Ventilation During Cardiopulmonary Resuscitation: What Have We Learned From Models?

Abstract

The optimization of ventilation during cardiopulmonary resuscitation (CPR) is a broad field of research. Recent physiological observations in this field challenge the current understanding of respiratory and circulatory interactions. Thanks to different models available (bench, animal, human), the understanding of physiological phenomena occurring during CPR has progressed. In this review, we describe the clinical observations that have led to the emerging concept of lung volume reduction and associated thoracic airway closure. We summarize the clinical and animal observations supporting these concepts. We then discuss the different contributions of bench, animal, and human models to the understanding of airway closure and their impact on intrathoracic pressure, airway closure, and hemodynamics generated by chest compression. The limitation of airway pressure and ventilation, resulting from airway closure reproducible in models, may play a major role in ventilation and gas exchange impairment observed during prolonged resuscitation.

High PEEP levels during CPR improve ventilation without deleterious hemodynamic effects in pigs

“…When using PEEP, lower shunt fractions could be detected, particularly in early resuscitation, suggesting improved recruitment and optimized ventilation. This aligns with studies that showed that using PEEP during resuscitation can prevent airway closure and ensure alveolar ventilation (19,20) and has positive effects on systemic oxygenation (4,5,21). In our trial, oxygenation was improved when using PEEP, especially in early resuscitation.…”

“…In our trial, oxygenation was improved when using PEEP, especially in early resuscitation. The ameliorated oxygenation could result from the prevention of atelectasis (4, 6, 7), thus decreasing shunt perfusion, improving lung recruitment and preventing airway closure (19,20). The EIT recordings showed normo-to hyperventilated lung areas when using PEEP, especially when ventilating with IPPV.…”

Effect of positive end-expiratory pressure on additional passive ventilation generated by CPR compressions in a porcine model

“…Investigators speculate that intrathoracic airway closure eliminates the transmission of negative alveolar pressure generated during chest recoil. Thus, negative alveolar pressure is not facilitating airway opening and therefore does not generate any inspiratory flow despite a significant pressure gradient [ 17 ].…”

“…Opening index, which was their bedside method of estimating airway patency of 20% to 70%, was still associated with low minute ventilation [ 14 ]. Thus, small amounts of PEEP (< 10 cmH 2 O) were able to maintain the airway patency, allowing the pressure gradient from the compression/recoil phases of CPR to reach the upper airway, improving effective alveolar ventilations caused by the compressions [ 14 , 17 ].…”

“…Cardiopulmonary resuscitation models show that positive end-expiratory pressure (PEEP) can improve ventilation during CPR. As such, these studies speculate that the mechanism for improved ventilation with PEEP is possibly due to reversing airway closure that limits gas flow, thereby taking advantage of the oscillations of gas produced by the compression and decompression phases of CPR [ 14 , 17 ]. However, the effect of different PEEP levels on improving ventilation generated by the compressions of CPR, as well as the optimal PEEP for ventilation remains undefined.…”