Contents
Why CRRT Matters on the CCRN
- The updated exam blueprint leans harder on renal support therapies — CRRT questions are no longer rare
- Expect stems about WHY a patient gets CRRT instead of intermittent hemodialysis (IHD)
- Citrate anticoagulation and its calcium math is a classic trap question
- Circuit alarms (access, return, TMP) test whether you can troubleshoot at the bedside
CRRT vs Intermittent Hemodialysis
- CRRT is for the hemodynamically UNSTABLE patient — slow, continuous solute and fluid removal causes far less hypotension
- IHD removes large volumes in 3–4 hours — a septic patient on norepinephrine will not tolerate it
- CRRT runs 24 hours/day at low blood-flow rates (typically 150–250 mL/min)
- Trade-offs: continuous anticoagulation exposure, patient tethered to the machine, slower potassium clearance in a true hyperkalemic emergency
- Classic stem: AKI + volume overload + MAP 62 on vasopressors → choose CRRT, not IHD
Indications: The A-E-I-O-U of Renal Replacement
- Acidosis — severe refractory metabolic acidosis (pH <7.1)
- Electrolytes — refractory hyperkalemia (K⁺ >6.5 or rising despite treatment)
- Intoxication — dialyzable toxins (lithium, salicylates, toxic alcohols)
- Overload — diuretic-refractory volume overload (pulmonary edema, anasarca)
- Uremia — symptomatic uremia: pericarditis, encephalopathy, bleeding
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Start Free Practice →The Four Modalities (SCUF, CVVH, CVVHD, CVVHDF)
- SCUF (slow continuous ultrafiltration): fluid removal ONLY — no meaningful solute clearance
- CVVH (hemofiltration): convection — solvent drag pulls solutes across the membrane; requires replacement fluid; better middle-molecule clearance
- CVVHD (hemodialysis): diffusion — solutes move down a concentration gradient into countercurrent dialysate; best for small solutes (K⁺, urea)
- CVVHDF (hemodiafiltration): convection + diffusion combined — dialysate AND replacement fluid
- Memory aid: H = hemofiltration = convection; D = dialysate = diffusion; HDF = both
Anticoagulation: Citrate vs Heparin
- The filter clots without anticoagulation — each clotted circuit costs the patient ~150–200 mL of blood
- Regional citrate (preferred): citrate chelates ionized calcium in the CIRCUIT only; calcium is re-infused to the patient on the return side
- Citrate monitoring: circuit ionized calcium (goal low, ~0.25–0.4 mmol/L) AND systemic ionized calcium (keep normal)
- Citrate toxicity (liver failure can't metabolize citrate): FALLING systemic ionized calcium + RISING total calcium (total:ionized ratio >2.5) + worsening anion-gap acidosis
- Heparin: systemic anticoagulation — monitor aPTT/anti-Xa, watch for bleeding and HIT
Electrolyte & Metabolic Traps
- CRRT removes MORE than toxins: expect hypophosphatemia, hypokalemia, hypomagnesemia — check labs q6h and replace per protocol
- Hypothermia is common (extracorporeal blood cooling) — it can MASK a fever, so don't rule out sepsis because the temp is normal
- Citrate is metabolized to bicarbonate → metabolic ALKALOSIS can develop over days
- Many drugs are cleared by CRRT (antibiotics especially) — dosing must be adjusted and levels monitored
- Fluid balance is prescribed hourly — accurate I&O is a core nursing responsibility, not a formality
Troubleshooting Circuit Alarms
- Access pressure extremely negative: the pump is sucking against the vessel wall → check for kinks, reposition the patient/catheter — do NOT just increase blood pump speed
- Return (venous) pressure high: obstruction on the way back — kinked line, clot in the return chamber, or clotted catheter lumen
- Rising TMP (transmembrane pressure): the filter is clotting — anticipate circuit change and evaluate anticoagulation adequacy
- Air-in-line alarm: clamp, protect the patient first — air embolism risk is real with high continuous flows
- Frequent unexplained alarms + falling filter life = inadequate anticoagulation or poor catheter position
Nursing Priorities During CRRT
- Hourly I&O with the prescribed fluid-removal (net ultrafiltration) target — titrate against MAP and vasopressor dose
- Monitor systemic ionized calcium on citrate protocols — hypocalcemia signs: paresthesias, tetany, prolonged QT, hypotension
- Continuous core temperature monitoring — warm the return line or use external warming as ordered
- Protect the vas-cath: it is the patient's lifeline — sterile dressing care, never use it for routine meds
- Minimize circuit downtime: every disconnection wastes filter life and blood — cluster care and travel
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 patient on CRRT with regional citrate anticoagulation develops perioral numbness, muscle twitching, and a prolonged QT interval. What is the priority action?
