Comparison of a 10-Breaths-Per-Minute Versus a 2-Breaths-Per-Minute Strategy During Cardiopulmonary Resuscitation in a Porcine Model of Cardiac Arrest

Abstract

BACKGROUND:

Hyperventilation during cardiopulmonary resuscitation (CPR) is harmful.

METHODS:

We tested the hypotheses that, during CPR, 2 breaths/min would result in higher cerebral perfusion pressure and brain-tissue oxygen tension than 10 breaths/min, and an impedance threshold device (known to increase circulation) would further enhance cerebral perfusion and brain-tissue oxygen tension, especially with 2 breaths/min.

RESULTS:

Female pigs (30.4 ± 1.3 kg) anesthetized with propofol were subjected to 6 min of untreated ventricular fibrillation, followed by 5 min of CPR (100 compressions/min, compression depth of 25% of the anterior-posterior chest diameter), and ventilated with either 10 breaths/min or 2 breaths/min, while receiving 100% oxygen and a tidal volume of 12 mL/kg. Brain-tissue oxygen tension was measured with a probe in the parietal lobe. The impedance threshold device was then used during an 5 additional min of CPR. During CPR the mean ± SD calculated coronary and cerebral perfusion pressures with 10 breaths/min versus 2 breaths/min, respectively, were 17.6 ± 9.3 mm Hg versus 14.3 ± 6.5 mm Hg (p = 0.20) and 16.0 ± 9.5 mm Hg versus 9.3 ± 12.5 mm Hg (p = 0.25). Carotid artery blood flow, which was prospectively designated as the primary end point, was 65.0 ± 49.6 mL/min in the 10-breaths/min group, versus 34.0 ± 17.1 mL/min in the 2-breaths/min group (p = 0.037). Brain-tissue oxygen tension was 3.0 ± 3.3 mm Hg in the 10-breaths/min group, versus 0.5 ± 0.5 mm Hg in the 2-breaths/min group (p = 0.036). After 5 min of CPR there were no significant differences in arterial pH, P_O2, or P_CO2 between the groups. During CPR with the impedance threshold device, the mean carotid blood flow and brain-tissue oxygen tension in the 10-breaths/min group and the 2-breaths/min group, respectively, were 102.5 ± 67.9 mm Hg versus 38.8 ± 23.7 mm Hg (p = 0.006) and 4.5 ± 6.0 mm Hg versus 0.7 ± 0.7 mm Hg (p = 0.032).

CONCLUSIONS:

Contrary to our initial hypothesis, during the first 5 min of CPR, 2 breaths/min resulted in significantly lower carotid blood flow and brain-tissue oxygen tension than did 10 breaths/min. Subsequent addition of an impedance threshold device significantly enhanced carotid flow and brain-tissue oxygen tension, especially in the 10-breaths/min group.