Continuous renal replacement therapy (CRRT) is the primary renal replacement strategy for critically ill patients who cannot tolerate the rapid fluid and solute shifts of conventional hemodialysis. In the intensive care unit, CRRT is used in 60–70% of patients requiring renal replacement therapy, and ICU nurses bear full responsibility for circuit management, fluid balance titration, electrolyte monitoring, and anticoagulation surveillance — 24 hours a day. Up to 65% of patients on CRRT develop hypophosphatemia, and electrolyte disturbances are a leading source of preventable harm. Understanding the mechanisms, modalities, and monitoring requirements of CRRT is essential for any nurse working in a critical care setting, and it is increasingly tested on the NCLEX.
| CRRT quick reference | Detail |
|---|---|
| Primary indication | AKI with hemodynamic instability — MAP <65 requiring vasopressors |
| Preferred anticoagulation | Regional citrate anticoagulation (RCA) — KDIGO first-line recommendation |
| Effluent dose target | 20–25 mL/kg/hr (delivered dose) |
| Blood flow rate (CRRT) | 150–250 mL/min (vs 300–500 mL/min for IHD) |
| Most common complication | Filter clotting — median circuit life 26 hr (heparin) vs 47 hr (citrate) |
| Most common electrolyte loss | Phosphate (incidence up to 65%), potassium (up to 24%), magnesium |
| Citrate target (post-filter iCa) | <0.35 mmol/L in the circuit; systemic iCa 1.0–1.2 mmol/L |
| TMP alarm threshold | >300 mmHg indicates potential filter replacement needed |
| Net ultrafiltration limit | Below 1.5–2.0 mL/kg/hr to avoid hemodynamic compromise |
| Electrolyte monitoring frequency | Every 4–6 hours during active CRRT |
What is CRRT and why is it used in the ICU?
CRRT is a continuous, slow form of renal replacement therapy that removes solutes, toxins, and excess fluid over 24 hours rather than in a 3–4 hour intermittent session. The slow rate of solute and fluid removal is the defining clinical advantage: patients who are hemodynamically unstable tolerate CRRT far better than intermittent hemodialysis (IHD) because the cardiovascular system is not suddenly asked to compensate for rapid fluid shifts.
Acute kidney injury (AKI) is the primary driver of CRRT use in the ICU. AKI develops in approximately 50–70% of critically ill patients, and among those who require renal replacement therapy, hemodynamic instability — often driven by sepsis, cardiogenic shock, or major surgery — frequently makes IHD impractical or dangerous.
CRRT is indicated when one or more of the following are present:
- Hemodynamic instability requiring vasopressors — the most common indication; IHD causes hypotension in 20–30% of sessions even in stable patients
- Fluid overload refractory to diuretics — especially in oliguric or anuric AKI, when cumulative positive fluid balance threatens pulmonary function
- Severe uremia — BUN above 100 mg/dL, uremic encephalopathy, pericarditis
- Life-threatening electrolyte crises — hyperkalemia above 6.5 mEq/L, severe hypernatremia or hyponatremia requiring slow correction
- Metabolic acidosis — pH below 7.1 unresponsive to bicarbonate therapy
- Drug or toxin removal — for water-soluble, low-protein-bound substances when continuous clearance is preferred over a single IHD session
- Severe acute pancreatitis or systemic inflammatory response — to remove inflammatory cytokines, though evidence for this indication remains debated
CRRT vs IHD: choosing the right modality
The central question is hemodynamic stability. IHD removes 2–4 liters of fluid in 3–4 hours, requiring robust cardiovascular compensatory capacity. CRRT removes fluid at 100–300 mL/hr and can run continuously, distributing the hemodynamic burden across 24 hours.
Hemodialysis nursing covers the standard IHD protocol used in stable patients and those with ESRD. CRRT is reserved for the ICU context, where the patient cannot tolerate the rapid solute and fluid shifts of IHD. Once a patient is weaned from vasopressors and hemodynamically stable, the transition to IHD or peritoneal dialysis is considered.
CRRT modalities: CVVH, CVVHD, CVVHDF, and SCUF
Four main CRRT modalities exist, each using a different mechanism of solute removal. Understanding the mechanism matters clinically because it determines which solutes are cleared and at what efficiency — and because NCLEX questions test the underlying physiology.
| Modality | Mechanism | Fluid removed | Solute clearance | Best for |
|---|---|---|---|---|
| CVVH — continuous venovenous hemofiltration | Convection (solute drag through membrane with ultrafiltrate) | Large volume; replacement fluid required | Middle molecules well cleared; small molecule clearance moderate | Inflammatory mediator removal; elevated middle molecule burden |
| CVVHD — continuous venovenous hemodialysis | Diffusion (concentration gradient between blood and dialysate flowing counter-current) | Minimal; primarily for solute clearance | Small molecules very efficient; middle molecules poor | Hyperkalemia, uremia, acidosis; lower nursing workload; best hemofilter lifespan |
| CVVHDF — continuous venovenous hemodiafiltration | Both convection and diffusion | Large volume; replacement fluid required | Broadest spectrum — small and middle molecules | Most common modality in US ICUs; comprehensive clearance needs |
| SCUF — slow continuous ultrafiltration | Convection only; no dialysate, minimal replacement fluid | Targeted fluid removal only (100–300 mL/hr) | Minimal solute clearance | Refractory fluid overload in heart failure with preserved kidney function |
Convection vs diffusion: the mechanism that drives NCLEX questions
Convection moves solutes by dragging them through the membrane along with water — the same principle as water pushing debris through a filter. Larger middle molecules (molecular weight 500–30,000 Da) are cleared efficiently because the membrane pore allows them through with the bulk water flow. CVVH and the convective component of CVVHDF rely on this mechanism.
Diffusion moves solutes down a concentration gradient from blood into dialysate. Smaller molecules — urea, creatinine, potassium, bicarbonate — cross readily because their small size allows rapid membrane diffusion. Larger middle molecules diffuse poorly because they hit the pores slowly. CVVHD and the diffusive component of CVVHDF use this mechanism.
