Halothane effects on subendocardial oxygen supply-demand balance: estimation from intramyocardial tissue pressure and left ventricular pressure.

We evaluated the effect of halothane on the balance of subendocardial oxygen supply and demand in six dogs by estimating the endocardial viability ratio (EVR) based on the pressure generated within the subendocardium (ENDO-IMP). Concurrently, the conventional EVR based on left ventricular pressure (LVP) was estimated and compared with the EVR based on ENDO-IMP. The subendocardial oxygen supply-demand ratio based on ENDO-IMP (IMP-EVR) was significantly less than EVR based on LVP (LVP-EVR) (0.87 +/- 0.03 vs 1.07 +/- 0.06, P less than 0.05) during the control period. With 0.5% halothane administration, IMP-EVR improved significantly (1.04 +/- 0.07, P less than 0.05) while LVP-EVR remained unchanged (1.08 +/- 0.09). No further changes in EVR (either IMP-EVR or LVP-EVR) were observed with increasing halothane concentrations up to 2%. The relationship between the two indices was weak (r2 = 0.44, P less than 0.001) but statistically significant. Because an estimate of EVR based on direct measurement of subendocardial tissue pressure (IMP-EVR) would reflect more accurately the oxygen supply-demand balance of this region than the LVP-EVR, our results suggest that the oxygen balance of the subendocardium improves with halothane administration. The use of LVP-EVR as a hemodynamic index of subendocardial oxygen balance during halothane anesthesia, therefore, is questionable.