Regular insulin should be administered intravenously and not subcutaneously in the intensive care unit (ICU). This is because the rate of subcutaneous insulin absorption is highly variable. Insulin absorption is slower with high insulin concentrations and in the typically high dose volumes that are often required to control blood glucose in the critically ill. In addition, decreased capillary surface area decreases insulin absorption; because of poor perfusion, critically ill patients often experience this condition secondary to cardiogenic shock, hypotension, or vasopressor therapy. Lastly, poor perfusion of the subcutaneous tissues may lead to slow or erratic absorption of subcutaneous insulin with resulting poor glucose control.