The physiology of ventilation during cardiac arrest and other low blood flow states

Introduction: Ventilation - the movement of fresh air or other gas from the outside into the lungs and alveoli in close proximity to blood for the efficient exchange of gases - enriches blood with O2 and rids the body of CO2 by movement of alveolar gas out of the lungs to the outside. The importance of ventilation in resuscitation is reflected in the “ABCs” (airway, breathing, circulation), which is the recommended sequence of resuscitation practiced in a broad spectrum of illnesses including traumatic injury, unconsciousness, and respiratory and cardiac arrest. Since the modern era of cardiopulmonary resuscitation (CPR) began in the early 1960s, ventilation of the lungs of a victim of cardiac arrest has been assumed to be important for successful resuscitation. This assumption has been questioned and the role of ventilation during resuscitation has been the subject of much research for more than a decade. A number of laboratory studies of CPR have shown no clear benefit to ventilation during the early stages of cardiac arrest with ventricular fibrillation. Furthermore, exhaled gas contains approximately 4% CO2 and 17% O2, thus making mouth-to-mouth ventilation the only circumstance in which a hypoxic and hypercarbic gas mixture is given as recommended therapy. With the introduction of the 2000 Guidelines for Cardiopulmonary Resuscitation, a new, evidence-based approach to the science of ventilation during CPR was introduced and continues with the publication of the 2005 edition. New evidence from laboratory and clinical science has led to less emphasis being placed on the role of ventilation following a dysrhythmic cardiac arrest (arrest primarily resulting from a cardiovascular event, such as ventricular fibrillation or asystole).