Cerebral oxygen saturation in relation to end-tidal CO2 in cardiopulmonary resuscitation - Separate views of brain and body?

Background: An increase in both regional cerebral oxygen saturation (rSO₂) measured by near-infrared spectroscopy (NIRS) and end-tidal carbon dioxide (etCO₂) during advanced life support for out-of-hospital cardiac arrest (OHCA) is associated with a higher likelihood of return of spontaneous circulation (ROSC) and may predict neurological outcome. However, it remains unclear which marker is more predictive for which outcome parameter. Methods: In this prospective observational study, we assessed rSO₂ and etCO₂ in patients treated for OHCA in the metropolitan area of Vienna between 05/2017 and 02/2022. Follow-up was performed for survival and neurological performance at hospital discharge and at six and 12 months after OHCA. rSO₂ and etCO₂ were compared between individuals with favourable and unfavourable outcomes, and cut-off values using ROC analyses were identified. Results: Median rSO₂ and etCO₂ values of the included 176 patients during CPR were higher in those achieving sustained ROSC (rSO₂: 59 % (IQR 16.1) vs 46 % (IQR 14.3), p < 0.001; etCO₂: 40 (IQR 18.7) vs. 25 (IQR 20.9) mmHg, p < 0.001) and in patients with cerebral performance category (CPC) 1 or 2 (rSO₂: 66 % (IQR 15.5) vs 48 % (IQR 14.8), p < 0.001; etCO₂: 50 (IQR 16.1) vs. 28 mmHg, p = 0.013). ROC analysis for median rSO₂ values yielded an optimal cutoff of 60 % (sensitivity 86 %, specificity 87 %) for CPC 1/2, and for median etCO₂ values 49 mmHg (sensitivity 67 %, specificity 94 %) for CPC 1/2. In ROC analyses, etCO₂ trends achieved better results for sustained ROSC prediction than rSO₂. In contrast, rSO₂ outperformed etCO₂ for the prediction of neurological outcome. Conclusion: Measuring RSO₂ and etCO₂ during advanced life support is associated with critical clinical outcomes. Our findings suggest that these two parameters reflect different physiological aspects of resuscitation and may provide complementary information. Further research should examine the potential of using rSO₂ alongside etCO₂ in CPR algorithms.