This study was designed to assess gas exchange during
closed-chest cardiac compression using different ventilatory
strategies. There was a significant increase in arterial
PO2 and a significant decrease in arterial PCO2 in pigs that
received assisted ventilation compared with those that did
not receive assisted ventilation.
Blood gas data from the airway-blocked and compression-
only groups indicate that passive air movement does
not allow physiologically significant pulmonary gas exchange.
In the absence of alveolar ventilation, there is a progressive
decline in the PO2 of the blood perfusing the heart and brain.
This cumulative deficit is reflected in the mixed venous blood
samples, which indicate the level of hypoxia and hypercapnia
present at the tissue level.
Compared with chest compression alone, assisted ventilation
with room air caused a significant increase in arterial
and venous PO2 and a decrease in arterial and venous
PCO2. The mixed venous blood gas analyses indicated that
there was a partial relief of the tissue hypoxia and hypercapnia
associated with inadequate perfusion. Nevertheless,
attempts to defibrillate these pigs after 20 minutes of CPR
were unsuccessful.