INTRATRACHEAL PULMONARY VENTILATION AT LOW AIRWAY PRESSURES IN A VENTILATOR-INDUCED MODEL OF ACUTE RESPIRATORY-FAILURE IMPROVES LUNG-FUNCTION AND SURVIVAL

Study objective: The pulmonary parenchyma in patients with acute respi ratory failure (ARF) is commonly not involved in a homogenous disease process. Conventional mechanical ventilation (MV) are elevated positiv e end-expiratory pressure (PEEP) and peak inspiratory pressure (PIP) a ims at recruiting collapsed or nonventilated lung units. Invariably, t hose pressures are also transmitted to the healthiest regions, with po ssible extension of the disease process (barotrauma). During intratrac heal pulmonary ventilation (ITPV), a continuous flow of fresh gas is d elivered directly at the carina, bypassing the dead space proximal to the catheter tip. In healthy sheep, it allows lowering tidal volume (V T) to as low as 1.0 mL/kg, at respiratory rates (RR) up to 120 breaths /min, while maintaining normocapnia. In a model of ventilator-induced lung injury, we wished to explore whether ITPV, applied at low VT and low PEEP and tailored to ventilate the healthiest regions of the lungs , could provide adequate oxygenation and alveolar ventilation, without any attempt to recruit lungs. Design: Randomized study in sheep. Sett ing: Animal research laboratory. Participants: We induced ARF in 12 sh eep following 1 to 2 days of MV at a PIP of 50 cm H2O, except that 5 t o 8% of lungs were kept on apneic oxygenation of 5 cm H2O, sparing tho se regions from the injury process. Interventions: Sheep were randomiz ed to volume-controlled MV (control group) (n = 6) with VT of s to 12 mL/kg, PEEP of 5 to 10 cm H2O, or to ITPV (n = 6) at PEEP of 3 to 5 cm H2O, VT of 2.5 to 4 mL/kg, PIP of <20 cm H2O, at RRs sufficient to su stain normocapnia. Measurements ana results: Hemodynamic status in the ITPV group progressively improved, and all six sheep were weaned to r oom air within 83 +/- 54 h. Sheep in the control group had progressive ly deteriorating conditions and all animals died after a mean of 50 +/ - 39 h. Barotrauna and postmortem histopathologic changes were more pr onounced in the control group.Conclusion: In this model of ventilator- induced lung injury, low PEEP-low VT ventilation with ITPV sustained n ormocapnia and prevented further lung injury, allowing weaning to room air ventilation.