Cardiovascular and biochemical changes in dogs during etomidate-nitrous oxide anaesthesia.

Abstract

Etomidate was infused in dogs to test whether the drug could be used for long-lasting stable anaesthesia. In six dogs anaesthesia was induced with pentothal (20 mg·kg−1) and continued with a constant infusion of etomidate (4 mg·kg−1·h−1). The animals were ventilated with a mixture of O2 and N2O (1:2). Several haemodynamic (heart rate, arterial pressure, central venous pressure, pulmonary artery pressure, left ventricular end-diastolic pressure, dP/dtLV, cardiac output, systemic vascular resistance) and biochemical (pO2, pCO2, pH, O2 content, lactate, glucose) variables together with the distribution of cardiac output (radioactive microsphere method) were studied for four and a half hours. In the course of the experiment cardiac output (thermodilution), stroke volume and dP/dtLV (catheter tip manometer) decreased by 38, 40 and 25% respectively while systemic vascular resistance increased (38%); the pH in mixed venous blood fell from 7.31 to 7.26. Blood flow to gastrointestinal tract, pancreas, skin and muscle decreased in proportion with the fall in cardiac output. Myocardial, renal, adrenal and splenic blood flow did not change. Hepatic artery flow decreased (67%). Liver perfusion was thus severely affected since portal blood flow also decreased. Oxygen consumption in the systemic, myocardial and splanchnic bed was not affected. In four other dogs blood etomidate levels were also measured. They rose gradually in the course of the experiment even though concentration and infusion rate of etomidate were kept constant throughout the four and a half hour experiment in these and all other dogs. Etomidate thus caused cardiovascular depression when it was used as long-lasting anaesthetic. Insufficient clearance of etomidate by the liver through deficient hepatic blood flow may be a causative factor.