Wednesday, November 10, 2010

What is your K+ threshold for dialysis?

Hyperkalemia can be a life-threatening condition. Nonetheless, in transplant recipients with delayed graft function, there is a tendency to try to avoid dialysis early after transplant. The reason behind this approach is that a session of hemodialysis further delays the recovery from ATN/ischemia and significantly drops urine output afterwards (indirect evidence - no randomized trials available). This is potentially related to hemodynamic changes associated with the dialytic procedure, even in the absence of volume removal (osmotic shift). So what are your options if you have a patient with a potassium of 6 about 72 hours after transplantation with low urine output?

First option, if he doesn’t have ECG changes, is to try a loop diuretic at a high dose to see if he can respond to that and produce some kaliuresis. If he doesn’t respond and has had a bowel movement since surgery, I would do a trial of sodium polystyrene sulfonate binding resins (e.g.Kayexalate). Now, it gets into a little controversial territory.

Last year, Sterns et al. in an editorial on JASN concluded that the use of SPS resins is largely unproven and potentially harmful, and should be considered only as a last resource. That was quite shocking to me since I have used it many times and I always saw a decrease of serum potassium levels. I do acknowledge the increased risk of colonic necrosis that has been reported with sorbitol commonly added to Kayexalate to increased bowel movements, but I was prescribing only mixed with water and other than the low palatability of the solution, no major side effects were seen.

Actually, after reviewing the literature, the most common side effects reported are nausea, vomiting and constipation. I was able to download the first trial using SPS resins published in the NEJM in 1961! Small number of patients (n=22) but the results looked quite impressive, since a median dose of 40g was able to decrease the potassium level by 1mEq/L and additional doses led to further decrease in levels (median decrease of 1.8mEq/L). It is important to know that the peak effect of SPS takes about 4-6 hours, so if ECG changes are present, you will need to use IV calcium for membrane protection and albuterol/insulin+dextrose for transient K+ shift to the intracellular. The majority of reported complications were associated with SPS/70% sorbitol enema. This combination should be avoided, especially in patients with compromised GI function (e.g. ileus post-op). As an alternative, lactulose could be used to stimulate the GI tract. Finally, Kayexalate releases sodium ions after uptake of potassium, so there is a potential side effect of edema due to sodium retention (not significant in 1-2 doses).

Is there a way to estimate how much resin you will require? Efficiency of a resin is dependent on several factors, including intrinsic properties of the resin (capacity and ion selectivity), [K+] and [Na+] extracellular concentrations and colonic transit time. In general, a decrease in 0.5mEq/l [K+} would require at least 30g of Kayexalate.

Going back to our patient: After a diuretic trial, I would recommend two doses of 30g of Kayexalate mixed with water PO with repeat labs in 8-12 hours. Caveat, if the patient has no urine output or have other potential indications for dialysis (e.g.volume), you should just buy the bullet and dialyse him.

More acute hyperkalemia management on this blog. Picture above from Jackson Hole - insane ski destination...

4 comments:

Anonymous said...

The practice of giving kayexelate follwing transplant surgery is completely prohibitive at our institution. We have had cases of bowel necrosis following kayexelate administration.Is your transplant surgery team ok with giving kayexelate to these patients??
Do you have evidence that HD delays graft recovery in these patients?

Francesco Iannuzzella said...

"... hemodialysis further delays the recovery from ATN/ischemia and significantly drops urine output afterwards"
There is no evidence to support HD avoidance following transplant surgery. However, HD avoidance is a largely diffuse, common sense approach in this setting. Notably, information from literature data regarding ATN in native kidney should not be applied to transplant pts (denervation!).
Back to the point: Kayexalate is my preferred option. Of course, do not forget to listen to peristalsis.

Matt Sparks said...

Interesting post. Any evidence that dialysis after transplant will cause a significant change in the the trajectory of delayed graft function. This would seem difficult to study, but any real data to support this?

Leonardo V Riella said...

Thanks for the comments. There are many indirect data suggesting that hemodialysis affects recovery of DGF and in practice urine output drops significantly after one session of HD. However, I have to admit that there is no randomized trials (ideal data) looking at this. Most data are retrospective or observational in nature (e.g. Bleyer et al. JASN 1999,10:154).

Regarding the first comment, our surgeons do support the use kayexalate in our service. Thanks again guys!