key: cord-280419-odqo3o4w
authors: Gibbons, John P.; Hayes, Joshua; Skerritt, Conor J.; O’Byrne, John M.; Green, Connor J.
title: Custom solution for PPE in the orthopaedic setting: retrofitting Stryker Flyte T5® PPE system
date: 2020-10-26
journal: J Hosp Infect
DOI: 10.1016/j.jhin.2020.10.016
sha: 
doc_id: 280419
cord_uid: odqo3o4w

The COVID-19 pandemic has meant that there is growing pressure on hospital resources not least the availability of appropriate personal protective equipment (PPE), specifically, facemasks and respirator masks. Within the field of orthopaedic surgery, it is a common sight to see orthopaedic surgery carried out in “space suits” (SS) which comprise of a helmet, hood and surgical gown. In this study the authors made modifications to two different SS systems to incorporate high-efficiency particulate air (HEPA) filters to the inlets to the fan to assess their potential as a method of providing a reusable system for PPE for the surgeon with regard to protection from a respiratory droplet spread virus. The testing was carried out using particle counter upstream and downstream on a manikin wearing two different SS systems with and without modifications to the inlet. The results show that using a layer of HEPA filter cut to size, and sealed to the inlet for the fan in the helmet will reduce the downstream particulate at the user’s mouth by over 99.5% which is equivalent to that of a respirator mask. HEPA filter material is relatively cheap and can be used repeatedly making this a viable alternative to disposable, and even re-sterilized, respirator masks in the setting of a respiratory droplet spread viral pandemic.

The emergence of the novel coronavirus COVID-19 as a pandemic affecting most of the world's population has led to concern regarding an international shortage of personal protective equipment (PPE). The World Health Organisation (WHO), in recent guidance with respect to rational use of PPE, stated that: "The current global stockpile of PPE is insufficient, particularly for medical masks and respirators" (1). Current advice from a number of bodies is that the use of FFP2 or N95 respirator masks with eye protection as well as gloves and gowns for specific procedures of which orthopaedic surgery is included (2) (3) (4) . More recently, guidance for all healthcare workers (HCWs) has advised that any person working within 2 metres of any patient who is suspected or confirmed COVID positive, should be using a respirator mask (4) (5) (6) . The use of respirator masks, such as N95 and FFP2 which provide at least 95% and 94% filtration of particles 0.3 μm, is advised based on the best and most broadly available masks to HCWs in terms of filtration of particles and that they offer a seal to the face. It is, however, not without its own limitations, as these masks are not custom made for face-fit to the individual, and require a face-fitting procedure, which has been shown to have limitations (7) .

The mean diameter of the coronavirus has been reported to be 78nm (8) . The filter efficiency of the N95 and FFP2 respirator masks relate to their ability to effectively filter submicron particles and are standardised against uncharged particles of sodium chloride measuring 300nm or airborne Staphylococcus aureus (7, 9) . There are studies that have questioned the validity of using these masks in providing protection against viruses and that the performance of such masks may underestimate the penetration of nanosized virions (7) . High-efficiency particulate air (HEPA) filters are standardised against the same particle size for their certification and are 99.97% efficient in their filtration, a study by NASA showed that HEPA filters are also efficient for particles in the size range of virions at one magnitude less in size, c. 10nm (10) .

The possibility of a global shortage of PPE, including facemasks, has led to bidding wars amongst governments to acquire PPE for the health care workers, the Irish government have stated this in no J o u r n a l P r e -p r o o f uncertain terms (11). We are now very much reliant on external supplies of PPE, it is imperative that we design methods to be more self-reliant should this particular pandemic endure or resurface, and be prepared for future pandemics. There are protocols being developed with regards to the standardization of sterilization of face masks that show acceptable retention of the efficiency of the filtration after 5 cycles (12, 13) . There are limitations with regard to re-sterilization, namely, that the masks may suffer mechanical damage during the process, disposable masks are often not face-fit for the individual and the fit may be damaged by the process. Sterilization of a mask is not performed if there is gross contamination of the mask, which, in the setting of orthopaedic surgery would render most masks not re-usable as there is often gross contamination of the PPE with blood spatter and splash-back from lavage. Orthopaedic surgery generates aerosolised human tissue, including bone and blood, through the use of power tools during procedures. These aerosol generating procedures (AGPs), and the inability to re-sterilise common respirators due to contamination with blood was what prompted the current authors to look at using the existing "space-suits" (SS) used in orthopaedic surgery as an alternative for re-usable masks.

