Effects of isoflurane-nitrous oxide and halothane-nitrous oxide anaesthesia on myocardial contractility assessed by transoesophageal echocardiography

In order to evaluate the direct effect of isoflurane-nitrous oxide and halothane-nitrous oxide anaesthesia on cardiac contractility in 20 adults, we have used a method based on left ventricular end-systolic wall stress (LVESWS) vs velocity of circumferential fibre shortening with corrected heart rate (Vcfc), obtained by transoesophageal echocardiography. We found that LVESWS (index of afterload) decreased significantly with isoflurane-nitrous oxide (n = 10) in concentrations of 1.5-1.95 MAC, but there were no significant changes in LVESWS with halothane-nitrous oxide (n = 10). Vcfc decreased significantly with halothane-nitrous oxide in concentrations of 1.5-1.95 MAC, but this index did not change significantly with isoflurane-nitrous oxide. However, there was no significant difference between the two groups in LVESWS or Vcfc. In the analysis of the LVESWS-Vcfc relationship, myocardial contractility associated with isoflurane-nitrous oxide anaesthesia did not differ significantly from that associated with halothane-nitrous oxide anaesthesia at equiMAC concentrations. The results suggest that halothane-nitrous oxide anaesthesia, at 1.5-1.95 MAC, maintained myocardial contractility in similar anaesthetic concentrations to isoflurane-nitrous oxide.