This research was divided into two stages. Stage 1 involved developing and validating a new fit-test method called the PRST. In Stage 2, PRST was evaluated in use during nursing activities in clinical settings.
The experiment was set up in an enclosed environment with an average air speed of 0.1775 m/s, using a low velocity flow analyser type 54N50, Dantec Type 54R10 (Dantec Dynamics, Skovlunde, Denmark) with a low velocity transducer, at a temperature of 20 °C and relative humidity 77% (HoBo data logger). The aerosol was measured by two real-time portable aerosol spectrometers, namely the PAS 1.109 (Grimm Technologies, Inc., Dorfstrasse, Germany). The PAS 1.109 measures particulates in the size range of 0.25–32 μm in 31 size channels. Stainless steel tubes (4mmOD × 3mmID) provided by the manufacturer were used as the inlets for the PASs. A particle generator Model 8026 (TSI Incorporated, Shoreview, MN, USA) was used to spray a suspension of polydisperse into a box chamber placed in one end of the chamber, and it was then mixed with a fan. The reservoir jar of particle generator was filled with clean tap water with one salt tablet added. The output adjustment screw was set to maximize the aerosol flow. The flow rate inside the box was maintained at 0.17 m/s, and was measured by a flow analyser (TSI Incorporated). Particles were measured in the chamber in real time with two PAS 1.109 instruments. PAS 1.109 was set to report size distribution every minute. The instruments were used to measure the aerosol particles in the chamber three times: at 5 min, 15 min and 30 min, to estimate measurement precision.
A method for evaluating the protection afforded by a respirator, similar to Lee et al. and named PRST, was set up (Fig. 1). The set-up consisted of five components: (i) sampling probe (Adaptor Kit 8025-N95, TSI Inc., St Paul, MN, USA); (ii) two Portable Aerosol Spectrometers 1.109 (Grimm Technologies, Inc.) for 31 size channels; (iii) 60 cm cylindrical plastic tubes; (iv) N95 respirators (Model 1860, 1860s, 1862, 3M); and (v) one backpack. Our equipment and test differed from Lee et al.'s study in three aspects. First, the cylindrical plastic tube was directly attached (with adhesive) to leak locations on the respirator rather than to the helmet. When attached to the helmet, the plastic tube hindered performance of nursing activities. Second, we used different leak locations. In this study, potential leakage was measured on the right and left sides of the bridge of the nose and at the chin (Fig. 1), instead of at the nose, left cheek and chin. Myers et al.'s study showed that 85% of leakage occurs at the nose, 20% leakage at the chin and 19% leakage at the cheek. Studies have showed that in using respirators, there is a higher chance of air leakage around the nose. Therefore, in this study, both sides of the nose were monitored. Third, we tracked particles 0.3 μm in size because they are the most penetrating. Because of these three characteristics of our study, we believed that PRST would be able to evaluate the fitness of the N95 respirator more meaningfully than previous methods.
Figure 1. Schematic representation of the PRST. , sites testing for leakage; , portable Aerosol Spectrometer (PAS006, PAS007). PRST, Personal Respiratory Sampling Test.
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Two Portable Aerosol Spectrometers 1.109 (Grimm Technologies, Inc.) were used for continuous measurement of the size distribution of various aerosol particles. These two spectrometers were put into the backpack. A sampling probe (Adaptor Kit 8025-N95, TSI Inc.) punctured the respirator and was secured with a push nut on from the other side of the respirator. One 60 cm-long cylindrical plastic tube was used to connect the exposed end of the sampling probe to the spectrometer for measuring size distribution of aerosol particles in the respirator, and one 60 cm-long cylindrical plastic tube was anchored to the outer surface of the respirator near the nose region to measure ambient concentration.
The pilot study provided a set of data for statistical analysis from which the sample size required for the main study could be estimated, that is, four in each group when the effect size was 0.86, with an achieved power of 62% and alpha was 0.05. Sample size for the main study was then obtained from the power table. The minimum required sample size was 18 in each group when the effect size was 0.40 and power was 80%.
Participants were recruited through convenience sampling. We put a poster to recruit participants in a local university. Participants were students 18 years of age or older, and all were Year 1 nursing students. To minimize the confounding effects resulting from prior clinical experience and training in how to wear an N95 respirator, the exclusion criteria were that a participant had learned how to perform fit test and fit check (a self-check the wearer performance to detect air leaks of the respirator when donning a respirator every time) before. Their lack of experience was important because experience can have a significant impact on fit-test results. Participants who were pregnant, or who had been diagnosed with respiratory problem or back injury, were excluded. The purposes and procedures of the study were explained to all participants. Written consent was obtained from each participant before the researcher recorded any personal information. The ethics was approved by the Human Subjects Ethics Sub-committee of the Hong Kong Polytechnic University.
Eighty-four eligible participants ranging in age from 18 to 21 years old were recruited for the study. They were divided randomly into four groups (Groups A to D), each group with 21 participants. Both Groups A and B participants received training on how to perform fit check. Whereas Group A participants performed the Portacount fit test, Group B participants did not.
Participants in Groups C and D did not receive training on how to perform fit check; therefore, they were not required to perform the fit-check demonstration. Whereas Group C participants were asked to perform the Portacount fit test, Group D participants did not. Researcher assessed all their performance in doing their fit checks by using a fit-check checklist developed by the researcher, based on the CDC guidelines. Participants in Groups A and C were told about the recommended type of N95 respirators after performing the fit test (Fig. 2).
In Session 1, participants were required to perform the quantitative fit test conducted with a Portacount Plus machine. In Session 2, participants performed fit testing by the PRST in performing bedside nursing procedures in a nursing laboratory. The laboratory test simulated the physical work that workers experience in clinical settings. The PRST was measured by two portable aerosol spectrometers at the same time; one (PAS1.109-007) measured the ambient air particle concentration outside the respirator, whereas the other (PAS1.109-006) measured the air particle concentration inside the respirator. The tests were conducted while the participants were wearing N95 respirators in doing bedside nursing procedures. Nursing procedures were suction, napkin changing (moving exercise) and normal breathing (non-moving exercise). The measurements were conducted continuously for 15 min, with particle concentration measurements averaged over 1 min.
Participants were required to close their mouths and breathe through their noses during the experiment to minimize water vapour generated from their mouth entering the sampling system. This prevented the mixing of particles that have leaked in around the face-seal of the facepiece with those that have been generated by the wearers. The plastic tubing was changed after each participant to prevent water content generated by the participant's exhalation from entering the instrument. Upon completion, participants, still wearing their N95 respirators, were asked to breathe normally.