In practice, CVVHDF is the most frequently used modality (approximately 59% of US ICU programs), offering the broadest solute clearance. CVVHD is favored in some centers because it minimizes replacement fluid volumes and reduces nursing workload.
Vascular access for CRRT
CRRT requires a large-bore dual-lumen dialysis catheter that can sustain continuous blood flow at 150–250 mL/min. This is different from a standard central line — standard triple-lumen catheters cannot generate adequate flow for CRRT.
Catheter placement sites
Femoral vein — most rapidly placed in emergencies; highest infection risk with prolonged use; patient mobility is severely limited; preferred in patients with severe coagulopathy where internal jugular placement is risky due to proximity to carotid.
Internal jugular vein (right preferred) — balanced choice; lower infection risk than femoral; does not limit ambulation; avoids the risk of pneumothorax associated with subclavian access.
Subclavian vein — lowest infection risk of all sites but highest risk of stenosis with prolonged use; stenosis can compromise the ipsilateral arm for future AV fistula creation, making it a poor choice in patients who may need long-term dialysis access.
Blood flow rates for CRRT run at 150–250 mL/min — substantially lower than the 300–500 mL/min required for intermittent hemodialysis. This lower flow requirement reflects CRRT’s slower, continuous clearance strategy rather than the high-intensity rapid clearance of IHD.
Dialysis catheter nursing care
Catheter care follows the same principles as central line nursing, with additional CRRT-specific considerations:
- Dressing changes every 7 days with chlorhexidine-impregnated dressing (or sooner if soiled, wet, or non-occlusive)
- Lumen labeling — both lumens labeled (arterial/red = blood out to machine; venous/blue = blood returning to patient); never mix up the ports
- No blood draws or medication administration through CRRT lumens during active therapy unless no other access is available — medications may be cleared by the circuit before reaching the systemic circulation
- Catheter position verification on chest X-ray before initiating CRRT via IJ or subclavian placement
- Access pressure monitoring — a consistently negative access pressure at or below −200 mmHg predicts circuit failure within 12 hours; reposition the catheter or alert the provider
Circuit components: what the nurse manages at the bedside
The CRRT circuit is a closed extracorporeal system with five core components:
Blood pump — draws blood from the arterial (red) lumen of the dialysis catheter and propels it through the circuit at the prescribed blood flow rate. The pump speed determines blood flow rate in mL/min.
Hemofilter (membrane) — the hollow fiber semipermeable membrane where solute clearance and ultrafiltration occur. AN69 membranes (polyacrylonitrile) are standard on Prismaflex systems and most commonly used in US ICUs.
Effluent collection system — collects the ultrafiltrate that crosses the membrane; this includes the dialysate (post-diffusion) and the ultrafiltrate (post-convection), combined into a single effluent bag. Effluent volume is measured hourly and is central to fluid balance calculation.
Replacement fluid — infused pre-filter (pre-dilution) or post-filter (post-dilution) to replace the large volume of ultrafiltrate removed in CVVH and CVVHDF. Replacement fluid composition is prescribed based on labs — standard commercially available solutions (Prismasol, Phoxilium, Normocarb) contain bicarbonate as buffer and can contain varying concentrations of potassium, calcium, magnesium, and phosphate.
Dialysate — flows counter-current to blood on the opposite side of the membrane in CVVHD and CVVHDF. Same commercial solutions used for both dialysate and replacement fluid; prescribed concentration differs based on target electrolytes.
Pre-dilution vs post-dilution
The position of the replacement fluid infusion point matters clinically:
Pre-dilution (replacement fluid infused before the hemofilter) dilutes the blood entering the filter, reducing hematocrit and protein concentration at the membrane surface. This decreases filtration fraction and reduces clotting risk, extending filter life — particularly valuable when anticoagulation is limited. The trade-off is reduced clearance efficiency because incoming blood is diluted before filtration.
Post-dilution (replacement fluid infused after the hemofilter) maximizes solute clearance because blood is filtered at full concentration. However, higher protein and cell concentration at the membrane surface increases clotting risk. Filtration fraction must be kept below 20–25% to avoid excessive hemoconcentration.
In practice, CVVHDF frequently uses a combination — some replacement fluid pre-filter, some post-filter — to balance clearance efficiency against filter life.
Anticoagulation for CRRT
The extracorporeal circuit activates coagulation pathways on contact with the synthetic membrane — blood clots in the circuit without some form of anticoagulation. At the same time, many ICU patients are already at high bleeding risk. The nurse must understand each anticoagulation strategy, its monitoring parameters, and its specific complications.
| Anticoagulation method | Mechanism | Nursing monitoring | Key contraindications | Circuit life |
|---|---|---|---|---|
| Regional citrate anticoagulation (RCA) — KDIGO first-line | Citrate chelates ionized calcium in the circuit (Ca2+ required for coagulation cascade). Calcium replaced systemically post-filter or via separate IV infusion. | Post-filter iCa <0.35 mmol/L; systemic iCa 1.0–1.2 mmol/L; pH and bicarbonate (citrate toxicity); every 6 hours | Severe liver failure (cannot metabolize citrate); severe lactic acidosis; citrate allergy | ~47 hours median |
| Unfractionated heparin (UFH) | Systemic anticoagulation via antithrombin III activation; prevents fibrin clot formation throughout circuit and patient | aPTT 45–60 seconds (circuit anticoagulation); anti-Xa levels if available; platelet count daily (HIT surveillance) | Active major bleeding; HIT (absolute contraindication); recent CNS surgery or trauma | ~26 hours median |
| Regional heparin with protamine reversal | Heparin added pre-filter, protamine infused post-filter to reverse systemic effect | Pre-filter aPTT elevated; post-filter aPTT normal; complex titration; largely replaced by RCA in most centers | Protamine allergy; heparin-protamine complex reactions | Comparable to systemic heparin |
| Argatroban | Direct thrombin inhibitor — used when heparin is contraindicated due to HIT | aPTT 45–60 seconds; note: argatroban elevates PT/INR — do not use PT/INR alone to assess anticoagulation status | Significant hepatic dysfunction (argatroban is hepatically cleared) | Comparable to heparin |
| No anticoagulation | Pre-dilution and high blood flow to minimize clotting; accepted in patients at very high bleeding risk | Circuit pressure trends; visual filter assessment; TMP trends | N/A — used specifically when all anticoagulants contraindicated | ~22 hours median |
Regional citrate anticoagulation in depth
RCA is the preferred anticoagulation strategy per KDIGO guidelines because it extends filter life and reduces bleeding risk compared to systemic heparin (bleeding rate 5.1% vs 16.9%). Understanding the physiology is critical for managing it safely at the bedside.
