The detrimental effects of ventilation during low-blood-flow states

In recent years, it has become increasingly apparent that resuscitative ventilatory procedures, classically thought to be life saving, may have profound detrimental effects.

Most assisted breathing techniques during resuscitation involve the provision of intermittent positive pressure ventilation to inflate lung zones for erythrocyte oxygenation and clearance of carbon dioxide. A growing number of studies involving low-flow states, however, have demonstrated that provision of overzealous (or even 'normal') ventilatory rates with intermittent positive pressure ventilation can significantly diminish both systemic and coronary circulation, most likely through inhibition of venous return. Recent laboratory studies of hemorrhage have shown not only a direct detrimental impact of each positive pressure ventilation breath on coronary perfusion, but also how dramatic improvements in blood flow can be achieved, without loss of oxygenation, by delivering breaths infrequently during such low-flow states. Likewise, in cardiac arrest models, studies have shown that interrupting chest compressions, even to provide breaths, can be extremely deleterious by abruptly (and continually) lowering the aortic pressure head to the coronary arteries, thus impairing restoration of spontaneous circulation. Even with endotracheal intubation and uninterrupted chest compressions, frequent positive pressure ventilation still inhibits circulation during cardiopulmonary resuscitation. Despite directed training, paramedics (and other rescuers) have been shown to still excessively ventilate during cardiac arrest resuscitations.

Ventilation can have profound detrimental hemodynamic effects in low-flow states, exacerbating the circulatory compromise. This underappreciated confounding variable may be one of the reasons many clinical trials of resuscitative interventions have failed despite dramatic successes in the laboratory.