Lung mechanical changes following bronchoaspiration in a porcine model: Differentiation of direct and indirect mechanisms

• An animal model was developed to distinguish the local and the systemic effects of bronchoaspiration.
• Unilateral aspiration of the gastric contents leads to a unilateral lung injury in the first 2 h.
• These changes were obvious exclusively on the affected side; the intact side remained unchanged.
• Application of a moderately high PEEP (10 cm H2O) prevented ventilation heterogeneities.
• Local treatment of bronchoaspiration is important over the adverse changes with systemic origin.

Bronchoaspiration results in local deterioration of lung function through direct damage and/or indirect systemic effects related to neurohumoral pathways. We distinguished these effects by selectively intubating the two main bronchi in pigs while a PEEP of 4 or 10 cm H2O was maintained. Gastric juice was instilled only into the right lung. Lung mechanical and ventilation defects were assessed by measuring unilateral pulmonary input impedance (ZL,s) and the third phase slope of the capnogram (SIII) for each lung side separately before the aspiration and for 120 min thereafter. Marked transient elevations in ZL,s parameters and SIII were observed in the affected lung after aspiration. Elevating PEEP did not affect these responses in the ZL,s parameters, whereas it prevented the SIII increases. None of these indices changed in the intact left lung. These findings furnish evidence of the predominance of the local direct damage over the indirect systemic effects in the development of the deterioration of lung function, and demonstrate the benefit of an initially elevated PEEP following aspiration.