Relationship between intra-thoracic pressure, lung volume and high-frequency jet ventilation in lungs predisposed to gas trapping: an animal study

High-frequency jet ventilation (HFJV) is used to manage severe respiratory failure in neonates, especially to manage gas trapping. To our knowledge, the role of HFJV rate on lung volume states and intra-tracheal and thoracic pressures has not been described. The aim of our study was to determine the impact of HFJV rate (HFJV rate ) on (1) total and regional end-expiratory lung volume (EELV) and (2) intra-thoracic pressure, specifically intra-tracheal pressure ( P trach ) and oesophageal pressure ( P oes ) in adult New Zealand white rabbits ( n = 5) prone to gas trapping. After stabilisation on HFJV (Bunnell LifePulse Ventilator; mean (SD) PEEP and HFJV PIP were 5.6 (1.3) cmH 2 O and 21 (2.6) cmH 2 O), HFJV rate between 150 and 900 bpm were randomly applied and regional EELV (electrical impedance tomography), P trach and P oes measured with gas exchange parameters. The non-gravity-dependent hemithorax demonstrated greater relative EELV with increasing HFJV rate , suggesting overdistension at higher rates. Δ P trach increased linearly from HFJV rate 150 to 900 bpm and conversely Δ P oes was more variable, decreased with increasing HFJV rate . There was a U-shaped relationship between HFJV rate and PaCO 2 with best CO 2 clearance occurring at HFJV rate 320–400 bpm. Impact In an animal model susceptible to gas trapping, high-frequency jet ventilation rate influenced volume state with increased carbon dioxide at low and high rates. This is the first study to define the mechanisms by which expiratory time during high-frequency jet ventilation alone can cause and relieve overdistension and atelectasis. Electrical impedance tomography was able to identify optimal lung volume, which may be useful in titrating the best high-frequency jet ventilation rate between 240 and 400 bpm for carbon dioxide clearance.