ABSTRACT
To investigate the cardioyascular effects of 1 MAC-and 2 MAC-isoflurane anesthesia, eight Mongrel dogs were anesthetized with intravenous thiopental sodium and maintained with endotracheal nitrous oxide (2 l/min) -oxygen(2 l/min) -isoflurane-pancuronium. Dogs were kept normothermic by the use of Aqua-Therm and normocapneic with controlled ven-tilation employing Airshield Ventimeter with frequent measurements of PaCO2. An 18G Medicut was inserted in the left femoral artery, a Swan Ganz catheter was passed into the pulmonary artery through the right femoral vein, and cardiovascular parameters were measured during control, 1 MAC-and 2 MAC isoflurane administration. The results are as follows : 1) Heart rate, mean arterial pressure, cardiac output, cardiac index, stroke volume, left ventricular stroke work index and left ventricular dp/dt max decreased during both MAC isoflurane anesthesia. These decreases were more prominent during 2 MAC-isoflurane administration. 2) Pulmonary capillary wedge pressure and pulmonary vascular resistance did not change significantly during the 1 MAC phase, but did during the 2 MAC phase. 3) Mean pulmonary arterial pressue decreased slighter during both phases. 4) Central venous pressure and srstemic vascular resistance did not change significantly throught the experiment. The above findings indicate that isoflurane does directly depress the myocardium and the hemodynamic function, and it is important to decrease isoflurane concentration acccordingly with the use of nitrous oxide.