The volatility of an anesthetic agent is directly propoional to lowering the flow in the poal vein. Poal flow is maximally reduced by:

Halothane reduces splanchnic and hepatic blood flow as a consequence of reduced perfusion pressure. This reduced blood flow has not been shown to produce detrimental effects on hepatic or GI function. The metabolism and clearance of some drugs (eg, fentanyl, phenytoin, verapamil) appear to be impaired by halothane. Ref: Morgan, Jr. G.E., Mikhail M.S., Murray M.J. (2006). Chapter 7. Inhalation Anesthetics. In G.E. Morgan, Jr., M.S. Mikhail, M.J. Murray (Eds), Clinical Anesthesiology, 4e.