PURPOSE:Non-invasive ventilation has been shown to improve clinical outcome in acute and chronic hypercapnic respiratory failure. Pressure ulcers of the facial skin (figure 1 A) due to prolonged application of facial masks are reported to be a major limitation to this form of therapy. We measured contact pressure and contact area of original and modified air-cushion masks in order to develop a model to predict contact pressure formation.
METHODS:We measured full face masks with original and narrowed air cushion and recorded cushion pressure (CD223, Validyne, Northridge, CA, USA, figure 1 B) at inspiratory pressures (IPAP) of 10, 15, 20, 25 and 30 cmH2O while expiratory pressure (EPAP) was kept at 5 cmH2O. We determined cushion contact area by planimetric measurements (Haff 315b, Pfronten, Germany) of colour imprints (figure 1 C).
RESULTS:Contact pressures during the inspiratory phase are just above inspiratory pressure independent of cushion size.Contact pressures increased during the EPAP phase of ventilation. The mask with narrowed cushion developed higher contact pressures. The equation: contact area IPAP x contact pressure IPAP + (IPAP-EPAP) x mask body area = contact area EPAP x contact pressure EPAP showed excellent correlation between calculated and measured data (R-square 1.0, figure 1 D).
CONCLUSION:Mask contact pressures are determined by IPAP pressures during the inspiratory phase and additionally by contact area, mask-body area and pressure difference between IPAP and EPAP during the expiratory phase.
CLINICAL IMPLICATIONS:Having this knowledge, physicians might adjust ventilators and medical equipment manufactures might design their mask accordingly to prevent skin breakdown during non-invasive ventilation.
DISCLOSURE:Dominic Dellweg, No Financial Disclosure Information; No Product/Research Disclosure Information