Spontaneous Agonal Respiration in a Swine Model of Out‐of‐hospital Cardiac Arrest

Abstract

Objective: To describe ventilator dynamics following the onset of ventricular fibrillation (VF) in an experimental swine model. Methods: Twelve female mixed‐breed domestic swine (mean mass 21.3 2 1.7 kg) were sedated with IM ketamine (10 mag) and xylazine (1 mgntg), anesthetized with α‐chloralose (40 mgkg loading dose, 10 mg/kg/hr rnaintenance infusion), incubated, 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 Tran thoracic 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 breathdmin. 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 supernormal 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. © 1995 Society for Academic Emergency Medicine