Acute Kidney Injury — AKI

A patient's creatinine jumps from 1.0 to 2.4 mg/dL in 48 hours with urine output dropping to 15 mL/hr. This isn't chronic disease — it's a reversible emergency if you catch it now.

Acute kidney injury is a sudden decline in kidney function defined by a serum creatinine rise of ≥0.3 mg/dL within 48 hours, a creatinine increase ≥1.5 times baseline within 7 days, or urine output below 0.5 mL/kg/hr for 6 hours. AKI is classified by cause: prerenal (decreased perfusion — hypotension, hemorrhage, dehydration, heart failure), intrarenal (direct kidney damage — nephrotoxic drugs like aminoglycosides, NSAIDs, IV contrast, or prolonged ischemia causing acute tubular necrosis), and postrenal (obstruction — but kidney stones specifics belong in the sibling atom). The BUN-to-creatinine ratio helps differentiate: prerenal AKI typically shows a ratio >20:1 because the kidneys reabsorb urea aggressively when underperfused. Intrarenal injury drops that ratio closer to 10:1. Nursing priorities center on strict I&O monitoring, daily weights, trending creatinine and potassium, avoiding nephrotoxic agents, and watching for fluid overload. Hyperkalemia is the most immediately life-threatening complication — potassium above 6.0 mEq/L can cause fatal dysrhythmias.

Key Distinctions

Don't confuse prerenal AKI (low perfusion, reversible with fluids) with intrarenal AKI (structural damage, requires time to heal) — the first-line intervention differs: give fluids for prerenal, restrict fluids for intrarenal with fluid overload. Students mix up AKI and CKD: AKI is sudden, potentially reversible, and shows normal-sized kidneys on imaging; CKD is gradual, irreversible, with small shrunken kidneys. BUN rises in both dehydration (a prerenal cause) and intrarenal AKI, but the BUN-to-creatinine ratio tells you which.

Clinical Pearl

Think of AKI in three zones: before the kidney (prerenal = pump or volume problem), at the kidney (intrarenal = toxic or ischemic hit), after the kidney (postrenal = blocked pipe).