 Surgeons will send you the patients for a marking and how exactly are you supposed to mark the vein is very very important because that carries a lot of implications as to the surgical success and many times it so happens that the surgeon has started the surgery or takes an incision and finds a thromboscephalic vein which just just cannot be used and it's a complete waste of all the effort. So a Doppler mapping done prior to this is really really helpful really useful so we'll go about certain protocols and certain principles which are used to mark the vein and literally guide the surgeon or in fact suggest the best possible site for construction of AV fistula. So what we use here are all the AIUM guidelines for the sizes of the vessels and so on with maybe a slight lower limit for the Indian population as we have smaller sizes of veins especially in the female population. We first always always start with the arterial system before we move on to the venous because if the feeder artery itself is no good there's you cannot just construct a fistula because the feeder artery has to have good flow. For the venous mapping of the terminology in the upper limb it's always good to use cranial and caudal instead of proximal or distal as it creates confusion instead of upstream downstream it's always better to use the word cranial and caudal. So we always begin with the scanning of the brachial artery for the anatomic variants. You can see the brachial artery very well over here and you can even see it dividing beautifully into the radial which is lateral and the ulnar which is radial. So what is preferred usually whenever you start the mapping it's always preferable to start it on the non-dominant arm for obvious reasons when the fistula is on the non-dominant arm it's more of more convenience to the patient it's more convenient for even the dialysis access as the right hand is not involved. So then you scan the radial artery properly from cranial to caudal and the best place is to do a radiocephalic distal radiocephalic fistula which is always better as you get a longer segment of the vein for future punctures. So that's your radial artery now you have to do certain checks on the artery before you say that yes this feeder artery is healthy enough to feed a fistula. I now do a good b-mode scanning of the artery measure the artery lumen diameter now here the artery is two point almost two point two point one or two millimeters which is sufficient usually the cutoffs given in many articles and literatures around one point six to one point seven millimeter and in the Indian population believe me you don't get arteries bigger than this. So looking at the radial artery then you after you have done a good b-mode evaluation of the radial artery you go ahead and do a proper Doppler insolation for the radial artery you need to keep the peripheral gains a little on the higher side so then you sample the radial artery and you see a signature which is a triphasic flow pattern. Now in this you need to do certain two three maneuvers for checking patency of the pharma arch and especially for pre-AVS mapping you also need to check the elasticity of the vessel. So how do you do this? You ask the patient to clench his fist tightly so he clenched his fist tightly once he's clenched it you take a you take a waveform which is going to be a very high resistance with obvious reasons and then once he's clenched it for few seconds you ask him to release it release so yes so you can now beautifully see the change over from the triphasic pattern of flow high resistance flow on your left to the high diastolic kind of pattern of flow to the right. Look at this slide in this you can see that physiological increment in blood flow after a period of ischemia is called as reactive hyperemia and this pre-operatively very well assesses the artery's ability to distend. So it's the elasticity property of the artery which is now checked here so you know your vessel is good enough so because when you're constructing a fistula you're diverting blood from the high resistance circulation to directly to a very low pressure circulation bypassing the capillary. So this change of hemodynamic should be acceptable to the artery as well as the vein. So this is a good test it's a good test called as reactive hyperemia which should appear in the report when you actually do the mapping. One more good test is the modified Allen's test in which you compress the vessel proximal transducer or rather cranially you compress the vessel and then you see a reversal of flow. So you start seeing the blue flow once I'm compressing the vessel cranially just cranial to my transducer the cranial head of the transducer so I see this reversal of flow so this reversal again tells me that my parma arch is patent. So after these two tests have been done and you know that you're not dealing with any distal vascular compromise it's also prudent to even sample the ulnar artery because once the radial is given away for the fistula you need to ulnar is also giving a good flow so yes your ulnar evaluation is also done which is normal here and then after this you move on to the venous evaluation. So according to the AIUM guidelines for venous evaluation it's good to actually make the patient sit for the peripheral veins, make the patient comfortable, give him a good pillow to rest his forearm. One important thing here is you need to tie a tourniquet proximally which I have already done and the tourniquet should be tight enough not too uncomfortable for the patient and now ask the patient to clench and release the fist two three times and then clench the fist properly. So this makes your peripheral veins distant it's also a good idea to even tap over the peripheral veins just as we do it before putting an intravenous cannula. So now I'm doing an evaluation of the catholic vein which is the best fistula for making a radiocatholic fistula. So now here you go it's easy to examine that there should be copious gel used very minimal compression so as to not compress the vein and get accurate readings of the vessel caliber. So here you can see the catholic vein so I measure the catholic vein distally in the forearm over here the diameter is around 1.6 then I move for further forward proximally into the mid and the proximal forearm I can take two three readings at this side one reading here proximally yes this reading is around 1.8 slightly better and the vessel becomes of a bigger caliber as we move cranially. So again in b mode b mode is best believe me you just don't need color evaluation over here because b mode gives a good picture about the compressibility which rules out thrombosis and in this b mode setting you can even beautifully see the wall thickening of the vein everything is very well visualized and you follow the vein proximally right till the subclavian catholic vein it usually may drain into the axillary vein or it may go proximally and drain into the subclavian vein when it drains into the subclavian vein it is known to pierce the clave pectoral fascia and then enter the subclavian venous circulation. I am tracing it cranially as much as I can sometimes you may not be able to see it draining into the subclavian so this is how we do a proper evaluation of the catholic vein as well as the distal arteries now before proceeding further and saying that yes a fistula can be made lastly you need to look at the deep veins which is a must you cannot complete your examination without evaluating the deep veins that is the subclavian and the internal juggler so quickly have a sweep over the neck to look at the ijv and then follow it up to look at the subclavian so it's important to see these veins as you need to rule out any deep venous or central venous stenosis or thrombosis because many times these patients who come to you are not healthy individuals but they all always have central venous lines HD catheters and their central veins may be already occluded or thrombosed so it's important to evaluate the subclavian and the internal juggler so that's the subclavian vein which we are sampling now yes you can see the pulsatility as well as the phasocity in the subclavian vein which is normally present this pulsatility is because of the transmitted cardiac pulsation and in case you have a central venous thrombosis or any of the inominate or the brachiocephalic veins are thrombosed this pulsatility is not transmitted to the subclavian and hence this is an indirect sign in that case you need to go ahead with investigations like maybe CT or MR to look at the central vein yes and marking of the vein is again important I cannot skip that so when you mark the vein see to it mark it distally and when you mark it it should be marked in a fashion so as to have only a small peripheral segment of the vein and one more thing is that if you can you can mark it with some permanent ink because they usually do the fissure like some one week or later or you're the best thing what I what I practice is I just keep a mehendi phone inside inside your ultrasound room and you can just put some mehendi over there the color stays longer and then the surgeon can do the fissure like even three to four days after you've done the venous evaluation there are certain size criteria which are important I've seen that in Indian population even if you have a vein of 2 or 2.2 millimeter you can give a green signal and you can say go ahead because you really don't get veins which are like 2.5 2.7 or 3 millimeter unless you have a well-built male sometimes it's patchy ethrosclerotic calcification so see to it that you don't mark an area which is calcified because anastomosis for the surgeon where the artery is calcified becomes difficult and again he may have to abandon the procedure especially in females it's a big problem they're frail they're weak with crf they're undergoing repeated hemodialysis and then they come with need of a fistula so even veins at smallest 2 millimeters I mark them and you can give them a chance once there's fairly good arterial size good healthy artery feeding the vein I think a fistula can be constructed