Renal failure & function Flashcards
Kidney Function
Kidney has five major functions: 1. Removal of water and wastes from the blood 2. Maintains electrolyte balance 3. Maintains acid-base balance 4. Regulate blood pressure by renin secretion 5. Stimulates production of red blood cells by erythropoietin secretion
GLOMERULAR FILTRATION RATE (GFR)
The glomerular hydrostatic (blood) pressure is the major factor forcing fluids out of the blood. This pressure has to overcome the colloid osmotic pressure and the capsular hydrostatic pressure.
Factors determining GFR are:
1. Total surface area available for filtration (number of nephrons)
2. Filtration membrane permeability
3. Net filtration pressure (glomerular blood hydrostatic pressure minus the combined pressure of the osmotic and capsular hydrostatic pressure)
Normal GFR depends on blood flow and BP
• Changes in BP either decrease or increase the nephron’s ability to make a filtrate
• Hypertension may impair blood flow to the
kidney by causing hypertrophy of the smooth muscles in the afferent arterioles reducing the lumen and therefore the blood flow.
• Hypertension can also cause damage to the endothelium that accelerates the progress of atherosclerosis, which can ê lumen of the decrease blood vessels and therefore decrease blood supply to
kidneys.
Kidneys receive 20-25% of the cardiac output to provide enough plasma for high rates of glomerular filtration needed for regulation of body fluid volumes.
• Decreased renal blood flow can result in
oliguria (<300-500ml/day) and anuria (<50ml/day).
• Decreased renal blood flow decreases the work of the kidney and therefore also O2 requirements of cells.
Blood flow below 20% of normal does not meet O2 requirements at rest and renal cells die.
RENAL FAILURE
Renal Failure is a decrease or cessation of
glomerular filtration.
• Chronic Renal Failure refers to a progressive and irreversible decline in glomerular filtration rate.
• Acute Renal Injury refers to an abrupt decrease or cessation of glomerular filtration rate or kidneys stop working. It is reversible if the patient gets correct and prompt treatment.
Causes of Acute Renal Injury
Complications of surgery, severe burns, trauma
• Renal ischaemia caused by blood clots, hypovolemia
• Drugs (antibiotics-gentamycin, streptomycin, NSAID aspirin, ibuprofen)
• Toxins (heavy metals, alcohol)
• Heatstroke
• Multiple organ failure
• Sepsis
• Obstructed urine flow
• Acute pyelonephritis
• Kidney stones
Causes of renal failure: pre-renal,
renal and post-renal
• Pre-renal mostly associated with lack of blood supply/low BP Also:
haemorrhage, extensive burns, severe vomitting &/or diarrhoea, cardiac failure, septic shock
• Renal affecting the nephrons directly
Ischemia, toxins, acute glomerulonephritis, transfusion reactions, toxaemia of pregnancy, transplant rejection, SLE, Goodpasture’s syndrome.
• Post-renal mostly due to back pressure due to obstructions.
Prostatic hypertrophy, bilateral ureteric obstruction, surgical accident, ruptured bladder, retroperitoneal fibrosis, external tumours.
Phases of Acute Renal Injury
> OLIGURIC- decreased urine output - ANURIA (<50 ml/24 hours) > DIURETIC- filtration is increased but absorption is impaired > RECOVERY- gradual return to normal functioning
Causes of Chronic Renal Failure
causes of chronic renal failure divided into 3 groups:
Some of these causes also apply to acute renal failure, if acute renal failure is not treated well it may become chronic
> PRE-RENAL (shock, ischaemia)
> RENAL (direct damage to nephrons due to infection, nephrotoxic injury)
> POST-RENAL (increased hydrostatic pressure in Bowmans capsule, slowing filtration due to the obstruction of ureters).
• Diabetes • Hypertension • Obstructive nephropathy (caused by kidney stones, prostate tumour) • Kidney disease (chronic glomerulonephritis, pyelonephritis, polycystic kidney disease) • Renal artery stenosis • Lead poisoning • Fatty plague deposits (atherosclerosis in kidney artery)
Obstruction
- Foreign body
- Ureteral stricture
- Narrowing of ureterovesical junction
- Benign prostatic hyperplasia
- Urethral stricture
Polycystic kidneys
Look disgusting!
Stages of Chronic Renal Failure
- DIMINISHED RENAL FLOW- no signs and
symptoms - RENAL INSUFFICIENCY- waste products
build up, inability to concentrate or dilute urine (75% or more nephrons are lost) - END STAGE- oliguria present, waste products build up and treatment required (90% or more nephrons are lost).
Lack of biochemical markers to identify developing renal failure
Renal Function, Tests and Interventions
• GFR (glomerular filtration rate) volume of fluid filtered from the glomerular capillaries into the Bowman’s capsule per unit time
• GFR can be calculated by measuring any chemical that has a steady level in the blood, & is freely filtered but neither reabsorbed nor secreted by the kidneys.
• GFR measured is the quantity of the substance in the urine that originated from a calculable volume of blood
GFR = Urine concentration x Urine flow /
Plasma concentration
• Most accurately measured by injecting an inert polysaccharide, inulin, into bloodstream. Rate of excretion is directly proportional to the rate of filtration of water and solutes across the glomerular filter
• In clinical practice GFR is usually estimated from creatinine clearance or estimates of creatinine clearance based on the serum creatinine level
Renal Function Tests
• Creatinine clearance rate (CCr or CrCl) is the volume of blood plasma that is cleared of creatinine per unit time
• Creatinine - break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the
body (depending on muscle mass)
• Creatinine clearance exceeds GFR due to creatinine secretion
• normal range of GFR, adjusted for body surface area, is similar in men and women, and is in the range of 100-130 ml/min/1.73m2
• blood urea nitrogen and creatinine will not be raised above the normal range until 60% of total kidney function is lost
Creatinine and Renal Functioning
• Creatinine is produced naturally by the body & is freely filtered by the kidney
• creatinine clearance or estimates of creatinine clearance based on the
circulating creatinine level are
used to measure GFR
Treatment in Renal Failure
• continuous ambulatory peritoneal dialysis
(CAPD)
• haemodialysis
• renal transplant
continuous ambulatory peritoneal dialysis - CAPD
Clean solution into peritoneal cavity, waste diffuses into solution, bag flipped and waste drains out.
