Oxygen Flow: First of all, you have to see how many LPM oxygen your patient needs.If a COVID patient needs oxygen at or below 5 LPM, a concentrator whose oxygen flow or capacity is less than 5 LPM will do the trick.But if the patient needs oxygen more than 5 LPM, then this concentrator will not work.In this case you will need a concentrator that gives 8LPM or 10LPM of oxygen.Generally, the higher the LPM of the concentrator, the larger its size and the higher the cost.You can buy oxygen concentrator at 1mg, Tushti Store, Healthklin, ColMed, Healthgenie, Nightingales India and IndiaMart.Brands that make concentrates include Equinox, Inogen, Oxlife, Philips, Aspen, Hemodiaz, Yuwell, HG, Life Plus, Devilbliss, Olex and Greens.If you want, you can find out about the rates etc. by visiting the website of these brands.