Sterility of open-topped jugs

[stauffenberg]

Everywhere I have been dialyzed, the potassium and bicarbonate baths have been attached to the dialysis machine by tubes leading into open-topped plastic jugs.  Since the contents of both of those baths are going directly into the patient's bloodstream, why is it deemed to be sufficiently sterile that these baths are in contact with the air and all the germs and dust of the surrounding atmosphere at the top of the jugs, which looks to be a little less than a square inch in dimenstion?  I have posed that question to nurses at my dialysis units and have gotten various replies, none of which sounded convincing.

[qwerty]

The fluid does not make direct contact with your blood. It facilitates diffusion through the dialyer membranes. It assist pulling select particles/molecules to make them "even" so to speak, such as potassium, glucose, sodium. Hope this helps. Things such as viruses, red blood cells, and bacteria is not able to diffuse through the membranes into your blood stream. Now what we call endotoxins (break down of bacteria) can. This is why we culture and try to maintain a "clean" enviroment.

[stauffenberg]

The way I have read it explained is that the dialysate fluid does make contact with the blood across the differentially permeable membrane, but the openings in the membrane are calibrated to screen out  microorganisms and endotoxins.  There seem to be no microorganisms or endotoxins smaller than a potassium (K2), bicarbonate, or water molecule flowing across the differentially permeable membrane, so none could be carried across on such a vehicle.  However, an endotoxin, as a toxic fragment of a microorganism, can in principle be any size, since it is just debris, but the answer must lie in the fact that at that small dimension it lacks the required biochemical character to cause any toxicity.

[qwerty]

It is a small semi-permable membrane that seperates your blood from the dialysate allowing certain particles to pass through to maintain balance. It's based on diffusion. It is not a "mixing" of blood and dialysate mixture. Also endotoxins can and do pass through and can result in severe reactions and untoward effects such as fever, sepsis, etc. The core cirriculum for dialysis techs is now published on line and easily downloaded for viewing or printing. It is also free and can be located http://www.meiresearch.org/CoreCurriculum/CC2006m6.pdf  It may help answer alot of questions regarding the techs responsiblities and some of the technical aspects of the procedures themselves.  There is also other information available on the site http://www.meiresearch.org/

[Rerun]

The other day chlorine got in our water system and they shut it down for 4 hours.  I guess chlorine can play havoc on red blood cells.  So, I guess chlorine must be a small particle if they didn't want any in the water.

[stauffenberg]

It is true that the patient's blood and the dialysate are separated by a semi-permeable membrane, and that there is a pressure gradient across that membrane which causes particles to be leached out of the blood and into the dialysate, so that the two fluids, which are flowing past each other, are in theory not mixing.
 
However, there are a few limitations on this ideal.  First, substances in the dialysate which have an electrical or chemical affinity for the blood, such as lipophilic substances, can be drawn across the membrane and flow into the blood.  An example of such a substance is the organic contaminant trichloroethyline, which can flow across the pressure differential and through the differentially permeable membrane and get into the patient's blood.  See Diana Poh, et al, "Organic Contamination in Dialysis Water," Nephrology, Dialysis, Transplantation, vol. 21, no. 6, pp. 1618-1625 (2006).

Also, by the laws of statistical mechanics, if two liquids or gases are placed next to each other and separated by a pressure gradiant, it is only a statistical truth that the flow will be only in one direction across the gradient.  In fact, because all the constituent particles of each liquid or gas are in constant random motion with different energy levels, some will flow against the gradient, even though the overwhelming majority will flow along the gradient.  But since only a tiny contamination can be sufficient to cause a serious infection with a virulent virus, in theory a clinically significant contamination against the gradient is possible, if the pores allow the substance to pass.

As J. Levy, at al, Oxford Handbook of Dialysis (Oxford: Oxford University Press, 2001) p. 82 conclude: "Ultra pure, pyrogen free dialysate and bicarbonate buffering are necessary because of the risk of back-filtrationj from dialysate into blood."

G. Pontoriero, et al, "The Quality of Dialysis Water," Nephrology, Dialysis, Transplantation, 18 Supplement 7, pp. 21-25 (August, 2003), sum things up by saying: "Every week, hemodialysis patients are exposed to approximately 400 liters of water used for the production of dialysis fluids which, albeit the interposition of a semi-permeable artificial membrane, come into direct contact with the bloodstream.  It is therefore clearly important to know and monitor the chemical and microbial purity of dialysis water."

Returning now to the problem of non-sterile fluid from open-topped jugs of potassium and bicarbonate flowing into the dialysate, it seems that we still have a potential problem of contamination from this source.

[jbeany]

I'll stick with my NxStage - it's all sealed, no air exposure for any part of the dialysate.  Before I switched to home hemo, my clinic was using jugs with lids with a hole just big enough for the tubing, which in theory should have helped lower the contamination risk, but in practice, they usually didn't screw the caps on tight, just dangled them over the edge with the tube in the jug.

Did any of the journal articles you cite actually discuss how often this is really a problem?

[BigSteve]

This is an enlighting discussion. Thanks qwerty for the reference to mei site. I downloaded some
good info on the machines. I looked at my HD set up and there are tops on both my
jugs with the tubes coming out of the tops.

[willieandwinnie]

Our clinic home nurse always told me that if the lid to either the bicarb or the 1K was not sealed, to pour it out and bring jug to clinic and she would replace it.