Aerosolised fluorescein can quantify FFP mask faceseal leakage: a cost-effective adaptation to the existing point of care fit-test.

Abstract

Background Filtering facepiece (FFP) respirators must provide an adequate faceseal to protect healthcare workers from harmful particles. A qualitative fit-test using bitter-tasting aerosols the commonest way to determine if an FFP mask is safe enough for clinical use. This taste-test is subjective and can be biased by placebo. We propose a cheap and quantitative modification of the taste-test, by measuring the amount of fluorescein staining filter paper behind the FFP mask after a fit-test protocol, using digital image analysis. Methods Medical grade fluorescein was added to bitter-tasting denatonium benzoate solution and Aerosolised during a mask fit-testing protocol. Scientific filter paper was placed on the inner surface of the mask. Participants were asked if they could taste the solution to determine their qualitative ‘pass’ or ‘fail’ result. Filter paper photographs were analysed after the test to quantify total fluorescence (TF). TF levels in the taste-test ‘pass’ and ‘fail’ groups were compared.Results Fifty-six healthcare professionals completed the fluorescein mask fit-test protocol. 32 (57%) ‘passed’ the qualitative (taste) test and the remainder ‘failed’. There was a significant difference in TF between the groups based on their qualitative results (p <0.001). A cut-off of TF = 5.0 x 106 fluorescence units was determined by analysing the precision (78%) and recall (84%) of the fluorescein test. Applying this cut-off resulted in 5 out of 56 participants (9%) being reclassified from ‘pass’ to ‘fail’ by the fluorescein test. 7 out of 56 (12%) participants were reclassified from ‘fail’ to ‘pass’.Conclusions Fluorescein is detectable and sensitive to identify faceseal leaks in FFP masks. The fluorescein fit-test is discriminating in its ability to divide people into ‘pass’ and ‘fail’ groups similarly to the taste-test. The adaptations are low-cost and could be incorporated in the point-of-care setting. After further validation the fluorescein test could increase safety for staff by reducing the number of false ‘pass’ by the taste-test. It could also reassure people who have ‘failed’ the taste-test that they have low levels of fluorescein leak, enabling them to return to clinical practice safely.

New wine in old skins

“…Adam Truelove to publish thought-leads on these topics -optimising personal protective equipment, emerging viral mutations and healthcare worker safety. [9][10][11][12] One of the consequences of the epidemic has been to make many doctors think of their work as a potential source of illness, both acutely and in the potential to contribute to burnout. A review by occupational medicine colleagues is a superb introduction to taking a focused work history.…”