Spontaneous agonal respiration in a swine model of out-of-hospital cardiac arrest.

OBJECTIVE To describe ventilatory dynamics following the onset of ventricular fibrillation (VF) in an experimental swine model. METHODS Twelve female mixed-breed domestic swine (mean mass 21.3 +/- 1.7 kg) were sedated with IM ketamine (10 mg/kg) and xylazine (1 mg/kg), anesthetized with alpha-chloralose (40 mg/kg loading dose, 10 mg/kg/hr maintenance infusion), intubated, and mechanically ventilated on room air. ECG, and aortic and pulmonary artery pressures were monitored continuously. VF was induced with a 3-sec, 60-Hz, 100-mA transthoracic shock, and left untreated for 8 minutes. Respiratory rate, tidal volume, and minute ventilation were recorded until respiratory activity ceased. RESULTS All 12 animals (100%) had agonal respirations through the first 2 minutes of arrest. This decreased to 11 (92%) at minute 3, five (42%) at minute 4, and two (17%) at minute 7. Mean respiratory rates ranged from 6 to 11 breaths/min. Mean tidal volumes ranged from 502 to 852 mL. Mean minute ventilations ranged from 3.3 to 5.8 L. CONCLUSION In this swine model, 11 of 12 (92%) continued to have spontaneous agonal respirations for the first 3 minutes of VF cardiac arrest. Many animals had supranormal tidal volumes, and near-normal minute ventilations. These findings have potential implications for lay-rescuer and first-responder contributions to resuscitation of victims of out-of-hospital cardiac arrest.