The effect of lung-recruiting ventilatory strategies in acutely injured atelectasis-prone rabbits
Introduction: Ventilation strategies play an important role in the development of lung injury. Strategies that permit alveolar de-recruitment and cyclic overdistension, such as conventional mechanical ventilation with low PEEP (CMV-LP) can induce progressive injury. Conversely, strategies that promote lung recruitment, such as high frequency oscillatory ventilation (HFOV), are associated with better short term outcomes. We hypothesized that HFOV and CMV with high PEEP (CMV-HP) would be associated with a more favorable outcome in comparison to a CMV-LP strategy. Methods: Thirty-six New Zealand White rabbits were anesthetized and instrumented with a tracheostomy and vascular catheters, and ventilated with a FiO2 of 1.0. Lung injury was induced by repeated saline lavage. Following injury (PaO2<100torr), all animals underwent HFOV (Paw: 16cmH2O, IT: 33%) interposed with periods of dynamic sustained inflation (Paw: 30cmH2O) for 15 sec, until PaO2>300 torr. The animals were then randomized to 1) continue HFOV (n=11), 2) CMV-HP (n=9, TV: 10ml/kg, PEEP: 10 cm/H2O) or 3) CMV-LP (n=8, TV: 10ml/kg, PEEP: 2cm/H2O). A group of uninjured animals (n=8) ventilated with a PEEP of 5 cm/H2O served as controls. The animals were ventilated for 4 hours prior to sacrifice. Results: Values are means plusmn; SD. The mean airway pressure 2 (MAP) for the HFOV, CMV-HP, CMV-LP and control groups was 15.6±0.5, 16±0.7, 13.2±2 and 8.6±0.8 cmH2O, respectively. *p<0.05 vs baseline. †p<0.05 vs HFOV, ‡p<0.05 vs CMV-HP (Anova) Conclusions: Strategies that promote lung recruitment, such as HFOV and CMV-HP, result in superior oxygenation in comparison to CMV-LP. Despite similar MAPs, the HFOV group exhibits higher PaO2 in comparison to CMV-HP. The CMV-HP group develops progressive alveolar de-recruitment over the course of the experiment.
Rotta, AT; Chilungu, M; Gunnarsson, B; Steinhorn, DM
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