Splanchnic circulation in cardiac surgery

Abstract: The studies addressed different techniques of monitoring hepatic and splanchnic blood flow(SBF) during open heart surgery. Calculations of gastric mucosal pH (pHi) using tonometrywas performed in 72 patients, and the effect of dopaminergic stimulation on pH1 was studiedin 33 patients. Transesophageal echocardiography (TEE) for determination of hepatic venousflow (HVF) was used in 18 patients and the method was validated against indicator dilutiontechnique with indocyanine green (ICG) in lO patients. In 9 patients estimations of SBF bylow-dose ethanol was validated against ICG.Specific aims: (1) To measure SBF in cardiac surgery with ICG. (2) To studv the effect ofcardiopulmonary bypass on pH1 and to evaluate the possible effect of dopexamine on apostoperatively low pHi. (3) To evaluate the possible effects on pHi of low-dose dopexamineand dopamine when used for 24 hours as a prophylactic infusion and started directly afterinduction of anesthesia for cardiac surgery. (4) To estimate HVF with echo-Doppler duringopen heart surgery and to assess right heart dynamics by recordings of hepatic venous flowpatterns. (5) To compare measurements of SBF with ethanol and ICG as indicators. (6) Tovalidate echo-Doppler measurements of HVF against dye extraction estimations of total SBFby continuous ICG infusion, before and during CPB and by low-dose ethanol infusion before,during and after CPB.Results: (I) SBF measured with ICG was 765 (s.e.m. 88) ml/min following induction ofanesthesia and did not change during surgery and CPB. (2) An increase in pHi was notedduring CPB (p<0.05) followed by a decrease compared to baseline after CPB. Dopexaminereduced pHi compared to the placebo group (p <0.05). (3) pHi and arterial pH did not differbetween patients receiving dopexamine or dopamine versus control patients. Both the carbondioxide tension of arterial blood (PaCO2) and of the saline in the tonometer (PtonCO2) changedin parallel with a decrease during CPB and an increase after CPB. (4) HVF measured by TEEwas unchanged during normothermic and reduced during hypothermic CPB. Six of 8 patientshad a normal predominant systolic flow pattern in the hepatic vein before CPB. In thepostoperative period 7 patients showed an abnormal predominant diastolic filling pattern. (5) A positive correlation (r=0.76, p < 0.01 was noted between SBF measured with ethanol and ICG.(6) The echo-Doppler measurements of HVF were on the average 46¡/o below those with ICG.There was no correlation between HVF measured with TEE and SBF measured with ICG.Conclusions: The maintained splanchnic blood flow and the absence of signs of anaerobicmetabolism, as measured with gastric tonometry, was indicative of a good perfusion techniqueduring CPB. Dopexamine did not increase a postoperatively low pHi, and dopaminergicstimu]ation with dopexamine and dopamine initiated after anesthetic induction was withouteffect on pHi. The gastric mucosal pH and PtonCO2 were changed in parallel to arterial pH andPCO2. The hepatic venous flow pattern was altered after CPB indicating changes in thediastolic function of the right atrium and the right ventricle. Indicator dilution technique withethanol did constitute an alternative to ICG in measuring SBF. The technique can be usedwithout hepatic vein catheterization. Determination of HVF with echo-Doppler technique wasnot suitable to quantify SBF. The technique as applied in the study can not be recommended indetermining flow changes in the individual patient.Key words: cardiopulmonary bypass; dopamine; dopexamine; echocardiography; ethanol,heart surgery; indocyanine green; intramucosal pHi; splanchnic circulation;Michael Gårdebäck, 1996ISBN 91-628-2113-X