RENAL REPLACEMENT THERAPY

Dr. SARMISTHA

Definition :

• Renal replacement therapy is a term used to encompass life-supporting treatments for renal failure.

• It includes a variety of treatment modalities.

Modality of RRT

• Intermittent hemodialysis (IHD)• Continuous renal replacement therapy (CRRT)• Hybrid therapies, like SLED• Peritoneal dialysis

MAJOR RRT TECHNIQUES

Indications-

• Acute kidney injury• Chronic renal failure /ESRD with following complications: i)severe hyperkalemia- >6.5 meq/l not responding to medical

treatment ii)fluid overload/ pulmonary oedema, anasarca iii)severe metabolic acidosis pH-<7.10 iv)UOP< 200ml/12hrs v)uremia i.e, BUN >80mg/dl or s.creatinine > 4mg/dl vi)severe dysnatremia- Na <115 meq/l or 160 meq/l vii)uremic pericarditis/encephalopathy viii)hyperthermia>40 deg C

Principles of dialysis• diffusion = passive movement of

solutes across a semi-permeable membrane down concentration gradient– Good for small molecules

• convection = solute + fluid removal across semi-permeable membrane down a pressure gradient (solvent drag)– Better for removal of fluid and

medium-size molecules

Principles of dialysis

•Miller's Anesthesia, 7th ed. 2009•Foot. Current Anaesthesia and Critical Care 2005; 16:321-329

Hemodialysis = solute passively diffuses down concentration gradient Dialysate flows countercurrent to blood flow. Urea, creatinine, K move from blood to dialysate Ca and bicarb move from dialysate to blood.

Hemofiltration: uses hydrostatic pressure gradient to induce filtration / convection plasma water + solutes across membrane.

Hemodiafiltration: combination of dialysis and filtration.

Hemo dialysis :

• The 3 essential components of HD are : Dialyzer Composition of dialysate Blood delivery system

DIALYZERDIALYZER : :• Hollow-fiber dialyzer, the most commonly used type of dialyzer, is

composed of bundles of capillary tubes through which blood circulates and the dialysate travels on the outside of the fiber bundles.

• The blood and the dialysate may circulate in opposite direction

Dialysis membrane :

• It can be synthetic or biological. Cellulose : .has low flux .poor in removing middle MW molecules. . More complement and leucocyte activation.

• SYNTHETIC : High flux membranes.

Made up of Polyamide, Polysulphone (PS).

Allows removal of middle MW substances.

Dialysate Fluid

Access location

AV FISTULA AV GRAFT

Vascular access in HD/CRRTSite Advantages disadvantages

IJV Straight access Swings in flow associated with respiration.

Subclavian Least association with infection.

Swings in flow as above.

Risks of pneumothorax

Femoral Ease of access Infection rates high.

PHARMACOLOGICAL MEASURES

• Unfractionated or low molecular weight heparins• Unfractionated heparin (UFH) [5-30kDa] is the most

commonly used anticoagulant • typical regime involves a 40-70 IU.kg-1 bolus followed by

a pre-filterinfusion at 5-10 IU.kg.-1hr-1• It is the most cost effective anticoagulant and is fully

reversible with protamine.

• Low molecular weight heparins (LMWH) [4.5-6kDa] • They are dependant on renal elimination so in this

setting their dosing needs to be guided by anti-factor Xa levels (aiming for 0.25-0.35 IU.ml-1

• The half life of LMWHs is longer than for UFH (2-6 hrs versus 1.5-3hrs) and their effect can only be partially reversed with protamine.

GUIDELINES FOR NO ANTICOAGULATION

•INR > 2-2.5• APTT > 60 seconds• platelet count < 60 x 10³.mm3

ProstaglandinsProstaglandins (prostacyclin or prostaglandin E2) inhibit

platelet function and can either be used on their own or in

combination with heparin ,they have a synergistic effect.

short half life ,administered as an infusion 4-8ng/kg/hr

anticoagulant effect stops within 2 hours of discontinuing

the infusion

The main side effect is vasodilation

Regional citrate anticoagulation

• It is alternative to heparin • Sodium citrate is infused into the circuit pre-filter which

chelates calcium and inhibits clot formation.

