Renal Replacement Therapy (RRT) Basics

Daniel Motta

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. There is some associated cponvective clearance, as solutes are removed via 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 (PD)

If someone with ESRD is admitted

  • Urgent ESRD consult if acute need (AEIOU), otherwise can consult them routinely
  • Routine orders include MWF phos checks and a renal diet
  • For PD patients, 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 (AEIOU): AKI leading to life-threatening changes in fluid, electrolyte, and acid-base balance or toxic ingestion
    • 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 include encephalopathy, pericarditis, platelet dysfunction
  • Can perform furosemide stress test to help predict who is likely to recover 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
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