Introduction The COVID-19 pandemic has unveiled widespread shortages of personal protective equipment including N95 respirators. Several centers are developing reusable stop-gap respirators as alternatives to disposable N95 respirators during public health emergencies, using techniques such as 3D-printing, silicone moulding and plastic extrusion. Effective sealing of the mask, combined with respiratory filters should achieve 95% or greater filtration of particles less than 1um. Quantitative fit-testing (QNFT) data from these stop-gap devices has not been published to date. Our team developed one such device, the “SSM”, and evaluated it using QNFT. Methods Device prototypes were iteratively evaluated for comfort, breathability and communication, by team members wearing them for 15-30min. The fit and seal were assessed by positive and negative pressure user seal checks. The final design was then formally tested by QNFT, according to CSA standard Z94.4–18 in 40 volunteer healthcare providers. An overall fit-factor >100 is the passing threshold. Volunteers were also tested by QNFT on disposable N95 masks which had passed qualitative fit testing (QLFT) by institutional Occupational Health and Safety Department. Results The SSM scored 3.5/5 and 4/5 for comfort and breathability. The median overall harmonic mean fit-factors of disposable N95 and SSM were 137.9 and 6316.7 respectively. SSM scored significantly higher than disposable respirators in fit-test runs and overall fit-factors (p <0.0001). Overall passing rates in disposable and SSM respirators on QNFT were 65% and 100%. During dynamic runs, passing rates in disposable and SSM respirators were 68.1% and 99.4%; harmonic means were 73.7 and 1643. Conclusions We present the design and validation of a reusable N95 stop-gap filtering facepiece respirator that can match existent commercial respirators. This sets a precedence for adoption of novel stop-gap N95 respirators in emergency situations.
Male Yorkshire pigs (40 ± 4 kg, Caughell Farms, ON, CA) were used to perform 17 orthotopic heart transplants. The experimental protocol was approved by our institutional animal care committee and followed the ARRIVE guidelines. 16 Animals were treated following the "Guide for the Care and Use of Laboratory Animals". Donor Procedure Anesthesia, monitoring and baseline measurements Premedication was undertaken with an intramuscular injection of Midazolam (0.3 mg/kg) and Ketamine (20 mg/kg). Anesthesia was induced and maintained using inhalational isoflurane through an oral endotracheal tube (end tidal concentration: 1-3%). An arterial line was inserted through the right common carotid artery, a central venous line was introduced into the left jugular vein, and a pulmonary artery catheter was inserted via the right jugular vein and directed into position beyond the pulmonary artery bifurcation. After performing a median sternotomy, the heart and great vessels were exposed. An umbilical tape was placed around the inferior vena cava, and a pressure-volume conductance catheter (Millar Instruments Inc, Houston, TX, USA) was inserted into the left ventricle through a small apical ventriculotomy. Systemic anticoagulation was achieved with an intravenous injection of 30,000 U heparin. Following a baseline assessment, donor animals were randomly assigned to undergo beating-heart donation (BHD; n=9) or DCD (n=8) (Figure 1). Beating-heart donation (BHD group) Following baseline evaluation, a purse-string suture was placed in the ascending aorta and inferior vena cava (IVC) to permit placement of a cardioplegia cannula and an 18F venous cannula via right atrium, respectively. We collected approximately 1.5 L of whole blood into an autotransfusion system (Frensenius Kabi C.A.T.S., Terumo, USA) to isolate the red blood cells (RBC). Simultaneously, the aorta was cross-clamped, and hearts arrested with 1L of histidine-ketoglutarate-tryptophan (HTK) solution at 4ºC. The heart was excised and placed in ice-cold HTK for 1 hour while being cannullated for ESHP. Donation after circulatory death (DCD group) Before cessation of mechanical ventilation, Propofol (1 mg/kg/min) and Remifentanyl (1 µg/kg/min) infusions were commenced, ensuring adequate anesthesia. Mechanical ventilation was discontinued
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