0990. Role of amplitude and rate of deformation in ventilator-induced lung injury

Introduction

Increasing both Tidal Volume (V_T) (amplitude of lung deformation) and Inspiratory Flow (V') (rate of lung deformation) augments incidence of Ventilator-Induced Lung Injury (VILI) [1].

Objectives

To clarify whether increasing V' at constant V_T augments incidence of VILI.

Methods

Twenty-eight healthy piglets were mechanically ventilated for up to 54 hours. Each animal was assigned to one of three groups of V_T (300-400 ml; 500-600 ml; 750 ml) and one of two groups of V'. Lower and higher V' were obtained by setting inspiratory-to-expiratory time ratio as high as 1:2 or as low as 1:9. Respiratory rate was always 15 breaths per minute. Interplay between V_T and V' was assessed at the beginning of the study as airway pressure-volume loop area (or dynamic respiratory system hysteresis). VILI was defined as pulmonary oedema (lung weight gain ≥10% across the study period).

Results

Main findings are reported in Table 1.

Table 1 Inspiratory flow and incidence of VILI

Conclusions

Increasing V' (rate of lung deformation) while maintaining V_T (amplitude of lung deformation) constant augments incidence of VILI. Further studies are needed to clarify whether dynamic respiratory system hysteresis is an independent predictor of VILI.