Intermittent hemodialysis

• Diffusive process• Movement of solutes occur along an electrochemical

gradient• A low permeability cellulose base membrane is

employed• Dialysate sol flows countercurrent to blood flow• Smaller molecules are removed efficiently• Solute removal is proportionate to dialysate n blood flow

rate Qb- 150-300ml/min, Qd- 300-500ml/min• Typically performed 4hrs thrice weekly or daily

DIALYSIS DOSE MEASUREMENT / ADEQUACY DIALYSIS DOSE MEASUREMENT / ADEQUACY :

• UREA REDUCTION RATIO : URR = Pre dialysis BUN – Post dialysis BUN * 100 Pre dialysis BUN Ideally it should be >65%• Single pool urea kinetics : = K T

v k = clearance of urea in ml/min t = time of dialysis in hrs V = vol of distribution Ideally it should be above 1.3

advantages disadvantagesRelatively inexpensiveRapid correction of acidosisRapid correction of fluid overloadMinimizes anticoagulant exposureMobility possible

Cannot be used in hemodynamically unstable pts( i.e. shock)

Continous Renal replacement therapy

SLOW CONTINUOUS ULTRAFILTRATION (SCUF) :

• Qb-100-250ml/min, Quf- 5-15ml/min• No fluids are administered either as dialysate or replacement

fluids.• Indicated in CCF refractory to diuretics and in volume

overload.

CONTINUOUS VENO-VENOUS CONTINUOUS VENO-VENOUS HEMOFILTRATION (CVVHF) HEMOFILTRATION (CVVHF) ::

• Solute clearance occurs by convection.• No dialysate , Qb-100-250ml/min,Quf-15-60ml/min• Replacement fluid provided to replace the excess volume that is being

removed and replenish desired solutes.• Effective method of solute removal.• Major advantage is that solute can be removed in large quantities

CONTINUOUS VENO-VENOUS CONTINUOUS VENO-VENOUS HEMODIALYSIS (CVVHD) HEMODIALYSIS (CVVHD) :

• blood is driven through a low permeability dialyzer• Qb= 100-250ml/min, Qd= 15-60ml/min, Quf= 1-8ml/min• Solute clearance is mainly diffusive, and efficiency is limited to small solutes only.

CONTINUOUS VENO-VENOUS HEMODIAFILTRATION (CVVHDF) :

• blood is driven through a highly permeable dialyzer• A replacement solution is needed to maintain fluid

balance• Has benefits of both diffusion and convection for solute

removal.• Qb=100-250ml/min,Qd=15-60ml/min,Qf=15-60ml/min

SLOW LOW- EFFICIENCY DIALYSIS : ( SLED )SLOW LOW- EFFICIENCY DIALYSIS : ( SLED )

•Uses dialysate low flow rates & low blood flow rates

•Excellent small molecule detoxification.

•Reduced anticoagulant requirement.

•11 hrs SLED is comparable to 24 hrs of CHD .

•Decreased costs compared to CRRT.

WHICH FORM OF RRT SHOULD WE USE?

2. The patient`s cardiovascular status• CRRT causes less rapid fluid shifts and is the preferred option if

there is any degree of cardiovascular instability.3. The availability of resources• CRRT is more labour intensive and more expensive than IHD• Availability of equipment may dictate the form of RRT.4. The clinician`s experience• It is wise to use a form of RRT that is familiar to all the staff

involved. 5. Other specific clinical considerations• Convective modes of RRT may be beneficial if the patient has

septic shock• CRRT can aid feeding regimes by improving fluid management• CRRT may be associated with better cerebral perfusion in patients

with an acute brain injury or fulminant hepatic failure.

PERITONEAL DIALYSIS PERITONEAL DIALYSIS :

• In peritoneal dialysis, 1.5 – 3 L of peritoneal dialyzate solution is infused into the peritoneal cavity and allowed to dwell for a set period of time, usually 2 to 4 hours.

• The rate of diffusion diminishes with time and eventually stops when equilibration between plasma and dialyzate is reached

COMPLICATIONS COMPLICATIONS :

• Peritonitis .

• Catheter associated infections .

• Protein loss .

• Interference with diaphragm function .

• Residual uremia .

• Peritoneal membrane failure.

Complications common to IHD, CRRT, and hybrid therapies

1.Complications related to the vascath (including line-related sepsis)

2.Haemodynamic instability3. Air emboli4. Platelet consumption5. Blood loss6. Electrolyte imbalances7.Hypothermia8.Effects of anticoagulation (bleeding or specific side-effects of

the anticoagulant used e.g. heparin induced thrombocytopenia).

Dialysis Disequilibrium Syndrome

• self-limited condition characterized by nausea, vomiting, headache, altered consciousness, and rarely seizures or coma.

• It typically occurs after first dialysis in very uremic patients.

• triggered by rapid movement of water into brain cells following development of transient plasma hypo-osmolality as solutes rapidly cleared from bloodstream during dialysis.

• incidence has fallen in recent yrs with more gradual institution of dialysis, precise prescription of dialysis to include such variables as membrane size, blood flow rate, and sodium profile.

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