Passive Ventilation in Chest Compression-Only CPR by Untrained Bystanders: A Reply
We also thank Nolan et al for the data by Safar et al3 on passive ventilation generated by chest compressions in anesthetized healthy volunteers. This study deserves a few considerations. First, even though the generated tidal volumes were modest, they exceeded anatomic dead space in the majority (57%) of patients in whom airway patency was secured by artificial airway devices/maneuvers.3 Notably, the authors followed a resuscitation protocol that recommended chest compressions to be 3–4 cm deep.4 It is, therefore, plausible that more vigorous compressions (at least 5 cm deep, allowing complete chest recoil), as recommended by current resuscitation guidelines,5 would have generated greater tidal volumes. Second, a 3-inch shoulder elevation was associated with tidal volumes exceeding anatomic dead space in 20% of the individuals. This is of clinical relevance because a slight shoulder elevation promotes a backward tilt of the head and thus passively mimics a (partial) chin-lift maneuver. We speculate, however, that appropriately applied chin lift would have allowed better airway patency thereby favoring improved passive ventilation in a greater proportion of study individuals. Third, although not ideal, even tidal volumes smaller than anatomic dead space can lead to gas exchange.
In spite of our speculations, and as noted by Nolan et al,1 Safar et al’s3 results “…demonstrate that a patent airway improves ventilation during compression-only CPR…” In this regard, it is hard to imagine that even a modest degree of ventilation is not beneficial during CPR when compared to no ventilation at all. This is particularly true in situations where CPR or defibrillation is delayed, the cause of arrest is respiratory, and early return of spontaneous circulation has not occurred. Indeed, provision of passive ventilation has been shown to improve outcomes, as cited in our article (see references 17 and 18 in Ho et al2).
Finally, we agree with Nolan et al that changes in medical recommendations and guidelines should be guided by strong clinical evidence. The ILCOR’s recommendation to eliminate airway patency maneuvers by untrained bystanders attending out-of-hospital cardiac arrest, however, seems to have not followed this pattern. As pointed out in our article,2 many reasons justify the reintroduction of such maneuvers into untrained layperson chest compression-only CPR, and it is our hope that ILCOR will reconsider.