Acute Renal Failure Flashcards
Risk factors for Acute Kidney Injury
Age greater than 75
DM
Preexisting chronic kidney dz
CHF
Liver failure
Sepsis
Exposure to IV contrast
Cardiac surgery
anything that reduces renal perfusion
Acute Kidney Injury Definition
abrupt decline (within 48hrs) in kidney function as manifested by: 1.increased serum creatinine
- decreased urine output
- or need for dialysis
Sx of acute renal injury
- *may be asymptomatic**
- N/V
- Malaise
- Altered sensorium
- HTN
- Pericardial effusion, arrhythmias
- pulm edema
- abd pain
- platelet dysfunction
- asterixis
- confusion
- seizures
- all of these are secondary to uremia/azotemia.
Decreased GFR leads to increased BUN in 2 ways, what are those?
- decreased flow through glomerulus
2. slower transport time allows for more BUN to be reabsorbed at the level of the PCT
What leads to increased levels of creatinine in the blood? BUN?
What is Normal BUN/Creat Ratio? elevated?
creat: increased with muscle breakdown (will be increased if greater mass)
BUN: breakdown of proteins
(tetracycline, burns, fever, steroids, GI bleeding)
Normal BUN/Creat = 10-20:1
Elevated: greater than 20:1
What are two mechanisms at the level of the nephron lead to increased serum creatinine?
- blockage at the sites in the DCT that allow for active secretion
- decreased GFR as there is less creatinine present at the glomerulus to be filtered out.
Kidney damage may lead to ____ serum Cr or ____ CrCl
kidney damage may lead to INCREASED SCr or INCREASED CrCl
What are some laboratory abnormalities with acute kidney injury?
- Increased BUN, creatinine
- decreased GFR
- Hyperkalemia
- Hypocalcemia
- Hyperphosphatemia
- Anemia
- Platelet dysfunction
- anion gap metabolic acidosis
Classification of acute kidney injury is based upon where the problem lies, what are the three types?
pre-renal (decreased renal perfusion )
Intrinisic (alteration of normal process within the kidney)
Post renal (inadequate drainage of urine distal to kidney)
Examples of Pre-renal failure
- low Cardiac output; CHF
- Hypotension: shock, sepesis
- Hypovolemia (bleeding. V/D)
- Renal artery stenosis
- Renal artery atheroembolic dz
- decreased glomerular perfusion pressure by dilation of efferent arteriole (ACEi/ARB) or afferent arteriole (NSAIDS)
Low perfusion pressure in prerenal failure, how does the kidney try to compensate?
-increases Na+ reabsorption in an attempt to increase volume. Water follows sodium
What is the urine sodium and urine osmalality be in prerenal failure? BUN/creat ratio? FENa%
Urine sodium is low(less than 20), urine water content is low which makes it very concentrated = high osmolality (greater than 500), high specific gravity (greater than 1.010).
BUN/creat ratio is elevated (greater than 20:1)
Fractional Excretion Na less than 1%
Tx of prerenal?
Treat the underlying cause**
maintain euvolemia and electrolyte balance
avoid nephrotoxic drugs
may require short course of dialysis
Most recover over time
Post Renal Acute Kidney Injury:
- what?
- most common cause
- reversible or not?
- other causes
What: obstruction somewhere in the kidney, ureter, bladder, or urethra.
MC Cause: prostatic obstruction
Reversible
Causes:BPH, Anticholinergic drugs(no shit, no spit, no pee, no see), Cancers, neurogenic bladder, urethral stones or strictures
Post Renal Acute Kidney Injury:
- SIgns and Sx
- Diagnostics
Signs and Sx:
- History is key!
- may or may not have oligura anuria
- flank pain
- low back or abdominal pain
- enlarged prostate or pelvic mass
- distended bladder
- inability to void
Dx:
- bladder ultrasound
- bladder catheterization (diagnostic and therapeutic)
- CT scan of the abdomen and pelvis (renal stones and hydronephrosis)
- Ultrasound of the kidney may show hydronephrosis
What is the urine sodium and urine osmalality be in post renal failure? BUN/creat ratio? Sediment?
Urine Na: variable
Urine osmolality: high in the beginning and end up less than 400.
