Abstract 290: Low Minute Ventilation Volume During CPR Disturbs the Relationship between End-Tidal CO2 and Coronary Perfusion Pressure
End-tidal CO2 (ETCO2) is important for monitoring CPR quality as a surrogate for coronary perfusion pressure (CPP) and flow. We hypothesized that sufficient minute volume ventilation is not only needed to control CO2 buildup, but also for the exhaled CO2 to CPP relationship to remain valid.
To test our hypothesis, we measured minute volume ventilation together with CPP, arterial PCO2 (PaCO2), and ETCO2 in a pig model. Ventricular fibrillation was induced in 24 pigs, after which automated CPR (5 cm, 100 cpm) followed for 20 minutes. Animals were ventilated manually using a bag-mask-valve, either continuously at 10 min-1 (group 1, n=8) or 30:2 mode (group 2, n=16). Correlation coefficients between CPP and ETCO2 were calculated for each pig during the CPR interval.
Minute volume ventilation during CPR was 3.4 ± 1.0 L/min for group 1 and 2.2 ± 0.3 L/min for group 2 pigs. In group 1, PaCO2 changed little during CPR (41.1 ± 7.6 mmHg initially vs. 38.6 ± 16.5 mmHg at 20 minutes), indicating suitable minute volume ventilation. ETCO2 decreased concurrently with CPP. The correlation coefficient between CPP and ETCO2 was 0.52 ± 0.39. Group 2 pigs showed a large increase in PaCO2 (49.8 ± 6.6 mmHg initially vs. 58.0 ± 13.6 mmHg at 20 minutes), consistent with small minute volume ventilation. This increase in PaCO2 was accompanied by a progressively increasing ETCO2, while the CPP consistently decreased. The CPP to ETCO2 correlation coefficient showed a low, but negative (-0.18 ± 0.51) relationship, strongly supporting that the indicator function of ETCO2 was lost. The figure shows an example.
In conclusion, insufficient ventilation affects ETCO2 and can disturb the relationship between ETCO2 and CPR quality as measured by CPP. This is reminiscent of hyperventilation effects. Ventilation minute volumes should therefore be monitored, and hypoventilation avoided, to prevent clinical misinterpretation of ETCO2 values.
- © 2013 by American Heart Association, Inc.