Effects of positive end expiratory pressure on oxygenation and coronary perfusion pressure during ACD CPR with the inspiratory threshold valve

Introduction. Intermittent impedance to inspiratory inflow of respiratory gases with a one-way valve during active compression-decompression (ACD) cardiopulmonary resuscitation (CPR) has recently been demonstrated to improve coronary perfusion pressure by enhancing venous return. We evaluated the effects of positive end exspiratory pressure (PEEP) ventilation on coronary perfusion pressure (CPP) and oxygenation during ACD CPR with the inspiratory threshold valve (ITV). Methods: ACD + ITV CPR was performed with an automatic device in a porcine model of ventricular fibrillation. All pigs received pressure controlled pure oxygen ventilation (pressure limit 60 ± 5 cm H₂O at a constant flow rate (160 L/min), and 5:1 compression-ventilation ratio. After 8 minutes of ACD + ITV CPR, pigs were randomized to further intermittent positive pressure ventilation (IPPV) alone (n = 8), or increasing levels of continuous positive pressure ventilation (CPPV) (n = 8) with 2.5, 5.0, 7.5, and 10 cm H₂O for 4 consecutive minutes each. Blood gases were assessed every 4 minutes. Defibrillation was attempted after 28 minutes of ACD + ITV CPR. Results: Mean ± SEM arterial POg decreased form baseline in the IPPV group from 145 ± 35, to 140 ± 35,120 ± 25 mm Hg, 120 ± 30, and 115 ± 30 torr, but increased with PEEP from 110 ± 10, to 135 ± 25, 155 ± 30, 155 ± 25 and 170 ± 25 torr, respectively (P>.05 at 5 PEEP, and P>.02 at 10 PEEP or corresponding time points versus values at 12 minutes within groups). Mean ± SEM CPP (diastolic aortic minus right atrial pressure) at baseline, and after increasing levels of PEEP were 25 ± 2, 27 ± 2, 28 ± 2, 28 ± 3 and 27 ± 3 mm Hg, versus 25 ± 5, 29 ± 6, 32 ± 6, 32 ± 6, and 28 ± 5 mm Hg in the IPPV group, at corresponding time points respectively (NS). 7/8 animals in the PEEP group and 5/8 animals in the IPPV group were successfully defibrillated. Conclusion: Increasing levels of PEEP during ACD CPR with an inspiratory impedance valve improves oxygenation and overall CPR efficiency. These data suggest that PEEP may provide a pneumatic press-like effect to enhance both oxygenation and blood transfer through the lungs during ACD CPR with the ITV.