Tissue Near InfraRed Spectroscopy (NIRS) in Critically Ill Patients

Hypotheses: 1. In the acute phase of early illness, tissue oxygen saturation and vascular occlusion test (VOT) are important adjuncts in differentiating severe critical illness requiring ICU admission from patients benefiting from less aggressive therapies (non-ICU admission). 2. An early feature of severe sepsis is abnormal microcirculatory vasoreactivity. 3. Microvascular reactivity can be measured by means of vascular occlusion test (VOT) using non-invasive near infrared spectroscopy (NIRS) to measure tissue Oxygen saturation (StO2). 4. Microvascular reactivity is significantly deranged in patients with early severe sepsis and is quantifiably different from non-septic critically ill patients. 5. Other measures of microcirculatory perfusion ie. sublingual orthogonal polarization spectral (OPS) video microscopy, are abnormal and will directionally correlate with VOT and StO2 in severe sepsis 6. In severely septic patients response to therapy can be assessed by VOT and StO2 monitoring and will correlate with prognosis. 7. A management protocol incorporating VOT and StO2 monitoring in addition to conventional hemodynamic and biochemical parameters as a guide to therapy will result in improved outcomes in severely septic patients. 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-inv