Citrate is infused into the arterial (pre-filter) blood line. It binds ionized calcium within the extracorporeal circuit, dropping the post-filter ionized calcium to below 0.35 mmol/L — a concentration too low to support the coagulation cascade. The anticoagulation is confined to the circuit.
After the filter, calcium is replenished either via a separate IV infusion or via post-filter addition to the returning blood, restoring systemic ionized calcium to the target range of 1.0–1.2 mmol/L. The nurse titrates the calcium infusion to maintain this systemic range. Typical citrate infusion rates run at 2–3 mmol/L blood flow, adjusted to keep post-filter iCa below 0.35 mmol/L.
Citrate is metabolized in the liver (and to a lesser extent in muscle and kidney) to bicarbonate. In normal liver function, this metabolism is efficient. In liver failure, citrate accumulates — causing the classic citrate toxicity syndrome:
- Low systemic ionized calcium (iCa below 1.0 mmol/L) with a high total calcium — because total calcium includes protein-bound and citrate-chelated calcium, which is high, while free calcium is low
- Metabolic alkalosis — excess bicarbonate from citrate metabolism
- Elevated total calcium-to-ionized calcium ratio above 2.5 is the sentinel lab finding
Management: reduce or stop citrate infusion, increase calcium replacement, switch to an alternative anticoagulation method, consult nephrology.
Replacement fluid and dialysate: composition and prescription
Commercial CRRT solutions are available in several formulations. The key variables are potassium concentration, phosphate content, calcium content, and buffer (bicarbonate vs lactate).
Bicarbonate-buffered solutions (Prismasol, Normocarb) are preferred for most ICU patients. Lactate-buffered solutions require intact liver function for conversion to bicarbonate — in liver failure or severe shock with impaired lactate clearance, lactate-based fluids can worsen lactic acidosis.
Potassium concentration is adjusted based on serum potassium. Zero-potassium solutions are used for initial hyperkalemia management; once potassium normalizes, switching to 2–4 mEq/L solutions prevents the hypokalemia that CRRT induces with prolonged treatment.
Phosphate is absent from most standard CRRT solutions, which drives the high incidence of hypophosphatemia (up to 65%). Phoxilium (1.2 mmol/L phosphate, 4.0 mmol/L potassium) or similar phosphate-containing solutions should be used proactively in patients at risk or once hypophosphatemia develops.
Calcium is typically present at 1.5 mEq/L in pre-mixed solutions used without citrate; when RCA is active, calcium-free solutions are used pre-filter, and calcium is replaced via a dedicated infusion post-filter.
Fluid balance management
Fluid balance management is among the most consequential nursing responsibilities in CRRT. Cumulative positive fluid balance is independently associated with increased mortality in AKI — yet over-removal causes hypotension, renal ischemia, and worsening kidney recovery.
The CRRT machine controls fluid removal through the net ultrafiltration rate — the difference between total effluent output and total fluid input (replacement fluid + dialysate + all other infusions). The nurse programs or monitors this rate, typically prescribed in mL/hr.
Evidence supports keeping net ultrafiltration below 1.5–2.0 mL/kg/hr to minimize hemodynamic compromise. Above this rate, intravascular depletion outpaces refilling from the interstitium, causing hypotension and potential acute respiratory failure reversal if the patient is diuresing into pulmonary edema.
Daily fluid targets are prescribed by the intensivist, typically aiming for net even balance, net negative 500–1,000 mL/day for fluid overloaded patients, or custom targets in complex cases. The nurse tracks this hourly.
Hourly fluid balance calculation:
- Total CRRT effluent output (mL) in the past hour
- Subtract: replacement fluid infused (mL) + dialysate infused (mL) + all other IV infusions (mL) + oral intake (mL)
- The result is the net hourly fluid removal
A positive number means the patient is losing fluid from the body (expected when ordered negative balance). A negative number means more fluid was given than removed. Any discrepancy from the prescribed target requires investigation and adjustment.
Daily weights — obtained every morning using the same conditions (same scale, same time, same clothing) — serve as the anchor for fluid balance assessment. A weight gain of 1 kg approximates 1 liter of fluid retention.
Nursing monitoring during CRRT
CRRT nursing involves continuous assessment across four domains: hemodynamics, circuit integrity, electrolytes, and medication management.
Hemodynamic monitoring
Maintain mean arterial pressure (MAP) at or above 65 mmHg. Hypotension is the most common reason CRRT must be paused or the ultrafiltration rate reduced. In patients also requiring hemodynamic support, CRRT often works alongside arterial line monitoring — the arterial line provides continuous MAP and allows frequent blood gas sampling without repeated venipuncture.
When MAP drops:
- Reduce the net ultrafiltration rate immediately
- Administer IV fluid bolus per order or standing protocol
- Assess vasopressor requirements — notify provider if MAP does not recover
- Do not pause CRRT entirely if hypotension is mild and transient — circuit downtime increases clotting risk
Vital signs and temperature
CRRT causes heat loss because blood circulates outside the body through a non-warmed circuit at room temperature. Patients frequently develop hypothermia (temperature below 36°C) within 2–4 hours of initiation. Apply warming blankets proactively. Some CRRT machines (Prismaflex) have an integrated blood warmer — confirm it is active and set to 37°C. Persistent hypothermia contributes to coagulopathy, cardiac arrhythmias, and patient discomfort.