The research question in this paper is if retrofitting a Stryker® helmet with a HEPA filter at the inlet draped in the usual hood and gown would improve the SS to a point of being comparable to a N95 or equivalent mask. This is a proof of concept study using a manikin to isolate the effectiveness of the retrofitted helmet with regard to the ability to filter air coming into the SS.

The experimental set up of this research involved a manikin (head and torso mounted on a stand to measure 180 cm in height) used for CPR training as the subject in all tests. The manikin was cleaned with chlorohexidine scrub prior to the experiment, all orifices other than the mouth and nose on the manikin were sealed with 3M Steri-Drape™. The particle detector was placed at the mouth and sealed with leucoplast sleek tape around the detector and mouth isolating it from the internal tubing J o u r n a l P r e -p r o o f of the manikin as well as taping over the nostrils of the manikin, (see Figure 1 ). The detector tubing was fed out through the bottom of the manikin and sealed with 3M Steri-Drape™.

The testing was performed in the orthopaedic theatre initially but the background particle count was found to be too low to discern a difference at the downstream penetration detector that would be reliable. The testing was then performed in the adjoining anaesthetic room and all doors and exhaust vents were closed but not sealed. An ambient recording was made to ensure that the distribution of background particulate was equal at both points for the detector in relation to the manikin without any donned PPE, which was confirmed.

The PPE systems used in this study were the Stryker Flyte T4® and T5® (14) . Both systems have a grill over the fan inlet which prevents the hood material being sucked into the inlet. The T4 helmet has a grill overlying the fan inlet that is not amenable to removal and replacement without damaging the plastic housing for this system. The grill was cut off and a housing containing a HEPA filter with a rubber gasket seal was mounted over the fan inlet (see Figure 2a ).

The T5 helmet has a similar grill but can be removed and replaced without damage to the housing. Figure 2b illustrates the experimental set up for the modified T5 system. This allowed for a HEPA filter to be placed over the inlet and sealed at the periphery to the helmet and then the grill replaced to prevent the hood being sucked onto the fan (see Figure 3 ). The HEPA filter material was taken from the SoniQ II™ system(15).

The particulate testing was carried out by a certified engineer who commissions ventilation systems for surgical healthcare infrastructure in this jurisdiction. The detection equipment used, Aerotrak®

Handheld Particle Counter Model 9306, (TSI, Minnesota, USA), is industry standard; it generates a 2.83 l/min intake and was set to read 6 channels to enable reading of all particles in the size range J o u r n a l P r e -p r o o f 0.3-10 μm. The testing protocol for each measurement of particulate penetration recorded at the mouth detector involved 4 upstream challenge samples taken for 60 seconds each at either the inlet to the Stryker hood or the same point in space relative to the head for testing without the hood on. 4 samples were taken upstream to ensure that the upstream challenge was consistent and this required that all four readings are within 15% of the mean, which they were for all tests. The downstream detector reading was also taken over 60 seconds and at least three readings were taken for each experimental set up outlined below and ten readings were taken for the configurations using the modified hoods.

The particulate counts were collected and tabulated using Microsoft Excel® and statistical analysis was performed with comparison of test configurations using Student's t-test.

The test configurations were performed using the following set up:

Ambient test -testing of background particulate to ensure similar readings at upstream and downstream with no PPE on the manikin. This test is required to ensure no difference in ambient distribution of particles around the manikin, which was confirmed.

Configuration 1: A Stryker T4® helmet and hood and a standard surgical gown around the neck without the fan running. Configuration 6: A Stryker T5® helmet with the same HEPA filter material cut to fit over the inlet of the T5 fan and sealed with sealant tape to the helmet housing to prevent any filter bypass, (see Figure 3 ) and then draped with hood and standard surgical gown around the neck with the fan running at medium speed.

In order to investigate gas levels within the modified T5 system and the non-modified T5 system with use, the second author, J.H., wore the each of the SS with serial collection of data from a standard anaesthetic machine used in the operating theatre (GE Datix Ohmeda Asyis & GE Carescape B650, Finland). The experiment was carried out in an operating theatre with a functional laminar airflow system. A narrow (1.2mm diameter) PVC CO2 sample tube, connected to a multi-gas analyser (GE Carescape E-CAiO Respiratory Module, Finland) was placed inside the hood at the level of the participants mouth to continuously measure ETCO2 (end tidal carbon dioxide) and ETO2 (end tidal oxygen). This side-stream gas analyser draws 150ml/minute from the user's airway gas, where the CO2 concentration is calculated via absorption of infrared light, according to the Beer-Lambert law, and oxygen concentration is calculated using paramagnetic analysis. No additional mask was worn.

