Renal Replacement Therapy (RRT) - ICU One Pager Summary
Indications (AIEOU):
 • A: Acidosis (usually severe metabolic)
 • E: Electrolyte derangements (hyperkalemia, hypercalcemia, etc)
 • I: Intoxications (APAP, Barbiturates, Lithium, carbamazepine, metformin, methanol, salicylates, thallium, theophylline, valproate, etc); see ExTRlP guidelines
 • O: Fluid Overload (pulmonary edema refractory to diuretics, uncontrolled hypertension, etc). Volume removal may also hasten liberation from ventilation.
 • U: Symptomatic Uremia (causing severe altered mental status, uremic pericarditis, bleeding diathesis, etc)
Components of a Hemodialysis Circuit & Parameters Set:
 • Ultrafiltration (UF) is the filtration of water from the blood, driven by the transmembrane pressure the blood & effluent. 
 • Blood Flow Rate (QB) is the flow rate of blood through the dialysis circuit.
 • Dialysate Solution is an isotonic fluid containing electrolytes, bicarbonate/acetate, glucose, & sometimes other small molecules. The dialysate is chosen to match serum osmolality & to correct any blood chemistry abnormalities.
 • Dialysate Flow Rate (QD) is a countercurrent flow of dialysate through the dialyzer. Higher flow rates enable greater clearance of small molecules via diffusion.
 • Dialyzer is rigid case that encloses thousands of semi-permeable polymer tubules. Blood flows through the tubules & dialysate flows in the opposite direction outside (countercurrent). 
 • Replacement Fluid (RF) can be used to restore fluid volume removed by UF in the dialyzer. 
 • Vascular Access can be permanent (such as an AV fistula or an AV graft) accessed using needles, semi-permanent (a tunneled CVC), or temporary (such as a non-tunneled CVC).
Modalities of RRT in the ICU:
 • IHD (Intermittent HD):  3-5 hr session using standard HD rnachine
 • SLEDD (Sustained low efficiency daily dialysis): ~12 hr session using standard HD machine
 • CRRT (Continuous renal replacement therapy): 24 hr (continuous) session using a CRRT machine
CRRT Modes:
 • SCUF: Slow continuous UF; UF removes fluid but provides almost no clearance and does not correct PH; no replacement fluid required. Corrects volume overload only.
 • CVVH: Continuous venovenous hemofiltration. Provides convective clearance by filtering a large volume of blood; Replacement fluid restores volume lost. Corrects uremia, lytes, pH and can remove volume.
 • CVVHD: Continuous venovenous hemodialysis. Provides diffusive clearance by running dialysate opposite blood flow. No replacement fluid used. Gently corrects uremia, lytes, pH
 • CVVHDF: Continuous venovenous hemodiafiltration. High clearance achieved using both UF & dialysate flow (both convection & diffusion). Replacement fluid used. Allows fluid removal and correction of electrolyte/pH. Good for toxin removal.

by Nick Mark MD @nickmmark

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