Determinants of skin contact pressure formation during non-invasive ventilation

doi:10.1016/j.jbiomech.2009.10.029

Journal of Biomechanics

Volume 43, Issue 4, 3 March 2010, Pages 652-657

https://doi.org/10.1016/j.jbiomech.2009.10.029 Get rights and content

Abstract

There is no published data about mask features that impact skin contact pressure during mask ventilation.

To investigate the physical factors of skin contact pressure formation.

We measured masks with original and reduced air cushion size and recorded contact pressure. We determined cushion contact and mask areas by planimetric measurements.

Contact pressures necessary to prevent air leakage during inspiration exceed inspiratory pressure by 1.01±0.41 hPa independent of cushion size.

Contact area, ventilator pressure and mask area during inspiration and expiration impact contact pressure. Mask contact pressures are higher during expiration. The contact pressure increases with increase in inspiratory pressures independent of the ventilator cycle. During expiration, the contact pressure will increase in proportion to the expiratory pressure reduction of the ventilator. The mask with reduced air cushion size developed higher contact pressures.

Contact pressure can be reduced by selecting masks with a small mask area in combination with a large mask cushion.

Introduction

Non-invasive ventilation (NIV) has become the standard treatment for many diseases (1, 2, 3, 4, 5, 6, 7, 8, 9, 10). NIV is frequently used for a substantial amount of time and sometimes in conjunction with low levels of sedation (Devlin et al., 2007). Skin ulcer formation ,as shown in Fig. 1, is a well-known problem and is frequently the limiting factor for NIV in critically ill patients. A broad variety of mask interfaces are commercially available and the correct mask choice is critical for effectiveness (12, 13), patient compliance and to avoid the development of complications (14, 15, 16, 17). The development of pressure-induced skin ulcers is one of the major complications during NIV (18, 19, 20). The main contributing factor appears to be the pressure applied to the skin (Thompson, 2005). The only previous study that measured contact pressures during NIV (Schettino et al., 2001) found out that the contact pressure during inspiration has to be slightly (+2 hPa) above inspiratory pressure to prevent leakage and that contact pressure rises during the expiratory phase of the ventilator cycle. No data are available regarding technical variables that determine the contact pressure of mask interfaces. We developed a bench model to elaborate the factors of impact.

Our hypothesis was that contact area of the cushion, mask area as well as inspiratory and expiratory pressures determine skin contact pressure formation.

Section snippets

Method

The nomenclature and illustration of variables are shown in Fig. 2.

Ideally we needed a bench model that could continuously measure contact pressure, contact area, mask area, leak flow and ventilator pressure under real-time conditions.

Dynamic measurements of contact area, however, are technically not feasible.

We approached this problem by conducting static measurements and creating characteristic pressure–area curves for our masks. To make these curves applicable to a bench model the following

Results

When we carefully adjusted the lead ball load until leak flow ceased during our CPAP trials we found that the contact pressure slightly exceeded the CPAP pressure. The average difference was 1.01±0.41 hPa. Contact pressures needed to achieve air tightness were independent of cushion size (p=0.5, Fig. 6).

Contact pressures were higher during expiration, Fig. 7 show a screenshot of online monitor tracings demonstrating the increased contact pressure when the ventilator shifts to expiration.

The

Discussion

Inspiratory pressure, expiratory pressure, as well as contact and mask areas at inspiratory and expiratory pressure levels impact skin contact pressure and are closely linked as shown by the following equation: $(P_{CI} \times A_{CI} + P_{I} \times A_{MI} = P_{CE} \times A_{CE} + P_{E} \times A_{ME}) .$

During inspiration, absolute contact pressures are independent of mask design and are just (+1 hPa) above inspiratory pressure. Our results are in line with previous data suggesting a minimal pressure difference of 2 hPa to prevent air leaks (Schettino et

Conclusion

Considering the relationships we described, one can reduce the skin ulcer risk by selecting masks with a small mask area in combination with a large mask cushion.

The contact pressure increases with increase in inspiratory pressures independent of the ventilator cycle. During expiration the contact pressure is higher with lower expiratory pressures. Additional shear forces might aggravate skin ulcer formation.

Conflict of interest statement

None of the authors has a personal or financial conflict of interest

Acknowledgment

The authors like to thank Professor Michael Polkey (Royal Brompton Hospital, London, UK) for his cooperation and advice.

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Determinants of skin contact pressure formation during non-invasive ventilation

Abstract

Introduction

Section snippets

Method

Results

Discussion

Conclusion

Conflict of interest statement

Acknowledgment

Chest

Chest

Arch. Phys. Med. Rehabilitation

Pressure ulcers among the elderly

N Engl. J. Med.

A multiple-center survey on the use in clinical practice of noninvasive ventilation as a first-line intervention for acute respiratory distress syndrome

Crit. Care Med.

Noninvasive ventilation for acute exacerbations of chronic obstructive pulmonary disease

N Engl. J. Med.

Clinical indications for noninvasive positive pressure ventilation in chronic respiratory failure due to restrictive lung disease, COPD, and nocturnal hypoventilation

Chest

Cephalic versus oronasal mask for noninvasive ventilation in acute hypercapnic respiratory failure

Intensive Care Med.

Short-term effect of controlled instead of assisted noninvasive ventilation in chronic respiratory failure due to chronic obstructive pulmonary disease

Respir. Care

Survey of sedation practices during noninvasive positive-pressure ventilation to treat acute respiratory failure

Crit. Care Med.

The interface: crucial for successful noninvasive ventilation

Eur. Respir. J.

Compliance with CPAP therapy in patients with the sleep apnoea/hypopnoea syndrome

Thorax

Early noninvasive ventilation averts extubation failure in patients at risk: a randomized trial

Am. J. Respir. Crit. Care Med.

Physiological effects of different interfaces during noninvasive ventilation for acute respiratory failure

Crit. Care Med.