Mask mechanics and leak dynamics during noninvasive pressure support ventilation: a bench study.
OBJECTIVE
To study the mask mechanics and air leak dynamics during noninvasive pressure support ventilation.


METHODS
Laboratory of a university hospital.


METHODS
A facial mask was connected to a mannequin head that was part of a mechanical respiratory system model. The mask fit pressure (P(mask-fit)) measured inside the mask's pneumatic cushion was adjusted to 25 cmH(2)O using elastic straps. Pressure support (PS) was set to ensure a maximal tidal volume distal to the mask (VT(distal)) but avoiding failure to cycle to exhalation.


METHODS
Airway pressure (P(aw)), P(mask-fit), mask occlusion pressure (P(mask-occl)=P(mask-fit)-P(aw)), VT proximal (VT(prox)), distal to the mask (VT(distal)), air leak volume ( Leak=VT(prox)-VT(distal)), and inspiratory air leak flow rate (difference between inspiratory flow proximal and distal to the mask) were recorded.


RESULTS
PS 15 cmH(2)O was the highest level that could be used without failure to cycle to exhalation (VT(distal) of 585+/-4 ml, leak of 32+/-1 ml or 5.2+/-0.2% of VT(prox), and a minimum P(mask-occl) of 1.7+/-0.1 cmH(2)O). During PS 16 cmH(2)O the P(mask-occl) dropped to 1.1+/-0.1 cmH(2)O, and at this point all flow delivered by the ventilator leaked around the mask, preventing the inspiratory flow delivered by the ventilator from reaching the expiratory trigger threshold.


CONCLUSIONS
P(mask-fit) and P(mask-occl) can be easily measured in pneumatic cushioned masks and the data obtained may be useful to guide mask fit and inspiratory pressure set during noninvasive positive pressure ventilation.
Schettino
G P
GP
Experimental Laboratory of Mechanical Ventilation, Respiratory ICU, Pulmonary Division, Hospital das Clínicas and Heart Institute, University of São Paulo Medical School, São Paulo, Brazil.
Tucci
M R
MR
Sousa
R
R
Valente Barbas
C S
CS
Passos Amato
M B
MB
Carvalho
C R
CR
D019544:Equipment Failure Analysis; D006801:Humans; D008348:Manikins; D008397:Masks; D011175:Positive-Pressure Respiration / Q000295:instrumentation*; D015656:Respiratory Mechanics