SGER: Thermal Monitoring of Gut Ischemia

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

0135783 Bowman In this application, it is proposed to apply the Thermal Diffusion Probe (TDP) technique which quantifies perfusion to monitor gut ischemia by a proxy measurement of rectal wall blood flow. Feasibility will be demonstrated by the correlation of rectal wall blood flow with small bowel blood flow in a porcine model. Successful demonstration of this correlation will be followed by the bioengineering of a non-invasive probe system for the measurement of rectal wall perfusion. Shock occurs when arterial pressure and subsequently tissue blood flow (perfusion) drop so low that the delivered oxygen is not able to meet the metabolic needs of the tissue. During shock, the body directs blood to the heart and the brain, often at the expense of "sacrificial" organs such as the liver, skin, muscle, and gut. Prolonged shock may diminish blood flow to the gut such that the normal intestinal barrier function is disrupted and gut-derived bacteria and endotoxins are translocated to other organs via the blood. This, in turn, may lead to bacteremia, sepsis, inflammatory response and ultimately multi-organ failure - one of the major causes of patient mortality in the ICU. Conventional resuscitation therapy is directed toward first assuring that oxygen is being supplied to the patient and that it is being transported through the circulation to the organs to support life. Circulatory distress is addressed with the infusion of fluids and pharmacological agents (inotropes) to increase cardiac output. Therapy is typically titrated to attain a target heart rate (HR), systolic blood pressure, mean arterial blood pressure (MAP), urine output, and normal arterial pH. Cardiac output (CO) may also be monitored. While these conventional parameters are thought to give an indirect indication of tissue oxygenation, they correlate poorly with survival in critically ill patients (Astiz and Rackow, 1993; Shoemaker et al., 1993). Techniques have been proposed to monitor parameters (pO2, pH, pCO2, lactate, etc.) in sacrificial tissues that are susceptible to hypoperfusion, hypoxia and ischemia to provide an optimal ipend pointll to guide resuscitation therapy. While these parameters are an attempt to assess the local tissue blood flow, and hence the oxygen delivery, they also depend on metabolism and their respective arterial blood concentrations. It is evident that a reliable monitor for gut ischemia could significantly impact the management of shock patients.