INTRATRACHEAL PULMONARY VENTILATION AND CONTINUOUS POSITIVE AIRWAY PRESSURE IN A SHEEP MODEL OF SEVERE ACUTE RESPIRATORY-FAILURE

Study objectives: Previously we have shown that optimal pulmonary gas exchange can be sustained at normal airway pressures in a model of sev ere acute respiratory failure (ARF), using intratracheal pulmonary ven tilation (ITPV), with weaning to room air, In an identical model of AR F, we have now explored whether ITPV, combined with continuous positiv e airway pressure (CPAP), can sustain adequate ventilation, with weani ng to room air. Design: Randomized study in sheep. Setting: Animal res earch laboratory at the National Institutes of Health. Interventions: ARF was induced in 12 sheep, using mechanical ventilation at peak insp iratory pressure of 50 cm H2O, bunt excluding 5 to 8% of lungs. Sheep were then randomized into two groups: the CPAP-ITPV group (n=6), in wh ich ITPV was combined with a novel CPAP system; and a control group (n =6) in which the same CPAP circuit was used, hut without ITPV. Measure ments and results: All sheep in the CPAP-ITPV group were weaned to roo m air in 38.7+/-14 h. PaO2/fraction of inspired oxygen (FIo(2)) progre ssively increased from 108.8+/-43 to 355.7+/-93.1; PaCO2 remained with in normal range; respiratory rate (RR) ranged from 18 to 120 breaths/m in, and tidal volume (VT) was as low as 1.1 mL/kg. All sheep in the co ntrol group (CPAP alone) developed severe respiratory-acidosis and hyp oxemia after 4.8+/-4 h, PaO2/FIo(2) decreased from 126.6+/-58.2 to 107 .2+/-52.5 mm Hg, with a final PaCO2 of 166.8-73.3 mm Hg. Conclusions: All sheep treated with CPAP-ITPV maintained good gas exchange without hypercapnia at high RR and at low VT, with weaning to room air. All co ntrol animals treated with CPAP alone developed severe hypercapnia, re spiratory acidosis, and severe hypoxemia, and were killed.