New indicators for optimal lung recruitment during high frequency oscillator ventilation

Abstract

Previous research has demonstrated the potential benefit derived from the combination of high frequency oscillatory ventilation and volume guarantee mode (HFOV‐VG), a procedure that allows us to explore and control very low tidal volumes. We hypothesized that secondary spontaneous change in oscillation pressure amplitude (∆Phf), while increasing the mean airway pressure (MAP) using HFOV‐VG can target the lung recruitment. Methods A two‐step animal distress model study was designed; in the first‐step (ex vivo model), the animal's lungs were isolated to visually check lung recruitment and, in the second one (in vivo model), they were checked through arterial oxygen partial pressure improvement. Baseline measurements were performed, ventilation was set for 10 min and followed by bronchoalveolar lavage with isotonic saline to induce depletion of surfactant and thereby achieve a low compliance lung model. The high‐frequency tidal volume and frequency remained constant and the MAP was increased by 2 cmH2O (ex vivo) and 3 cmH2O steps (in vivo) every 2 min. Changes in ΔPhf to achieve the fixed volume were recorded at the end of each interval to describe the maximum drop point as the recruitment point. Results Fourteen Wistar Han rats were included, seven on each sub‐study described. After gradual MAP increments, a progressive decrease in ΔPhf related to recruited lung regions was visually demonstrated. In the in vivo model we detected a significant comparative decrease of ΔPhf, when measured against the previous value, after reaching a MAP of 11 cmH2O up to 17 cmH2O, correlating with a significant improvement in oxygenation. Conclusion The changes in ∆Phf, linked to a progressive increase in MAP during HFOV‐VG, might identify optimal lung recruitment and could potentially be used as an additional lung recruitment marker.

Lung recruitment in neonatal high‐frequency oscillatory ventilation with volume‐guarantee

“…29,33 To date, the possible role of pressure amplitude in recruitment maneuvers has been shown mostly in animal models, with only the small study by Tana et al 27 suggesting changes in ΔPhf followed by recruitment and surfactant administration. Our results show that in clinical practice it is feasible to guide these maneuvers by ΔPhf changes, which would put this parameter in an interesting position 17 to avoid transitional hyperoxygenation and overdistention in these situations as oxygen saturation changes might not reflect blood PaO 2 immediately and do not only depend on recruitment. 15 This will need, however, further studies to confirm our findings and establish the exact role of ΔPhf in recruitment.…”

“…In HFOV and with the addition of VG, ΔPhf is automatically adjusted in real time to deliver stable tidal volumes. In previous animal models, it has been proved that this makes ΔPhf a reliable marker in lung recruitment, 17 since it will gradually decrease when compliance is better and lower pressure differences are needed to obtain the same tidal volumes. This can be very useful because oxygenation saturation changes, which have been classically used to guide recruitment maneuvers, can take time after optimal pressure | 3005 has been reached 13 and might be dependent on other factors rather than recruitment status.…”

“…As lung mechanics, atelectasis, or overdistension can influence tidal volumes, delta pressure also changes with variations in the lung volume. Due to this, VG protects the lung from overventilation during recruitment, and ΔPhf can reliably identify lung recruitment earlier than oxygenation changes in animal models 17 . To date, however, there are no published studies describing the association between ΔPhf and lung recruitment in clinical settings.…”