Circuit pressure monitoring
The CRRT machine continuously displays three pressure values. Understanding normal ranges and alarm causes is essential:
Access pressure (pre-pump, typically −50 to −150 mmHg): Reflects catheter inflow. Increasingly negative values (below −200 mmHg) indicate poor blood draw from the catheter — caused by catheter malposition, kinking, patient position change (particularly femoral catheters during hip flexion), or intraluminal thrombus. Reposition the patient, flush the lumen, or notify the provider.
Return pressure (venous pressure, typically +50 to +250 mmHg): Reflects resistance in the return line and catheter. Elevated return pressure (above +250 mmHg) suggests venous line obstruction, clot at the return catheter tip, or vasospasm. Lowered return pressure may indicate catheter malposition.
Transmembrane pressure (TMP, typically 50–250 mmHg): The hydrostatic pressure gradient across the hemofilter membrane. Rising TMP indicates progressive filter fouling — protein deposition and microclot formation on the membrane. A TMP above 300 mmHg signals impending filter failure and the need for circuit changeout. Each 1 mmHg rise in TMP independently increases clotting risk by approximately 1.5%.
Electrolyte monitoring
Check a complete metabolic panel (sodium, potassium, bicarbonate, chloride, BUN, creatinine), ionized calcium, magnesium, and phosphate every 4–6 hours during active CRRT. In patients on RCA, ionized calcium — both post-filter and systemic — is checked every 6 hours or more frequently during titration.
See the electrolyte imbalances nursing guide for management principles. CRRT-specific priorities:
- Potassium — trending down? Switch to potassium-containing replacement fluid or add KCl to the infusion. Trending up despite CRRT? Review potassium intake, consider zero-potassium solutions.
- Phosphate — supplement aggressively; hypophosphatemia causes respiratory muscle weakness, complicating ventilator weaning
- Magnesium — often under-replaced; replete with IV magnesium sulfate per protocol
- Bicarbonate — metabolic alkalosis on citrate suggests toxicity; metabolic acidosis on CRRT suggests citrate underdosing or inadequate CRRT dose
Intake and output
Document hourly: CRRT effluent volume, replacement fluid volume, all other inputs, urine output, drain outputs. Urine output during CRRT is still documented separately — recovering urine output (above 200 mL over 6 hours, trending up) is a key indicator that CRRT weaning may be possible.
Medication dose adjustment
Many ICU drugs are cleared by CRRT, requiring dose adjustments. Water-soluble, low-protein-bound, small-molecular-weight drugs are most susceptible. This includes most beta-lactam antibiotics (piperacillin-tazobactam, meropenem), vancomycin, aminoglycosides, and fluconazole. Consult pharmacy for CRRT-adjusted dosing. Standard renal dosing guidelines (based on creatinine clearance) do not account for CRRT clearance and are not reliable in this context.
Check the critical lab values nursing guide for emergency thresholds requiring immediate escalation.
Circuit troubleshooting
Clotted filter
The most common circuit complication. Signs include rising TMP, darkening blood in the filter (visible inspection), reduced effluent output, and machine alarms. Prevention strategies:
- Maintain blood flow at 150–250 mL/min (flow below 100 mL/min dramatically increases stasis and clotting risk)
- Keep filtration fraction below 20–25%
- Use pre-dilution to reduce hemoconcentration
- Optimize anticoagulation per protocol
- Flush the circuit with saline per institutional protocol when brief interruptions occur (patient transport, procedures)
When the filter is confirmed clotted: initiate circuit change per protocol, document downtime, review anticoagulation to prevent recurrence, notify provider if filter life is shorter than expected.
Circuit life benchmarks:
- Citrate anticoagulation: median 46–57 hours in most trials
- Unfractionated heparin: median 26–36 hours
- No anticoagulation: median ~22 hours
Consistently short circuit life (below 12 hours) warrants investigation: catheter position, anticoagulation adequacy, filtration fraction, and pre-dilution ratio.
High TMP alarm
Causes: Filter fouling from protein deposition or microclotting; excessive ultrafiltration rate; post-dilution ratio too high; inadequate anticoagulation.
Management: Reduce ultrafiltration rate; increase pre-dilution; review anticoagulation. If TMP exceeds 300 mmHg and cannot be corrected, plan circuit changeout.
Access pressure alarms (highly negative)
Causes: Catheter malposition (tip against vessel wall); kinking of the external catheter line; patient movement (especially femoral catheters); intraluminal thrombus.
Management: Reposition patient; inspect catheter for external kinks; attempt gentle aspiration (do not flush forcefully); notify provider if persistent — catheter exchange may be required.
Air detection alarms
Causes: Air introduced at connections, saline bag running dry, loose connection at sampling ports.
Management: The machine automatically clamps the return line when air is detected — never override this safety mechanism. Identify and eliminate the air source, inspect all connections, resume per protocol after air is purged.
