When I was a fellow I got an opportunity to write the chapter in Intensive Care in Nephrology
on Disorders of Potassium Homeostasis.
, the editor and my fellowship program director, told me that I couldn't use review articles or text books as references. It was a golden experience. I systematically went through all of the pearls I had collected on potassium and drilled down to the original data.
The primary conclusion I had after months of exploring the stacks of The Crerar
was that the wall of knowledge that I had assumed backed up all of our clinical practices was more like a chain link fence with isolated points of solidity but mostly holes. Science could provide a rough outline but too much of medicine is based on conjecture and reasoned guesses.
One of my finds was the near total lack of data showing cation-exchange resins to be effective. In the chapter I wrote:
...Two recent studies have questioned the effectiveness of SPS [sodium polysterene] resins, but until larger studies corroborate these findings, SPS resins remain part of the therapy for acute hyperkalemia. (106, 122, PDF) SPS and sorbitol usage have rarely been associated with intestinal necrosis; whether this is due to sorbital, the resin, or other factors is unclear. (123, 124, 125)
The key table from the Gruy-Kappal article showing the lack of effectiveness of SPS resins
This was actually the revised paragraph. The first draft was much stronger. I railed against the use of kayexylate given the lack demonstrated benefit and the emerging data on the dangers of this medication. I was ready to throw kayexalate on the hyperkalemic trash heep along with bicarbonate. My co-author, John Asplin
calmed me down and had me moderated the section. He explained that despite the lack of data, SPS resins have a long history of use and explained that though I have the option of using dialysis, intensivists often find themselves in binds where dialysis is not available and they need an extra-renal method for potassium clearance.
I can appreciate Asplin's wisdom now. In the last decade I have used SPS resins innumerable times in patients with and without ESRD, though my data is circumstantial I am believer in the effectiveness of this drug. I hope the latest publicity
about the purported ineffectiveness of Kayexalate leads to well done large studies rather than a loss of this effective medicine.