MONITORING OF TISSUE OXYGENATION IN SHOCK - AN EXPERIMENTAL-STUDY IN PIGS

Objective: To evaluate different methods and markers for assessing ade quacy of tissue oxygenation in shock. Design: Prospective, controlled animal trial. Two groups of six pigs, subjected to either a superior m esenteric artery occlusion shock or a hemorrhagic shock. A third group of five pigs served as controls. Setting: Hospital animal research la boratory. Subjects: Anesthetized, ventilated, juvenile, domestic pigs. Interventions: Clamping of the superior mesenteric artery for 5 hrs, followed by reperfusion or withdrawal of blood to achieve a mean arter ial pressure of 50 mm Hg for 3 hrs was performed, followed by resuscit ation using the withdrawn whole blood. Invasive hemodynamic monitoring with arterial and pulmonary artery catheters was done. A tonometer wa s placed in the terminal ileum. Measurements and Main Results: Ileal i ntramucosal pH, systemic base excess (or deficit), lactate concentrati on in systemic venous and arterial blood as well as in portal blood, a scitic fluid, and thoracic duct lymph, hemodynamics, and oxygen-relate d variables were measured. Five hours of intestinal ischemia caused no significant changes compared with the control group with regard to ba se excess or any of the hemodynamic or oxygen-related variables measur ed. However, lactate concentrations in the ascitic fluid and intramuco sal pH were significantly altered within 1 hr of regional ischemia. La ctate concentration in the thoracic duct lymph was significantly incre ased after 2 hrs of ischemia, while lactate concentrations in the port al, systemic, and arterial blood were significantly increased after 2 hrs of regional ischemia. Reperfusion was associated with a high morta lity rate, and only one animal survived the reperfusion period. In the hemorrhagic shock group, cardiac output and mean arterial pressure we re significantly (intentionally) decreased 60 mins after the hemorrhag e, while the heart rate, base excess, and systemic and portal blood la ctate concentrations were significantly increased after 2 hrs of gener al hypoperfusion compared with those values in the control group. Ilea l intramucosal pH, mixed venous oxygen saturation, oxygen delivery, ox ygen extraction, and lactate concentrations in the arterial blood and thoracic duct lymph were significantly different from those values in the control group 3 hrs after the onset of hemorrhagic shock. Reperfus ion induced a normalization of the hemodynamic and metabolic status of the animals. Conclusion: Many conventional markers of tissue hypoxia are useful when assessing general hypoperfusion, whereas intestinal in tramucosal pH is the only reliable and clinically useful indicator of inadequate regional intestinal tissue oxygenation.