High-pressure ventilation during CPR with 95% O2:5% CO2.

The effects of two different breathing-gas mixtures on blood flow, blood pressure, and arterial blood pH and PCO2 were measured in dogs during 2 different modes of CPR with high-pressure ventilation (50 cm H2O). Ventilation was either applied simultaneously with every compression (1:1) or interposed after every fifth compression (1:5). Ventilation with pure oxygen under either condition caused severe arterial alkalemia with hypocarbia after 2-min episodes of cardiac arrest and resuscitation (pH = 7.63, PCO2 = 5.0 after 1:1; pH = 7.63, PCO2 = 5.4 after 1:5). Ventilation with 5% CO2-enriched oxygen during CPR maintained acid/base status near prearrest values (pH = 7.22, PCO2 = 30.3 after 1:1; pH = 7.26, PCO2 = 28.0 after 1:5). Values obtained with radioactive microspheres for cardiac output (CO) and regional blood flow to brain, heart, and kidney were not significantly different under the 4 conditions. Electrical ventricular defibrillation was easily accomplished despite arterial alkalemia and hypocarbia. Ventilation at high pressures with CO2-enriched oxygen does not alter hemodynamics during CPR, but does prevent severe arterial alkalemia.