Dialysis Flashcards
Drugs cleared by dialysis
BLAST - barbiturate, lithium, alcohol (methanol, ethylene glycol) salicylates, theophyllines
Types of dialysis
Haemodialysis
* Hameofiltration
* Haemodiafiltration
* Sustained low efficiency dialysis
* Continuous veno-veno HD, HF, HDF
Peritoneal dialysis
* Automated peritoneal dialysis
* Continuous ambulatory peritoneal dialysis
Main indications for dialysis in NZ/Australia
In order of most common
* Diabetic nephropathy
* Glomerulonephritis
* Hypertenion
* Polycystic kidney disease
Principles of dialysis
Diffusion
* Based on concentration gradient across a semi-permeable membrane
* Good for clearing small molecules
* E.g. haemodialysis and peritoneal dialysis
Convection
* Relies on hydrostatic pressure across a semi-permeable membrane
* Effective for clearing larger molecules
* E.g. haemofiltration
Benefits/disadvantages of haemodialysis
Benefits
* Rapid access - commonly used acutely
* Better for patients who require supervision
* Long-term dialysis - PD membranes often fail with time
* Can still work e.g. noctural dialysis or evening shift
Difference between haemodialysis and haemofiltration
Haemodialysis
* Dialysate added to circuit provides concentration gradient
Haemofiltration
* Replacement fluid added to dialyser = provides hydrostatic pressure
* When it is added to the circuit before it enters the dialyser = pre-dilution haemofiltration
* When it is added to the circuit after it goes through the dialyser = post-dilution haemofiltration
Haemodiafiltration
* Both dialysate and replacement fluid added to circuit - uses both diffusion and convection waste
Access options for haemodialysis
Temporary
* Non-tunneled catheter (Vascath) -> femoral or internal jugular veins
* Tunneled cather (Permacath) -> usually internal jugular veins, tip sits in SVC, cuff sits under the skin and over time the body forms scar tissue around the cuff
Complications dialysis catheters
* Infection - exit site, tunnel infection
* Malfunction - malposition, cracked/broken/kinked, fibrin sheath formation, retraction
* Central vein stenosis (when catheter has to be placed in central veins rather than internal jugular) -> can cause SVC obstruction - will see collateral veins and upper limb oedema
Permanent
AV fistula - ideal fistula -> sufficient blood flow, easy to cannulate, does not restrict blood supple, non-dominant arm, requires 6-8 weeks to mature
* Common sites -> radiocephalic, brachiocephalic, brachiobasilic
* Associated with less morbidity and moratlity compared to other alternatives
Complications
* Ischaemia - Steel syndrome
* Bruising/haematoma
* Aneursymal fistula - can cause high output heart failure - large portion of cardiac output -> fistula, also risk of bleeding
** * Loop graft** - made with synthetic material, for those with inadequate native veins, complications similar to AV fistula and catheters
Practicalities of haemodialysis prescription
See slide
* Standard outpatient prescription is 3x weeks for 4 hours at a time
* Higher the blood flow rate - the more dialysis you are getting
* Patients starting out on dialysis usually start with the small dialysier - usually for a shorter time with low blood flow rates and dialysate flow rates -> build up from there
* Ultrafiltration rate - how quickly you want to remove fluid - ?how much fluid needs to be taken off
* Anticoagulation needed to keep the circuit running - usually unfractionated or LMWH - may be omitted if patient is about to go to surgery or is bleeding
* EPO - does not cross dialysis membrane
Note time on machine main determinant of dose - blood flow, dialyslate flow, membrane charactersitics and membrane surfact area only change dose to a small degree
Complications of haemodialysis
Dialysis-dysequilibrium syndrome
* Cerebral oedema due to osmotic effects of urea
* Start dialysis slowly to avoid
Intradialytic hypotension and cramps
* Pause of cease fluid removal
Dialysis related amyloidosis
* Long-term ( > 5 years) accumulation of B2-microglobulin
* Not seen much anymore since changing to high flux dialysers
Principles and advantages of peritoneal dialysis
- Peritoneal membrane is semipermeable membrane
- Different types of bags - based on glucose to draw fluid
- Sometimes used as acute therapy
- PD catheters generally left in 2-4 weeks before using to reduce risks of leaks and malfunction
Benefits
* Lifestyle/work/travel
* Better for maintaining residual renal function
Considerations
* Not lifelong option - sclerosed membrane
* Exposure to high glucose
Notes on different modalities of peritoneal dialysis
** Continuous ambulatory PD**
- Manually change the bags throughout the day - can require 5 changes
- Connect fliuid bag in - after a few hours connect bag to drain out
Peritoneal dialysis
- Machine does the exchanges several times throughout the night
Notes on peritoneal dialysis prescription
Peritoneal membrane type
* Determined via peritoneal equilibrium test
* Assessent of solute transfer rates and how they equilbrate
* Gives you the transport status - low (slow), high (fast), average
* Slow transport status more suited to CAPD, high transport status more suited to APD
Peritoneal dialysis fluids
* Physiologic concentrations of sodium, calcium, magnesium, chloride. Lactate as buffer
* Glucose is the principal osmotic agent - concentrations of 1.5% (yellow), 2.5% (green), 4.25% (red) - higher the concentration the more filtration, but increased diabetes and membrane ultrafiltration failure
** Other solutions**
* Icodextrin - no glucose, induces higher ultrafiltration volume and can be used up to 18 hours
* Amino acid solutions
Notes on PD complications
Catheter infection
- Exit site
- Tunnel infection
Catheter malfunction
- Malposition (constipation +++), and kinks
- Pericatheter leaks
PD Peritonitis
- Present with abdominal pain and often coudy peritoneal bags
- Send PD fluid off for cell count and culture
- Most infections due to coagulase negative staph or staph aureus
- Treatment - intraperitoneal antibiotics and oral antibiotics
Pleuroperitoneal leak
- Diaphragmatic defect
Membrane sclerosis -> PD failure
Encapsulating peritoneal sclerosis
- Progressive inflammatory process -> fibrosis of the peritoneal
- Can encase the small bowel -> bowel obstruction
- High mortality
Contraindications to peritoneal dialysis
You need
- Functioning peritoneal membrane
- Home
- Willingness to do PD
Relative contraindications
- Abdominal hernia
- Previous abdominal surgery
- High BMI
- Dexterity/vision/strength
Absolute contraindications
- Non-compliance
- Major psychiatric history
- Inability to maintain hygiene /sterile environment
- Poor social circumstances
Measures of dialysis adequacy
- Symptoms
- Nutritional
- Fluid balance & BP control
Biochemical
- Kt/V - represents clearance of urea in the context of time and volume - aim for 1.2 - 1.3 in haemodialysis, 1.7 in PD. Doesn’t take into account fluid clearance & middle molecule clearance
- Urea reduction radio - Urea pre-dialysis - post-dialysis/urea pre-dialysis = less prescise measure
- Peritoneal equilbtation test - also gives you a measure of creatinine clearance which you want to be > 60
