Pathophysiology and Prevention of Manual-Ventilation-Induced Lung Injury (MVILI)

Abstract

Manual ventilation, most commonly with a bag-valve mask, is a form of short-term ventilation used during resuscitative efforts in emergent and out-of-hospital scenarios. However, compared to mechanical ventilation, manual ventilation is an operator-dependent skill that is less well controlled and is highly subject to providing inappropriate ventilation to the patient. This article first reviews recent manual ventilation guidelines set forth by the American Heart Association and European Resuscitation Council for providing appropriate manual ventilation parameters (e.g., tidal volume and respiratory rate) in different patient populations in the setting of cardiopulmonary resuscitation. There is then a brief review of clinical and manikin-based studies that demonstrate healthcare providers routinely hyperventilate patients during manual ventilation, particularly in emergent scenarios. A discussion of the possible mechanisms of injury that can occur during inappropriate manual hyperventilation follows, including adverse hemodynamic alterations and lung injury such as acute barotrauma, gastric regurgitation and aspiration, and the possibility of a subacute, inflammatory-driven lung injury. Together, these injurious processes are described as manual-ventilation-induced lung injury (MVILI). This review concludes with a discussion that highlights recent progress in techniques and technologies for minimizing manual hyperventilation and MVILI, with a particular emphasis on tidal-volume feedback devices.

Keywords: Ambu; CPR; bag-valve mask; emergency; hyperventilation; lung injury; manual; pulmonary injury; resuscitation; ventilation.

Figure 1

Mechanisms of MVILI. Manual hyperventilation increases intrathoracic pressure leading to adverse hemodynamic changes, including decreased venous return (VR), cardiac output (CO), and coronary perfusion pressure (CPP). Additionally, increased inspiratory pressures can open the lower esophageal sphincter, causing gastric insufflation, regurgitation, and aspiration. Vigorous manual ventilation may also lead to acute barotrauma (pneumothorax, pneumomediastinum, pneumoperitoneum, and subcutaneous emphysema) and possibly a sub-barotraumatic, inflammation-driven injury lung injury. Graphic design by David Wright.

Figure 2

Tidal-volume feedback devices. Authors’ rendering of the TVD based on [67]. Cropped and edited images of the Amflow^® [68], RTVFD (a, tidal volume; b, inspiration time; c, peak pressure) [69], VFD [70], and BENGI [71] reproduced under Creative Commons Attribution Non-Commercial License 4.0.