Mechanical-Ventilatory Cardiac Support

Abstract

A large body of experimental data indicates that blood flows during CPR because of elevations of intrathoracic pressure and the uneven peripheral transmission of this pressure. Data from humans are less extensive, but also strongly support the mechanism of intrathoracic pressure. It should be remembered that the intrathoracic pressure and direct cardiac compression hypotheses are not mutually exclusive, and that effective CPR is above all dependent on vigorous chest compression. Maintenance of sternal displacement for 40% to 50% of each compression-release cycle, intense alpha-adrenergic stimulation, and avoidance of vasodilators are also essential to the maximization of cerebral and myocardial perfusion. Whether movement of blood by manipulation of intrathoracic pressure can be applied successfully to other disease states is unknown. What is established is that vigorous chest compression, adequate ventilation, and generous use of epinephrine, along with prompt defibrillation, form the basis of an effective strategy for life support. Provision of chest compression and mouth-to-mouth ventilation by bystanders prior to delivery of definitive care has been shown to increase survival rates from 8% to 36% in Columbus, Ohio, and from 21% to 43% in Seattle. Bystander-initiated CPR also reduced the frequency of neurologic impairment at the time of hospital discharge from 55% to 4% in the Seattle experience. For patients receiving the full program of chest compression, ventilation, drug therapy, and defibrillation, resuscitation rates in excess of 50% have been reported in both in-hospital and out-of-hospital arrests. Of those who survive to hospital discharge, 6-month survival rates of 80% have been reported from these patients cohorts, with return-to-work rates of 70%. These data demonstrate that CPR is an effective means of supporting the circulation during cardiac arrest. The majority of survivors return to a meaningful existence, and the technique has not burdened society with a large load of neurologically impaired patients. Thus, CPR is very much worthy of the full attention and support of the medical community.