Different tidal volumes induce similar elevation of lung injury markers in animals sensitized to injury by previous anesthesia and surgery

Introduction

Large tidal volumes and transpulmonary pressures play a central role in pathogenesis of ventilator-induced lung injury. Moderate tidal volumes are considered safe in healthy lungs [1]. Recent studies suggested that insults like endotoxin [2] or surgery [3] sensitize the lung to injury by priming for an exaggerated response to a second stimulus. Our aim was to investigate how animals sensitized to lung injury by previous anesthesia and surgery respond to mechanical ventilation (MV).

Methods

Twenty-two male adult Sprague–Dawley rats instrumented surgically under ether anesthesia with vascular catheters on the previous day were anesthetized, tracheostomized and randomly allocated to two mechanically ventilated groups – MVLP group (FiO₂ 1.0, respiratory rate 60/min, tidal volume 10 ml/kg, PEEP 2 cmH₂O, n = 8) and HVZP group (FiO₂ 1.0, respiratory rate 20/min, tidal volume 30 ml/kg, PEEP 0 cmH₂O, n = 8) – and a no MV group C (n = 6). After randomization (C group) or after 2 hours of MV, rats were sacrificed, the P–V curve of the respiratory system constructed, and bronchoalveolar lavage fluid (BALF) and aortic blood samples obtained.

Results

Comparison of P–V curves suggested derecruitment of the lung in the MVLP group, but no significant difference in airway pressures at maximal lung volume (14 ml) was observed between groups. Total protein (μg/ml) in BALF was similar in both the MVLP and HVZP groups (0.21 (0.16, 0.30) and 0.22 (0.18, 0,50), P = 0.366) and lower in the C group (0.13 (0.07, 0.16), P < 0.05) versus both MV groups. Similar results were obtained for IL-6 levels (pg/ml) in BALF (102.0 (93.4, 111.8) and 120.0 (53.7, 130.0) for the MVLP and HVZP groups, P = 0.628 and 48.5 (43.4, 56.4) pg/ml for the C group, P < 0.05 vs both MV groups).

Conclusion

Both moderate and high tidal volumes induce a similar elevation of lung injury markers in mechanically ventilated animals sensitized to injury by previous anesthesia and surgery.