Changes of oxygen transport variables and serum lactate during open-chest cardiac massage in dogs

Abstract

The aim of this study was to investigate the influence of critically low cardiac output (CO) upon oxygen transport. We especially focused on the changes of mixed venous oxygen saturation (S−vO₂) in the presence of oxygen consumption ($\dot VO_2$) debts. Additionally, we examined the correlation between the cumulative oxygen deficit (Def$\dot VO_2$) and serum lactate. Def$\dot VO_2$ was calculated as the integrated area under the tissue$\dot VO_2$) deficit (baseline$\dot VO_2$-acutal$\dot VO_2$) and time curve. To produce severe low CO, we performed openchest cardiopulmonary resuscitation (CPR) in 11 anesthetized dogs for 1 h. We made the measurements before (baseline values) and during the CPR at 10-min intervals. Supplydependent$\dot VO_2$ was observed when CO decreased below 40 ml·min⁻¹·kg⁻¹. The mean value of S−vO₂ in the range of supply-dependent$\dot VO_2$ was 13±2% and did not change significantly during 1 h of CPR. The changes of lactate from baseline values were linearly correlated with Def$\dot VO_2$ (r=0.62,P<0.01), but absolute values of serum lactate were not.