ON THE CARDIOVASCULAR EFFECT OF PROPRANOLOL DURING HALOTHANE ANAESTHESIA EN NORMOVOLAEMIC AND HYPOVOLAEMIC DOGS

Abstract

SUMMARY The circulatory effects of propranolol during halothane anaesthesia were investigated in fifteen dogs, in eight of which a moderate hypovolaemia was produced. Mean aortic pressure and flow, stroke volume, cardiac performance, and time of presssure rise showing infusion of adrenaline were measured or derived. The investigation led to the following findings: (1) The circulatory responses were similar in normo- and hypovolaemic animals. The ability of the latter to maintain an adequate cardiac output was markedly restricted. (2) Halothane significantly reduced flow, pressure, cardiac performance in both groups, and heart rate in the normovolaemic group. There was a non-significant decrease of heart rate in the hypovolaemic group and of stroke volume in both groups. (3) Propranolol significantly prolonged the time of pressure rise, slowed down and stabilized the heart rate and reduced the flow. The fall of stroke volume was significant in the normovolaemic group and the fall of cardiac performance was significant in the hypovolaemic group only. There was no significant change of pressure. (4) Adrenaline significantly increased pressure and cardiac performance after beta blockade but caused non-significant changes in other parameters except stroke volume in the hypovolaemic group. Two hypovolaemic animals had an irreversible asystole. It is emphasized that, particularly in hypovolaemia and under propranolol during halothane anaesthesia, reliance on estimation of the arterial pressure may lead to completely false conclusions.