[Pharmacodynamic effects of the phosphodiesterase inhibitor enoximone during exposure to the volatile anesthetics halothane and isoflurane in coronary surgery patients].

AIM OF THE STUDY

We investigated the pharmacodynamic effects of the phosphodiesterae inhibitor enoximone in the presence of halothane and isoflurane in 20 patients, ASA class III, aged 45-75 years, undergoing coronary artery bypass grafting. The study was approved by the local Medical Ethics Committee and patients' informed written consent was obtained.

METHODS

After induction of anaesthesia (midazolam, fentanyl, etomidate and pancuronium) all patients received either halothane 1 MAC (group I, n = 10) or isoflurane 1 MAC (group II, n = 10), followed 20 min later by enoximone 0.5 mg/kg. Haemodynamic variables were measured and blood samples (arterial, mixed venous) were obtained before the administration of the volatile anaesthetics (control, t0), immediately (t1) and 5 (t2) min after steady state conditions with halothane or isoflurane, as verified by the end-expiratory concentration and 5 (t3) and 10 (t4) min after the injection of enoximone. Heart rate (HR), mean arterial pressure (MAP), mean pulmonary artery pressure, pulmonary capillary wedge pressure and right atrial pressure were recorded. Cardiac (CI) and stroke volume indices, systemic (SVR) and pulmonary vascular resistance, oxygen availability (AO2) oxygen consumption and oxygen extraction rate were calculated using standard formulae.

RESULTS

In both groups HR remained essentially unchanged throughout the investigation period. MAP decreased significantly in both groups under steady state conditions with the volatile anaesthetics (group I: 19%; group II: 30%) but remained unchanged after subsequent injection of enoximone. After administration of halothane SVR remained essentially unchanged, whereas isoflurane decreased SVR significantly by 20%. After enoximone, there was a significant decrease in SVR in both groups (group I: 26%; group II: 25% compared with the values obtained after halothane and isoflurane respectively). Halothane and isoflurane decreased CI significantly and to a similar degree (group I: 17%; group II: 17%). After the injection of enoximone CI increased significantly and reached control values in both groups. AO2 decreased significantly after administration of the volatile anaesthetics (group I: 19%; group II: 21%) and increased significantly after administration of enoximone, returning to control values. Halothane (7%) and isoflurane (13%) produced a significant increase in oxygen extraction. After bolus injection of enoximone oxygen extraction decreased significantly and returned to control value in group II. In group I enoximone decreased oxygen extraction significantly compared with control.

CONCLUSION

Our results suggest that in the presence of halothane or isoflurane the phosphodiesterase inhibitor enoximone produces a comparable increase in cardiac output and decrease in systemic vascular resistance in patients with coronary artery disease.