April 25, 2016 - Acute Kidney Injury I Flashcards
Ultrasound of Kidneys
Ultrasound of kidneys should be performed when you suspect acute kidney injury.
Small, shrunken kidneys are more consistent with chronic renal disease.
Large, swollen kidneys are more consistent with acute renal disease.
Individual Creatinine
There is less than a 10% daily variation in the serum creatinine of an individual.
Because of this, it is critically important that you cannot rely on the normal ranges to determine of AKI has occured. For example, if a patient normally as a creatinine of 12, and now has a creatinine of 70, both numbers are still in the range but this patient likely has AKI because that is a huge jump for that one patient.
GFR and Serum Creatinine
This is NOT a linear relationship.
On the healthy side of the scale, you need to lose approximately 50% of your kidney function to notice even a slight increase in creatinine. Once the kidneys become damaged however, a small decrease in kidney function will result in a massive rise in creatinine.
ACEi Renoprotective Effect
ACEi’s decrease the efferent arteriole moreso than the afferent arteriole, so that less blood is filtered through the kidney. This prolongs the life of the kidney, because the nephrons (filters) are already working over-capacity to try to maintain filtration rates and by decreasing the flow through them, they will last longer and therefore the kidney will last longer before going into kidney failure.
Rise in Creatinine During AKI
Creatinine levels will go up gradually.
Over a period of a week, creatinine values can rise to 600 or so.
Symptoms of AKI
Usually none
Can also have symptoms of primary illnesses such as SLE, sepsis, vasculitis, dehydration, HUS (whatever is causing the AKI)
Sometimes will have symptoms of uremia (usually <20% normal GFR)
Complications of AKI
When a patient develops AKI they have an increased risk of developing chronic kidney failure, they have an increased risk of developing end-stage kidney disease, and they have an increased risk of death.
Cause of AKI
Usually a rapid (often reversible) decline in GFR and the retention of nitrogenous waste products.
This can occur pre-renal (30%), renal (60%), or post-renal (10%)
Approach to AKI
Take a history and perform a physical examination #obvi
1. Is this pre-renal? This is important because if it is, you need to re-establish vascular volume.
2. Is this post-renal? This is important because if it is, you need to relieve the obstruction.
3. If it is not either of these, it is renal.
Renal Kidney Injury
AKA Parenchymal Kidney Injury
Will either be a problem with the…
1. Glomeruli (glomerular nephritis 10%)
2. Blood vessels (10%)
3. Tubules (acute tubular necrosis 75%)
4. Interstitium (interstitial nephritis 5%)
Creatinine Measurements - Serum vs. Urine
In the serum it is measured in micromoles - umol/L
In the urine it is measured in milimoles - mmol/L (multiply by 1000)
Hyaline Cast
AKA urinary cast
Cylindrical structures produced by the kidney and present in the urine. These form in the distal convoluted tubule and collecting ducts of the nephrons before they dislodge and pass into the urine where they can be detected by microscopy.
Fractional Sodium Excretion
The percentage of sodium filtered by the kidney which is then excreted in the urine. A good indication of whether the kidneys are working and determining acute kidney injury and low urine output.
FENa = [(UNa/SNa) / (UCr/SCr)] x 100
You can also look at the U/S Cr ratio which should be above 30
Urine / Serum Creatinine Ratio
You can also look at the U/S Cr ratio to assess kidney function. This value should be above 30.
Causes of Pre-Renal Kidney Injury
- Cardiovascular causes (primary pump failure)
- Volume depletion (secondary pump failure)
- Reduced vascular resistance (eg. sepsis)
