Comparative Effects of Volutrauma and Atelectrauma on Lung Inflammation in Experimental Acute Respiratory Distress Syndrome

Abstract

Objective Volutrauma and atelectrauma promote ventilator-induced lung injury, but their relative contribution to inflammation in ventilator-induced lung injury is not well established. The aim of this study was to determine the impact of volutrauma and atelectrauma on the distribution of lung inflammation in experimental acute respiratory distress syndrome. Design Laboratory investigation. Setting University-hospital research facility. Subjects Ten pigs (five per group; 34.7–49.9 kg) Interventions Animals were anesthetized and intubated, and saline lung lavage was performed. Lungs were separated with a double-lumen tube. Following lung recruitment and decremental positive end-expiratory pressure trial, animals were randomly assigned to 4 hours of ventilation of the left (ventilator-induced lung injury) lung with tidal volume of approximately 3 mL/kg and 1) high positive end-expiratory pressure set above the level where dynamic compliance increased more than 5% during positive end-expiratory pressure trial (volutrauma); or 2) low positive end-expiratory pressure to achieve driving pressure comparable with volutrauma (atelectrauma). The right (control) lung was kept on continuous positive airway pressure of 20 cm H2O, and Co2 was partially removed extracorporeally. Measurements and Main Results Regional lung aeration, specific [18F]fluorodeoxyglucose uptake rate, and perfusion were assessed using computed and positron emission tomography. Volutrauma yielded higher [18F]fluorodeoxyglucose uptake rate in the ventilated lung compared with atelectrauma (median [interquartile range], 0.017 [0.014–0.025] vs 0.013 min−1 [0.010–0.014min−1]; p < 0.01), mainly in central lung regions. Volutrauma yielded higher [18F]fluorodeoxyglucose uptake rate in ventilator-induced lung injury versus control lung (0.017 [0.014–0.025] vs 0.011 min−1 [0.010–0.016min−1]; p < 0.05), whereas atelectrauma did not. Volutrauma decreased blood fraction at similar perfusion and increased normally as well as hyper-aerated lung compartments and tidal hyperaeration. Atelectrauma yielded higher poorly and nonaerated lung compartments, and tidal recruitment. Driving pressure increased in atelectrauma. Conclusions In this model of acute respiratory distress syndrome, volutrauma promoted higher lung inflammation than atelectrauma at comparable low tidal volume and lower driving pressure, suggesting that static stress and strain are major determinants of ventilator-induced lung injury.

The authors reply

“…We thank Dr. Tonetti and colleagues for their interest (1) in our recently published study in Critical Care Medicine , where we showed that the specific uptake rate of 18F-fluorodeoxyglucose, a marker of lung inflammation, was higher during volutrauma than atelectrauma in pigs with experimental acute respiratory distress syndrome (ARDS) (2). …”

Lung imaging: how to get better look inside the lung

“…In a recent paper, opening pressures were higher than what is commonly considered safe especially in moderate and severe ARDS (22): the clinician must therefore balance between the risk of lung de-recruitment and atelectrauma and that of volutrauma (23). Moreover, CT acquisition parameters can affect the quantitative analysis, especially for the quantification of the hyper-aerated lung tissue (24).…”

“…Another study using 68 Ga-marked albumin aggregates suggested also that, in the early stages of lung injury, perfusion is redistributed towards healthier regions due to hypoxic vasoconstriction or direct compression of vessels by oedema (64 (66). In a study on a porcine model of ARDS, PET compared the inflammatory response due to atelectrauma compared to volutrauma, with the latter being significantly more relevant (23), suggesting extreme caution in applying the elevated PEEP levels required to achieve an open lung strategy (22). PET is unlikely to become a routine diagnostic tool, due to its low availability, high cost and high radiation exposure, but it could be useful in selected cases.…”

Optimal mechanical ventilation strategies to minimize ventilator-induced lung injury in non-injured and injured lungs

“…One recent paper compared high PEEP set above the level where dynamic compliance increased more than 5% during PEEP trial (static strain) versus low PEEP (dynamic strain). Static strain promoted higher lung inflammation than dynamic strain at comparable low V T and ΔP [10].…”