Assessment of metabolic liver function and hepatic blood flow during cardiopulmonary bypass

A modified monoethylglycinexylidide (MEGX) test was performed in 14 patients undergoing myocardial revascularization to evaluate liver function during cardiopulmonary bypass (CPB). MEGX is the principal metabolite of lidocaine. Different studies have shown a decrease in MEGX formation in patients with impaired liver function. Following a low-dose bolus application of 0.3 mg/kgBW lidocaine MEGX concentrations were measured in five-minute intervals for half an hour. This was done once before and once during CPB. Arterial and hepatic vein blood samples were obtained in order to avoid the effects of hemodilution by CPB priming. Hepatic blood was calculated using the indocyanine green (ICG) infusion extraction technique. MEGX formation during CPB decreased. After the 10 and 15 minutes measurement points the mean arterio-hepatic venous concentrations were 61 +/- 7.2 micrograms/L and 63 +/- 7.3 micrograms/L respectively in comparison to pre-CPB values of 36 +/- 5.8 micrograms/L and 42 +/- 5.1 micrograms/L. Hepatic blood flow increased insignificantly from a mean of 835 +/- 54 ml/min prior to CPB to 913 +/- 83 ml/min during CPB. As a result the MEGX clearance calculated 15 minutes after administration of lidocaine bolus application did not differ significantly before (51.2 +/- 6.4 micrograms/min) and during CPB (40.2 +/- 5.7 micrograms/min). In conclusion, a decrease in MEGX formation was found during CPB. However, due to increased hepatic blood flow there was no significant change in MEGX clearance before and during CPB.