every hour if the patient is requiring a fluctuating insulin infusion. If the patient is on a stable insulin infusion blood glucose samples will be obtained every 2 hours. If the patient is not on an insulin infusion glucose levels will be obtained at least every 4 hours per pre-existing SICU protocols. All arterial or capillary glucose levels will be entered into the Guardian RT® system. Blood glucose measurements will be per the SICU routine. All SICU staff, physicians and study personnel will be blinded to the CGMS readings. Sensors will be changed after 72 hours and when the system identifies a problem with the sensor that can not be corrected through standard system diagnostics per manufacturer recommendations. Total attempts at sensor placement will be limited to a maximum of 4 over the course of each subject's participation in the study. Sensors will be removed when the patient is transferred from the SICU, if the patient expires, or if the patient's care is transitioned to comfort measures only. At the end of the second sensor life-time (144 hours) the sensor will be removed and data collection will be terminated.