(SYNOPTIC) Renal - AKI Flashcards
Define Acute Kidney Injury (AKI)
An abrupt/acute (developing over hours/days) decline in kidney function (e.g. glomerular filtration) based on how much the serum creatinine has increased from its normal (baseline) level over a set period of time, or how much the urine volume has decreased over a set period of time
What are the 2 factors AKI is based on?
- Serum Creatinine
- Urine Output
What are the 3 stages of AKI and explain each one
- Stage 1 - Serum creatinine levels = 1.5-1.9 times baseline OR ≥0.3mg/dl (≥26.5mmol/L) increase, Urine Output = <0.5ml/kg/h for 6-12 hours
- Stage 2 - Serum creatinine levels = 2.0-2.9 times baseline, Urine Output = <0.5ml/kg/h for ≥12 hours
- Stage 3 - Serum creatinine levels = 3.0 times baseline OR Increase in serum creatinine to ≥4.0mg/dl (≥353.6mmol/L) OR Initiation of renal replacement therapy OR In patients <18 years, decrease in eGFR to <35ml/min per 1.73²m, Urine Output = <0.3ml/kg/h for ≥24 hours OR Anuria for ≥12 hours
What are the classifications of AKI?
- Pre-renal
- Post-renal
- Intrinsic
What do the 3 classifications of AKI depend on?
where in the kidney the injury has taken place
What are the 3 classifications of AKI, mechanisms and causes of each one
- Pre-renal = Blood flow to the kidney is reduced e.g. decreased perfusion (if not managed, it can cause ischaemic injury)Causes: Reduced blood pressure, hypovolaemia, dehydration, gastro-intestinal (GI) bleed, sepsis, cardiac and liver failure, burns, medications
- Post-renal = Obstruction to outflow from the kidneys (kidney itself functions fine, but urine can’t flow out of kidney due to blockage of ureter e.g. tumour is blocking)Causes: Benign prostatic hypertrophy (BPH), prostate cancer, renal calculi, retroperitoneal fibrosis, medications
- Intrinsic = Damage to the functional tissues of the kidneyCauses: Acute interstitial nephritis (hypersensitivity reactions which are often drug induced), myeloma, rhabdomyolysis, immunological renal disease (e.g. vasculitis), medications
What is pre-renal AKI?
Reduced blood flow to the kidney
What causes pre-renal AKI?
- Reduced BP
- Hypovalaemia (decreased blood volume)
- Dehydration
- GI bleed
- Sepsis
- Cardiac & liver failure
- Burns
- Medications
What is post-renal AKI?
Obstruction to outflow from the kidneys
What causes post-renal AKI?
- Benign prostatic hypertrophy (BPH)
- Prostate cancer
- Renal calculi
- Retroperitoneal fibrosis
- Medications
What is intrinsic AKI?
Damage to the functional tissues of the kidney
What causes intrinsic AKI?
- Acute interstitial nephritis
- Myeloma
- Rhabdomyolysis
- Immunological renal disease
- e.g. vasculitis/ medications
What is the most and least common classification of AKI?
Most common = Pre-renal (75-80%)
Least common (rarest) = Post-renal (5-10%)
What are the risk factors for AKI?
- ≥65 years old
- dehydration
- CKD (AKI on CKD)
- history of urological obstructions
- chronic conditions such as heart failure, liver disease, diabetes
- sepsis/sever infections
- medications (NSAIDs, ACE inhibitors, Diuretics, Aminoglycoside e.g. Gentamycin)
- dyes (Iodine-based contrast agents)
Why is it important to check blood creatinine levels in renal patients?
- Kidneys maintain blood creatinine at specific levels
- If creatinine levels in the blood are rising, it could indicate that the kidneys are not functioning to their full ability to clear the creatinine
- Therefore blood creatinine levels are a good indicator of kidney injury (Higher creatinine = Worse kidney function)
What is the measurement of creatinine concentration used for?
- To determine sufficiency of kidney function
- To determine severity of kidney damage
What are the 2 clinical measures used to determine renal function?
- eGFR - estimated Glomerular Filtration Rate (ml/min/1.73m²)
- Creatinine Clearance (ml/min)
What are the units for eGFR?
ml/min/1.73m²
What are the units for the Cockcroft & Gault equation used to calculate creatinine clearance?
ml/min
What is eGFR?
Estimated glomerular filtration rate
Calculated in labs
Why is eGFR an estimation?
because it doesn’t take into account patient’s weight (can underestimate renal function if you have renal failure)
What does eGFR take into account?
- age
- gender
- ethnicity
- serum creatinine
What doesn’t eGFR take into account?
patient’s body weight
What are disadvantages of using eGFR to estimate GFR?
- Does not account for a patient’s bodyweight
- Can dramatically underestimate the creatinine clearance in renal failure
- Not interchangeable between labs
How is creatinine clearance measured?
using the Cockcroft + Gault equation
What is the equation used to calculate creatinine clearance?
Cockcroft & Gault equation (ml/min) = F(140 - Age) x Weight / Serum Creatinine
(F = 1.04 in Females, F = 1.23 in Males)
What is F in females?
1.04
What is F in males?
1.23
Which method of GFR calculation is more accurate?
Creatinine clearance
Why is the Cockcroft & Gault equation (creatinine clearance) used more than eGFR in practice?
because the Cockcroft & Gault equation (creatinine clearance) takes into account patient’s weight
When must the Cockcroft & Gault equation (creatinine clearance) be used instead of eGFR?
Patients that are:
- Taking DOACs e.g. Apixaban, Edoxaban
- Taking nephrotoxic drugs e.g. Gentamicin
- > 75 years old
- Extremes of muscle mass (because eGFR doesn’t take body weight into account)
- Taking drugs that are ++ renally excreted e.g. Gentamicin
- Taking narrow therapeutic index drugs e.g. Theophylline, Vancomycin (where toxic dose is very close to therapeutic dose)
What action should be taken after finding out eGFR or CrCl is low?
- Establish whether the patient is in AKI or CKD (symptoms can differentiate between AKI and CKD e.g. No urine output = More likely AKI)
- Review all medications and see whether the drug dose/frequency needs adjusting, holding or stopping e.g. may withhold ACE inhibitors (nephrotoxic) in AKI
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