 I have a patient of a functioning baby fishula, you can see a big scar over here where the fishula is constructed and I can palpate the thrill over there which tells me yes that there is flow across the fishula. The indications for doing a Doppler of fishula when it is sent to you is basically maybe the surgeon is not able to palpate the thrill, it is taking too long for a hemodialysis, there is sometimes difficulty in puncturing the veins, the vein is not very well visualized by the dialysis technology and so on. So in those cases you need to evaluate the fishula. So here we have a gentleman who is having a distal radiocephalic fishula, you can see the scar over here and what we now start doing is a good B-mode, remember a good B-mode is important before switching on color, do a good B-mode evaluation from cordial to cranial. Here this is the radial artery which I am tracing. So you can very well see here that here you are having anastomosis and this is the draining vein, this is the area of anastomosis and this is the draining vein which continues proximally. So I now trace the draining vein entirely along its course with copious gel with minimal compression. So this is the draining vein, now along the course of the draining vein it is important to look for any thrombus, it is important to look for any stenosis, any narrowing which you can pick up on B-mode itself that gives you a guidance as to where you need to sample and measure the velocities. You need to look at the venous walls, you need to look for any aneurysmal dilatation, you need to look for collections around the draining vein, so here I am tracing the draining vein all along proximally. One more important thing is that you need to even look at certain channels which may be coming from the vein and going deeper and sometimes these venous channels may cause diversion of the fistula flow and that can hamper adequate dialysis, so this should be borne in mind. So here we can trace the vein right till its proximal portion, now the vein along its course as we can see shows a few areas of aneurysmal dilatation which are very well evident, we can measure the vein over here, yeah it is around 7.6 mm, now an optimal diameter for a draining vein is around 4 to 6 mm size and fistulae which have reached a 4 to 6 mm size of a draining vein in them almost 70% of the fistula are mature and ready to use, it takes around 3 to 6 weeks for adequate maturation of an av fistula. So once again from cordial to cranial we trace the fistula, this is the artery, here you are seeing the actual nostromosis and we are coming proximally, so this is the feeder artery here, this is the anastomosis and we are coming proximally all along the draining vein, now the volume flow in a fistula is an important calculation and must be taken around roughly around 10 cm proximal to the anastomosis, so here we calculate the volume flow, now for the volume flow it is important to get the time average mean velocity, so for that you need to have sample at least 3 to 4 cardiac cycles, it is better done manually if your machine auto settings are good enough, you can go ahead with them, so here you can see the velocities of the draining veins reaching around 150, so usually draining veins have velocities of around 50 to 120, this is maybe 150 slightly on the higher side, so we take the volume flow measurement now, so it is better to select it manually, select around 3 to 4 cardiac cycles and then you need to measure the vessel diameter at the site of sampling, not anywhere else, volume flow of around 1000 ml per minute here is calculated which is good enough for a good dialysis and he is undergoing hemodialysis without any problems, so this is practically a functioning fistula with some amount of aneurysmal dilatation in between which is acceptable, now what you cannot forget is again sampling the artery distilled to the anastomosis or rather caudal to the anastomosis, so here is my anastomosis, I go for the caudal and now I can see the radial artery at the wrist, I have to sample it for a possible phenomenon called reversal or steam, look at the angle of intonation and look at the curve, it is reversal of flow and we now go to the ulnar, ulnar is showing forward flow, so this definitely this, this fistula is definitely because of the aneurysmal dilatation, it is definitely causing retrograde or reversal of flow in the radial artery, so he is saying yes there are, there is a sensation of numbness and paracetias over the fingers which is because of this radial artery retrograde flow and this is how importance of checking the patency of the parma arch becomes important because this gentleman if the ulnar artery also was diseased and a fistula was created, his hand would have become ischemic, now that the ulnar artery is healthy and it is showing forward flow, it is supporting the circulation in the parma arch is patent, so this is very important before going ahead and giving the sight of marking for the fistula, you also need to look at the deep wave of the subclavian vein before we finish, so you need to establish the subclavian vein patency because any central venous obstruction can also lead to venous hypertension and the limb, the patient can come with a swollen limb and the fistula may have to be abandoned, so here you can again see a nice, basic and a pulsatile subclavian venous flow which is normal, when you look at the anastomosis, you sample the velocities of the anastomosis and you also go 2 cm upstream or 2 cm cranial into the feeding artery, so the ratio of 3 is to 1, if the velocities of the anastomosis are 3 times more than that of the feeding artery, yes there could be anastomotic stenosis but sometimes you do get very high velocities of the anastomosis because of the surgical technique itself, so it is a good practice to go into the draining vein, look for any stenosis along the draining vein, look for volume flow along the draining vein and I think you get answers to most of your questions.