New volumetric capnography-derived parameter: a potentially valuable tool for detecting hyperventilation during cardiopulmonary resuscitation in a porcine model

BACKGROUND: Volumetric capnography is increasingly being applied in cardiopulmonary resuscitation. However, during cardiopulmonary resuscitation, the abnormal ventilation state affects the monitoring effect of the most commonly used capnography-derived parameter, the partial carbon dioxide end-tidal pressure (PetCO(2)). In this study, we evaluated the ability of a new volumetric capnography-derived parameter, the ratio between the PetCO(2) and the volume of carbon dioxide (CO(2)) eliminated per min and per kilogram of body weight, for detecting hyperventilation during cardiopulmonary resuscitation. METHODS: We used 12 porcine models of primary ventricular fibrillation-induced cardiac arrest. Ventricular fibrillation was induced and left untreated for 4 min. Standardized chest compressions were performed throughout the experiment using mechanical cardiopulmonary resuscitation. Following 5 min of normal ventilation as a washout period, each animal underwent 4 types of ventilation. The main outcome measures were the PetCO(2), the ratio between the PetCO(2) and the volume of CO(2) eliminated per min and per kilogram of body weight with each ventilation type. RESULTS: Different ventilation types had a significant effect on the volumetric capnography-derived parameters. The PetCO(2) and ratio between the PetCO(2) and the volume of CO(2) eliminated per min and per kilogram of body weight values during cardiopulmonary resuscitation was significantly higher in non-hyperventilating than in hyperventilating animals. The ratio reflected hyperventilation accurately and immediately, with an area under the curve (AUC) of 0.98. The optimal cut-off point of the ratio for discriminating hyperventilation from non-hyperventilation was 6.36, with a sensitivity and specificity of 0.99 and 0.89, respectively. CONCLUSIONS: The ratio between the PetCO(2) and the volume of CO(2) eliminated per min and per kilogram of body weight showed good performance in discriminating hyperventilation from non-hyperventilation and was sensitive to changes in ventilation status. This ratio may be a valuable clinical indicator for monitoring the ventilation status during cardiopulmonary resuscitation.