Inadequate lung volume recruitment after sustained lung inflation in high frequency oscillatory ventilation: Pathophysiology and inflammation in an animal RDS model

Objective: We hypothesized that a single sustained inflation (SI) of the lung as a volume recruitment maneuver during high frequency oscillatory ventilation (HFO-SI) would improve pathophysiologic, inflammatory responses when compared to conventional inflation (CI) during both HFO (HFO-CI), volume targeted synchronized intermittent mandatory ventilation (SIMV+V) in spontaneously breathing newborn piglets with surfactant washout.

Design: Prospective, randomized animal study.

Subjects: Thirty-two newborn piglets.

Interventions: Animals underwent saline lavage to produce lung injury, received surfactant and randomized to one of 3 treatment groups. Lung volume recruitment (LVR) protocol followed and ventilation continued for 6 hours.

Measurements and main results: Vital signs and arterial blood gases were continuously monitored. End expiratory lung volume (ΔEELV) changes were estimated during LVR using respiratory impedance plethysmography (RIP). At baseline, post lung injury, 6 hours: serum, bronchoalveolar lavage (BAL) samples for proinflammatory cytokines were collected and static pressure volume (P/V) curves obtained. At 6 hours animals were euthanized and lungs fixed for morphometrics, histopathology. ΔEELV during LVR was greatest using SIMV+V, HFO-CI (p<0.05); HFO-SI required higher P $_{aw}$ for LVR compared to SIMV+V (p< 0.005), while ΔEELV change was lowest. Oxygenation was greatest with SIMV+V. Inflammatory responses, histopathology and morphometrics were similar.

Conclusions: Single SI during HFO is not adequate for LVR. SIMV+V and HFO-CI adequately recruited lung volumes without creating more lung injury.