A 38-year-old woman with severe sepsis secondary to urosepsis presents with acute kidney injury stage 3 (KDIGO criteria). She is hypotensive (MAP 55 mmHg) despite 30 mL/kg crystalloid bolus and has oliguria (urine output 0.3 mL/kg/hour). Blood cultures are pending. After initiation of broad-spectrum antibiotics and vasopressor support (noradrenaline), what is the drug of choice for renal replacement therapy initiation in this patient?

Explanation

## Renal Replacement Therapy in Septic AKI **Key Point:** Continuous veno-venous hemofiltration (CVVH) or other continuous renal replacement therapy (CRRT) modalities are the preferred choice for hemodynamically unstable patients with septic shock and AKI. CVVH provides superior hemodynamic tolerance compared to intermittent hemodialysis in this setting. ### Pathophysiology of Septic AKI Sepsis causes: 1. Systemic inflammation and endothelial dysfunction 2. Renal hypoperfusion and acute tubular necrosis 3. Fluid accumulation (edema, pulmonary edema) requiring aggressive fluid removal 4. Hemodynamic instability requiring vasopressor support ### Why CVVH is Superior in Septic Shock | Feature | CVVH | IHD | |---------|------|-----| | **Hemodynamic stability** | Excellent (slow, continuous) | Poor (rapid fluid shifts) | | **Cardiovascular tolerance** | High | Low in shock | | **Fluid removal rate** | Gradual (0.5–2 L/hour) | Rapid (3–5 L/session) | | **Intracranial pressure** | Minimal risk | Risk of cerebral edema | | **Electrolyte swings** | Minimal | Significant | | **Cytokine clearance** | Moderate (convection) | Minimal | | **Vasopressor requirement** | Often decreases | Often increases | **High-Yield:** CVVH is the modality of choice in hemodynamically unstable patients (MAP <65 mmHg, on vasopressors, or with septic shock). It allows gradual ultrafiltration without sudden intravascular volume depletion. ### Mechanism of CVVH ```mermaid flowchart TD A[Veno-venous access]:::action --> B[Blood pump: 150-250 mL/min] B --> C[Hemofilter: convective clearance] C --> D[Replacement fluid infusion] D --> E[Gradual ultrafiltration] E --> F[Hemodynamic stability maintained]:::outcome G[Septic AKI + Shock]:::urgent --> A ``` ### Clinical Evidence **Clinical Pearl:** The RENAL trial (2009) and subsequent meta-analyses show no difference in mortality between CRRT and IHD in AKI, but CRRT is superior for hemodynamic stability. In septic shock specifically, CRRT is strongly preferred because: - Avoids rapid fluid shifts that worsen hypotension - Allows continuation of vasopressor weaning - Permits adequate nutrition delivery - Reduces need for sedation/anesthesia ### Indications for RRT Initiation in AKI 1. **Absolute:** Severe hyperkalemia (K >6.5 with ECG changes), severe acidosis (pH <7.1), pulmonary edema unresponsive to diuretics, uremia with encephalopathy 2. **Relative:** Oliguria >5–7 days, rising creatinine despite optimization, fluid overload in sepsis **Warning:** Do NOT delay RRT initiation in septic shock if oliguria persists despite adequate fluid resuscitation and vasopressor support. Early RRT may improve outcomes by reducing inflammatory burden and allowing aggressive fluid management. ### Why Other Modalities Are Suboptimal **Mnemonic:** AVOID IHD in SHOCK — **A**cute hemodynamic instability, **V**asopressor dependence, **O**liguria with sepsis, **I**ntracranial pathology risk, **D**iabetic ketoacidosis (relative), **I**nstability from rapid fluid shifts, **H**yperkalemia (use CRRT instead), **D**ehydration risk.