- Increase the citrate infusion rate
- Check the systemic ionized calcium and anticipate reducing citrate
- Give a fluid bolus for hypotension
- Flush the return line with heparinized saline
Rationale: Perioral numbness, twitching, and QT prolongation are signs of systemic ionized hypocalcemia — the hallmark of citrate accumulation. Verify the systemic ionized calcium and anticipate reducing the citrate dose or increasing the calcium infusion....
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Premium Practice Question
Which patient is the BEST candidate for CRRT rather than intermittent hemodialysis?
- Stable CKD patient missing an outpatient dialysis session
- Septic shock on norepinephrine with AKI and worsening volume overload
- Hyperkalemia of 7.2 with ECG changes and stable hemodynamics
- Chronic lithium user with a mildly elevated level
Rationale: CRRT is chosen when the patient cannot hemodynamically tolerate rapid fluid and solute shifts. A vasopressor-dependent septic patient with AKI and volume overload is the classic CRRT candidate....
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Premium Practice Question
The CRRT machine alarms with an extremely negative access pressure. What should the nurse do FIRST?
- Increase the blood pump speed to overcome the pressure
- Assess the catheter and tubing for kinks and reposition the patient
- Silence the alarm and document the reading
- Prepare to change the filter immediately
Rationale: A very negative access pressure means the machine cannot pull blood — usually a kinked line or the catheter tip against the vessel wall. Assess and reposition first; increasing pump speed worsens the suction....
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Related CCRN Guides
Frequently Asked Questions
Why is CRRT used instead of regular hemodialysis in the ICU?
CRRT removes fluid and solutes slowly and continuously over 24 hours, so it causes far less hypotension than intermittent hemodialysis, which pulls large volumes in 3–4 hours. That makes CRRT the therapy of choice for hemodynamically unstable patients — especially those in shock on vasopressors.
What is the difference between CVVH, CVVHD, and CVVHDF?
CVVH clears solutes by convection (solvent drag with replacement fluid), CVVHD clears by diffusion (countercurrent dialysate), and CVVHDF combines both. SCUF removes fluid only. Remember: H = hemofiltration = convection; D = dialysate = diffusion.
How does citrate anticoagulation work in CRRT?
Citrate chelates ionized calcium in the extracorporeal circuit, preventing clotting only in the circuit, while a calcium infusion on the return side keeps the patient's systemic calcium normal. Nurses monitor both circuit and systemic ionized calcium levels.
What are the signs of citrate toxicity?
A falling systemic ionized calcium with a rising total calcium (total-to-ionized ratio above ~2.5) plus a worsening anion-gap metabolic acidosis. It occurs when the liver cannot metabolize citrate — think liver failure or shock liver. Symptoms mirror hypocalcemia: paresthesias, tetany, prolonged QT, hypotension.
Which electrolytes drop during CRRT?
Phosphate, potassium, and magnesium are all continuously removed — hypophosphatemia is especially common. Labs are typically checked every 6 hours with protocolized replacement. CRRT also cools the blood, so hypothermia can mask fever.
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