Splanchnic perfusion in cardiac surgery

Abstract

Splanchnic ischemia in cardiac surgery is considered a risk factor in the development of the Multiple Organ Dysfunction Syndrome (MODS), which is the leading cause of morbidity and mortality in the intensive care unit. Splanchnic ischemia/reperfusion may lead to an injury of the intestinal mucosa and induce a systemic inflammation (SIRS), which is proposed to precede MODS. The aims of the studies were to evaluate different methods for measurement of splanchnic perfusion and metabolism perioperatively in cardiac surgical patients and in healthy volunteers. In addition we wanted to investigate the effect of three inotropic agents and cardiopulmonary bypass (CPB) on splanchnic perfusion and metabolism.In 11 healthy volunteers we evaluated the effect of mild central hypovolemia, induced by lower body negative pressure technique, on jejunal mucosal perfusion (JMP) measured with endoluminal laser Doppler flowmetry (LDF) technique. Furthermore, 32 cardiac surgical patients were studied before during and after CPB. In 10 patients the impact of CPB on JMP, gastric tonometry, splanchnic metabolism and on central hemodynamics was studied. In another 12 patients we simultaneously measured splanchnic perfusion after cardiac surgery with three different techniques; indocyanine green (ICG) clearance, gastric tonometry and LDF. We evaluated the correlation between the three methods and their respective association to metabolism. In the remaining 10 patients we investigated the effects of equipotent doses of the three inotropic agents dopamine, dopexamine and dobutamine on JMP, central hemodynamics and on splanchnic metabolism after cardiac surgery. Mild central hypovolemia induced a jejunal mucosal vasoconstriction. The phenomenon jejunal mucosal vasomotion was recognized in the LDF signal in about 75% of the 43 subjects. JMP, gastric mucosal-arterial pCO2 difference, splanchnic lactate and oxygen extraction increased during and one hour after CPB. Postoperatively there was an increase in splanchnic oxygen extraction and gastric-arterial pCO2-difference. There was no consistent relationship between postoperative changes in splanchnic perfusion assessed by the three different methods described above. The increase in JMP by dopamine (2.7µg/kg/min) (27%) and dopexamine (0.7µg/kg/min) (20%) was more pronounced compared to dobutamine (2.7µg/kg/min) (7%), whereas the effects on hemodynamics and metabolism were similar. Conclusions: Jejunal mucosal perfusion (JMP) may continuously be measured in volunteers, anesthetized and sedated patients by endoluminal LDF technique. Mild central hypovolemia induces a jejunal mucosal vasoconstriction via a sympathetic baroreceptor-reflex. The splanchnic mismatch between oxygen delivery/demand seen during and one hour after CPB, mainly due to hemodilution and rewarming from cold bypass, is not accompanied with splanchnic lactate production or a decrease in JMP. The increase in JMP, during and after CPB, is probably due to an augmented jejunal mucosal microcirculation caused by lowered hematocrit and increasing mucosal metabolism. Postoperative changes in splanchnic perfusion assessed by three different techniques were not significantly correlated probably due to the different techniques used and increasing tissue metabolism. A marginal splanchnic perfusion may occur postoperatively in cardiac surgical patients. Dopamine or dopexamine might be preferred to dobutamine as a postoperative inotropic agent, when the therapeutic goal is to improve gut mucosal perfusion.