Oxygen delivery and consumption in comatose out-of-hospital cardiac arrest patients are affected by blood pressure targets

Abstract

Abstract Funding Acknowledgements Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Grosserer L. F. Foghts Fond Background Hemodynamic instability is common after resuscitated out-of-hospital cardiac arrest (OHCA). Preventing inadequate oxygen delivery (DO2) to the cells and thus not meeting oxygen demand is crucial to prevent further organ dysfunction. Additionally, oxygen uptake in the cells may be impaired. Oxygen consumption (VO2; the amount of oxygen consumed by the body per minute) could thus also be affected in OHCA. Purpose This study aimed to describe the effect of different mean arterial blood pressure (MAP) and partial arterial oxygen pressure (PaO2) targets on DO2 and VO2. Methods This post-hoc study is based on the BOX trial, a 2x2 factorial design that randomized OHCA patients to a MAP of either 63 mmHg (MAP63) or 77 mmHg (MAP77) and a partial pressure of arterial oxygen of 9 to 10 kPa or a liberal oxygen target of a PaO2 of 13 to 14 kPa at two cardiac centers in Denmark. Pulmonary artery catheters were placed to evaluate cardiac output and collect mixed venous blood samples at prespecified time points. Oxygen blood contents were calculated for arterial (CaO2) and mixed venous blood (CvO2) as Hgb (mg/dl) x 10 x 1.39 x Saturation O2 (proportion) + 0.0225 x PaO2. DO2 = CO x CaO2, and VO2 = CO x (CaO2-CvO2). Results This study included 715 patients (90% of the total cohort with a pulmonary catheter) for analysis. A restrictive or liberal oxygen supplement did not affect DO2 or VO2 during the initial 48 hours. The MAP77 group exhibited on average 11% higher DO2 (95%CI: 6%-15%) and on average a 6% higher VO2 in the first 48 hours (95%CI: 3%-10%) compared to the MAP63 group (see Figure 1). Conclusion Targeting a PaO2 of either 9 to 10 kPa or 13 to 15 kPa resulted in no significant changes in the provision of oxygen to the cells, nor did it increase the consumption of oxygen. In contrast, targeting a MAP of 77 mmHg resulted in an increase in both the provision of oxygen and consumption of oxygen compared to a MAP target of 63 mmHg.Figure 1