Relation between Plasma Lignocaine Levels and Induced Haemodynamic Changes

Intravenous lignocaine (1 mg./kg. body weight) was found to produce insignificant haemodynamic changes, and in particular no reduction in myocardial contractility. A rate of 2 mg./minute infused intravenously is suggested for therapeutic purposes. In anaesthetized dogs an infusion of 13·5 mg./minute caused moderate haemodynamic depression and a maximum plasma level of 7 μg./ml. Massive injections of 200 and 400 mg. of lignocaine produced a maximum plasma level of 13·8 and 27·8 μg./ml., respectively, and in the latter failure of myocardial contraction in the presence of a normal E.C.G. ensued (“pump failure”). Lignocaine appears to alter the uptake of calcium by myocardial sarcoplasmic reticulum, and this may explain the negative inotropic effect of large doses.