Effect of peak inspiratory flow on gas exchange, pulmonary mechanics, and lung histology in rabbits with injured lungs

Abstract

The aim of this study was to evaluate, using a rabbit model, the little-known effect of different levels of peak inspiratory flow on acutely injured lungs. Fourteen male rabbits (body weight, 2,711 +/- 146 g) were anesthetized and their lungs were injured by alveolar overstretch with mechanical ventilation until Pa(O(2)) was reduced below 300 mmHg. Injured animals were randomly assigned to: the P group-to receive pressure-regulated volume-control ventilation (PRVCV; n = 7); and the V group-to receive volume-control ventilation (VCV; n = 7). Other ventilator settings were: fraction of inspired oxygen (FI(O(2)), 1.0; tidal volume, 20 ml x kg(-1); positive end-expiratory pressure (PEEP) 5 cmH(2)O; and respiratory rate, 20 min(-1). The animals were thus ventilated for 4 h. Throughout the protocol, ventilatory parameters and blood gas were measured every 30 min. After the protocol, the lung wet-to-dry ratio and histological lung injury score were evaluated in the excised lungs. Throughout the protocol, peak inspiratory flow and mean inspiratory flow values in the P group were significantly higher than those in the V group (26.7 +/- 5.0 l x min(-1) vs 1.2 +/- 0.2 l x min(-1), and 4.3 +/- 0.3 l x min(-1) vs 1.1 +/- 0.1 l x min(-1); P < 0.05). The wet-to-dry ratio in the P group was also significantly higher than that in the V group (7.7 +/- 0.9 vs 6.3 +/- 0.5; P < 0.05). More animals in the P group than in the V group had end-of-protocol Pa(O(2))/FI(O(2)) ratios below 200 mmHg (43% vs 0%; P = 0.06). In rabbits with injured lungs, high peak inspiratory flow with high tidal volume (V(T)) reduces the Pa(O(2))/FI(O(2)) ratio and increases the lung wet-to-dry ratio.