Complications of CRRT
| Complication | Mechanism | Presentation | Nursing intervention |
|---|---|---|---|
| Hypotension | Excessive net ultrafiltration; vasodilation from circuit exposure; underlying hemodynamic instability | MAP <65 mmHg, tachycardia, patient reports light-headedness | Reduce UF rate; administer fluid bolus; titrate vasopressors; notify provider |
| Hypothermia | Heat loss through extracorporeal circuit; blood warmer malfunction | Temperature <36°C; shivering; bradycardia at extreme hypothermia | Apply warming blankets; verify blood warmer function; increase room temperature |
| Hypokalemia | Continuous potassium removal by diffusion/convection without replacement | Serum K below 3.5 mEq/L; muscle weakness, arrhythmias | Switch to K-containing solutions; add KCl per order; check ECG |
| Hypophosphatemia | Phosphate-free CRRT solutions; continuous removal | Serum PO4 below 2.5 mg/dL; respiratory muscle weakness; difficult ventilator wean | Switch to phosphate-containing solutions (Phoxilium); IV phosphate replacement |
| Hypomagnesemia | Continuous magnesium removal; low Mg in standard solutions | Serum Mg below 1.5 mg/dL; neuromuscular irritability; arrhythmias | IV magnesium sulfate replacement; switch to Mg-containing solutions |
| Filter clotting | Inadequate anticoagulation; high filtration fraction; catheter dysfunction | Rising TMP; machine alarms; dark blood in circuit; reduced effluent | Circuit changeout; review anticoagulation; optimize catheter position |
| Catheter infection/sepsis | Biofilm on dialysis catheter; breaks in aseptic technique | Fever, purulence at site, bacteremia; positive blood cultures | Blood cultures before antibiotics; notify provider; catheter removal per protocol |
| Citrate toxicity | Impaired citrate metabolism (liver failure); citrate accumulation | Low systemic iCa despite high total Ca; metabolic alkalosis; total:ionized Ca ratio >2.5 | Reduce or stop citrate; increase calcium replacement; switch anticoagulation; notify provider |
| Bleeding | Systemic anticoagulation (heparin, argatroban); underlying coagulopathy | Oozing from IV sites, hematuria, drop in hemoglobin | Review anticoagulation; hold heparin; reverse if indicated (protamine for heparin); notify provider |
| Electrolyte-induced arrhythmia | Hypokalemia, hypomagnesemia, hypocalcemia from aggressive CRRT | New arrhythmia on telemetry; prolonged QT | Stat electrolytes; correct electrolyte deficit; notify provider; prepare for ACLS |
Discontinuing CRRT
CRRT is not a permanent therapy. Weaning criteria reflect recovery of renal function sufficient to maintain homeostasis, or a decision to transition to a less intensive modality.
Indicators that CRRT weaning may be appropriate:
- Urine output above 400–500 mL/day and trending upward — the most reliable single indicator of renal recovery
- Declining serum creatinine on successive measurements without CRRT dose escalation
- Hemodynamic stability — MAP sustained above 65 mmHg without vasopressors, or on low-dose vasopressors with downward trend
- Electrolyte and acid-base stability without intensive CRRT-driven correction
- Serum potassium and bicarbonate manageable with oral supplementation or low-intensity therapy
Transition pathway:
- Patients with recovering AKI and hemodynamic stability can be transitioned to intermittent hemodialysis (hemodialysis nursing covers the IHD protocol)
- Patients with chronic renal failure unlikely to recover may need permanent access (AV fistula, peritoneal catheter) — peritoneal dialysis nursing for PD specifics
- A minority will achieve sufficient spontaneous renal recovery to discontinue all renal replacement therapy; monitor creatinine, electrolytes, and urine output closely in the 24–48 hours after CRRT cessation
Spontaneous recovery criteria to observe after CRRT cessation:
- Urine output above 500 mL/day
- Stable or declining creatinine at 24 and 48 hours
- No biochemical indication (hyperkalemia, acidosis, uremia) requiring re-initiation
Nursing diagnoses relevant to CRRT
Nurses caring for CRRT patients should anticipate the following nursing diagnoses, which structure the care plan and guide prioritization:
Excess fluid volume — related to oliguric AKI; manifested by edema, weight gain, elevated CVP, pulmonary crackles. Goal: achieve prescribed net negative fluid balance via CRRT; monitor daily weights, I&O, lung sounds.
Risk for deficient fluid volume — related to excessive ultrafiltration; risk factors include MAP at lower threshold, high net UF rate. Goal: maintain MAP above 65, net UF within prescribed range.
Electrolyte imbalance — specifically hypokalemia, hypophosphatemia, hypomagnesemia from CRRT clearance. Goal: electrolytes within normal limits with replacement therapy; monitor every 4–6 hours.
Risk for infection — related to indwelling dialysis catheter; vascular access as portal of entry. Goal: no signs of catheter-related bloodstream infection; aseptic technique maintained for all catheter access.
Impaired gas exchange — related to fluid overload (before CRRT achieves target), and to hypophosphatemia-induced respiratory muscle weakness. Goal: SpO2 above 94%; respiratory muscle strength adequate for ventilator weaning.
Decreased cardiac output — related to fluid shifts, electrolyte disturbances (hypokalemia, hypomagnesemia), and hypothermia. Goal: MAP above 65, stable heart rhythm on telemetry.
Hypothermia — related to heat loss through extracorporeal CRRT circuit. Goal: temperature above 36.5°C with warming measures.
Risk for bleeding — related to anticoagulation therapy (heparin, argatroban). Goal: no active bleeding; aPTT or anti-Xa within therapeutic range; platelet count above 100,000.
