Objective: To assess the value of monitoring abdominal and rib cage tidal displacement as an indicator of optimal mean airway pressure (Paw) during high-frequency oscillatory ventilation (HFOV).
Design and setting: Prospective observational study in a university research laboratory.
Animals: Eight piglets weighing 12.0+/-0.5 kg, surfactant depleted by lung lavage.
Interventions: Compliance of the respiratory system (C(rs)) was calculated from a quasistatic pressure volume loop. After initiation of HFOV lung volume was recruited by increasing Paw to 40 cmH(2)O. Then mean Paw was decreased in steps until PaO(2)/FIO(2) was below 100 mmHg. Proximal pressure amplitude remained constant.
Measurements and results: Abdominal and rib cage tidal displacement was determined using respiratory inductive plethysmography. During HFOV there was maximum in tidal volume (Vt) in seven of eight piglets. At maximal mean Paw abdominal and rib cage displacement were in phase. Phase difference between abdominal and rib cage displacement increased to a maximum of 178+/-28 degrees at minimum mean Paw. A minimum in abdominal displacement and a maximum of Vt was found near the optimal mean Paw, defined as the lowest mean Paw where shunt fraction is below 0.1.
Conclusions: During HFOV abdominal and rib cage displacement displayed mean Paw dependent asynchrony. Maximal Vt and minimal abdominal displacement coincided with optimal C(rs), oxygenation, and ventilation, suggesting potential clinical relevance of monitoring Vt and abdominal displacement during HFOV.