title: Clinical impact of leak compensation during non-invasive ventilation.
abstract: BACKGROUND
  This study aimed to assess the impact of leak compensation capabilities during pressure- and volume-limited non-invasive positive-pressure ventilation (NPPV) in COPD patients.
  
  
  METHODS
  Fourteen patients with stable hypercapnic COPD who were receiving long-term NPPV were included in the study. For both modes of NPPV, a full face mask and an artificial leak in the ventilatory circuit were used at three different settings, and applied during daytime NPPV, either without leakage (setting I), with leakage during inspiration only (setting II), and with leakage during inspiration and expiration (setting III). Ventilation pattern was pneumotachy-graphically recorded.
  
  
  RESULTS
  NPPV was feasible with negligible leak volumes, indicating optimal mask fitting during the daytime (setting I). In the presence of leakage (settings II and III), the attempt to compensate for leak was only evident during pressure-limited NPPV, since inspiratory volumes delivered by the ventilator increased from 726+/-129 (setting I) to 1104+/-164 (setting II), and to 1257+/-166 (setting III) ml during pressure-limited NPPV, respectively (all p<0.001); however, they remained stable during volume-limited NPPV. Leak compensation resulted in a decrease in leakage-induced dyspnea. However, 83%/87% (setting II/III) of the additionally-delivered inspiratory volume during pressure-limited NPPV was also lost via leakage. Expiratory volume was higher in setting II compared to setting III (both p<0.001), indicating the presence of significant expiratory leakage.
  
  
  CONCLUSIONS
  The attempt at leak compensation largely feeds the leakage itself and only results in a marginal increase of tidal volume. However, pressure-limited--but not volume-limited--NPPV results in a clinically-important leak compensation in vivo.
  
  
  BACKGROUND
  www.uniklinik-freiburg.de/zks/live/uklregister/Oeffentlich.html Identifier: UKF001272.
authors.affiliation: Department of Pneumology, University Hospital Freiburg, Killianstrasse 5, D-79106 Freiburg, Germany.
authors.forename: Jan Hendrik
authors.initials: JH
authors.lastname: Storre
authors.forename: Philipp
authors.initials: P
authors.lastname: Bohm
authors.forename: Michael
authors.initials: M
authors.lastname: Dreher
authors.forename: Wolfram
authors.initials: W
authors.lastname: Windisch
mesh_terms: D000368:Aged; D004417:Dyspnea / Q000503:physiopathology / Q000517:prevention & control*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology / Q000517:prevention & control*; D008297:Male; D008397:Masks / Q000009:adverse effects* / Q000592:standards; D011175:Positive-Pressure Respiration / Q000009:adverse effects* / Q000379:methods / Q000592:standards; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology / Q000628:therapy*; D013990:Tidal Volume / Q000502:physiology