Measures for ETCO2, ETO2 and FiO2 were recorded at 5-minute intervals with both the modified T5 system hood and the non-modified helmet. J o u r n a l P r e -p r o o f system without filter and the two generations of Stryker Flyte system with HEPA filters modifications were performed for total of 10 readings. Table 2 presents the statistical analysis using a Student ttest and the significance of the differences observed. Figure 4 For the Stryker Flyte T5® system, the SS alone provides a similar degree of protection as the previous generation of SS at 10.9% (σ=0.3%), which was not significantly different from the T4 system. Similar to the T4 system above, once the fan was turned on the penetration downstream increased to 20.54% (σ = 3.78%), again this was not statistically significantly different to the T4 system with the fan operating. With the modification of the HEPA filter to the inlet of the T5 helmet as described, the downstream penetration was reduced to 0.46% (σ = 0.24%) which is significantly better than all other test configurations and offers a particulate filtration similar to FFP3 and N99 or other equivalent respirator mask. Figure 5 illustrates the downstream penetration for each experimental set up for each of the 6 channels recorded by the Aerotrak® Particle Counter, showing that there was less than 0.5% penetration at all particle sizes for the modified T5 system. An additional experiment was run with the addition of an impenetrable cover over the hood except for the area over the inlet did not significantly improve the efficiency leading one to conclude that the positive pressure experienced in the SS provides enough pressure to negate any possible infiltration of particulate though the hood material not directly over the fan inlet.

The results of the gas measurement testing are outlined in Table 3 and illustrated in Figures 6-8. ETCO2 remained steady state throughout the recording. The level of ETCO2 was higher in the modified T5 system compared to the non-modified T5 system (see Figure 6 ). FiO2 appeared to be slightly lower under the modified T5 system compared to the non-modified T5 system. FiCO2, the inspired concentration of carbon dioxide, is normally 0. It was observed that the use of both systems results in an increase in FiCO2 (see Figure 7) . The normal FiO2 level is 21% and the readings demonstrated that there is a reduction in FiO2 with both modified and non-modified SS use (see Figure 8 ). The user did report mild discomfort when wearing the modified hoods however this was rated equivalent to wearing a regular FFP3 mask.

The results of this study show that the SS operating without a fan offer close to 90% reduction in downstream penetration of particles, however, once the fan is turned on the downstream penetration increases to 20-25% for the T4 and T5 systems respectively. When the modifications using HEPA filter at the inlet to the fans described in this study are implemented there is a significant reduction in downstream penetration, specifically, for the T5 system the downstream percentage penetration is less than 0.5% which is comparable with that offered by respirator masks. The HEPA filters have a significantly greater life-span compared with respirator masks even with the potential re-sterilization of masks (12, 13) . This is a pilot study of the potential modification of SS with HEPA filters and would require further testing to confirm a recommended life-span for operating, establishing timing of regular quality assurance checks on the efficacy of the filters, and possible further modification of the inlet to protect the HEPA filter material (16, 17) .

Derrick et al previously looked at the feasibility of the SS with regards to their use as a method of PPE (18) . They had concluded that the Stryker T4® suit alone was insufficient to protect the HCW in J o u r n a l P r e -p r o o f relation to submicron particles (18) which is confirmed in the results of this study for non-modified SS. Their comparative was using volunteers using either a Stryker T4® SS to that of a combination of a N100 filtering facepiece respirator combined with a surgical facemask and a full-face shield. In their methodology the detector was placed in the breathing zone for the SS, 1 cm below the bottom edge of the transparent face piece whilst for the facepiece respirator the probe was passed through both the respirator and covering surgical mask 1 cm to the right of the valve. There are a number of confounders to the results observed that could result from such in vivo testing, being:

1. The detector in the surgical mask is not necessarily replicating the possible true particles entering the mouth allowing for possible entrainment of surrounding air if there is even the slightest breach in the face-fit (7); 2. Similarly, the detector for the SS was placed in the breathing area, not at the mouth, and their study design would not account for the possibility of particles from the subject's hair or skin counting towards the readings given that the SS offers a positive pressure environment from the top of the hood downwards.

