Abstract 50: The Association Between Carbon Dioxide, Cerebral Oxygenation and Survival in Post--Cardiac Arrest Patients
Purpose: the relationship between arterial carbon dioxide (CO2), cerebral saturation (SctO2) and patient survival has been poorly investigated in post-cardiac arrest patients. Current guidelines recommend to target CO2 levels between 40-45 mmHg although some authors recommend higher CO2 levels based on the hypothesis that hypercapnia may lead to increased cerebral perfusion. Therefore the aims of the present study were to explore the relationships between CO2, SctO2 and survival.
Methods: Prospective observational study in 82 post-cardiac arrest patients treated with therapeutic hypothermia. Blood gasses were obtained with a 1 hour interval during the first 24 hours after admission. Cerebral saturation was monitored every 2 seconds with near infrared spectroscopy (NIRS)
Results: The mean CO2 was 40±5mmHg and the mean SctO2 65±4%. Thirty-nine patients died and 43 survived (43/82 patients, 52%) until ICU discharge. The mean CO2 range during the first 24 hours after admission associated with maximal survival was 38-42mmHg (OR 2.84, 95% CI [1.15; 7.05], p=0.02). Subsequently, 2100 paired CO2/SctO2 measurements were analyzed. Based on our previous observation that the presumed ideal SctO2 is around 67%, the CO2/SctO2 scatterplot can be divided in 3 sections: (1) Hypocapnic cerebral desaturation: we found a strong linear relationship between CO2 and average SctO2 when CO2 was between 28-39mmHg (SctO2=0.50 x CO2 + 47, R2 0.76). (2) Normocapnic plateau phase: CO2’s between 40-45mmHg resulted in average SctO2’s between 66.5 and 67.5%. (3) Hypercapnic cerebral hypersaturation: we found a linear relationship between CO2 and average SctO2 when CO2 was between 46-62mmHg (SctO2=0.40 x CO2 + 47, R2 0.39). The predicted optimal CO2 (40-45mmHg) based on this physiological model corresponding with a SctO2 of 67% matched with the optimal CO2 (38-42mmHg) associated with maximal survival.
Conclusion: Based on the relationship between CO2 and SctO2 and extensive survival analysis, the target CO2 in post-cardiac arrest patients seems to be 40mmHg. Since all patients received fully controlled mechanical ventilation, it is likely that there is causal relationship between iatrogenic hyperventilation/hypocapnia, cerebral desaturation and increased mortality.
Author Disclosures: K. Ameloot: None. C. De Deyne: None. I. Meex: None. C. Genbrugge: None. D. Verhaert: None. W. Mullens: None. F. Jans: None. M. Dupont: None. J. Dens: None.
- © 2014 by American Heart Association, Inc.