Acidosis and pulmonary hemodynamics in hemorrhagic shock

Studies were performed on 20 anesthetized dogs to determine the effects of acidosis on the increase in pulmonary vascular resistance (PVR) occurring in hemorrhagic shock. Measurements included pulmonary arterial pressure (Ppa), pulmonary arterial wedge pressure (Ppw), and systemic arterial pressure (Psa); arterial and mixed venous pH, Pco₂, Po₂, and O₂ and CO₂ contents; minute volume, and O₂ and CO₂ concentrations in expired gas. Pulmonary blood flow (Qp) was calculated by the Fick method for oxygen. Data were obtained prior to and following hemorrhage to a mean Psa of 25-50 mm Hg maintained for 1 hr. In 12 dogs, sodium bicarbonate was infused to prevent a fall in arterial pH. In acidotic dogs, a mean decrease in Psa of 71% resulted in a mean decrease in Ppa of only 28% and a mean increase in PVR of 152%. In dogs given bicarbonate, a mean 72% fall in Psa was accompanied by a mean 53% decrease in Ppa and no significant change in PVR. In both groups, Qp fell similarly and Ppw remained unchanged or decreased minimally. Results indicate that maintenance of Ppa and the increase in PVR in hemorrhagic shock are prevented by infusion of bicarbonate.