James H. Baxter

Studies of Cyclopropane: III. The Relation of Electrocardiographic Changes to the Arterial Concentration of Oxygen, Carbon Dioxid and Cyclopropane in Dogs Anesthetized with Cyclopropane*

1. Electrocardiographic records have been taken and correlated with the arterial concentrations of oxygen, carbon dioxide, and cyclopropane in dogs under cyclopropane anesthesia. 2. Except for a few extrasystoles during a rapid induction of anesthesia in one dog (no. 18), no cardiac irregularities were observed until some minutes after respiratory arrest. At this time auriculoventricular block, nodal rhythm, multiple focus ventricular tachycardia, and fibrillation were noted in various dogs. 3. Arterial blood samples taken at the onset of cardiac irregularities contained an average of 2.8 volumes per cent oxygen. 4. With artificial respiration the arrhythmias disappeared and the concentration of cyclopropane in the blood was increased 30 per cent over the amount necessary for respiratory arrest without any apparent damage to the heart as shown by electrocardiographic records. 5. It is shown that the cardiac irregularities which develop at the time of or soon after respiratory arrest are not due to cyclopropane but to anoxemia. 6. In dogs in which the vagi have been cut, the arrhythmias develop at about the same oxygen, carbon dioxide, and cyclopropane content as in the normal dog, but there is one significant difference: In the group with the vagi cut, there is no disturbance in conduction as indicated by the absence of an increase in the P-R interval or more severe types of auriculoventricular block.