[Is MAC effected by liver dysfunction?--Bilirubin and MAC]

If MAC is decreased in patients with liver injury, the amount of inhaled anesthetic administered to these patients could be reduced, and thereby reducing the impact of the anesthetic in such patients. The effect of jaundice in liver injury on halothane MAC was investigated in this study. After MAC for control was determined, 12 mongrel dogs received ligation of the common bile duct (CBD). MAC determination followed 1, 2, and 3 weeks after CBD ligation in 6 dogs in experiment 1. The other 6 dogs received bilirubin i.v. 1 week after CBD ligation, and MAC was determined before and after bilirubin, i.v. in experiment 2. Halothane was the only anesthetic used throughout the studies. In experiment 1, serum total bilirubin (TBil) increased to 7mg.d1-1; bilirubin did not enter the cerebro-spinal fluid (CSF); and MAC did not decrease significantly. In experiment 2, TBil increased to 21mg.dl-1; bilirubin entered the CSF; MAC significantly decreased 15% from control; and the correlation between MAC decrease and TBil increase was statistically significant (P less than 0.05). The results suggest that increase in serum bilirubin in liver injury will decrease MAC.