Cardiopulmonary effects of direct venous CO2 insufflation in ewes. A model for CO2 hysteroscopy

In order to mimic the delivery of CO2 into the pelvic circulation during sustained hysteroscopic surgery, direct insufflation of CO2 was done into the femoral vein of six anesthetized ewes. Following the establishment of baseline values in each animal, cardiac output, pulmonary arterial pressure (Ppa), pulmonary arterial wedge pressure (Ppw), arterial pH and gas levels, and ECG changes were recorded at ten-minute intervals. CO2 was delivered into the femoral circulation for 30 minutes. Following the experiment, measurements were repeated during a 20-minute recovery period. Ppa and Ppw increased significantly during the experiment but returned to baseline values after 70 minutes. Cardiac output, which increased significantly, remained high after the same period and was paralleled by cardiac rate. There was no significant change in systemic blood pressure or arterial oxygenation. Only at the highest flow rate were there observable changes in PCO2, accompanied by mild acidosis. One of the six animals displayed premature ventricular contractions at the inception of the highest flow rate. Since the delivery rate of CO2 per kilogram of body weight clearly exceeded that generally used in human hysteroscopic surgery (35-100 mL/min), these experimental results suggest that CO2, when employed as a distension modality in hysteroscopic surgery, displays a wide margin of safety.