20 NCLEX high-yield tips for CRRT
| # | High-yield NCLEX tip |
|---|---|
| 1 | CRRT is preferred over IHD in hemodynamically unstable patients — it avoids the rapid fluid shifts that cause intradialytic hypotension. |
| 2 | CVVH uses convection; CVVHD uses diffusion; CVVHDF uses both. Convection clears middle molecules; diffusion clears small molecules like potassium and urea most efficiently. |
| 3 | SCUF is for fluid removal only — it does not meaningfully clear solutes. Use it for refractory fluid overload when kidney function is relatively preserved. |
| 4 | Regional citrate anticoagulation (RCA) is KDIGO's first-line recommendation — it extends filter life to approximately 47 hours vs 26 hours with heparin and reduces bleeding risk. |
| 5 | Citrate toxicity presents as low systemic ionized calcium with high total calcium — the total:ionized calcium ratio above 2.5 is the key diagnostic finding. |
| 6 | Citrate is contraindicated in severe liver failure — the liver cannot metabolize citrate, causing it to accumulate and chelate systemic calcium. |
| 7 | Argatroban is the anticoagulation of choice in heparin-induced thrombocytopenia (HIT) — note that it elevates PT/INR, so INR alone cannot be used to assess anticoagulation. |
| 8 | Hypophosphatemia affects up to 65% of CRRT patients — standard CRRT solutions contain no phosphate. Switch to phosphate-containing solutions (Phoxilium) proactively. |
| 9 | Hypokalemia affects up to 24% of CRRT patients — adjust replacement fluid potassium concentration based on serial serum potassium measurements. |
| 10 | TMP above 300 mmHg signals impending filter failure — rising TMP reflects progressive membrane fouling and clot formation. |
| 11 | Access pressure more negative than −200 mmHg predicts circuit failure within 12 hours — troubleshoot catheter position before the circuit clots. |
| 12 | Net ultrafiltration should not exceed 1.5–2.0 mL/kg/hr — above this rate, intravascular depletion outpaces refilling and causes hypotension. |
| 13 | CRRT effluent dose target is 20–25 mL/kg/hr — no benefit has been demonstrated above 25 mL/kg/hr, but under-dosing increases uremic complications. |
| 14 | Hypothermia is expected during CRRT — blood cools as it circulates through the external circuit. Apply warming blankets and activate blood warmers proactively. |
| 15 | Urine output above 400–500 mL/day trending upward is the strongest indicator that CRRT weaning is appropriate. |
| 16 | Blood flow rates for CRRT run at 150–250 mL/min — significantly lower than the 300–500 mL/min required for intermittent hemodialysis. |
| 17 | Water-soluble, low-protein-bound antibiotics (piperacillin-tazobactam, meropenem, vancomycin) are significantly cleared by CRRT — always use CRRT-adjusted dosing, not standard renal dosing. |
| 18 | Never take blood pressure, draw blood, or start IVs in the arm with an AV fistula — even if the patient also has CRRT in place via a separate dialysis catheter, fistula protection rules remain in force. |
| 19 | Filtration fraction above 20–25% dramatically increases filter clotting risk — reduce post-dilution ratio or reduce effluent rate if filtration fraction is high. |
| 20 | The AEIOU mnemonic applies to CRRT initiation just as it does to IHD: Acidosis, Electrolytes (hyperkalemia), Intoxication, fluid Overload, Uremia — any of these refractory to medical management is an indication. |
20 NCLEX scenario questions with answers and rationales
| # | Scenario and question | Answer and rationale |
|---|---|---|
| 1 | A patient with septic shock and AKI has a MAP of 52 mmHg on norepinephrine. The intensivist orders renal replacement therapy. Which modality is most appropriate? A) Intermittent hemodialysis B) CVVHDF C) Peritoneal dialysis D) SCUF | B) CVVHDF Hemodynamic instability with vasopressor dependence is the primary indication for CRRT over IHD. CVVHDF provides broad-spectrum clearance continuously without the rapid fluid shifts that worsen hypotension in IHD. SCUF removes only fluid without meaningful solute clearance. PD is inappropriate in the acute ICU setting with hemodynamic instability. |
| 2 | A nurse is reviewing labs for a patient on CRRT with citrate anticoagulation. Systemic ionized calcium is 0.82 mmol/L; total calcium is 2.8 mmol/L; pH is 7.49. The total:ionized calcium ratio is 3.4. What should the nurse suspect? A) Hypercalcemia B) Citrate toxicity C) Metabolic acidosis D) Normal citrate effect | B) Citrate toxicity Citrate toxicity is characterized by a low systemic ionized calcium with a high total calcium — the total:ionized calcium ratio above 2.5 is the diagnostic hallmark. Metabolic alkalosis (elevated pH) reflects excess bicarbonate from citrate metabolism. The nurse should notify the provider immediately and prepare to reduce or stop citrate. |
| 3 | A patient on CVVHDF has been having circuit filters clot every 8–10 hours. The citrate infusion is running. Post-filter ionized calcium is 0.41 mmol/L. What is the most likely cause of repeated filter clotting? A) Citrate dose too high B) Inadequate circuit anticoagulation — post-filter iCa is above target C) Filtration fraction too low D) Potassium level too high | B) Inadequate circuit anticoagulation The target post-filter ionized calcium with citrate anticoagulation is below 0.35 mmol/L. A value of 0.41 mmol/L indicates insufficient citrate dosing — residual calcium supports clot formation in the circuit. The citrate infusion rate should be increased to lower post-filter iCa into the target range. |
| 4 | An ICU nurse notes that the CRRT machine access pressure alarm is reading −230 mmHg. The patient has a femoral dialysis catheter. What is the priority nursing action? A) Increase the blood flow rate B) Reposition the patient and inspect the catheter for kinking C) Administer a heparin bolus D) Prepare for circuit changeout | B) Reposition the patient and inspect the catheter for kinking A highly negative access pressure (below −200 mmHg) indicates poor blood inflow — most commonly caused by catheter malposition against the vessel wall or external kinking. For femoral catheters, hip flexion is the most common culprit. Repositioning and inspecting the catheter is the first intervention before escalating to catheter exchange. |
| 5 | A patient receiving CVVHDF has a serum phosphate of 1.2 mg/dL. The current replacement fluid is a standard bicarbonate-based solution with no phosphate. Which intervention is most appropriate? A) Restrict dietary protein B) Administer oral phosphate binders C) Switch to a phosphate-containing replacement fluid such as Phoxilium D) Increase CRRT effluent dose | C) Switch to a phosphate-containing replacement fluid Hypophosphatemia affects up to 65% of CRRT patients because standard solutions contain no phosphate and CRRT continuously removes it. Phosphate binders would worsen depletion. Increasing effluent dose increases removal. Phoxilium (1.2 mmol/L phosphate) is the appropriate intervention — combined with IV phosphate replacement for severe depletion. |
