CIRCULATORY EFFECTS OF CONTROLLED ARTERIAL HYPOTENSION WITH TRIMETAPHAN DURING NITROUS OXIDE/HALOTHANE ANAESTHESIA

Studies were made in ten patients of the circulatory changes occurring during the administration of trimetaphan to produce hypotension during nitrous oxide/halothane anaesthesia. Ventilation was spontaneous throughout. There were significant falls in arterial pressure and peripheral resistance. Cardiac output was relatively unaffected. Heart rate sometimes increased and this was associated with a fall in stroke volume. Central venous pressure fell in all but one patient, but the change did not reach statistical significance. It is felt that the safety of this hypotensive technique is related to the fact that cardiac ouput is not seriously reduced when lying horizontal. Patients tilted into the head-up posture, however, usually exhibit a lowered cardiac output. Although controlled hypotension has been a standard anaesthetic technique for many years, there appear to be few data on its effects upon central haemo-dynamics. Theye and Tuohy (1965) studied a group of patients anaesthetized with halothane and artifi