Gas exchange, pulmonary mechanics and haemodynamics in adult respiratory distress syndrome: experimental results in Lewe miniature pigs

Abstract

Adult respiratory distress syndrome (ARDS) is a common medical emergency in respiratory care complicating a great variety of traumas and diseases. An animal model from Lewe miniature pigs has been developed to study the ARDS under standardized conditions; it is based on aspiration pneumonitis, a disorder often observed in ARDS, injuring the lung alveolar surfactant system. The experimental study was conducted under neuroleptanalgesia. ARDS was produced by intratracheal application of hydrochloric acid (0.2 mol/l) in an amount of 1.0 ml/kg body wt. The animals were ventilated automatically by a standardized ventilatory pattern in IPP mode. In all animals the time course of oxygenation ratio P a,O 2 F 1 O 2 ), arterial CO 2 tension ( Pa,CO 2), ratio of alveolo-arterial oxygen tension difference to inspired oxygen fraction ( A a,DO 2 F 1 O 2 ), oxygen exchange ratio ( A aDO 2 P a,O 2 ), lung compliance ( C L), inspiratory airway resistance (RrsI), dead space ratio ( V D V T ), pulmonary artery pressure (PAP) and systemic blood pressure were studied. Changes in quasi-static volume-pressure curves, percentage change in lung water content and gross pathological finding were used to integrate the findings into a system of pathophysiological changes in ARDS. The animal group to which hydrochloric acid was administered shows severe pulmonary distress leading to death within 3.5–7.5 h. No significant changes in the measured parameters could be observed in the control group over a 14 h period. The results suggest that aspiration pneumonitis in Lewe miniature pigs is very suitable to investigate various problems in pathogenesis of ARDS. The model provides reproducible results which correlate very well with findings in different ARDS states. The model serves both to compare clinical states and to search for newer therapeutic manoeuvres.