Oxygen Delivery and Consumption in Patients Who Are Comatose After Out‐of‐Hospital Cardiac Arrest Are Affected by Blood Pressure Target

Abstract

Background In the management of patients resuscitated from out‐of‐hospital cardiac arrest, a primary goal is to restore sufficient oxygen delivery (DO2) to meet demands in oxygen consumption (VO2). Methods and Results This post hoc analysis of the BOX (Blood Pressure and Oxygen Targets) study included adult patients who were comatose and experienced out‐of‐hospital cardiac arrest from a presumed cardiac cause, who were randomized to a mean arterial blood pressure (MAP) target of 63 mm Hg (MAP63) or 77 mm Hg (MAP77) and a Restrictive PaO2 target of 9 to 10 kPa versus a Liberal target of 13 to 14 kPa in a 2×2 factorial design. A pulmonary artery catheter was inserted following randomization. DO2 and VO2 were calculated as: DO2=cardiac output × arterial oxygen content, and VO2= cardiac output × arteriovenous oxygen difference. Of 789 patients, 730 (92.5%) were included in this substudy. A total of 362 patients were randomized to MAP77, and 368 to MAP63, 368 to a liberal Pao2 target, and 362 to a restrictive target. At all prespecified time points, DO2 in MAP77 was higher compared with MAP63, with a cumulative treatment effect of 203 L (95% CI, 132–274) O2 after 36 hours. VO2 was higher in MAP77 after 36 hours, with a cumulative treatment effect of 21.9 L (95% CI, 5.8–38) O2, compared with the MAP63 group. Conclusions Targeting a MAP of 77 mm Hg resulted in an overall increase in DO2 and a smaller increase in VO2 compared with a MAP target of 63 mm Hg. A higher Pao2 target did not result in any difference in DO2 or VO2.

Keywords

• blood pressure
• Fick's principle
• hemoglobin
• out‐of‐hospital cardiac arrest
• oxygen consumption
• oxygen delivery