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Presented at Renal Trainee Seminar October 2012 - Belfast City Hospital

Presented at Renal Trainee Seminar October 2012 - Belfast City Hospital

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  • General who has found a scapegoat for his own sexual inadequacies in the Russkies, Commies are unaffected by the plot to pollute the water of the world because they drink vodka.

Hd and hdf Hd and hdf Presentation Transcript

  • Principles of HaemodialysisRichard McCrory10/10/2012
  • Summary• A description of the HD technique– Physics of solute and fluid removal• Diffusion / Convection– Haemodialysis vs. Haemofiltration vs.Haemodiafiltration• The importance of water purity• Dialysate– Sodium Profiling
  • The Aim of Haemodialysis‘To deliver blood in a fail safe manner from thepatient to the dialyzer, to enable an efficientremoval of uraemic toxins and fluid, and todeliver the cleared blood back to the patient’
  • Components of HaemodialysisBlood CircuitPatient | Vascular AccessBlood Tubing and HD MachineDialysate CircuitDialysate / Dialysis TubingWater Treatment SystemThe Dialyzer
  • The DialyzerComposition1)Blood Compartment2)Dialysate Compartment3)Semipermeable membrane4)Membrane support structure
  • Dialyzer DesignHollow Fibre – ‘Cylinders within cylinders’An ‘ideal’ dialyzer– Maximises surface area– Smallest amount of volume at given time
  • And now for some mathematics…The Hagen-Pouseille Equation‘Blood flow more strongly dictated by radiusrather than length’
  • Diffusive Clearance• Solute transfer across semipermeablemembranes along concentration gradients– Mass transport without bulk motion
  • Factors influencing Diffusion Rate• Concentration gradient• Molecular weight/size• Membrane surface area• Membrane Permeability• Blood flow rate (Qb)• Dialysate flow rate (Qd)
  • Relationship between blood flowand solute clearance is non-linear
  • Convective ClearanceSolutes move independent of solute activity(size, concentration) but dependent on therate of solvent flow– Provided size of pore permits movementSolutes travel at the same rateirrespective of size
  • The Flux of a DialyzerDetermined by Ultrafiltration CoefficientQuantity of pressure that must be exertedacross dialysis membrane (transmembranepressure) to generate a given volume ofultrafiltrate per unit timeLow Flux – Less leaky to waterHigh Flux – More leaky to water
  • The Sieving Co-efficientS = Cfiltrate / CplasmaAny value between 0 (no transport) and 1 (unrestrictedtransport)For HIPS 20SBeta-2Microglobulin = 0.8SAlbumin = 0.005
  • Summary: Overall Clearance of SoluteSmall Molecules– Dictated mostly by diffusion– Efficacy limited by fluid flowMiddle Weight Molecules– Dictated mostly by convection– Efficacy limited by properties of the membrane
  • Techniques of Haemodialysis
  • Haemodialysis
  • Isolated Ultrafiltration
  • Haemofiltration
  • Haemodiafiltration
  • Haemodiafiltration• HDF combines diffusive, convective andadsorptive clearances in the same unit• More clearance of middle weight moleculeswithout failure of small molecule removal
  • QuestionHaemodialfiltration as a modality of dialysis hasbeen associated with:a) Improved EPO responseb) Improved Phosphate Clearancec) Reduction in rates of intradialytichypotensiond) Improved Mortality Riske) All of the above
  • QuestionHaemodialfiltration as a modality of dialysis hasbeen associated with:a) Improved EPO responseb) Improved Phosphate Clearancec) Reduction in rates of intradialytichypotensiond) Improved Mortality Riske) All of the above
  • QuestionWhich component of a HD water system is mostimportant in ensuring that HD patients are notexposed to microbiological or chemicalcontamination?A)Good quality water from water providerB)Carbon FiltersC)Ion Exchange FiltersD)Reverse OsmosisE)Effective Disinfection of the HD machine
  • QuestionWhich component of a HD water system is mostimportant in ensuring that HD patients are notexposed to microbiological or chemicalcontamination?A)Good quality water from water providerB)Carbon FiltersC)Ion Exchange FiltersD)Reverse OsmosisE)Effective Disinfection of the HD machine
  • ‘As human beings,you and I needfresh, pure waterto replenish ourprecious bodilyfluids.’
  • Water Exposure in Haemodialysis• Haemodialysis patients may be exposed to350 to 500 L of water per week through a non-selective membrane, depending upon theirtreatment time and dialysate flow rate.– In contrast to an average 12 litres per weekthrough a highly selective membrane (intestinaltract) in healthy individuals.
  • Regulation of Water Purity‘Guideline on water treatment facilities,dialysis water and dialysis fluid quality forhaemodialysis and related therapies’ – Jan2012Association of Renal Technologistshttp://www.artery.org.uk
  • International Regulation of WaterPurity for RRT• BS ISO 13959; 2009: Water for haemodialysis andrelated therapies,• BS ISO 11663; 2009: Quality of dialysis fluid forhaemodialysis and related therapies,• BS ISO 26722; 2009: Water treatment equipment forhaemodialysis and related therapies.• BS ISO 23500; 2011: Guidance for the preparationand quality management of fluids for haemodialysisand related therapies
  • Standards (From ART Guidelines 2012)‘…dialysis water shall contain a total viable microbial count of less than100 CFU/ml and an endotoxin concentration of less than 0.25 EU/ml‘HOWEVER‘…The concentrations of microbial contaminants and endotoxin inultrapure dialysis fluid shall be < 0.1 CFU/mL and < 0.03EU/mLrespectively when used for high flux haemodialysis…’
  • Water Treatment System
  • Aluminium ToxicityAluminum, in the form of alum, is added to water toremove suspended colloidal matter; this process iscalled flocculation.Chronic exposure to aluminum is also associated withsevere bone disease and erythropoietin-resistantanemia– Speech abnormalities– Myoclonic muscle spasms– Personality changes– Seizures– Dementia
  • Dialysate‘Dialysate characteristics influence the finalconcentration of blood solute, intermediaryprotein, carbohydrate, and lipid metabolismand affect systemic vasomotor tone, cardiaccontractility and rhythm, pulmonary gasexchange, and bone turnover.’AJKD, Vol 46, No 5 (November), 2005: pp 976-981
  • Composition• Sodium (standard or ‘profiled’)• Potassium (variable)• Calcium (variable)• Buffer– Bicarbonate– Kept separate from the remainder of dialysate toprevent precipitation of calcium carbonate– Mixed in machine to achieve pH=7.40
  • Sodium ProfilingConsidered a means of reducing intradialytichypotension2 hypotheses:1) High dialysate sodium at the beginning of dialysiscombats movement of extracellular water into theintracellular space.2) Diffusion of sodium from dialysate into plasmawater would exert an osmotic effect tending toincrease plasma volume filling.
  • Fluid shifts during Ultrafiltration
  • Fluid Movement during ‘Standard’ HD
  • Sodium Profiling• Requires techniques to accurately follow thechanges in plasma sodium levels during thesession.• Only advantageous for the patient in the long-term if it results in a neutral sodium balance.– Otherwise excess sodium will lead to higher IDWG,thirst, hypertension
  • Summary• Haemodialysis achieves its aims by acombination of diffusive and convectiveclearance.• High standards of water purity required forsafety of the HD patient• HDF holds promise for improved dialysisoutcomes but hurdles for implementationneed overcome