Monitoring Patient Respiratory Effort During Mechanical Ventilation: Lung and Diaphragm-Protective Ventilation

Abstract

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2020. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2020. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Fig. 1

Transpulmonary pressure (P_L) is generated differently in passive mechanical ventilation (upper panel) and assisted mechanical ventilation (lower panel). During passive ventilation, the pleural pressure swing is positive and transpulmonary pressure is therefore lower than airway pressure (P_aw). During assisted ventilation a vigorous inspiratory effort generates a negative swing in pleural pressure resulting in an additive increase in transpulmonary pressure; transpulmonary pressure may therefore be much higher than airway pressure. P_es esophageal pressure

Fig. 2

Mechanisms of lung-diaphragm injury in spontaneous breathing patients under assisted mechanical ventilation. Note that some of these mechanisms also apply under controlled mechanical ventilation (e.g., reverse triggering). PEEP positive end-expiratory pressure

Fig. 3

Computing inspiratory muscle pressure (P_mus) from the esophageal pressure (P_es) swing. P_mus derives from the difference between P_es and the added muscle pressure generated to overcome the chest wall elastic recoil (P_cw). P_cw represents the elastic recoil of relaxed chest wall; it can be computed as the product of tidal volume and chest wall elastance (E_cw). The P_mus area over time constitutes the pressure-time product (PTP) (yellow and blue area together)

Fig. 4

Measuring plateau pressure (P_plat) during assisted mechanical ventilation (AMV). A brief inspiratory hold permits a reliable measure of P_plat in AMV, provided the patient relaxes with no immediate expiratory efforts. The difference between P_plat and positive end-expiratory pressure (PEEP) results in the driving pressure ΔP_aw. In panel (a), the patient’s inspiratory effort is vigorous (greater esophageal swing): during inspiratory hold, the airflow stops and P_plat rises above P_peak; the previous activated respiratory muscles relaxes and expires, causing P_aw to increase. In panel (b), the patient’s inspiratory effort is low: the difference between P_peak and P_plat is minimal, indicating minimal respiratory muscle effort during the current breath. This technique enables respiratory muscle activity to be assessed by measuring P_plat. (Modified from [29] with permission)

Fig. 5

Airway occlusion pressure (P_0.1) is the airway pressure (P_aw) generated in the first 100 ms of inspiration against an expiratory occlusion. Importantly, the 100 ms time for P_0.1 calculation should start at the point where the expiratory flow trace reaches zero (dashed line) to correct for potential intrinsic positive end-expiratory pressure (PEEP). PS pressure support level. (From [34] with permission)