Kidney failure and replacement Flashcards
What are the 4 main functions of the kidneys?
Regulating fluid compartment volumes (ECF, ICF, Na+ and H2O)
Electrolyte balance (K+ and pH)
Excretion of metabolic wastes (urea and loads of others)
Hormones (EPO and vit D)
What are the 4 different consequences of kidney failure?
Oedema (fluid compartment volumes)
Hyperkalaemia (electrolyte balance)
Vomiting and drowsiness (excretion of metabolic wastes)
Anaemia and bone weakness (hormones)
What is the main measure of kidney function?
Glomerular filtration rate (GFR)- amount of filtrate produced by kidneys
What is normal GFR?
90-120ml/min
How do you determine GFR?
Creatinine
What is creatinine?
Small molecule so it filters very easily so the amount that is in the filtrate is the same as the amount of creatinine in the blood and isn’t reabsorbed so creatinine clearance rate isn’t similar to GFR
What are benefits of creatinine?
It is cheap and widely available
What is inulin used for?
A method of accurately measuring GFR
Why is the normal range for the relationship between creatinine and GFR not a good concept?
The relationship between the two is non-linear so you can lose a lot of kidney function (go from GFR of 120 to 60) without much of a change in serum creatinine so not sensitive to early changes in kidney function
Also lots of other factors affect creatinine clearance- age, ethnicity and muscle mass
What are the two main formulae used to interpret changes in serum creatinine?
Cockcroft-Gault
MDRD
These adjust the measurement of GFR based on other factors (gender, weight and race)
What symptoms occur with gradually decreasing kidney function?
Fluid retention (first to happen)
Anaemia and bone disease
Electrolyte abnormalities
Uraemia
What are the differences between acute and chronic renal failure?
Acute: Hyperkalaemia and vomiting/drowsiness
Chronic: Oedema and anaemia/bone weakness
What are the three different types of renal failure?
Pre-renal
Renal
Post-renal
What causes pre-renal failure?
Associated with diseases where the perfusion through the kindest is low. Causes include hypovolaemia and heart failure
What are the features of pre-renal failure?
Usually obvious why they’ve got it
Always oliguric
What are the causes of intrinsic renal failure?
Acute tubular necrosis- usually gets better by itself
Nephritis
Chronic renal failure
What are the two main groups of ATN?
Ischaemic and toxic
What does ATN often result from?
ATN often results from a pre-renal or post-renal kind of renal failure- so once you’ve corrected the problem, it may take time to get better because ATN has to resolve
What is important about nephritis?
There is a type of intrinsic renal failure that doesn’t get better by itself
What are the three main causes of chronic renal failure?
Diabetes mellitus
Reflux
Hereditary kidney conditions
When does post-renal failure occur?
Occurs when there is a blockage to the flow of urine. It can occur with ureteric obstructions or problems with bladder outflow
What are the clinical features of post-renal?
Enlarged bladder
Hydronephrosis
How do you immediately manage renal failure?
Make patient safe- deal with hyperkalaemia (highest priority):
IV calcium, IV glucose and IV sodium bicarbonate
Optimise fluid state- not all kidney failure patients need fluid- some may have low fluid which is causing their kidney failure
Optimise drug chart- gentamicin, NSAIDs and acyclovir can cause kidney failure
Does the patient need dialysis?
How do you manage renal failure after a few hours?
Imaging- to figure out if its pre-renal, intrinsic or post-renal
Screening- some forms of nephritis (blood tests can be useful)
Specialist advice- nephritis requires biopsy and chronicity- ongoing dialysis
How would you diagnose post-renal kidney failure?
Ultrasound scan to see if urinary flow is blocked
What do the urinary spaces look in a healthy kidney?
You can’t see them at all
How does original dialysis work?
There is some cellulose tubing inside a glass cylinder, blood passes along the cellulose tubing on the inside. There is a diasylate fluid (like saline with other things in) passing along the outside. Dialysis is just diffusion that takes place between blood and diasylate fluid. Things that are abundant in blood of someone with kidney failure but isn’t present in the diasylate fluid will diffuse across into diasylate fluid (urea and K+)
How did dialysis technology change?
The technology changed to create a pressure gradient across the two compartments- ultrafiltration. Helps get rid of fluid in fluid overloaded patients and drags large molecules across pressure gradient
What are fistulas?
Artificial joints between arteries and veins which has continuous flow and causes that vein to become dilated and thickened
How is dialysis connected to fistula?
Via a couple of big needles
What is an alternative to fistula use?
Some people need a dialysis line which inserts into a large central vein
What access complications are there for haemodialysis?
Fistulas can become very large
Distal ischaemia- could require amputation
Infection
How does a dialysis nurse figure out how much fluid needs to be removed?
Measure the patient’s weight- short term weight gain is caused by fluid
What can dialysis not fix?
It doesn’t replace the hormonal functions of the kidneys: Anaemia and calcium and phosphate metabolism
It doesn’t restore life expectancy
Why is anaemia a harmful problem for kidney function?
It makes you tired and breathless and this causes compensatory changes in the heart.
How is anaemia caused by kidney failure treated?
EPO
How is calcium and phosphate metabolism a problem in kidney failure?
You don’t excrete as much phosphate as usual so the phosphate increases. You also don’t activate as much vitamin D so calcium reabsorption is reduced so plasma calcium levels decrease. This will cause secondary PTH release, which is initially good at increasing plasma Ca2+ and increasing phosphate excretion (it makes the kidney failure worse)
What are the consequences of disruption of calcium and phosphate metabolism?
Bone resorption -> bone weakness. It causes softening of bone so bones become deformed
What are the causes of mortality in people on dialysis?
They are not the same as general population, there is a larger amount of infectious causes and a huge amount due to vascular disease.
What is the association between obesity and mortality in dialysis?
Different to normal- fatter you are, the longer you live
What is the most common type of dialysis and the other type?
Haemodialysis- more common
Peritoneal dialysis
Where is the dialysis fluid put into in peritoneal dialysis?
Into the peritoneal space
How does peritoneal dialysis work?
It is put into peritoneal space and then through the lining of the peritoneal membrane you get diffusion taking place. You can also achieve ultrafiltration by putting sugar into the dialysis fluid- this means that there is osmotic pressure drawing fluid into peritoneal space. This happens continuously 24/7 and you have to refresh the fluid 3 or 4 times per day by draining out the old drainage bag and putting on a new solution bag
What are the pros and cons of peritoneal dialysis compared to haemodialysis
Pros:
Allows more freedom (home) and just as effective
Cons:
Not available indefinitely- peritoneal membrane will change such that peritoneal dialysis no longer works effectively. Works for about 5 years
Where are kidneys transplanted?
They are attached lower down in the abdomen because it’s easier to access that site and donated kidneys come with a short ureter
What are the complications of kidney transplants?
Rejection
Immunosuppression- increased risk of infection and cancer
Availability of kidneys (main problem)
What is the outcome of kidney transplantation?
Long-term- better overall survival
immediate post op period you go through a period of increased risk
Older people have a greater immediate risk following transplant
What is the most important thing to do if you develop chronic kidney disease?
Stop smoking
Give a summary of renal replacement therapy (RRT) modalities?
Haemodialysis- done in hospital, 3x per week, universal, indefinite
Peritoneal dialysis- at home, 3x per day, available for patients to manage, stops being effective after 5 years
Kidney transplantation- best survival, independent lifestyle, fit for surgery, lasts for around 10 years
