Functions of the kidneys and which dialysis can perform
Metabolic waste excretion
Endocrine functions
Drug metabolism
Control of solutes and fluid status
Blood pressure control
Acid Base balance
nothing other than a transplant is going to effectively replace all of these functions
Aims of dialysis
Aim of dialysis therapy = Homeostasis
- Removal of nitrogenous waste products
- Maintenance of normal electrolytes
- Maintenance of normal extracellular volume
- Correction of metabolic acidosis
When to dialyse
Acute
- Hyperkalemia resistant to medical therapy
- refractory pulmonary oedema
- Metabolic acidosis
- Uraemic complications (pericarditis)
- Severe uraemic symptoms (uraemic encephalopathy)
Chronic
ESRF stage 5 - lots of symptoms
- anorexia
- vomitting
- itch
- restless legs
- weight loss
- metallic taste
What are the options for RRT
- transplant (living or deceased)
- Dialysis
- Haemodialysiss
- peritoneal dialysis
- CVVH
- Conservative care
What is haemodialysis?
- patient is connected to the machine
- removal of solutes e.g postassiumm, urea.
- Movement of solutes by diffusion down a concentration gradient across a semi-permeable membrane in to dialysate
- dialysate is flushed out and discarded
- Removal of fluid: via ultrafiltration (oscmotic pressure)
- movement of fluid via ultrafiltration down a pressure gradient so blood volume falls
Blood out - diffusion removes the solute - filtration removes fluid- dialysate discarded- blood in
Practicalites of HD
- Hospital or home based – hospital much more common
- Standard: 4h, 3 times a week
- Multiple other options – mainly home based:
- 6h 3 times a week
- Short daily dialysis
- Daily overnight
- Home based treatment gives greater flexibility and empowerment but need carer, space and capital investment
Vascular acess in haemodialysis
Need to create an arteriovenous fistula
- radiocephalic (wrist)
- Brachiocephalic (elbow)
The artery is anastomosed onto the vein then arterialised and hypertrophys.
If fail
- tunnled line - risk of infection
Haemodialysis complications
- ‘Crash’ - Hypotension (fluid out of intravascular, means fluid needs to be brought in by extravascular fluid, too much fluid out quickly then hypotension)
- Dialysis disequilibrium - urea levels drop too quickly
- Cramps
- Fatigue
- Hypokalaemia
- Air embolism
- Blood loss
- Access problems
Peritoneal dialysis treatment
- Need intraperitoneal Tenchkoff catheter
- Use the patients own peritoneal membrane - diiffusion of solutes
- Infuse fluid into the patients periteneal cavity
- Dilaysate is at low concentration of solute
- Solutes from blood capillaries in the peritenum diffuse across the peritoneal membrane into the peritenum
- Glucose as osmotic gradient - Fluid by osmosis
- Add glucose to the dialysate
- creates an osmotic gradient
- enables fluid to move from the capillary intot he peritenum
Two types of periotenal dialysis
- Continous abulatory peritenoeal dilayssi
- Manual exchages by patient
- 4 times a day
- APD (automated peritoneal dialyssi)
- machine performs automated exchanges whilst asleep
- more exchanges overnight
Practilicalites of PD
- Home based therapy
- Better with some residual renal function
- Different glucose concentrations of dialysate to provide more or less ultrafiltration
- Dialysate contains other electrolytes like in HD
- Gradual treatment – no good for AKI
- Simple procedure once taught
- Maintain independence
Complications of PD
- Infection - peritonitis
- Glucose load – development or worsening control of diabetes
- Mechanical – hernia, diaphragmatic leak, dislodged catheter
- Peritoneal membrane failure
- Hypoalbuminaemia
- Encapsulating peritoneal sclerosis
Some patients not suitable:
- •Grossly obese
- •Intra-abdominal adhesions
- •Frail
- •Home not suitable
Modality choice considerations
- Lifestyle
- Frailty
- Vascular access
- Time – travel to and from hospital
- Carer
- Physical – concurrent medical problems e.g. disseminated malignancy, severe dementia, severe psychiatric disease
Problems not helped by dialysis
- Anaemia – need erythropoesis supplementing agents and iron
- Renal bone disease – need phosphate binders and vitamin D
- Neuropathy
- Endocrine disturbances
Remember – dialysis only gives around 10ml/min eGFR, not as good as a transplant
Prognosis of patients on haemodialysis
-
UTI/Pyelonephritis46
-
Glomerulonephritis37
-
Acute Kidney Injury31
-
Chronic kidney disease26
-
Tumours and Stones16
-
Prescribing in specific circumstances4
-
Pyelonephritis And congenital disease of the kidneys26
-
Cystic Kidney disease30
-
Tubulo-intestitial disease27
-
Systemic diseases affecting the kidneys19
-
Dialysis15
-
Transplant20
