Ventilation during CPR: two-rescuer standards reappraised.

Current American Heart Association standards for ventilation during two-rescuer CPR recommend that a 0.8- to 1.2-L breath be delivered in 0.5 second after every fifth chest compression. Delivering a high-volume breath over a brief inspiratory time (TI) may lead to hypoventilation and gastric insufflation in victims with an unprotected airway. We reasoned that lengthening TI would lower peak inspiratory pressure and peak inspiratory flow rate, and thus improve lung inflation. To study this possibility, a mechanical model of the airway and upper gastrointestinal tract was designed. A ventilator delivering a sinusoidal wave form was used to simulate artificial ventilation. A 0.8-L breath was delivered at 0.5, 1.0, or 1.5 seconds at three lung compliances (CLs). Also, the effect of lengthening TI was studied with increased airway resistance. Lengthening TI improved lung inflation and decreased gastric insufflation at all CLs, but more so with normal CL than with decreased CL. This study demonstrates the need for evaluating alternative ventilatory patterns with longer TI during CPR.