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

Abstract

REBEL A, LOMBARD C. Effect of N,O on segmental left ventricular function and effective arterial elastance in pigs when added to a halothane-fentanyl-pancuronium anesthetic technique. Anesth .4nalg 1989;69:313-22.The interaction of various concentrations of N 2 0 and a stable halothane-fentanyl-pancuronium anesthetic technique was examined in nine pigs. Segmental myocardial contractility was measured with the end-systolic pressurelength relationship (E&, and the effective arterial elastance importance to left function. (EJ was quantified based on the Windkessel model. The addition of 30, 50, and 70% iV,O did not change myocardial contractility or the effectiue arterial elastance. During the 30 and 70% N,O challenge, however, arterial capacitame decreased significantly from a mean (f SEM) 0.86 f 0.15 to 0.71 f 0.0.12 mL/mm Hg with 30% N 2 0 ( P < 0.05) and from 0.90 * 0.09 to 0.72 f 0.07 mL/mm Hg (P < 0.05) with 70% N 2 0 . A dose-response relationship for the effect on the arterial capacitance could not be demonstrated. W e concluded that in the presence of halothane, fentanyl, and pancuronium, N 2 0 does not depress the normal myocardium or change left ventricular afterload. The decrease in arterial capacitance that occurred when 30 and 70% N 2 0 were given was not suficient to change the efective afterload and appears to be of no Key Words: ANESTHETICS, G a s E s -n i t r o u s oxide. HEART, END-SYSTOLIC PRESSURE-LENGTH RELATIONSHIP.The cardiovascular effects of N 2 0 have been evaluated in many previous studies (1-12). However, the problems with quantifying myocardial contractility and left ventricular afterload make it difficult to draw conclusions from some of these studies. For example, regional myocardial shortening is a volume-based index of myocardial function and afterload interaction and does not necessarily reflect myocardial contractility (11). thetic technique combining a potent inhalation anesthetic agent with a short-acting analgesic and a muscle relaxant is very common, and this study was, therefore, devised to answer the following questions: 1. Does N,O depress left ventricular (segmental) myocardial contractility as measured by segmental maximal time-varying elastance (E,,)? 2. Does N,O change the arterial afterload (E,)? -.Because N2° is not as a sing1e in genera' anesthesia, we thought it w ' d d be informative to These questions were studied in pigs with a normal heart anesthetized with halothane and fentanyl evaluate the effect of N,O in the presence of other commonly used anesthetic agents. A balanced anesafter induction of anesthesia with thiopental.