Yes I have a answer for him it is called the Poiseuille effect. If velocity remains the same, pump speed at 350 let’s say, and the needle is one inch, the pressure from the one inch is greater than the 3/5 inch needle. When using the 3/5 needle, the arterial and venous pressures drop from 40 if pump is speed at 300 to 120 if the pump speed is 500. What does this mean? Longer life out of an AVF and a lot less jet blast. Look this up on Google and the article will show up. Take that with you.
If he still says no, I will personally send you enough for one month and you can see for yourself. One other fact--does it make any sense to push 4/5 saying that your access is 1/5 inch deep and most forearm fistulas are that way? So when you push a 4/5 needle down the vessel wall, the tip of the needle comes in contact with the vessel wall and causes scrapes or infiltrations. If scraping occurs, the bodies' response is to send fibrin to heal the blood clot sites. It makes sense so go for the 3/5 needle. Cost should not enter into this. Ask him this: "Does a carpenter just use a hammer to build a house?" No, it takes what it takes to get the job done and that is the 3/5 cannulation needle and I swear by them and so do many others. By the way, MediSystems is the only company that makes these.