This project will investigate the use of a non-invasive near infrared light (NIR) device in conjunction with brief arm compression to measure the microcirculation in critically ill patients. It is know that in patients with overwhelming infections, their blood vessels do not respond normally and the NIR device can help measure how abnormal their blood vessels are. This type of testing is non-invasive and can be performed repeatedly without harm to the patient and may provide an earlier way to determine whether they have overwhelming sepsis and also may help to optimize the treatments they receive and better tailor their treatments to the degree of blood vessel abnormalities that are found. If our hypotheses are correct, this simple non-invasive test could provide a very rapid means of assessing patients that could be done more safely and quickly than some of the current methods. This would have an important effect to enhance patient safety and improve outcomes in such critically ill patients.