AKI and CKD Flashcards
what is Glomerular Filtration Rate (GFR)
the rate at which the glomerulus is filtering the blood to form the filtrate
Males 90-140 ml/min
Females 80-125ml/min
how do you estimate GFR?
To be able to measure GFR we need a substance that is:
- completely filtered
- not re-absorbed
- not secreted
- not metabolised by the nephron
(10ml of solution in blood - collect urine and there is 10ml)
Inulin fits this profile (100% gets filtered) BUT it requires an infusion into the blood therefore not practical - it takes a long time
In practice – creatinine clearance is measured
what is creatinine?
what is it produced by?
It is a chemical waste molecule that is generated from muscle metabolism
Produced from creatine, a molecule of major importance for energy production in muscles
Released into the circulation at a constant rate
Removed from the circulation by filtration and excreted in urine
Why is it important to check blood creatinine levels?
Measurement of creatinine concentration is used to:
- Determine sufficiency of kidney function - Determine severity of kidney damage - Monitor progression of kidney disease
Kidneys maintain blood creatinine at a specific levels
If creatinine levels in the blood are rising it could indicated that the kidneys are not functioning to their full ability to clear the creatinine
Problems with kidney function may lead to: Loss of nutrients from the body Failure to remove toxins Affect drug treatments Affect blood pressure
what is creatinine clearance
It is a value which indicates the volume of creatinine (in millilitres) removed by the kidneys over a period of time (per minute)
how is creatinine clearance measured?
24 hour urine collection = not practical
In practice: blood is taken from the patient. This is measuring the amount of creatinine in the blood plasma.
The higher the level of creatinine in the blood, the slower the kidneys are working = low creatinine clearance (mL/min)
How can creatinine clearance be calculated?
Cockcroft & Gault equation:
```
CrCl = F(140-age) x weight / Serum Creatinine
F = 1.04 in females, F = 1.23 in males
Units = ml/min
~~~
difference between eGFR and creatinine clearance
eGFR = estimated glomerlus filtration rate = which is measured via blood tests in labs = this has a chance of over estimating renal function
when does creatinine clearance have to be calculated
DOACs Nephrotoxic drugs > 75 years Extremes of muscle mass Drugs that are ++renally excreted Narrow therapeutic index drugs
how can serum creatinine be affected?
1) The amount of muscle tissue you have
- Men tend to have higher levels of blood creatinine because they have more skeletal muscle tissues than women
2) High protein in diet
3) Exercise, particularly if muscle building
4) Any injuries involving damage to the muscles
- e.g. severe burns or conditions resulting in acute muscle wastage
5) Malnutrition leading to dramatic weight loss
what is acute kidney injury (AKI)
AKI is NOT a disease but is the result of another clinical problem
AKI should be regarded as a spectrum of injury that may progress to organ failure
AKI occurs most commonly in patients who are at risk, who either are acutely ill or have had major surgery
what is acute kidney injury (AKI)
AKI is NOT a disease but is the result of another clinical problem
AKI should be regarded as a spectrum of injury that may progress to organ failure
AKI occurs most commonly in patients who are at risk, who either are acutely ill or have had major surgery
what are the risk factors of AKI?
Age >75 years Previous AKI Pre-existing CKD (eGFR <60ml/kg/1.73m2) Heart failure Atherosclerotic peripheral vascular disease (PVD) Diabetes mellitus Liver disease Debility and dementia
what are triggers for AKI
Sepsis or infection
Hypotension (Mean arterial pressure <65 mmHg, systolic pressure <90 mmHg)
Hypovolaemia (dehydration, bleeding)
Nephrotoxic medications e.g. gentamicin, NSAIDs, iodinated contrast
Anti-hypertensives e.g. ACE inhibitors, loop diuretics
what are the three classifications of AKI
Pre renal - inadequate perfusion - not enough blood at sufficient pressure to allow filtering
renal - cellular damage/ intrinsic - damage to the cells that makes filtering mechanisms possible
post renal - obstruction - urine unable to drain adequately - system ‘backed up’
Pre - renal
mechanism
causes
mechanism - Blood flow to the kidney reduced i.e. decreased perfusion. If not managed it can cause ischaemic injury.
cause :
- Intravascular volume depletion e.g. diarrhoea, vomiting or haemorrhage
- Decreased arterial pressure e.g. heart failure or sepsis
- Nephrotoxic medications e.g. ACEIs, ARBs, NSAIDs
- Kidney function typically returns to baseline after volume status established or nephrotoxic
medication discontinued
post renal AKI
mechanism
causes
mechanism - Obstruction to outflow from the kidneys.
causes:
Causes waste (urine) to build up in the kidneys
Common causes include:
- kidney stones: mainly occurs in the ureters but may also develop in the urethra
- benign prostatic hyperplasia (BPH)
- CNS disorders that may affect outflow such as stroke, multiple sclerosis, spinal cord injury,
- blood clots in the ureters or urethra
- cancer of the prostate, cervix or colon
- nephrotoxic medications
Renal/ intrinsic AKI
mechanism
causes
mechanism:
Damage to the functional tissues of the kidney
causes:
Can be categorised by the component of the kidney that is affected e.g.
- Glomerular: glomerulonephritis
- Tubular: acute tubular necrosis; rhabdomyolysis; myeloma
- Interstitial: interstitial nephritis
Acute tubular necrosis (ATN) is most common in hospitalised patients
In contrast to pre-renal causes, ATN does not improve with adequate repletion of intravascular volume
May resolve over time but temporary renal replacement therapy (i.e. dialysis) may be required
Common cause is usually ischaemic (prolonged hypotension) or due to nephrotoxic drugs
what is the management for pre-renal AKI
hydration with IV fluids
what is the management for post-renal AKI
refer patient to a urologist
what is the management for intrinsic?
treat the damage…if treatable!
what are other management options for AKI ( in terms of medication)
Hold all nephrotoxic medications
Adjust doses of all other medications that are prescribed
what are possible further complications of AKI?
Hyperkalaemia high potassium levels in blood
Metabolic acidosis blood is too acidic; pH <7.25
Fluid overload peripheral and/or pulmonary oedema
Uraemic encephalopathy high urea levels in the blood
what is the management of hyperkalemia?
AKI causes concentration of potassium in the blood stream to increase
Can have very severe consequences, in particular altering electrophysiology leading to cardiac arrhythmias
Acute treatment with Insulin or Salbutamol causes a shift of potassium from the blood stream into cells
Dietary potassium should be restricted
If potassium persistently high, patients may need to undergo urgent dialysis