Mechanical ventilation with high positive end-expiratory pressure and small driving pressure amplitude is as effective as high-frequency oscillatory ventilation to preserve the function of exogenous surfactant in lung-lavaged rats

Abstract

Objective 

To demonstrate that under well-defined conditions, pressure-controlled ventilators (PCV) allow settings that are as good as high-frequency oscillatory ventilators (HFOV) at preserving the function of exogenous surfactant in lung-lavaged rats.

Design 

Experimental, comparative study.

Setting 

Research laboratory of a large university.

Subjects 

Sixteen adult male Sprague-Dawley rats (280–310 g).

Interventions 

Lung injury was induced by repeated lavage. After last lavage, all animals received exogenous surfactant and were then randomly assigned to two groups (n = 8 per group). The first group received PCV with small pressure amplitudes and high positive end-expiratory pressure. The second group received HFOV. In both groups, an opening maneuver was performed by increasing airway pressure to improve Pao₂/Fio₂ to ≥500 torr.

Measurements and Main Results 

Blood gases were measured every 30 mins for 3 hrs. Airway pressures were measured with a tip catheter pressure transducer. At the end of the study period, a pressure-volume curve was recorded and a broncho-alveolar lavage was performed to determine protein content and surfactant composition. The results showed that arterial oxygenation in both groups could be kept >500 torr during the 3-hr study period by using a mean airway pressure of 13 ± 3 cm H₂O in PCV and 13 ± 2 cm H₂O in HFOV. Further, there were no differences in the Gruenwald index, protein influx, or ratio of small to large aggregates between the study groups.

Conclusion 

PCV with sufficient level of positive end-expiratory pressure and small driving pressure amplitudes is as effective as HFOV to maintain optimal gas exchange, to improve lung mechanics, and to prevent protein influx and conversion of large into small aggregates after exogenous surfactant therapy in lung-lavaged rats.