A novel capnogram analysis to guide ventilation during continuous chest compressions resuscitation. From clinical to experimental observations

Background: Cardio-Pulmonary Resuscitation (CPR) decreases lung volume below the functional residual capacity and can generate intrathoracic airway closure. Conversely, large insufflations can induce thoracic distension and jeopardize circulation. The capnogram (CO 2 signal) obtained during continuous chest compressions can reflect intrathoracic airway closure and we hypothesized here that it can also indicate thoracic distension. Objectives: to test whether a specific capnogram may identify thoracic distension during CPR and assess its impact on gas exchange and hemodynamics. Methods: 1. In out-of-hospital cardiac arrest patients, we identified on capnograms three patterns: intrathoracic airway closure, thoracic distension or regular pattern. An algorithm was designed to identify them automatically.2. To link CO2 patterns with ventilation, we conducted three experiments:i) Reproducing the CO2 patterns in human cadavers. ii) Assessing the influence of tidal volume and respiratory mechanics on thoracic distension using a mechanical lung model. iii) Exploring the impact of thoracic distension patterns on different circulation parameters during CPR on a pig model. Measurements and main results Clinical data: 202 patients were included. Intrathoracic airway closure was present in 35%, thoracic distension in 22% and regular pattern in 43%. Experiments:i) Higher insufflated volumes reproduced thoracic distension CO 2 patterns in 5 cadavers. ii) In the mechanical lung model, thoracic distension patterns were associated with higher volumes and longer time constants. iii) In six pigs during CPR with various tidal volumes, a CO 2 pattern of thoracic distension, but not tidal volume per se , was associated with a significant decrease in blood pressure and cerebral perfusion. Conclusions: During CPR, intrathoracic airway closure, thoracic distension or regular pattern can be identified by capnogram analysis. A thoracic distension pattern on the capnogram may indicate a negative impact of ventilation on blood pressure and cerebral perfusion during CPR, not predicted by tidal volume per se .