Respiratory Mechanics and Neural Respiratory Drive of Untreated Gasping During Cardiac Arrest in a Porcine Model

Introduction: Although the effects on hemodynamics of gasping during cardiac arrest (CA) have received a lot of attention, less is known about the respiratory mechanics and physiology of respiration in gasping. This study aimed to investigate the respiratory mechanics and neural respiratory drive of gasping during CA in a porcine model. Method: Pigs weighing 34.9 ± 5.7 kg were anesthetized intravenously. Ventricular fibrillation (VF) was electrically induced and untreated for 10 min. Mechanical ventilation (MV) was ceased immediately after the onset of VF. Hemodynamic and respiratory parameters, pressure signals, diaphragmatic electromyogram data, and blood gas analysis data were recorded. Results: Gasping was observed in all the animals at a significantly lower rate (2-5 gaps/min), with higher tidal volume ( VT ; 0.62 ± 0.19 L, P < 0.01), and with lower expired minute volume (2.51 ± 1.49 L/min, P < 0.001) in comparison with the baseline. The total respiratory cycle time and the expiratory time tended to be lengthened. Statistically significant elevations in transdiaphragmatic pressure, the pressure-time product of diaphragmatic pressure, and the mean of root mean square diaphragmatic electromyogram values (RMSmean) were observed ( P < 0.05, P < 0.05, and P < 0.001, respectively); however, VT /RMSmean and transdiaphragmatic pressure/RMSmean were reduced at all time points. The partial pressure of oxygen showed a continuous decline after VF to reach statistical significance in the 10th minute (9.46 ± 0.96 kPa, P < 0.001), whereas the partial pressure of carbon dioxide tended to first rise and then fall. Conclusions: Gasping during CA was characterized by high VT , extremely low frequency, and prolonged expiratory time, which may improve hypercapnia. During gasping, increased work of breathing and insufficient neuromechanical efficacy of neural respiratory drive suggested the necessity of MV and appropriate management strategies for MV during resuscitation after CA.