BUN/Creat: 10-20:1 (normal)
Urine sediment may be normal, have RBC, WBC, possibly crystals
Treatment of Postrenal Acute Kidney Injury
-relieve obstruction temporarily by bladder cath
- Refer!!!!…to urology for definitive tx.
- -ureteral stent
- -urethral stent
- -ureterolithiasis
- -Lithotripsy
- -Nephrostomy tube
- -Prostate resection
Intrinsic acute renal injury :
- what is this?
- examples?
What: renal parenchyma dz (glomerulus, interstitium, tubules, or vasculature)
examples: glomerulonephritis, acute tubular necrosis
Acute Glomerulonephritis:
- what?
- sub categories of GN
- most common lab finding
What: immunologic mechanism triggers inflammation and proliferation of glomerular tissue that can result in damage to basement membrane, mesangium, or capillary endothelium.
Sub Categories:
- post strep GN
- Systemic Illness (SLE, Wegeners, Goodpastures)
Lab findings: RED CELL CASTS and significant proteinuria
Acute interstitial Nephritis:
- causes
- Common sx hx
- common urinalysis findings
Cause: mediation use MC, bacterial, viral or fungal infections of kidney
-Sx Hx: maculopapular rash, fever, arthralgias
Urinalysis: RBC casts, proteinuria, eosinophils
Acute Tubular Necrosis:
- MC cause of what?
- 3main causes
- what is this?
MC cause of acute intrinsic renal injury
3 Main Causes:
- ischemia, sepsis, nephrotoxic drugs
- COMMIT THESE TO MEMORY*
-Acute tubular necrosis occurs when the tubules fail to function.
What is the urine sodium and urine osmalality be in Acute Tubular Necrosis? BUN/creat ratio? Sediment?
Urine Na: elevated, greater than 20
Urine osmolality: low, less than 450
BUN/Creat ratio: low, less than 10:1
Sediment: muddy brown casts, renal tubular epithelial cells, and epithelial cell casts
** are d/t failure to reabsorb.
ATN can be secondary to ischemia, what may lead to nephron ischemia?
-tubular damage from site of low perfusion
- inadequate GFR but also decreased renal blood flow to the renal cellular functional units.
- prolonged hypotension
- hypoxemia
- shock
- sepsis
- prolonged surgery
ATN secondary to Toxins:
- most common drugs causing nephrotoxicity
- may occur how long after exposure?
Drugs:
- aminoglycosides
- Amphoteracin B
- Chemo
- Acyclovir
- Ethylene glycol
- Sulfonamides, cephalosporins
- Multiple Myeloma
- Uric Acid
- Myoglobin
- Blood transfusion rxn
- hemolytic anemia
-may occur 5-10 days after exposure
Contrast Nephropathy:
- what is this?
- when does it occur?
- risks?
- mechanism?
- prevention
What: for of ATN
Occurs 24-48hrs post contrast exposure
Risk factors: DM, CKD, high contrast load, concurrent use of nephrotoxic drugs, age
Mechanism: unclear
Prevention:
- minimize amount of contrast
- hydrate pre and post procedure w/ NS****
- Mucomyst (N-acetylcystein)
- stop metformin the day of contrast load and 48hrs post (may lead to lactic acidosis)
What is the purpose of FENa?
useful in determining if the cause of acute kidney injury is prereanl or ATN.
if pre-renal FENa is less than 1%
if intrinsic FENa is greater than 2%
What associated urine particles are found in each of the following conditions:
- ATN
- Acute interstitial nephritis
- Proliferative/necrotizing GN
ATN: muddy brown granular casts, epithelial casts
AIN: WBC and WBC casts
GN: RBC and RBC casts
Mainstay management and general work up of acute kidney injury
- treat underlying cause
- manage electrolyes
- manage BP
- stop all nephrotoxic drugs
- may need temporary dialysis
WOrk up:
- assess volume status
- UA (dipstick, micro exam, urine Na, urine cr)
- CBC
- Serum BUN and Creat
- Fractional excretion of Na
- Renal ultrasound
- bladder scan
- CT/MRI
- renal Bx
What is the most common type of acute kidney injuyr?
WHat test is the most important noninvasive test in the diagnostic evaluation of these pts?
Intrinisc
UA
