WILTIMS #499: A surgery revisited

Image from Kbik at English Wikipedia

Back in my surgery clerkship I spent an unusually long 3-weeks on the vascular surgery team. One of the bread-and-butter surgeries that the vascular folk do is create AV fistulas for patients starting chronic dialysis. An arteriovenous (AV) fistula is an artificial connection between an artery and vein, usually in the arm, that allows for the higher blood pressure of an artery to inflate a low-pressure vein. Dialysis machines require a high rate of blood extraction in order for the treatment time to be a brisk 3-4 hours instead of all day. That means you either need to pull from a very large, strong vein (requiring a surgical procedure to place an infection-prone catheter) or divert arterial pressures into smaller, weaker veins (if you pull too hard on small veins, they simply collapse).*

One of the potential problems of having an AV fistula placed is that, once you divert all that blood to the veins, it bypasses the lower arm and hand. If the hand doesn't get enough blood it can become painfully ischemic (starved of nutrients). This phenomenon is called "steal," as in the vein stealing the blood from the arteries that go to the hand. Steal is very easy to diagnose: pinch off the AV fistula and the hand will almost immediately feel better. Fixing it requires more work; you have to do a revision surgery ASAP.

YesterdayIL: When the hand/arm loses blood flow like that, it hurts, but why it hurts can be complicated. The tissue is essentially suffocating and it tells the hand/arm nerves to tell your brain to change something. When you return flow it usually gets better. But if the steal was too great, or left too long, or the nerves were already damaged from prior disease like diabetes, then the nerves themselves can suffocate. But nerves heal slowly, if they heal at all. This pain doesn't go away right after the blood flow is returned and may even be permanent.

Another nerve pain problem with AV fistulas can happen if a nerve is compressed by the anatomical changes from the surgery or post-op inflammation. This pain, however, should only affect whichever nerve is being pinch, not the whole limb.

*The reason you can't just use arteries is that they are complicated with nerves and muscles that give them thick walls and make them very painful to access. Veins are just thin stretchy tubes.