End-expiratory lung volume and ventilation distribution with different continuous positive airway pressure systems in volunteers.
BACKGROUND
Continuous positive airway pressure (CPAP) has been shown to improve oxygenation and a number of different CPAP systems are available. The aim of this study was to assess lung volume and ventilation distribution using three different CPAP techniques.


METHODS
A high-flow CPAP system (HF-CPAP), an ejector-driven system (E-CPAP) and CPAP using a Servo 300 ventilator (V-CPAP) were randomly applied at 0, 5 and 10 cmH₂O in 14 volunteers. End-expiratory lung volume (EELV) was measured by N₂ dilution at baseline; changes in EELV and tidal volume distribution were assessed by electric impedance tomography.


RESULTS
Higher end-expiratory and mean airway pressures were found using the E-CPAP vs. the HF-CPAP and the V-CPAP system (P<0.01). EELV increased markedly from baseline, 0 cmH₂O, with increased CPAP levels: 1110±380, 1620±520 and 1130±350 ml for HF-, E- and V-CPAP, respectively, at 10 cmH₂O. A larger fraction of the increase in EELV occurred for all systems in ventral compared with dorsal regions (P<0.01). In contrast, tidal ventilation was increasingly directed toward dorsal regions with increasing CPAP levels (P<0.01). The increase in EELV as well as the tidal volume redistribution were more pronounced with the E-CPAP system as compared with both the HF-CPAP and the V-CPAP systems (P<0.05) at 10 cmH₂O.


CONCLUSIONS
EELV increased more in ventral regions with increasing CPAP levels, independent of systems, leading to a redistribution of tidal ventilation toward dorsal regions. Different CPAP systems resulted in different airway pressure profiles, which may result in different lung volume expansion and tidal volume distribution.
Department of Anesthesiology and Intensive Care Medicine, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Sweden. bertil.andersson@vgregion.se
B
B
Andersson
S
S
Lundin
S
S
Lindgren
O
O
Stenqvist
H
H
Odenstedt Hergès
D000328:Adult; D000399:Air Pressure; D045422:Continuous Positive Airway Pressure / Q000295:instrumentation*; D017097:Electric Impedance; D005105:Expiratory Reserve Volume / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009584:Nitrogen; D015656:Respiratory Mechanics / Q000502:physiology*; D016683:Supine Position / Q000502:physiology; D013990:Tidal Volume
D009584:Nitrogen