18. CPK OF DIALYSIS Flashcards
(21 cards)
Define “hemodialysis (HD)”
Perfusion of blood & physiologic solution on opposite sides of semi-permeable membrane
How does the size of solute affect the speed of diffusion?
Fast for small solutes, slower for larger solutes
Define “diffusion”
Movement down a concentration gradient
Define “convection”
Ultrafiltration (water movement) drags dissolved solutes across the membrane (if the pores are large enough)
List the types of HD membranes
Conventional
Semi-synthetic
Synthetic
Describe the relationship between drug clearance and MW in HD
Drug clearance decreases as MW increases
Describe the drug clearance for a:
conventional / low-flux membrane
drug MW > 500 (to 800)
no effective removal
Describe the drug clearance for a:
conventional / low-flux membrane
drug MW ≤ 500
Blood flow dependent clearance
Describe the drug clearance for a:
synthetic / high-flux membrane
drug MW ≤ 500
Higher Cl than conventional
Describe the drug clearance for a:
synthetic / high-flux membrane
drug MW > 500 (to 1500)
Significant clearance
List factors that impact dialysis removal
- water solubility
- protein binding
- volume of distribution
Describe how a drug’s water solubility impacts its dialysis removal
Hydrophilic drugs are more easily removed
Poorly water soluble drugs – limited transport into dialysate
Describe how a drug’s protein binding impacts its dialysis removal
As protein binding increases, dialytic clearance decreases
Describe how a drug’s volume of distribution impacts its dialysis removal
Drugs with large Vd will have limited removal
Describe the dialysis removal of a drug with a Vd < 1 L/kg
efficient removal
Describe the dialysis removal of a drug with a Vd 1-2 L/kg
intermediate removal
Describe the dialysis removal of a drug with a Vd > 2 L/kg
poor removal
Describe the impact of dialysis on drug eliminations
Faster drug elimination during dialysis → drug levels drop rapidly during session
During dialysis, ClD (dialytic clearance) increases, so the elimination rate constant (k) increases, and half-life (t½) decreases
When is a supplemental dose indicated after a dialysis session?
If a drug has significant ClD and the concentration drops below therapeutic range, a post-dialysis dose is needed—especially for drugs with narrow therapeutic windows (e.g., aminoglycosides, vancomycin)
Continuous Kidney Replacement Therapy (CKRT) drug clearance increases when the drug has what characteristics?
- Low protein binding (high free fraction)
- High ultrafiltration/dialysate rate
- Small molecular weight
What variable describes membrane permeability for HD?
Sieving Coefficient (SC)
