Use of an inspiratory impedance valve improves neurologically intact survival in a porcine model of ventricular fibrillation

Background - This study evaluated the potential for an inspiratory impedance threshold valve (ITV) to improve 24-hour survival and neurological function in a pig model of cardiac arrest. Methods and Results - Using a randomized, prospective, and blinded design, we compared the effects of a sham versus active ITV on 24-hour survival and neurological function. After 6 minutes of ventricular fibrillation (VF), followed by 6 minutes of cardiopulmonary resuscitation (CPR) with either a sham or an active valve, anesthetized pigs received 3 sequential 200-J shocks. If VF persisted, they received epinephrine (0.045 mg/kg), 90 seconds of CPR, and 3 more 200-J shocks. A total of 11 of 20 pigs (55%) in the sham versus 17 of 20 (85%) in the active valve group survived for 24 hours (P<0.05). Neurological scores were significantly higher with the active valve; the cerebral performance score (1=normal, 5=brain death) was 2.2±0.2 with the sham ITV versus 1.4±0.2 with the active valve (P<0.05). A total of 1 of 11 in the sham versus 12 of 17 in the active valve group had completely normal neurological function (P<0.05). Peak end-tidal CO₂ (PETCO₂) values were significantly higher with the active valve (20.4±1.0) than the sham (16.8±1.5) (P<0.05). PETCO₂>18 mm Hg correlated with increased survival (P<0.05). Conclusions - Use of a functional ITV during standard CPR significantly improved 24-hour survival rates and neurological recovery. PETCO₂ and systolic blood pressure were also significantly higher in the active valve group. These data support further evaluation of ITV during standard CPR.