Currently, for most jurisdictions, the recommendation is for the use of respirator facemasks when dealing with suspected or confirmed cases of SARS-CoV-2(4). A respirator mask is reliant on the adequacy of the face-fit, however, studies have shown that the adequacy of a face-fit even in controlled environments is variable and can depend on the respiratory rate of the user as well as the position of the user(7). There is previous work with regard to SS in relation to the effect of the positive pressure exerted within the suit; and the pressure that this can exert all the way down to any breach including the glove sleeve interface (19, 20) . Although these tests were carried out on a static manikin, the air provided to the user is that of a highly filtered positive pressure source with less than 0.5% particle penetration which is not reliant on a face-fit, rather, the mechanical seal that is then protected by the plastic housing in the helmet that remains static.

The reason that a manikin is used in this study is to assess the efficiency of the SS as a form of PPE using the detection methods for downstream penetration of the ambient environment. A manikin reduces the shedding of the millions of particles that would occur from forced air being pushed over the users head/hair/face, as well as the particles breathed out by a living person, hence changing the microenvironment within the SS, that would not be accounted for upstream and therefore give a systematic bias that could influence the findings that would pull into question the efficiency of the filtration system between the outside environment and inside the SS. We feel that this is a valid method to assess the modified SS at acting as a form of PPE for the user by reducing the confounding factor of having a person breathing and shedding particles that would inherently change the microenvironment inside the SS downstream of the HEPA filter that is responsible for protecting the user.

Another possible benefit to the use of these modified SS in the orthopaedic setting during this pandemic and in the setting of any possible blood borne viruses is that the SS would provide further reassurance to the operating surgeon who may be cutting bone and creating aerosolised blood and tissue material. Although the possibility of transmission of SARS-CoV-2 is not yet known, coronavirus RNA has been detected in blood donation samples and there is a theoretical risk of transmission(21,

A more recent study, by Erickson et al. has used a 3-D printed inlet manifold with HEPA filters, retrofitted to the helmet, to provide a HEPA filtered airflow to the user (23) . This study did not provide details on the particulate filtered but stated that it was independently verified to meet HEPA standards (23) . The system used adds to the overall volume and weight of the hoods and has two plastic hoses that exit the toga posteriorly that could jeopardise sterility of a surgical field. In contrast the setup described for the T5 system in this study does not add any further encumberment to the user and under the hood there can be no difference in the outward appearance compared to a non-modified SS.

It appears that both modified Stryker hoods are safe to use with no appreciable interval increase in ETCO2 or FiCO2 with time. ETCO2, an approximation of arterial carbon dioxide concentration, appears to be slightly higher with use of the modified T5 system, however, it does not continue to increase with time. We speculate that the increase in FiCO2 may be due to a reduced fresh gas flow as a result of the additional HEPA filter. This does not appear to impact respiration over a prolonged period as there was no significant interval deterioration in gaseous exchange noted over the duration of the study. Similarly, the normal FiO2 level is 21% and the readings demonstrated that there is a reduction in FiO2 with both modified and non-modified systems. However, although the FiO2 is reduced in both systems the reductions are steady state with respect to time suggesting that there is adequate ventilation sufficient to keep up with the oxygen consumption of the user.

The purpose of this study was to evaluate if the SS could be used as a reasonable alternative to facemask PPE. This study uses the well-established SS used in routine orthopaedic surgery to potentially provide a solution to such a shortage. By fitting a SS with a HEPA filter that can be used for months at a time before needing to be assessed or changed, the orthopaedic surgeon can be one less HCW for facemask PPE requirements and use.

This study is a proof of concept study and by no means rigorous in the testing and validation required for mass roll-out, but it does, validate and provide evidence that this solution could be used safely as PPE in the setting of a respiratory droplet spread, viral pandemic. The gown material without a HEPA filter and not operating the fan provides some protection to the user with c. 10% downstream penetration, however, the concerns of the fan raised in previous studies are valid, whereby, the suction effect allows an increase in particulate detected downstream to 25%. The SS must be operated with the fan on and so the addition of a HEPA filter at the intake significantly reduces the particulate count to less than 5% for the configuration with a HEPA filter housing mounted to the helmet. The downstream penetration is even better, at less than 0.5% downstream J o u r n a l P r e -p r o o f penetration, with a HEPA filter cut to the shape of the inlet and with edges sealed to the T5 helmet.

The level of particulate penetration is at the level of a FFP3 mask (>99% filtration of 0.3μm particles), or equivalent can provide and greater than that of the recommended N95 respirator. For the purposes of reducing reliance on the supply of facemasks that are used in all areas of healthcare during such a pandemic the modification of the SS may present a viable alternative that would be palatable to orthopaedic surgeons. 

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There was no funding received for the production of this paper by the present authors.J o u r n a l P r e -p r o o f