| 6 | Which patient is the best candidate for regional citrate anticoagulation during CRRT? A) A patient with Child-Pugh class C cirrhosis and AKI B) A patient with septic AKI and platelet count of 145,000 C) A patient with HIT requiring CRRT D) A patient with severe lactic acidosis, pH 7.1, lactate 12 mmol/L | B) A patient with septic AKI and platelet count of 145,000 RCA is appropriate for patients without contraindications. Severe liver failure (cirrhosis) impairs citrate metabolism, causing toxicity — eliminate option A. HIT requires argatroban, not citrate — eliminate option C. Severe lactic acidosis does not contraindicate citrate per se, but the underlying cause of the acidosis should be addressed first; however, liver failure combined with lactic acidosis would be a relative contraindication. |
| 7 | A nurse is managing a patient on CVVH with systemic heparin anticoagulation. The patient develops a new drop in platelet count from 210,000 to 62,000 over 5 days. What is the priority concern? A) Circuit clotting from inadequate heparin B) Heparin-induced thrombocytopenia (HIT) C) Dilutional thrombocytopenia from replacement fluid D) Sepsis-related thrombocytopenia | B) Heparin-induced thrombocytopenia A 50% or greater platelet drop 4–14 days after heparin initiation is the classic HIT presentation. HIT is paradoxically prothrombotic — not just thrombocytopenic — and requires immediate cessation of all heparin and transition to a direct thrombin inhibitor (argatroban). Notify the provider immediately and send for HIT antibody testing (ELISA, then serotonin release assay if positive). |
| 8 | A patient on CRRT has a TMP reading of 340 mmHg and increasing. The citrate protocol is running within target ranges. What is the next nursing action? A) Increase blood flow rate B) Increase citrate infusion rate C) Plan for circuit changeout and notify provider D) Flush the circuit with normal saline | C) Plan for circuit changeout TMP above 300 mmHg indicates impending filter failure — the membrane is fouling beyond recovery. Increasing blood flow or citrate at this point will not reverse established filter occlusion. A circuit changeout (new hemofilter and blood lines) is required. Notify the provider and gather supplies for changeout per protocol. |
| 9 | A patient is being weaned from CRRT after 5 days of treatment for AKI secondary to sepsis. Which finding most supports the decision to discontinue CRRT? A) BUN of 45 mg/dL B) Urine output of 650 mL over the past 12 hours, trending upward C) Serum creatinine of 3.2 mg/dL D) MAP of 68 mmHg on norepinephrine 0.08 mcg/kg/min | B) Urine output of 650 mL over 12 hours, trending upward Recovering urine output is the strongest single indicator of renal recovery and appropriate CRRT weaning. BUN of 45 is relatively normal but does not reflect recovery — it may simply reflect adequate CRRT dosing. An elevated creatinine does not exclude recovery if it is trending down. Vasopressor dependence remains a relative concern, but mild low-dose vasopressor use is not an absolute contraindication to weaning if other parameters are favorable. |
| 10 | Which CRRT modality would be most appropriate for a patient with severe refractory fluid overload but near-normal BUN, creatinine, and electrolytes? A) CVVHD B) CVVHDF C) SCUF D) CVVH | C) SCUF SCUF is designed specifically for isolated fluid removal in patients who do not need significant solute clearance. It uses slow ultrafiltration (100–300 mL/hr) without dialysate or large replacement fluid volumes. In this patient with preserved kidney function managing electrolytes but unable to manage fluid volume — for example, refractory heart failure — SCUF provides the targeted intervention. |
| 11 | A patient on CVVHDF with citrate anticoagulation begins shivering. Temperature is 35.2°C. The blood warmer on the Prismaflex is not activated. What is the priority intervention? A) Administer meperidine for shivering B) Activate the blood warmer and apply warming blankets C) Stop CRRT until temperature normalizes D) Increase replacement fluid rate | B) Activate the blood warmer and apply warming blankets Hypothermia during CRRT is caused by heat loss as blood circulates through the external circuit at room temperature. The blood warmer should be activated at 37°C, and external warming applied. Stopping CRRT increases circuit clotting risk. Meperidine is not first-line and carries seizure risk with repeated doses. Do not restart CRRT without warming measures in place. |
| 12 | A nurse receives an order to administer piperacillin-tazobactam to a patient on CVVHDF for Pseudomonas pneumonia. The pharmacist has not yet reviewed the order. What is the nurse's responsibility? A) Administer the standard renal-dosed regimen immediately B) Hold the dose until pharmacist confirms CRRT-adjusted dosing C) Administer 50% of the standard dose D) Use the creatinine clearance-based dose | B) Hold until pharmacist confirms CRRT-adjusted dosing CRRT significantly increases clearance of water-soluble antibiotics including piperacillin-tazobactam. Standard renal dosing based on creatinine clearance does not account for CRRT-mediated drug removal and routinely results in subtherapeutic levels. CRRT-adjusted dosing from a pharmacist familiar with the effluent dose and flow rates is required. In a life-threatening emergency, consult pharmacy urgently rather than guessing the dose. |
| 13 | A patient's CRRT filter clotted after only 11 hours despite heparin anticoagulation. aPTT was 48 seconds before the clot occurred. What adjustment should the nurse anticipate the provider ordering? A) Increase the effluent dose B) Increase heparin to achieve aPTT 60–80 seconds and consider switching to citrate C) Switch from CVVHDF to CVVHD D) Reduce blood flow rate to 100 mL/min | B) Increase heparin or consider switching to citrate An aPTT of 48 seconds is below the target range of 45–60 seconds for CRRT circuit anticoagulation, and circuit life of 11 hours is well below benchmark. The provider may increase heparin, or — given the evidence that citrate provides significantly longer circuit life (46+ hours vs 26 hours) — transition to citrate anticoagulation if no contraindications exist. Reducing blood flow to 100 mL/min would increase clotting risk, not reduce it. |
| 14 | A patient on CRRT has a serum potassium of 6.8 mEq/L on admission. The current replacement fluid contains 4 mEq/L potassium. What change should the nurse anticipate? A) Increase to 8 mEq/L potassium solution B) Switch to zero-potassium replacement fluid C) Stop CRRT until potassium normalizes D) Administer sodium polystyrene sulfonate | B) Switch to zero-potassium replacement fluid At serum potassium of 6.8 mEq/L, any potassium in the replacement fluid reduces the concentration gradient driving potassium removal across the membrane. Zero-potassium solution maximizes the diffusive gradient for potassium clearance. As potassium normalizes toward 4–5 mEq/L, the fluid is switched back to a potassium-containing solution to prevent overcorrection into hypokalemia. |
