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Intensive Care Med. 2001 Dec;27(12):1887-91. Epub 2001 Nov 10.

Mask mechanics and leak dynamics during noninvasive pressure support ventilation: a bench study.

Author information

1
Experimental Laboratory of Mechanical Ventilation, Respiratory ICU, Pulmonary Division, Hospital das Clínicas and Heart Institute, University of São Paulo Medical School, São Paulo, Brazil.

Abstract

OBJECTIVE:

To study the mask mechanics and air leak dynamics during noninvasive pressure support ventilation.

SETTING:

Laboratory of a university hospital.

DESIGN:

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.

MEASUREMENTS:

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.

CONCLUSION:

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.

PMID:
11797024
DOI:
10.1007/s00134-001-1146-9
[Indexed for MEDLINE]
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