What are the basic principles and practical guidelines for initiating and managing continuous renal replacement therapy (CRRT) in an adult septic‑shock patient with refractory hypotension and acute kidney injury?

CRRT Basic Principles

In a septic shock patient with refractory hypotension and AKI, use CRRT rather than intermittent hemodialysis as the preferred modality, deliver an effluent volume of 20-25 mL/kg/h, and use regional citrate anticoagulation unless contraindicated 1.

When to Initiate CRRT

Absolute indications requiring emergency initiation:

• Life-threatening hyperkalemia refractory to medical management
• Severe volume overload unresponsive to diuretics causing pulmonary edema
• Severe metabolic acidosis (pH <7.15 despite resuscitation)
• Uremic complications (pericarditis, encephalopathy, bleeding) 1

In the absence of absolute indications, consider the broader clinical context rather than single BUN or creatinine thresholds alone. Evaluate trends in laboratory values, presence of oliguria despite adequate resuscitation, and the overall trajectory of illness 1. Recent evidence suggests earlier initiation (within 6-12 hours of AKI onset) may improve outcomes in septic patients, with one study showing 4.83-fold higher mortality risk when CRRT was delayed beyond 24 hours 2, 3. However, the 2020 KDIGO update acknowledges optimal timing remains controversial outside life-threatening indications 4.

Modality Selection

For hemodynamically unstable patients (your septic shock scenario): CRRT is preferred over intermittent hemodialysis 1, 5. The continuous nature provides better hemodynamic tolerance and facilitates fluid management in vasopressor-dependent patients 6.

Additional CRRT advantages in sepsis:

• Superior fluid balance control in patients requiring large-volume resuscitation
• Avoids rapid intracranial pressure shifts if cerebral edema present
• Allows continuous removal of inflammatory mediators 5, 7

Vascular Access

Site selection priority:

1. Right internal jugular vein (first choice)
2. Femoral vein (second choice, acceptable despite older concerns)
3. Left internal jugular vein (third choice)
4. Subclavian vein (last resort—avoid due to stenosis risk) 1, 5

Technical requirements:

• Use ultrasound guidance for insertion (strong recommendation) 5
• Obtain chest X-ray before first use for jugular/subclavian lines 5
• Use uncuffed non-tunneled catheter for acute initiation 4, 5
• Ensure adequate catheter length to minimize recirculation 5

Anticoagulation Strategy

Regional citrate anticoagulation is preferred over heparin for CRRT unless contraindications exist 1, 5. This is particularly important in septic patients who often have coagulopathy or bleeding risk.

Citrate contraindications:

• Severe liver failure (cannot metabolize citrate)
• Severe lactic acidosis
• Severe shock with tissue hypoperfusion

If citrate contraindicated: Use unfractionated heparin or low-molecular-weight heparin 1, 5.

If patient has heparin-induced thrombocytopenia: Use direct thrombin inhibitors (argatroban) or Factor Xa inhibitors—all heparin must be stopped 5.

CRRT Dosing

Deliver effluent volume of 20-25 mL/kg/h (strong recommendation, high-quality evidence) 1, 5. This is the delivered dose—prescribe higher to account for downtime and circuit issues 1.

Practical calculation: For a 70 kg patient, target 1,400-1,750 mL/h effluent volume.

Buffer selection: Use bicarbonate rather than lactate in dialysate/replacement fluid, especially critical in septic shock patients who may have impaired lactate metabolism 5.

Hemodynamic Management During CRRT

Since your patient has refractory hypotension:

• Do NOT use low-dose dopamine for renal protection—this is ineffective and potentially harmful 6
• Continue norepinephrine as first-line vasopressor 6
• CRRT allows more aggressive fluid removal once hemodynamics stabilize with vasopressors 6
• The continuous nature of CRRT prevents the hemodynamic instability seen with intermittent dialysis in vasopressor-dependent patients 4, 5

Monitoring and Adjustment

Assess delivered dose frequently to ensure prescription targets are met—circuit downtime and clotting reduce actual delivery 5.

Monitor for complications:

• Citrate accumulation (rising total calcium/ionized calcium ratio >2.5)
• Electrolyte disturbances (hypocalcemia, hypokalemia, hypophosphatemia)
• Hypothermia from continuous extracorporeal circulation
• Circuit clotting requiring replacement

Discontinuation

Consider stopping CRRT when:

• Kidney function recovers (urine output >400-500 mL/day is most reliable predictor) 4
• Life-threatening complications resolve
• Vasopressor requirements decrease substantially
• Patient can tolerate transition to intermittent hemodialysis 4, 1

Common pitfall: Premature discontinuation before adequate recovery leads to rebound metabolic derangements. Ensure stable renal function for at least 7 days before declaring successful weaning 8.

The evidence strongly supports CRRT over intermittent modalities in your hemodynamically unstable septic shock patient, with specific dosing targets and anticoagulation strategies that differ from chronic dialysis management.