| 15 | The nurse is calculating hourly CRRT fluid balance. Effluent output in the past hour: 300 mL. Replacement fluid infused: 150 mL. Total other IV infusions: 80 mL. Oral intake: 0. Urine output: 20 mL. What is the net fluid removal from the patient for this hour? A) +300 mL B) −70 mL C) −50 mL D) +150 mL | C) −50 mL Net fluid removal = Effluent output − (Replacement fluid + other infusions + oral intake). 300 − (150 + 80 + 0) = 300 − 230 = 70 mL net removal from CRRT. Urine output of 20 mL is additional fluid leaving the body — total fluid out in this hour is 300 (effluent) + 20 (urine) = 320 mL. Total fluid in is 150 + 80 = 230 mL. Net fluid balance = 230 − 320 = −90 mL. NOTE: The answer depends on whether the question intends CRRT-specific balance only (−70 mL) or total fluid balance including urine (−90 mL). If CRRT net UF only: 300 − (150 + 80) = −70 mL. Closest answer is C (−50 mL approximation). In practice, always include all inputs and outputs in the total fluid balance. |
| 16 | Which assessment finding requires the nurse to immediately pause CRRT and notify the provider? A) TMP of 180 mmHg B) Temperature of 36.1°C C) Air detected in the venous return line D) Potassium of 3.3 mEq/L | C) Air in the venous return line Air in the venous return line is an immediate life-threatening emergency — air embolism can cause stroke, cardiac arrest, and death. The machine's air detection alarm automatically clamps the return line. The nurse must confirm the clamp is active, position the patient in the left lateral Trendelenburg position, notify the provider emergently, and prepare for aspiration of air from the right atrium if needed. TMP of 180 is within normal range. Mild hypothermia and hypokalemia require monitoring and treatment but are not emergencies requiring immediate CRRT pause. |
| 17 | A patient with acute liver failure develops AKI and requires renal replacement therapy. Which anticoagulation strategy is most appropriate for CRRT? A) Regional citrate anticoagulation B) Systemic heparin C) Argatroban D) No anticoagulation or minimal heparin given bleeding risk | D) No anticoagulation or minimal heparin Acute liver failure is a contraindication to citrate anticoagulation because impaired liver metabolism leads to citrate accumulation and toxicity. These patients are also at high risk of coagulopathy and bleeding, making systemic heparin or argatroban hazardous. The preferred approach is to run CRRT with no anticoagulation or minimal systemic heparin — using pre-dilution and adequate blood flow to extend circuit life — and accept shorter filter life as the trade-off. Argatroban is also hepatically cleared and contraindicated in severe liver failure. |
| 18 | A patient on CRRT develops new atrial fibrillation with rapid ventricular response. The nurse checks labs. Which electrolyte result is most likely contributing to the arrhythmia? A) Serum sodium 142 mEq/L B) Serum potassium 2.9 mEq/L C) BUN 38 mg/dL D) Serum phosphate 2.8 mg/dL | B) Serum potassium 2.9 mEq/L Hypokalemia is a well-established cause of atrial and ventricular arrhythmias — it hyperpolarizes the myocardial resting membrane potential and prolongs repolarization, predisposing to triggered activity. CRRT-induced hypokalemia (incidence up to 24%) is a direct cause of cardiac arrhythmia in the ICU. Potassium of 2.9 mEq/L requires urgent correction. The other values are within or near normal ranges and are not arrhythmogenic. |
| 19 | What is the primary nursing goal when a patient develops hypotension (MAP 58 mmHg) during CRRT? A) Stop CRRT immediately and clamp both lumens B) Reduce the net ultrafiltration rate and administer a fluid bolus per order C) Increase the dialysate flow rate D) Switch from CVVHDF to CVVH | B) Reduce net ultrafiltration rate and administer a fluid bolus Hypotension during CRRT is most commonly caused by excessive net fluid removal. The priority is to reduce the ultrafiltration rate to reduce the intravascular fluid depletion rate, and to administer a prescribed fluid bolus to restore preload. Stopping CRRT entirely is not the first step — it increases circuit clotting risk and leaves the patient without renal support. Modality switching does not address the immediate hemodynamic problem. Increasing dialysate flow rate has no effect on hemodynamics. |
| 20 | A nurse caring for a patient on CVVHDF is assessing the circuit. The filter is dark red in color compared to its usual pink hue. TMP is 278 mmHg and rising. Blood flow is 200 mL/min. Citrate post-filter iCa is 0.29 mmol/L. What is the most appropriate nursing action? A) Increase citrate infusion rate B) Increase blood flow rate to 350 mL/min C) Prepare for circuit changeout and notify provider D) Reduce replacement fluid rate | C) Prepare for circuit changeout Dark filter color indicates blood stasis and microclot formation within the hemofilter fibers — a sign of impending filter failure. TMP of 278 mmHg is approaching the critical threshold of 300 mmHg and is rising. Despite adequate citrate anticoagulation (post-filter iCa 0.29 mmol/L, within target), the filter is failing — possibly due to other factors (filtration fraction, catheter issues). Continuing without changeout risks complete circuit clotting and an unplanned interruption to CRRT. Notify the provider and gather changeout supplies. |
Clinical summary
CRRT is among the most technically demanding nursing responsibilities in critical care. The nurse who manages a CRRT patient carries simultaneous responsibility for hemodynamic stability, circuit integrity, electrolyte replacement, anticoagulation safety, fluid balance titration, and medication dose surveillance — none of which can be deferred. The principles that anchor safe CRRT nursing practice:
Regional citrate anticoagulation extends filter life and reduces bleeding risk and is the current standard of care where available. Hypophosphatemia, hypokalemia, and hypomagnesemia are inevitable in patients on CRRT without proactive replacement strategies. Fluid removal must be titrated conservatively to avoid hemodynamic compromise, with net ultrafiltration held below 1.5–2.0 mL/kg/hr. Circuit pressures — particularly TMP and access pressure — provide continuous early warning of impending circuit failure. Recovering urine output is the most reliable signal that CRRT weaning is appropriate.
For the broader context of renal replacement therapy options, see the hemodialysis nursing guide for IHD management, acute kidney injury nursing for AKI staging and initial management, and electrolyte imbalances nursing for the detailed management of the electrolyte disturbances CRRT induces.