Abstract 188: Arterial Oxygen Saturation May Be the Limiting Factor for O 2 Delivery During Compression-Only CPR

Abstract

Background Previous studies show that there is no difference in outcomes between bystander conventional and chest-compression-only (CCO) CPR. However, several points need to be addressed: 1) the equivalent, but low, survival rate indicates that there is much room for improvement. The question is whether effective ventilation can be achieved during CPR regardless of approach. 2) the subgroup of patients whose cardiac arrest was not of cardiac origin did not sustain any benefit from ventilation. This finding would imply that adequate ventilation was not achieved. Because cardiac output (CO) generated by chest-compression is low, O 2 delivery (DO 2 ) is mainly dependent on arterial O 2 content. We hypothesize that DO 2 is the rate limiting factor and improvement in DO 2 is mainly determined by O 2 content of arterial blood, since CO is at best only 1/3 of the normal value. Methods We modeled DO 2 in a range of 0 to critical DO 2 (8.2 ml/kg/min) at variable CO and O 2 contents of arterial blood. We assumed a 70kg patient with a hemoglobin level (Hb) of 15g/dl. Arterial O 2 Content (ml/L) = Hb × Arterial O 2 Saturation × 1.34 ×10. DO 2 (ml/min) = Arterial O 2 Content (ml/L) × CO (L/min). Result The half-critical DO 2 at arterial blood O 2 saturation of 80% can be achieved with CO of 1.8L/min. While to achieve the same level of DO 2 at O 2 saturation 40%, require CO of 3.6 L/min. Critical O 2 delivery and half-critical DO 2 are represented with horizontal yellow and red lines respectively. The vertical mahogany and blue lines represent the CO where half-critical delivery at O 2 saturations of 80% and 40%, respectively. Conclusion Since the CO obtained with chest compression is at best 1/3 of the normal value; to reach half-critical O 2 delivery requires an O 2 saturation of 80%. CCO seems unlikely to produce O 2 saturation greater than 80%. Therefore, effective ventilation during CPR is essential. Further study is needed to demonstrate whether confirmed adequate ventilation improves outcome during CPR.