Contents
What Is AKI?
- An abrupt decline in kidney function over hours to days
- Defined by rising creatinine and/or falling urine output (KDIGO)
- Leads to retention of nitrogenous wastes, fluid, and electrolyte/acid-base disturbances
- Very common in critically ill, septic, and post-operative patients
Three Categories of AKI
- Prerenal: decreased perfusion (hypovolemia, hypotension, shock, heart failure)
- Intrarenal (intrinsic): direct kidney damage — ATN is most common (ischemia, nephrotoxins)
- Postrenal: obstruction to outflow (stones, BPH, tumor, clots)
- Prerenal is reversible if perfusion is restored quickly; prolonged prerenal → ATN
Acute Tubular Necrosis (ATN)
- Most common cause of intrinsic AKI in the ICU
- Ischemic (prolonged hypoperfusion/shock) or nephrotoxic (contrast, aminoglycosides, NSAIDs)
- Phases: onset → oliguric → diuretic → recovery
- Muddy-brown granular casts in urine are classic for ATN
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Start Free Practice →KDIGO Staging
- Stage 1: creatinine 1.5–1.9× baseline OR urine <0.5 mL/kg/hr for 6–12 hr
- Stage 2: creatinine 2.0–2.9× baseline OR urine <0.5 mL/kg/hr for ≥12 hr
- Stage 3: creatinine ≥3× baseline OR urine <0.3 mL/kg/hr ≥24 hr / anuria ≥12 hr / on dialysis
- Staging guides urgency and prognosis
Key Labs to Differentiate
- BUN:Cr ratio: >20:1 suggests prerenal; ~10–15:1 suggests intrinsic
- FENa: <1% prerenal (kidney conserving Na⁺); >2% ATN/intrinsic
- Urine osmolality: high (concentrated) in prerenal; isosthenuric in ATN
- Urine sediment: bland in prerenal, muddy-brown casts in ATN
Urine Output & Fluid Status
- Oliguria: <0.5 mL/kg/hr; anuria: essentially no output
- Monitor daily weights, I&Os, and volume exam (edema, JVD, crackles)
- Fluid overload is a common, dangerous complication (pulmonary edema)
- Match fluid management to the cause — resuscitate prerenal, restrict in overload
Hyperkalemia (the urgent threat)
- Failing kidneys retain K⁺ → risk of life-threatening arrhythmia
- ECG: peaked T waves → widened QRS → sine wave → arrest
- Stabilize the membrane: IV calcium gluconate/chloride first
- Shift K⁺ into cells: insulin + dextrose, albuterol, (bicarb if acidotic)
- Remove K⁺: diuretics, GI binders, or dialysis
Indications for Dialysis (AEIOU)
- Acidosis — severe metabolic acidosis refractory to therapy
- Electrolytes — refractory hyperkalemia
- Intoxications — certain dialyzable toxins
- Overload — refractory fluid overload / pulmonary edema
- Uremia — symptoms such as pericarditis, encephalopathy, bleeding
CRRT vs Intermittent Hemodialysis
- CRRT: continuous, gentle fluid/solute removal — preferred for hemodynamically unstable ICU patients
- IHD: fast, intermittent — rapid correction but risks hypotension
- Monitor for hypotension, bleeding (anticoagulation), and electrolyte shifts
- Protect and assess vascular access; track filter patency in CRRT
Nephrotoxins & Prevention / Nursing Priorities
- Avoid/limit nephrotoxins: NSAIDs, aminoglycosides, IV contrast, vancomycin (monitor levels)
- Maintain renal perfusion: treat hypovolemia/hypotension early
- Adjust drug doses for renal function; monitor levels
- Track creatinine, K⁺, acid-base, urine output, and volume status closely
Can you answer these 3 CCRN questions?
Here are 3 questions in the style of our premium bank. The full rationale explains exactly why the right answer is right — and why the distractors trap most test-takers.
Premium Practice Question
A hypotensive, dehydrated patient has BUN:Cr of 28:1 and FENa of 0.6%. This pattern is most consistent with:
- Acute tubular necrosis
- Prerenal AKI
- Postrenal obstruction
- Glomerulonephritis
Rationale: A BUN:Cr above 20:1 with a FENa below 1% reflects kidneys avidly conserving sodium in response to poor perfusion — classic prerenal AKI....
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Premium Practice Question
A patient in AKI has a serum K⁺ of 6.9 with peaked T waves and a widening QRS. The FIRST medication to give is:
- Insulin with dextrose
- IV calcium gluconate
- Albuterol nebulizer
- Sodium polystyrene sulfonate
Rationale: With ECG changes from hyperkalemia, IV calcium is given first to stabilize the cardiac membrane; shifting and removal therapies follow....
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Premium Practice Question
Which finding is an indication for urgent dialysis in AKI?
- BUN of 40 mg/dL
- Refractory hyperkalemia with ECG changes
- Urine output of 0.6 mL/kg/hr
- Creatinine of 1.6 mg/dL
Rationale: Using AEIOU, refractory hyperkalemia (Electrolytes) is a classic urgent indication for dialysis, along with severe acidosis, intoxications, fluid overload, and uremic complications....
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Frequently Asked Questions
What are the three types of AKI?
Prerenal (decreased perfusion from hypovolemia, hypotension, or heart failure), intrarenal/intrinsic (direct kidney damage, most often acute tubular necrosis from ischemia or nephrotoxins), and postrenal (obstruction of urine outflow).
How do labs distinguish prerenal AKI from ATN?
Prerenal AKI typically shows a BUN:Cr ratio above 20:1, a FENa below 1%, concentrated urine, and bland sediment because the kidney is conserving sodium and water. ATN shows a BUN:Cr around 10–15:1, a FENa above 2%, isosthenuric urine, and muddy-brown granular casts.
How is hyperkalemia in AKI managed?
First stabilize the cardiac membrane with IV calcium if there are ECG changes, then shift potassium into cells with insulin plus dextrose, albuterol, and bicarbonate if acidotic, and finally remove potassium with diuretics, GI binders, or dialysis.
What are the indications for dialysis?
Remember AEIOU: severe Acidosis, refractory Electrolyte abnormalities (hyperkalemia), dialyzable Intoxications, fluid Overload, and Uremic symptoms such as pericarditis or encephalopathy.
When is CRRT preferred over intermittent hemodialysis?
CRRT is preferred for hemodynamically unstable critically ill patients because it removes fluid and solutes slowly and gently, reducing the hypotension that can occur with the rapid shifts of intermittent hemodialysis.
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