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•Diffusion •Convection •Adsorption 5/5/2010 Objectives: Renal Replacement • Review the concepts of different Therapies (RRT) for the modalities of RRT Non-Nephrologist • Examine the necessaryyp components involved in RRT • Examine the indications for RRT Kevin Harned, MD • Review particular caveats to specific University of Kentucky Medical Center treatment modalities Division of Nephrology, Bone & Mineral Metabolism November 3, 2009 3 physiologic principles of Physiology: RRT: • Diffusion: Process of movement of •Diffusion molecules across an area due to differences in concentration gradients – Moves from high-to-low concentration until •Convection the concentrations for both areas are equal – Adequate for clearing small molecules (<1kDa) •Adsorption – Na, K, Ca, Creatinine, Urea, Gentamicin Physiology: Physiology: • Convection: Using suction to physically • Adsorption: Binding of substances to pull water across a membrane, and with the surface of the filter/membrane the fluid shift anyygthing else that can “fit” – More a factor of electrical charge of the through the membrane’s pores as it substance, organic vs inorganic (as in rides with the water (aka “Solvent drag”) removal by charcoal filters) – Think of the white-water rafter being “pulled” downstream by the river – Better for clearance of middle molecular weight molecules (up to 60kDa) – Vancomycin, cytokines (IL-1, IL-8, etc) 1 5/5/2010 Physiology: Terminology: • Peritoneal dialysis (PD) • Adsorption: Binding of substances to • Intermittent Hemodialysis (IHD) the surface of the filter/membrane • Continuous Renal Replacement Therapies (CRRT) – More a factor of electrical charge of the – Continuous veno-venous hemofiltration (()CVVH) substance, organic vs inorganic (as in – Continuous veno-venous hemodialysis (CVVHD) removal by charcoal filters) – Continuous veno-venous hemodiafiltration (CVVHDF) – Sustained, low-efficiency daily hemodialysis (SLEDD) – High-volume hemofiltration (HVHF) • Slow continuous ultrafiltration (SCUF) • “Liver Dialysis” − Molecular Adsorption Recirculating System (MARS) Courtesy of WR Clark, CRRT 2007 Symposium − “Prometheus” (Not in the United States) PD: PD: • Diffusion >>> Convection • Can be performed via manual exchanges • Uses peritoneum as a semi-permeable or automated cycler machine at night membrane for exchange • 3 Glucose concentrations: • Fluid infused into abdominal cavity via PD catheter • 15%1.5% •2.5% • Solute clearance is a factor of: • 4.25% • Volume of fluid infused (usually 2-3L) • The higher the Glucose concentration, the more • Time allowed to dwell (factor of the properties of water will be removed from the pt d/t higher the peritoneum) osmolality of the PD fluid compared to the plasma • % of Glucose in fluid (convective component) • Fluid removal solely dependent upon % of Glucose in fluid Typical PD Rx (manual): Typical PD Rx (cycler): • Volume = 2.5L • Volume = 2.5L • Time = Dwell x 3hrs • Time = 1hr 40min fill/dwell; 20min drain • # of exchanges = 3 • Length of tx = 7PM – 7AM • Need 9-12hrs of RRT to be sufficient • Fluid = 1.5% Dianeal • Fluid = 1.5% Dianeal 2 5/5/2010 PD: PD: • D/t logistics of placing PD catheter, as well • Not good candidates if: as its efficiency limitation, PD is not ideal • Morbidly obese (insufficient dose) for the Acute Kidney Injury (AKI) pt • Multiple abdominal surgeries (scarring of requiring RRT peritoneum) • Better if slowly progressed to ESRD • Pt is blind (can’t care for catheter = infxn) • Good candidates if: • Pt has ascites (regardless of etiology) • High-fxn’ing pt (allows them to keep their independence) • Still has residual kidney fxn • Pt’s w/ CHF (fluid shifts are more gentle) PD: IHD: • Complications • Diffusion >>> Convection –PD inadequacy •Ingredients • Peritoneal membrane eventually develops • Vascular Access properties that make clearance inadequate •Bldiilood circuit • Usually d/t numerous episodes of peritonitis • Filter w/ semipermeable membrane – Peritonitis • Dialysate fluid circuit • Approx 1 infxn/15 months • Diffusive component – Encapsulating Peritoneal sclerosis • Ultrafiltrate circuit = fluid removed •<1% of PD pt’s • Convective component • Bowel obstruction, hemorrhagic ascites • Anticoagulation • Mortality 30-50% IHD: Vascular Access IHD: Blood circuit • Temporary dialysis catheter (Uldall, •BFR= Blood Flow Rate Quinton, Vascath) – Target = 300 – 500ml/min • Tunneled dialysis catheter (Cannon, •PA= Arterial port pressure Palindrome, Decathalon) – This is a negative # measured inside the lines of the RRT circuit that represents the amount of suction • Native arterio-venous fistulas (AVF’s) required to physically pull the blood from the patient • Synthetic and native arterio-venous grafts – Goal -75 to -250mmHg (AVG’s) •PV= Venous port pressure – This is a positive # measured inside the lines of the RRT circuit that represents the amount of pressure required to PUSH the blood back to the patient – Goal 100 to 250mmHg 3 5/5/2010 IHD: Blood circuit IHD: Blood circuit • PA alarms ONLY when it is too low (<-250) • PV alarms typically when it is too high – ALWAYS represents an ACCESS problem (>250) • Improper needle placement (AVF/AVG) – ACCESS problem • Insufficient arterial inflow of blood into the • Improper needle placement (AVF/AVG) access (AVF/AVG) • Outflow stenosis (AVG >> AVF) – Venous anastomosis (AVG) • Kink in dialysis catheter – Draining vein (needle stick sites, proximal swing segment • Catheter sucking against interior wall of of transposed brachial-basilic AVF’s, Cephalic Arch, central vein venous stenosis) • Kink in dialysis catheter • Clot at tip of catheter acting as a one-way • Clot inside lumen of tip of catheter obstructing valve outflow – Thrombosis of Venous Drip chamber Caveat to monitoring the IHD: Filter pressures • Each pressure is measured via a line connected to the machine that is screened through a Dialysis discoid filter where the line attaches to the Fluid machine pppump – If these filters get wet (with fluid or blood), they will not be able to permit the air pressure to transmit across properly – Consequently, the machine will give you false readings IHD: Dialysate circuit IHD: Dialysate circuit • DFR = Dialysate Flow Rate • Solutes we can control: – Target = 500-750ml/min – Metabolic acidosis – Provides the DIFFUSION component for solute –K+ clearance – Ca2+ – NO EFFECT ON VOLUME STATUS OF PT –Uremia –Na (somewhat) – Phos (somewhat) 4 5/5/2010 IHD: Filter IHD: Ultrafiltrate circuit • UF = Actual volume removal – Requires CONVECTION to physically pull the fluid from the pt’s blood across the membrane O O O O – Nothing selectively removes just water! 2 2 2 2 H H H H O O O O • Small amount of clearance simply d/t solvent drag 2 2 2 2 H H – Amount of UF entirely dependent on H intravascular volume status of pt and his/her O O O O blood pressure 2 2 2 2 H H H H P OH O O O 2 2 2 2 H – The volume of fluid removed is what leads to U u H H H hypotension, not the actual BFR F m p Continuous Renal Replacement IHD: Anticoagulation Therapies (CRRT) • Heparin = #1 type used worldwide • Continuous veno-venous hemofiltration – Bolus only (CVVH) – Bolus + infusion • Continuous veno-venous hemodialysis – Infusion only (CVVHD) – “Tight” Heparin • Continuous veno-venous hemodiafiltration (CVVHDF) • No anticoagulation • High-volume hemofiltration (HVHF) • Sustained, low-efficiency daily • If already anticoagulated for another hemodialysis (SLEDD) reason, nothing additional is given. CVVH: CVVH: • All CONVECTION • Replacement Fluid Rate/Substitution Fluid • Blood flow rates 150-400ml/min Rate • Uses a higher fluid removal rate than required – Clearance of solutes by solute drag tt“li”to restore “euvolemia” – Mac hine PULLS thi s vol ume and gi ves thi s – Pull 2-6 LITERS from the patient/hr volume back • Requires use of replacement fluid to prevent – No fluid balance is lost/gained patient from becoming hypotensive – Target = 35ml/kg/hr – Most machines BOTH REMOVE AND REPLACE this volume, so the net fluid loss is ZERO •UF – Extra fluid that is NOT replaced, leading to • Net fluid loss = (RFOUT + UF) - RFIN actual water-loss 5 5/5/2010 CVVH: Filter CVVH: • Blood flow rates 150-400ml/min • Uses a higher fluid removal rate than O O O O required to restore “euvolemia” 2 2 2 2 H H H H O O O O – Pull 2-6 LITERS from the patient/hr 2 2 2 2 H H • Requires use of replacement fluid to H prevent patient from becoming O O O O P 2 2 2 2 H H H H OH O O O hypotensive 2 2 2 2 H u H H H m * • Net fluid loss = Total UF rate - Replacement fluid rate p Palevsky, PM; “Continuous Renal Replacement Therapies.” ASN Board Review Course—August 2001. HDCN online symposium. CVVHD: CVVHD: • Diffusion >>> Convection (just like IHD) • Blood flow rate 150-400ml/min • Blood flow rate 150-400ml/min • Solute removal dependent on diffusion across • Solute removal dependent on diffusion across membrane w/ dialysate memb/diltbrane w/ dialysate – Dialysate is counter-current to blood flow in order to maximize concentration gradients across entire length of the – Dialysate is counter-current to blood flow in order to filter maximize concentration gradients across entire length of the – Usually on the order of 1.5-3L/hr filter – Usually on the order of 1.5-3L/hr • UF set only at rate that pt hemodynamically • UF set only at rate that pt hemodynamically can withstand, w/ goal of restoring can withstand, w/ goal of restoring “euvolemia” (0-150ml/hr) “euvolemia” (0-150ml/hr) Palevsky,• PM; Net“Continuous fluid Renal loss Replacement = UF Therapies.” rate ASN Board Review Course—August 2001. HDCN online symposium. CVVHDF:
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