Intermittent and continuous positive-pressure ventilation in the prophylaxis of endotoxin-induced lung insufficiency. A study in pigs.

The effects of intermittent and continuous positive-pressure ventilation (IPPV and CPPV) instituted prophylactically were evaluated in a porcine model of endotoxin-induced pulmonary and cardiovascular failure. Pigs under ketamine anaesthesia were infused i.v. with E. coli endotoxin over 6 h. Twenty animals, breathing air spontaneously, received endotoxin without treatment. Fifteen animals were treated prophylactically with IPPV (normoventilation with air). Nine animals received prophylactic treatment with CPPV (positive end-expiratory pressure 0.8 kPa (8 cmH2O). Endotoxin infusion in spontaneously breathing animals caused profound deterioration of pulmonary gas exchange, a marked rise in pulmonary vascular resistance (PVR) and a moderate increase in extravascular lung water (EVLW). Cardiac output (Qt) and O2 delivery decreased considerably. Metabolic acidosis indicated oxygen deficit. Eleven of 20 animals died during the observation period. IPPV improved arterial oxygenation during endotoxin infusion, and the increase in EVLW tended to be lower. The alterations in pulmonary haemodynamics, Qt and O2 delivery, were of the same magnitude as in spontaneously breathing animals. Survival was improved. CPPV fully prevented the deterioration in pulmonary gas exchange and the development of pulmonary oedema. There was an accentuated increase in PVR. Qt and O2 delivery decreased markedly and a severe metabolic acidosis developed. All animals treated with CPPV died during the observation period. These results indicate that prophylactic IPPV and CPPV may counteract the development of sepsis-induced lung insufficiency in man. However, it must be emphasized that adequate cardiovascular support is essential in optimizing the treatment.