Assisted ventilation modes reduce the expression of lung inflammatory and fibrogenic mediators in a model of mild acute lung injury

Abstract

Purpose The goal of the study was to compare the effects of different assisted ventilation modes with pressure controlled ventilation (PCV) on lung histology, arterial blood gases, inflammatory and fibrogenic mediators in experimental acute lung injury (ALI). Methods Paraquat-induced ALI rats were studied. At 24 h, animals were anaesthetised and further randomized as follows (n = 6/group): (1) pressure controlled ventilation mode (PCV) with tidal volume (V _T) = 6 ml/kg and inspiratory to expiratory ratio (I:E) = 1:2; (2) three assisted ventilation modes: (a) assist-pressure controlled ventilation (APCV1:2) with I:E = 1:2, (b) APCV1:1 with I:E = 1:1; and (c) biphasic positive airway pressure and pressure support ventilation (BiVent + PSV), and (3) spontaneous breathing without PEEP in air. PCV, APCV1:1, and APCV1:2 were set with P _insp = 10 cmH₂O and PEEP = 5 cmH₂O. BiVent + PSV was set with two levels of CPAP [inspiratory pressure (P _High = 10 cmH₂O) and positive end-expiratory pressure (P _Low = 5 cmH₂O)] and inspiratory/expiratory times: T _High = 0.3 s and T _Low = 0.3 s. PSV was set as follows: 2 cmH₂O above P _High and 7 cmH₂O above P _Low. All rats were mechanically ventilated in air and PEEP = 5 cmH₂O for 1 h. Results Assisted ventilation modes led to better functional improvement and less lung injury compared to PCV. APCV1:1 and BiVent + PSV presented similar oxygenation levels, which were higher than in APCV1:2. Bivent + PSV led to less alveolar epithelium injury and lower expression of tumour necrosis factor-α, interleukin-6, and type III procollagen. Conclusions In this experimental ALI model, assisted ventilation modes presented greater beneficial effects on respiratory function and a reduction in lung injury compared to PCV. Among assisted ventilation modes, Bi-Vent + PSV demonstrated better functional results with less lung damage and expression of inflammatory mediators.