Effect of N2O on Segmental Left Ventricular Function and Effective Arterial Elastance in Pigs When Added to a Halothane-Fentanyl-Pancuronium Anesthetic Technique

Abstract

The interaction of various concentrations of N2O and a stable halothane-fentanyl-pancuronium anesthetic technique was examined in nine pigs. Segmental myocardial contractility was measured with the end-systolic pressure-length relationship (Ees), and the effective arterial elastance (Ea) was quantified based on the Windkessel model. The addition of 30, 50, and 70% N2O did not change myocardial contractility or the effective arterial elastance. During the 30 and 70% N2O challenge, however, arterial capacitance decreased significantly from a mean (+/- SEM) 0.86 +/- 0.15 to 0.71 +/- 0.0.11 mL/mm Hg with 30% N2O (P less than 0.05) and from 0.90 +/- 0.09 to 0.71 +/- 0.07 mL/mm Hg (P less than 0.05) with 70% N2O. A dose-response relationship for the effect on the arterial capacitance could not be demonstrated. We concluded that in the presence of halothane, fentanyl, and pancuronium, N2O does not depress the normal myocardium or change left ventricular afterload. The decrease in arterial capacitance that occurred when 30 and 70% N2O were given was not sufficient to change the effective afterload and appears to be of no importance to normal left ventricular function.