Myocardial Resistance to Metabolic Acidosis

Abstract

SOME OF the cardiovascular problems and difficulties in resuscitation occurring during shock, massive transfusions, hypothermia, and the postcardiac arrest period have been attributed to the myocardial depressant effects of the concomittant metabolic acidosis.^1-5 Preliminary investigations on the effect on the cardiovascular system of the interaction between simultaneous changes in pH, K+, and Ca+ + indicated, however, that the depressant effects of metabolic acidosis were considerably less than suspected. Studies were designed to explore this finding further in intact dogs and isolated guinea pig atria. The results of these studies are presented herein. Methods Dogs. —Ten mongrel dogs, weighing 20 to 25 kg (44 to 55 lb), were used. Anesthesia was induced with 15 to 20 mg/kg thiopental administered intravenously. After insertion of an endotracheal tube, nitrous oxide, oxygen, and succinylcholine were administered.⁶ Intermittent positive pressure ventilation was maintained throughout the experiment with a Harvard nonrebreathing respirator. Rate and tidal