Abstract 142: Relationship Between End Tidal CO2 and Hemodynamic Flow in a Swine Model of Prolonged Cardiac Arrest
Introduction: There is growing consensus that end-tidal CO2 (ETCO2) is a surrogate for blood flow and quality of chest compressions in cardiac arrest. From a hemodynamic perspective, cardiac arrest and subsequent CPR is a dynamic process in which blood flows and pressures vary due to quality of chest compressions (CC) and the intra-individual physiologic response to CC. We examined the relationship between ETCO2, inferior vena cava (IVC) flow, and coronary perfusion pressure (CPP) in a swine model of prolonged cardiac arrest with varying CC depths.
Methods: CPR hemodynamics in twelve domestic swine (~30 Kg) were studied using standard physiological monitoring. A flow probe was placed on the inferior vena cava (IVC). CPP was determined as the difference between right atrial and aortic pressure. Ventricular fibrillation (VF) was electrically induced. Mechanical CC were started after ten minutes of untreated VF. 54 min of CC were delivered at a rate of 100 per minute and at a depth of 1.25 inches (n=9) and 1.9 inches (n=3).
Results: Across all depths and the duration of the experiments, ETCO2 was moderately correlated with IVC flow (r = 0.49, p<0.001) and CPP (r = 0.50, p<0.001). However, the strength of the relationship was reduced at 1.25 inch CC (IVC flow: r = 0.23, p<0.01; CPP: r = 0.37, p<0.001) and increased at 1.9 inch CC (IVC flow: r = 0.81, p<0.001; CPP: r = 0.85, p<0.001). At 1.9 inch CC the strength of the relationship was also dependent on the duration of CC. The strongest correlations were observed during the middle phase (18 to 28 min post-CC) of the experiment when flows were decreasing despite ongoing CC. During the middle phase at 1.25 inch CC, the relationship between ETCO2 and IVC flow was not significant (r=0.19)
Conclusions: In this model, the strength of the relationship between ETCO2, IVC flow, and CPP varies based on the duration and the depth of chest compressions. These data suggest that ETCO2 is an unreliable single metric of venous return but becomes more reliable if used in conjunction with other information such as duration and depth of compressions.
- © 2013 by American Heart Association, Inc.