Page 137 - Critical Care Notes

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Acute Kidney Injury (AKI)
■ Acute kidney injury (AKI) was previously referred to as acute renal failure
(ARF).
■ AKI is a clinical syndrome characterized by rapid decline in renal function
(within 48 hr) → progressive azotemia and ↑ creatinine. It is associated with
oliguria, which can progress over hours or days with ↑ in BUN, creatinine,
+
and K with or without oliguria. It is usually reversible.
■ Chronic kidney disease develops slowly over months to years and necessi-
tates the initiation of dialysis or transplantation. Chronic kidney disease is
not a critical care issue. Although it is seen regularly in an ICU setting, it is
generally not the reason for admission to the ICU.
Pathophysiology
The three primary causes of AKI are:
■ Prerenal failure: Caused by renal hypoperfusion conditions such as hem-
orrhage, myocardial infarction, heart failure, cardiogenic shock, sepsis, and
anaphylaxis → impaired blood flow to kidneys → hypoperfusion of kidneys
→ retention of excessive amount of nitrogenous compounds → intense
vasoconstriction →↓ GFR. Patient can recover if fluid is replaced. Most
common cause of AKI.
■ Intrarenal failure: Caused by burns, crush injuries, infections, glomeru-
lonephritis, lupus erythematosus, diabetes mellitus, malignant HTN,
nephroseptic agents → acute tubular necrosis → afferent arteriole vasocon-
striction → hypoperfusion of the glomerular apparatus →↓ GFR → obstruc-
tion of tubular lumen by debris and casts, interstitial edema, or release of
intrarenal vasoactive substances. Nonrecovery is common.
■ Postrenal failure: Caused by any obstruction to urine flow such as blad-
der tumors, renal calculi, enlarged prostate, or blocked catheter between
the kidneys and urethral meatus →↑ pressure in kidney tubules →↓ GFR.

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