Prerenal Flashcards
What does pre-renal azotemia indicate?
Renal pathology due to reduced renal blood flow
This occurs over the sub-acute to chronic time frame.
How does the kidney respond to perceived low blood volume in pre-renal azotemia?
By increasing retention of fluid through reabsorption of urea and sodium
What is the typical BUN/Cr ratio in pre-renal azotemia?
BUN/Cr >20
Indicates high blood urea nitrogen levels.
What is the typical fractional excretion of sodium (FENa) in pre-renal azotemia?
FENa <1%
Indicates low sodium levels in urine.
What is the time frame for acute decreased perfusion leading to acute tubular necrosis?
Seconds to minutes
This differs from the sub-acute to chronic time frame of pre-renal azotemia.
What conditions can cause acute tubular necrosis due to acute decreased perfusion?
Blood loss, acute heart failure exacerbation, or arrhythmia (Example: VFib for 30 seconds before resuscitation.)
What is the expected renal outcome if a patient loses significant blood during surgery and then develops oliguria and decline in renal function two days later?
Acute tubular necrosis
Despite decreased renal perfusion, the timing indicates acute tubular necrosis, not pre-renal azotemia.
Why is the proximal convoluted tubule (PCT) particularly susceptible to anoxic/hypoxic injury?
Due to the concentration of ATPase transporters
This makes it vulnerable to acute drops in blood flow.
True or False: Pre-renal azotemia is caused by acute drops in renal perfusion lasting seconds to minutes.
False
Acute drops in perfusion lead to acute tubular necrosis, not pre-renal azotemia.
What is the cause of oliguria in a post-op patient who was started on ketorolac?
Hypoperfusion
This scenario illustrates how NSAIDs can lead to post-operative oliguria due to pre-renal causes.
Name 4 common causes of pre-renal azotemia relevant for the USMLE.
- NSAID use
- Diuretic use
- Chronic left heart failure
- Dehydration from days of vomiting/diarrhea
These are key conditions to consider when evaluating pre-renal azotemia.
What medications are commonly associated with causing pre-renal oliguria in patients?
NSAIDs and diuretics
Examples include naproxen and ibuprofen.
What is the effect of NSAIDs on sodium excretion in pre-renal azotemia?
Decreased renal excretion of sodium
This occurs due to increased reabsorption of sodium in the proximal convoluted tubule (PCT).
Fill in the blank: In cases of pre-renal azotemia, the fractional excretion of sodium (FENa) is typically _______.
<1%
This indicates that the kidneys are conserving sodium due to low perfusion.
Vignette of patient who is on an NSAID + now has peripheral edema + they ask why there’s edema
“Decreased renal excretion of sodium.” This is because the PCT reabsorption of sodium in pre-renal (FENa <1%).
What is the recommended action when a patient on an NSAID develops edema?
Discontinuation of ibuprofen
This is a common approach to manage NSAID-related edema.
What is the typical clinical presentation of a patient experiencing pre-renal azotemia due to dehydration?
Oliguria and increased creatinine
This presentation is often seen in patients who have days of vomiting or experiencing diarrhea.
Hepatorenal syndrome is
A severe form of Prerenal AKI caused by Splanchnic vasodilation causing renal hypoperfusion
Hepatorenal syndrome presents with
Bland urinalysis (no blood or protein) makes intrinsic AKI unlikely
No obstruction (postrenal) on imaging
Very low urinary sodium
Lack of response volume expansion (albumin)
