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Renal Replacement Therapy (RRT) Basics

Daniel Motta-Calderon

Background/Terminology

  • Dialysis (diffusive clearance)- solutes diffuse down concentration gradients through a semipermeable membrane separating blood and dialysate

  • Dialysate (dialysis bath)- electrolyte solution used to create concentration gradient for dialysis. Customizable to treat specific electrolyte and acid-base derangements

  • Effluent- Fluid removed during dialysis or ultrafiltration

  • Ultrafiltration- Hydrostatic pressure “pushing” water through a membrane. There is no dialysate solution used during ultrafiltration. Solutes are removed through the process of solvent drag. The effluent in this case is isotonic to plasma

  • Total ultrafiltration (UF) - overall ultrafiltration volume produced during treatment

  • UF net - net ultrafiltrate volume removed from the patient by the machine. The overall volume can be completely replaced (net even), partially replaced, or not replaced at all. UF net is the difference between UF and the volume replaced in the circuit

  • Timing of dialysis- There are several studies in this space (IDEAL, IDEAL-ICU, AKIKI, STARRT, ELAINE). In both the outpatient and the inpatient setting, there is no compelling evidence that early start dialysis improves mortality compared to later starts

Outpatient Modalities

  • Intermittent hemodialysis (iHD)

  • In home hemodialysis

  • Peritoneal dialysis

If someone with ESRD is admitted:

  • Urgent ESRD consult if acute need, otherwise can consult them routinely

  • Routine orders include MWF phos checks and a renal diet

  • For peritoneal dialysis pts, their diet can be more liberal and include low phos only or even regular diet (Can just ask what diet he/she follows at home)

Acute Setting

  • Indications: AKI leading to life-threatening changes in fluid, electrolyte, and acid-base balance or toxic ingestion [AEIOU]

    • Acidosis: Severe metabolic acidosis (serum pH\<7.1) refractory to correcting volume status or other electrolyte derangements

    • Electrolytes: Severe hyperkalemia >6.5 despite medical management (e.g. loop diuretics, IV fluids, GI cation exchangers, correcting acidemia, etc.)

    • Intoxication: Dialyzable toxins and medications

      • Alcohols: ethylene glycol, methanol, isopropyl alcohol, diethylene glycol, and propylene glycol

      • Medications: lithium, salicylates, valproic acid, phenytoin, barbiturates, carbamazepine, vancomycin, aminoglycosides, etc.

    • Overload: Severe fluid overload (e.g., pulmonary edema) refractory to diuretics

    • Uremia: Uremic complications: encephalopathy, pericarditis, platelet dysfunction

  • Can perform furosemide stress test to help predict who is likely to recover their kidney function

    • If Lasix naïve, administer 1mg/kg as a bolus. If on a loop diuretic, administer 1.5 mg/kg as a bolus

    • If within the hour they have made 200 cc of urine, then they are likely to regain kidney function

  • Modalities

    • iHD: Ideal for removal of toxins (e.g. alcohols, dialyzable meds). Use with caution in hypotensive patients

    • CRRT: Set a rate of volume removal (typically 0-200 cc/hr) less rapid fluid/electrolytes shifts -> better tolerated in patients with hemodynamic instability

      • Anti-coagulation options- to prevent clotting of circuit
        • None
        • Heparin (preferred). Can be either within the circuit or systemic if indicated for another reason (e.g. DVT/PE).
        • Citrate (need to monitor calcium frequently)
      • Complications of CRRT: Infections, hypophosphatemia

  • Access

    • Dialysis catheter (aka: Vascath)

      • Non-tunneled catheter (Trialysis) used for acute dialysis

      • Different lengths depending on site (see procedures section)

    • Tunneled dialysis catheter (ex: Permcath)

      • Typically used as a bridge to fistula/graft placement

      • Placed by IR

Peritoneal Dialysis Peritonitis

Background

  • Typically occurs due to contamination with pathogenic skin bacteria during exchanges or due to exit-site/tunnel infection

  • Usually presents with cloudy effluent fluid and abdominal pain. Can also be asymptomatic

  • Important history to obtain: recent contamination, accidental disconnection, endoscopic or gynecologic procedure, as well as the presence of constipation or diarrhea

  • Definitive diagnosis requires 2 of the following:

    • Clinical features consistent with peritonitis

    • Positive dialysis effluent culture

    • Dialysis effluent with WBC > 100 with PMN > 50%

      • Even if WBC count \< 100, presence of > 50% PMNs is still strong evidence of peritonitis in pts with rapid cycle PD

Evaluation

  • Examine catheter exit site

  • Culture peritoneal fluid (requires specific technique, done by nephrology)

  • Peritoneal cell count with diff, gram stain and culture

  • Obtain peripheral blood cultures if there is concern for sepsis

Management

  • All PD orders, intraperitoneal antibiotics, and prescription adjustments should be directed by ESRD consult service (page them overnight if concerns)

  • Treatment with intraperitoneal antibiotics should be started immediately after specimens have been obtained if there is high clinical suspicion

  • Empiric antibiotics regimen should cover both gram-positive and gram-negative organisms, typically with vancomycin and third generation Cephalosporin

  • Systemic antibiotics are generally not necessary unless pts have systemic signs of sepsis

  • Pts with relapsing, recurrent or repeat peritonitis will likely need catheter removal

Secondary prevention

  • Treatment with intraperitoneal OR IV antibiotics (for any infection requiring > 1 dose of antibiotics) requires prophylaxis for fungal peritonitis with either:

    • Nystatin 400,000 to 500,000 units orally TID

    • Fluconazole 200 mg every other day or 100 mg qdaily

  • Dialysate should be drained the day of endoscopies or gynecological procedures