Current KDOQI Guidelines recommend the use of some type of vascular mapping studies in order to prepare for the creation of an AV fistula or an AV graft. While physical exam is useful--typically, application of a tourniquet around the upper extremity and gross measurement of veins which could potentially be used as targets--it is often unable to identify suitable targets in many individuals who are obese or have deeper veins.
Two other options are available for mapping: either duplex ultrasound or angiography, both of which have their benefits and drawbacks. Duplex ultrasound is attractive because it is non-invasive, and can be performed in both potential arterial and venous targets. There are also accepted ultrasound criteria which appear to predict, at least partially, the success of AVF maturation: in general, pre-op arterial diameter should be greater than 1.6mm and the venous diameter should be greater than 2.5mm at the site of anastamosis. Optimally, veins should be less than 0.5cm deep from the skin and should have an 8-10 cm straight segment for repeated cannulation. Duplex ultrasound is the preferred method of pre-op mapping according to KDOQI.
Angiography appears to be comparable to ultrasound in terms of pre-op AVF/AVG planning, but has the advantage of being able to more directly identify central stenoses--an all-too-common finding in individuals with previous dialysis catheters or central lines that can easily prevent the successful development of an AVF/AVG if present. The main disadvantage of angiography, of course, is that it is invasive and involves the injection of contrast dye--which may not be wise for individuals with advanced CKD whose renal function is so tenuous that dialysis planning is underway.