Preliminary observations in systemic oxygen consumption during targeted temperature management after cardiac arrest

Limited data suggests low oxygen consumption (VO₂), driven by mitochondrial injury, is associated with mortality after cardiac arrest. Due to the challenges of measurement in the critically ill, post-arrest metabolism remains poorly characterized. We monitored VO₂, carbon dioxide production (VCO₂) and the respiratory quotient (RQ) in post-arrest patients and explored associations with outcome.

Using a gas exchange monitor, we measured continuous VO₂ and VCO₂ in post- arrest patients treated with targeted temperature management. We used area under the curve and medians over time to evaluate the association between VO₂, VCO₂, RQ and the VO₂:lactate ratio with survival.

In 17 patients, VO₂ in the first 12 h after return of spontaneous circulation (ROSC) was associated with survival (median in survivors 3.35 mL/kg/min [2.98,3.88] vs. non-survivors 2.61 mL/kg/min [2.21,2.94], p = .039). This did not persist over 24 h. The VO₂:lactate ratio was associated with survival (median in survivors 1.4 [IQR: 1.1,1.7] vs. non-survivors 0.8 [IQR: 0.6,1.2] p < 0.001). Median RQ was 0.66 (IQR 0.63,0.70) and 71% of RQ measurements were <0.7. Patients with initial RQ < 0.7 had 17% survival versus 64% with initial RQ > 0.7 (p = .131). VCO₂ was not associated with survival.

There was a significant association between VO₂ and mortality in the first 12 h after ROSC, but not over 24 h. Lower VO_2: lactate ratio was associated with mortality. A large percentage of patients had RQs below physiologic norms. Further research is needed to explore whether these parameters could have true prognostic value or be a potential treatment target.