Concept of stress and strain in pediatric mechanical ventilation

Abstract

Studies have shown that the airway pressures displayed on the screen of the ventilator monitor do not correlate with the actual alveolar distending pressures known as transpulmonary pressure or stress. The change in tidal volume (Vt) on top of the available functional residual capacity (FRC), also known as strain, is an essential factor directly related to stress. Even the correlation of driving pressure (DP) with ventilator-induced lung injury (VILI) needs to be interpreted in the background of what Vt, respiratory compliance (Crs) and at what positive end-expiratory pressure (PEEP) is that DP calculated and at what was the chest wall compliance, and the flow rate at that time. Stress and strain are related to all these factors, either directly or indirectly. The impact of stress and strain should be interpreted in “dynamic terms” over time rather than at one point. Hence, VILI is minimized by optimizing the Strain (using appropriate PEEP and Vt against available FRC) and stress (transpulmonary inspiratory and expiratory pressures), applied at an optimal respiratory rate and flow. In the pediatric age group, pulmonary mechanics also change as age changes. Moreover, children respond differently to lung injury than adults, adding another layer of complexity to the concept of stress and strain in the pediatric population. Despite this, most knowledge about stress and strain has come from studies in the adult population. Therefore, more extensive studies focussing on pediatric age groups are needed to improve our understanding of stress and strain in pediatric ventilated patients.