Modification by propranolol of cardiovascular response to hypercapnia during halothane anaesthesia

The purpose of this study is to determine the effect of propranolol on the cardiovascular response to carbon dioxide (0-20%) during anaesthesia with 1% halothane in oxygen (blood level 16.3 mg/100 ml S.D. +/- 5) in dogs each with a chronically implanted electromagnetic flow probe on the ascending aorta. Cardiac output, stroke volume; heart rate, mean arterial pressure (MAP) and total peripheral resistance (TPR) were obtained and paired with arterial blood gas determination after each step of increased concentration of carbon dioxide with or without propranolol. Propranolol (0.06-0.9 mg/kg) prevented the response to elevation of inspired carbon dioxide of increased heart rate, stroke volume, and cardiac output, TPR and MAP were reduced by CO2 and only slightly changed in the propranolol series.