Continuous Glucose Monitoring With a Subcutaneous Sensor During Critical Illness and Surgery

Inclusion Criteria: * Patients admitted to the general surgical ICU (SICU), medical ICU (MICU), cardiac surgery intensive care unit (CSICU), or neurological intensive care unit (NeuroICU), are being treated with IIT, and have an arterial line in place * Patients scheduled for open cardiac surgery or craniotomy that have diabetes mellitus or will be given high dose glucocorticoids. All of these patient will have an arterial line placed at the time of surgery as a part of their usual care Exclusion Criteria: * Age less than 18 years * Enrollment in another clinical trial that modifies their glucose management (e.g. trial of modified IIT algorithm or modified glucose monitoring regimen) In order to obtain adequate representation of patients with physiological alterations that might decrease correspondence between blood and ISF glucose, we will recruit 50 subjects in each of five groups: 1. Patients undergoing craniotomy who are either diabetic or will be given high dose corticosteroids 2. Diabetic patients undergoing open cardiac surgery 3. Patients admitted to one of the participating ICUs with an arterial line in place and receiving IIT who are vasopressor dependent, defined by continuous infusion of at least 60 mg/min phenylephrine, 5 mg/min norepinephrine, or 10 mg/kg/min of dopamine, or any combination of two agents for at least 90 continuous minutes in the last 8 hours 4. Patients admitted to one of the participating ICUs with an arterial line in place and receiving IIT with pitting peripheral or dependent edema, defined by the persistence of pitting to at least 5 mm depth for 5 seconds after pressure is applied to a dependent area of the trunk or two limbs. 5. Critically ill patients admitted to one of the participating ICUs with an arterial line in place and receiving IIT who do not fall into groups 1-4.