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Acute kidney injury is one of the most common organ failures in the ICU, and it rarely arrives alone — it is usually the kidney's response to the same shock, sepsis, or nephrotoxin that put the patient in the unit. For the bedside nurse, AKI is a monitoring job before it is a dialysis job: catching the rising creatinine and the falling urine output early, protecting the kidney from a second hit, and, when the kidney fails outright, running continuous renal replacement therapy safely for days on end. This article walks through what the nurse actually does.
Acute kidney injury is defined by how fast the kidney's function drops, not by a single number. The widely used KDIGO criteria stage AKI by change in serum creatinine and by urine output, whichever is worse. You do not need to memorize the exact thresholds to be a good bedside nurse, but you should recognize the pattern: a creatinine climbing day over day, or a urine output that has fallen below roughly half a milliliter per kilogram per hour and stayed there, is AKI until proven otherwise.
| Stage | Creatinine | Urine output |
|---|---|---|
| 1 | 1.5–1.9× baseline | < 0.5 mL/kg/hr for 6–12 hr |
| 2 | 2.0–2.9× baseline | < 0.5 mL/kg/hr for ≥ 12 hr |
| 3 | ≥ 3× baseline, or on dialysis | < 0.3 mL/kg/hr for ≥ 24 hr, or anuria ≥ 12 hr |
The practical takeaway: urine output is the earliest, cheapest, most sensitive number you own. A creatinine lags a day behind the injury, but the urine falls in real time. An accurate hourly output — a good Foley, a clean measurement, and honest documentation — is the single most useful thing the nurse contributes to catching AKI early.
Everything that injures a kidney sorts into one of three places, and the bucket determines the fix.
Once a kidney is injured, the nurse's job shifts to preventing further insult while it tries to recover. That means being the person who flags nephrotoxins on the MAR — the vancomycin trough that is due, the NSAID that should not be there, the contrast study being ordered on a patient already in AKI — and advocating for renal dosing or a hold. It means keeping the mean arterial pressure in the range the team wants so perfusion stays adequate, and watching for the volume overload that a failing kidney cannot offload. A patient in oliguric AKI who is still getting maintenance fluids and multiple IV piggybacks will drown; totaling the real intake and voicing it is nursing work that changes management.
Not every AKI needs dialysis — many recover with time and support. Renal replacement therapy is started when a complication of kidney failure becomes dangerous, and the classic memory aid is AEIOU: Acidosis (severe metabolic acidosis the kidney can't correct), Electrolytes (refractory hyperkalemia — the one that kills fastest), Intoxications (certain dialyzable poisons and drugs), Overload (fluid overload causing pulmonary edema unresponsive to diuretics), and Uremia (symptomatic — pericarditis, encephalopathy, bleeding). When you see a potassium climbing past 6.5 with ECG changes in an anuric patient, you are looking at the most time-critical dialysis indication there is.
Continuous renal replacement therapy does the work of intermittent hemodialysis but spreads it across 24 hours a day instead of a 3–4 hour session. The reason is hemodynamics: a hypotensive, pressor-dependent ICU patient cannot tolerate having several liters pulled off in a few hours, but they tolerate a slow, continuous removal of fluid and solute far better. CRRT trades speed for gentleness, which is exactly what an unstable patient needs. Common modes — CVVH, CVVHD, CVVHDF — differ in whether they clear solute by convection, diffusion, or both, but the nurse's monitoring job is largely the same across them.
Running CRRT is a continuous nursing responsibility, and a handful of things demand constant attention. Fluid balance is the headline number: the machine's net ultrafiltration goal is set by the team, and you are titrating the patient's real-time volume status against it — pulling too fast drops the pressure, pulling too little leaves them overloaded. Circuit patency matters because the blood outside the body wants to clot; rising filter and access pressures warn you the circuit is clotting off, and a clotted circuit means lost blood and lost therapy time. Anticoagulation — usually regional citrate or systemic heparin — keeps the circuit open, and citrate brings its own trap.
| CRRT problem | What the nurse sees / does |
|---|---|
| Filter clotting | Rising transmembrane / filter pressure, darkening circuit; check anticoagulation, flag for possible circuit change |
| Hypotension | Often from pulling fluid too fast; reassess the ultrafiltration rate with the team |
| Citrate accumulation | Low ionized calcium with rising total calcium; the classic citrate-lock picture — notify provider |
| Electrolyte swings | CRRT clears potassium, phosphate, magnesium continuously — patients can go low; monitor and replace per protocol |
| Hypothermia | Blood cooled outside the body; use the warmer and monitor temperature |
Regional citrate anticoagulation keeps the circuit from clotting by binding calcium inside the circuit — clotting needs calcium, so removing it locally stops the clot without anticoagulating the patient. Calcium is then replaced back to the patient after the blood returns. The trap is citrate accumulation: if the patient can't metabolize the citrate load (liver failure, shock), it builds up and locks calcium throughout the body. The tell is a rising total calcium with a falling ionized calcium — a widening gap — often with a worsening metabolic acidosis. Nurses running citrate CRRT monitor ionized calcium on a schedule for exactly this reason, and a widening total-to-ionized gap is a call-the-provider finding.
AKI is caught by the nurse who trusts the urine output before the creatinine confirms it, and it is kept from getting worse by the nurse who guards the kidney from the next nephrotoxin and the next hypotensive stretch. When the kidney fails and CRRT starts, the therapy is only as safe as the nurse watching the fluid balance, the circuit pressures, and the ionized calcium. None of it is glamorous, but it is some of the most consequential monitoring in critical care — the difference between a kidney that recovers and one that doesn't often runs through the bedside nurse's flowsheet.
This piece pairs with the ICU electrolyte and volume guides on the site, including hypocalcemia and calcium repletion, the massive transfusion protocol, and the DIC guide, since coagulopathy, transfusion, and citrate all bend the calcium.
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