5 - Peritoneal Dialysis Flashcards
What are the treatments for end-stage renal disease?
- Renal replacement therapy (dialysis)
- Renal transplantation
What is the peritoneum?
- Semi-permeable membrane lining peritoneal cavity
- Acts as “dialyzer”
How does peritoneal dialysis work?
Transport of solutes/water across the membrane separating 2 fluid-containing compartments (blood in peritoneal capillaries and dialysis solution in peritoneal cavity)
What is found in the dialysate solution and why?
- Dextrose
- Higher concentrations of dextrose increase amount of fluid removed and enhances solute removal
What are some advantages of PD?
- Done at home vs. in hospital or health centre
- Travel/vacation is more feasible (portable)
- Less impact on work life
- Better for px requiring hemodynamic stability
- Less blood loss
What are some disadvantages of PD?
- Need adequate storage space at home
- Need family support (risk of pt burnout)
- Risk of peritonitis
- Catheter malfunction, exit site and tunnel infections (many px require chronic laxatives to prevent catheter blocks)
- Glucose exposure (reduced appetite, hyperglycemia, weight gain)
Describe the peritoneal dialysis procedure
Dialysis solution placed to dwell in peritoneal cavity for some period, then spent dialysate is removed and process is repeated
How is the osmotic gradient across peritoneum increased (increased solute removal)?
- Increasing number of exchanges per day
- Increasing volume of each exchange
- Higher dialysate dextrose [ ]
- Increase in dwell time
Describe CAPD
- Continuous ambulatory PD
- 4-5 exchanges (1.5-3 L each) per day
- Manually (done by gravity)
- Usual dwell = 4-6 h
- Long night dwell (> 6 h)
Describe CCPD
- Type of automated PD
- Continuous cycling PD (night cycler w/ day dwell)
Describe IPD
- Type of automated PD
- Intermittent PD (night cycler w/ no day dwell)
Is there higher antibiotic clearances by CAPD or APD?
APD
How long does CAPD normally take?
- 10-20 min for 2 L to flow into peritoneal cavity
- 10 min if 200 mL/min to drain the peritoneal cavity
Describe ultrafiltration
Water moves from area of low solute conc to high solute conc via osmotic gradient between relatively hypertonic dialysis solution and relatively hypotonic peritoneal capillary blood
Describe the 3 pore model in PD
- Transcellular pore (< 0.8 nm) – transfers water
- Small pore (< 4-6 nm) – 99% of all pores; transfers small solutes like urea, creatinine, and potassium
- Large pore (> 20 nm)
In PD, drug removal occurs by _____
Diffusion
What are the 2 directions of drug movement in PD?
- Blood to dialysate
- Dialysate to blood (after IP administration)
What factors affect movement of drugs from blood into dialysate?
- Molecular weight (smaller molecules < 1000 daltons pass more easily through peritoneal membrane)
- Protein binding (low plasma protein binding < 50% will be able to pass into dialysate when given systemically)
- Vd (small Vd < 1 L/kg are water soluble so mostly exist in body water and circulatory system, so can pass into dialysate)
- PD fluid flow rates
- Peritoneal membrane solute transport status
- Residual renal function
What affect do PD fluid flow rates have on movement of drugs from blood into dialysate?
- Factors = volume of fill per exchange and frequency of dialysate exchanges
- Greater drug movement from blood to dialysate w/ large volumes, frequent exchanges, and long dwell time (facilitates removal of large drugs)
For peritoneal clearance to be clinically important, its value should be at least __% of total body clearance
20%
Drug clearance by CAPD cannot exceed _____
Dialysate outflow
What is the equation for Cl PD?
Dialysate outflow rate (total volume per day in L/ 24 h) * fraction unbound
What is the equation for Cl ESRD?
Ke ESRD * Vd
What is the equation for Cl total?
Cl ESRD + Cl PD
How can you calculate the estimated half life for a pt based on their PD regimen?
- Calculate Cl PD and Cl ESRD
- Calculate total PD
- Calculate ke from Cl total / Vd, then convert to t1/2
What is examined in a peritoneal equilibration test (PET)?
Relative passage of creatinine and glucose across peritoneal membrane
What effect does peritonitis have on movement of drugs across peritoneal membrane?
- Enhances movement of drugs (inflammation increased diffusion)
- Enhances movement from blood to dialysate and from dialysate to blood
Urine output of ____ mL per day or more is considered significant for antibiotics
100 mL
What factors affect movement of drugs from dialysate to blood?
- Vd (large Vd will have faster movement)
- MW
- Type of PD (APD will have higher flow rates and greater clearance)
- Peritonitis
How do you calculate PD clearance for a drug administered IP?
Cl PD = (C dialysis * V dialysis) / (C serum * T dialysis)
- C dialysis = drug conc in dialysate effluent
- V dialysis = volume of dialysate effluent
- C serum = serum drug conc at midpoint of dwell
- T dialysis = duration of drug dwell
How do you calculate the predicted steady state serum peak level on a PD regimen?
- Calculate Cl total
- Calculate ke (Cl total / Vd)
- Use equation Cpss = [F IP * D] / [Vd * 1-e^-ke*T]
- F IP = IP bioavailability
How do you calculate the predicted steady state serum trough level on a PD regimen?
Ctss = Cpss * e^-ke*T
