Acute Kidney Injury Flashcards
AKI
Defined as abrupt decrease in renal function leading to retention of creatinine and BUN. Low urine output (oliguria as less than 500cc/d) is not required for AKI
Prerenal AKI
1) Reduced renal perfusion
2) Common causes include:
a) hypovolemia (hemorrhage, dehydration, burns)
b) cardiogenic shock
c) sepsis
d) anaphylaxis
e) drugs (ACEIs, NSAIDs)
f) Renal artery stenosis
g) Lower effective circulating volume from hypoalbuminemia (cirrhosis and nephrotic syndrome)
h) abdominal compartment syndrome
i) hepatorenal syndrome
Intrinsic AKI
1) Injury within the nephron unit
2) Common causes:
a) ischemic or nephrotoxic acute tubular necrosis
b) allergic interstitial nephritis
c) glomerulonephritis
d) thromboembolism
e) atheroembolic disease
f) rhabdo
Postrenal AKI
1) Urinary outflow obstruction
2) Common causes:
a) prostatic disease
b) pelvic tumor
c) intratubular crystalluria causing obstruction (indinavir/acyclovir)
d) retroperitoneal fibrosis
e) bilateral nephrolithiasis
History and exam for AKI
Symptoms of uremia like malaise, fatigue, confusion, oliguria, anorexia and nausea
Exam may show a pericardial rub, asterixis, HTN, low UO, and an increased RR (compensation of metabolic acidosis or from pulm edema secondary to volume overload)
1) Prerenal - Thirst, ortho hypo, tachycardia, low skin turgor, dry MMs
2) Intrinsic - history of drug exposure (aminoglycosides, NSAIDs), infection, or exposure to contrast media or toxins (myoglobin, myeloma protein). Hematuria or tea-colored urine, foamy urine (from high protein), HTN, and/or edema may also be present. Other features of systemic diseases that may cause glomerulonephritis include lupus-related hair loss, and unilateral peripheral neuropathy of vasculitis
3) Atheroemboli - subQ nodules, livedo reticularis, digital ischemia
4) Postrenal - prostatic disease, low UO leading to suprapubic pain, distended bladder and flank pain
Dx of AKI
1) Check serum lytes. Examine urine for RBCs, WBCs, casts and urine eosinophils
2) An FeNa less than 1%, a urine sodium below 20, a urine specific gravity above 1.020 or a BUN/Cr over 20 suggest prerenal
3) Urinary catheter and renal US can help rule out obstruction. US can also identify kidneys that are smaller, as occurs with chronic kidney disease
4) In patients with oliguria, the FeNa can help identify prerenal failure and distinguish it from intrinsic renal disease
5) Obtain a renal bx only when the cause of intrinsic renal disease is unclear
Tx for AKI
1) Balance fluids and lytes, avoid nephrotoxic drugs
2) In acute or allergic interstitial nephritis, discontinue offending meds
3) Dialyze if indicated using hemodialysis. Peritoneal dialysis should be considered only for long-term dialysis patients or for patients who are not hemodynamically stable
4) In the setting of postrenal acute kidney injury, treatment often includes an intervention such as nephrostomy tubes, ureteral stents, or a suprapubic catheter
Complications of AKI
1) Metabolic acidosis; hyperK leading to arrythmias
2) HTN (from renin hypersecretion)
3) Volume overload leading to CHF and pulmonary edema
4) CKD may result, requiring dialysis to prevent the buildup of K, H, PO4 and toxic metabolites
Indications for urgent dialysis
AEIOU
1) Acidosis
2) Electrolyte issues (hyperK)
3) Ingestions (salicylates, theophylline, methanol, barbituates, lithium, ethylene glycol)
4) Overload (fluid)
5) Uremic symptoms (pericarditis, encephalopathy, bleeding, nausea, pruritus, myoclonus)
Metformin and renal failure
Avoid! May worsen lactic acidosis
Hyaline casts
Normal finding, but an increased amount suggests volume depletion
This is prerenal
Red cell casts, dysmorphic red cells
Glomerulonephritis
This is intrinsic
White cells, eosinophils in urine sediment
Allergic interstitial nephritis or atheroembolic disease
This is intrinsic
Granular casts, renal tubular cells, “muddy brown casts”
ATN
This is intrinsic
White cells, white cell casts in urine sediment
Pyelonephritis
This is postrenal
