Bag ‘em or tube ‘em: how to decide

Abstract

In an effort to identify or at least shed light on optimal out-ofhospital cardiac arrest (OHCA) airway management strategies, McMullan et al [1] compared OHCA outcomes between patients receiving endotracheal intubation (ETI) vs supraglottic airway (SGA) and between patients receiving ETI or SGA and those receiving no advanced airway. They found that survival was higher among OHCA receiving ETI than those receiving SGA and for patients who received no advanced airway than those receiving ETI or SGA. Although their findings of an association of improved outcomes with no advanced airway management are consistent with previous reports, they urged caution in the interpretation of those and the current findings. Confounding by indication is of major influence in studies of medical interventions. It was noted that, unlike the comparison of ETI vs SGA, the observed survival differences between the airway and nonairway groups were very large, even after stratification by initial electrocardiographic rhythm, propensity score adjustment, and propensity score matching. They suggested that the large associations—despite the use of multivariable adjustment and propensity score matching— reflected the presence of unmeasured and immeasurable confounders. One significant confounding factor that was not accounted for in their analyses is the presence of witnessed gasping and/or gasping upon arrival of emergency rescuers. Gasping is the only source of clinically significant ventilation during chest compressions only (CCO) cardiopulmonary resuscitation (CPR) [2-4]. Moreover, studies in animals demonstrate that spontaneous gasping alone during ventricular fibrillation cardiac arrest generates cardiac output, maintains more optimal amplitudes of ventricular fibrillation waveforms, circulates blood to the brain, and decreases intracranial pressure (ICP) [5-7]. Furthermore, the elevation of intrathoracic pressure during standard CCO-CPR in animals (caused by air trapping in the lungs [8]) not only generates carotid pressure and flow but also increases ICP [9]. Intracranial pressure is also known to increase during the chest compression phase of conventional CPR in humans andmay be what limits cerebral blood flow [9]. The lower ICP is, the lower resistance is to forward blood flow to the brain. This may explain why performance of standard CCO-CPR in animals at 100 per minute results in only 25% of normal perfusion to the brain, but during LUCAS CCO-CPR, cortical cerebral blood flow is significantly increased [10]. Therefore, gasping not only significantly improves the effective-