關於 water treatment filtration ，我們在網路上蒐集到這些相關的討論、資訊與評價

From a real life fabric expert friend (not merely a FB friend). This is hugely helpful. Please pass it along and stop the bad practices regarding masks.

Q1. Why can't we wear mask made of 100% cotton even if it is difficult to buy surgical masks nowadays?

Although it is easy to DIY cotton mask, but the outcome will be worse than no mask. It seems that we can wash the cotton mask everyday so that the bacteria count is low, but the water flow of DIY mask is two way whilst surgical mask only allows one way flow, means if there is one COVID-19 patient nearby and his/her saliva drops on your face mask, it will spread into the mask as cotton is hydrophilic and will enhance diffusion into the mask. Moreover, due to the humid and warm temperature inside the mask, it will further promote the growth of bacteria. Also as the water flow is two way, the bacteria will reach the face of the wearer if the mask is wet. So it’s not really true that having a mask is better than none, it really depends on the material and construction of the mask.

Q2. Why can surgical mask not be reused, even after sanitization, steaming or washing?

Most ppl may think if surgical mask reached nano type level will filter virus effectively. However, the real concept behind is due to its “electret treatment “ to filter the virus and bacteria, plus the ability to kill bacteria(cannot kill viruses). The electric field built by the electret treatment will create a protective shield to attract the viruses and the ability to kill the bacteria. After 4 hrs or 8 hrs of use, these electric field will consume all its static energy, like a dead smartphone without battery, then the electret treatment will no longer effective to attract viruses. That’s why we can only wear mask for less than one day. This electret treatment is the key concept behind a surgical mask, that’s why even though we can sanitize, steam or wash the mask to reduce the total bacteria count, but we cannot recharge the electric field to make it function again, thus its ability of attracting/filtering the viruses and killing bacteria cannot be revived.

Q3: Does a stuffy mask means better filtration ability?

The answer is, not really, but there are many exceptional cases. We already mentioned in Q2 that surgical mask used electric treatment to handle viruses/ bacteria. The size of COVID-19 virus is 120nm (nanometer), the gap between fibers of surgical mask is over 120 nm, so the virus can penetrate the gap between the fibers and reach our face theoretically. However, the electret treatment will create an electric field to attract those viruses and keep them between the gaps of the fibers, so viruses cannot penetrate through the mask and reach the wearer. The high breathability of mask with electret treatment will let wearer feels more comfortable, whilst still effectively filter viruses(usually larger than 100nm) and bacteria.

ARDS 的血行動力學

Experts’ opinion on management of hemodynamics in ARDS patients: focus on the effects of mechanical ventilation

Acute respiratory distress syndrome (ARDS) is frequently associated with hemodynamic instability which appears as the main factor associated with mortality. Shock is driven by pulmonary hypertension, deleterious effects of mechanical ventilation (MV) on right ventricular (RV) function, and associated-sepsis. Hemodynamic effects of ventilation are due to changes in pleural pressure (Ppl) and changes in transpulmonary pressure (TP). TP affects RV afterload, whereas changes in Ppl affect venous return. Tidal forces and positive end-expiratory pressure (PEEP) increase pulmonary vascular resistance (PVR) in direct proportion to their effects on mean airway pressure (mPaw). The acutely injured lung has a reduced capacity to accommodate flowing blood and increases of blood flow accentuate fluid filtration. The dynamics of vascular pressure may contribute to ventilator-induced injury (VILI). In order to optimize perfusion, improve gas exchange, and minimize VILI risk, monitoring hemodynamics is important.
During passive ventilation pulse pressure variations are a predictor of fluid responsiveness when conditions to ensure its validity are observed, but may also reflect afterload effects of MV. Central venous pressure can be helpful to monitor the response of RV function to treatment. Echocardiography is suitable to visualize the RV and to detect acute cor pulmonale (ACP), which occurs in 20–25 % of cases. Inserting a pulmonary artery catheter may be useful to measure/calculate pulmonary artery pressure, pulmonary and systemic vascular resistance, and cardiac output. These last two indexes may be misleading, however, in cases of West zones 2 or 1 and tricuspid regurgitation associated with RV dilatation. Transpulmonary thermodilution may be useful to evaluate extravascular lung water and the pulmonary vascular permeability index. To ensure adequate intravascular volume is the first goal of hemodynamic support in patients with shock. The benefit and risk balance of fluid expansion has to be carefully evaluated since it may improve systemic perfusion but also may decrease ventilator-free days, increase pulmonary edema, and promote RV failure. ACP can be prevented or treated by applying RV protective MV (low driving pressure, limited hypercapnia, PEEP adapted to lung recruitability) and by prone positioning. In cases of shock that do not respond to intravascular fluid administration, norepinephrine infusion and vasodilators inhalation may improve RV function. Extracorporeal membrane oxygenation (ECMO) has the potential to be the cause of, as well as a remedy for, hemodynamic problems. Continuous thermodilution-based and pulse contour analysis-based cardiac output monitoring are not recommended in patients treated with ECMO, since the results are frequently inaccurate. Extracorporeal CO2 removal, which could have the capability to reduce hypercapnia/acidosis-induced ACP, cannot currently be recommended because of the lack of sufficient data.
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