Intravenous Infusion of Halothane Dissolved in Fat. Haemodynamic Effects in Dogs

Eight harrier dogs received an i.v. infusion of halothane dissolved 1:9 in a fat emulsion for i.v. nutrition (Intralipid, Vitrum). The rate of infusion was adjusted to maintain end-tidal halothane concentrations of 0.7% and 1.4%. At 1.4%, mean arterial pressure decreased to 76 ± 8 mmHg (10.1 ± 1.0 kPa) (mean ± s.e.mean) from a pre-infusion value of 122 ± 6 mmHg (16.2 ± 0.8 kPa) ( P <0.01). The concomitant decrease in cardiac output was 39% and left ventricular maximum dp/dt decreased by 50% ( P <0.01). Changes in systemic vascular resistance and pulmonary arterial pressure were small. The haemodynamic responses during halothane inhalation, to corresponding end-tidal concentrations, were similar. Arterial and mixed venous halothane concentration increased in proportion to end-tidal concentration. There were no changes in arterial Po2 during the halothane-in-fat infusion. Triglyceride concentrations in plasma increased 12-fold. Haemodynamic recovery after the infusion was fast. We conclude that the halothane-in-fat infusion caused a dose-dependent depression of myocardial contractility and arterial pressure, similar to that seen during inhalation, and that end-tidal concentration could be used for control of the infusion rate.