osmolarity of dialysis?

  1. My patient I will have later today is on CAPD, with a solution change every 6 hours. Of course, last night did all my research on the procedure, condition, drugs, etc. The one thing I can't figure out is about the osmolarity of the solution. My instructor wanted me to figure out what it meant.

    The solution is Dianeal 4.25% with some cefazolin and heparin in it. I would assume that the higher the % of solution, the greater the osmolarity and concentration gradient, therefore the faster the dialysis? So, if the solution was a lower number, like 2.5%, it would take longer to dialysize (sp?) than the 4.25%.

    It logically seems right, just wanting someone to confirm I guess. I already posted on the student board, and tried to google and use medical sites, but everything I found just told that it came in different osmolarities, not why!Thought I would post over here for some help. Thanks!
  2. 1 Comments

  3. by   ageless
    Dialysis is basically moving of a solvent through a semipermeable membrane that tends to equalize the concentrations of solute on the two sides of the membrane.

    The solution percent Rx is based how much fluid the patient is retaining. If the patient is relatively dry, one would choose to use the 1.25% and then vice versa. The percent has to do with how much glucose is in the solution. Glucose is what pulls the excess fluid across the membrane, into the peritoneal cavity, and then out through the tenckhoff catheter.

    Peritoneal dialysis is not about how fast or slow one dialyzes. Look at the concentrations of K+, Ca++ etc. That determines how the body will respond to treatment. Example" If the the soln. has a 3 K+ bath and the patient has a potassium of 5-6 then the result should produce a patient with a K+ of roughly 3-4 K+. The soln contains no BUN or creat. These (by-products of metabolism) are removed, or diffused, in greater numbers.
    Remember, how long the soln dwells and how many exchanges are done within a certain period of time are the keys to how well the excess electrolytes will diffuse.

    Heparin is added to the soln to prevent fibrin from clogging the catheter and impeding flow. (Heparin, in the peritoneal cavity, will not be absorbed into the bloodstream and will not affect the PTT. The antibiotic is most probably ordered for peritonitis.

    Also of note, diabetics will have insulin added to the bags of fluid because of the glucose. the higher the % in the bag, the more insulin needed.

    Hope this helps..........