EFFECTS OF ISOFLURANE NITROUS-OXIDE AND HALOTHANE NITROUS-OXIDE ANESTHESIA ON MYOCARDIAL-CONTRACTILITY ASSESSED BY TRANSESOPHAGEAL ECHOCARDIOGRAPHY

In order to evaluate the direct effect of isoflurane-nitrous oxide and halothane-nitrous oxide anaesthesia on cardiac contractility in 20 ad ults, we have used a method based on left ventricular end-systolic wai l stress (LVESWS) vs velocity of circumferential fibre shortening with corrected heart rate (v(cfc)), obtained by transoesophageal echocardi ography. We found that LVESWS (index of afterload) decreased significa ntly with isoflurane-nitrous oxide (n = 10) in concentrations of 1.5-1 .95 MAC, but there were no significant changes in LVESWS with halothan e-nitrous oxide (n = 10). v(cfc) decreased significantly with halothan e-nitrous oxide in concentrations of 1.5-1.95 MAC, but this index did not change significantly with isoflurane-nitro us oxide. However, ther e was no significant difference between the two groups in LVESWS or v( cfc). In the analysis of the LVESWS-v(cfc), relationship, myocardial c ontractility associated with isoflurane-nitrous oxide anaesthesia did not differ significantly from that associated with halothane-nitrous o xide anaesthesia at equiMAC concentrations. The results suggest that h alothane-nitrous oxide anaesthesia, at 1.5-1.95 MAC, maintained myocar dial contractility in similar anaesthetic concentrations to isoflurane -nitrous oxide.