Terminology • LITFL • CCC Renal

Terminology • LITFL • CCC Renal
January 12, 2019 0 Comments

Reviewed and revised 21 November 2016


This web page defines and discusses the next Renal Alternative Remedy (RRT) terminology and nomeclature:

  • extracorporeal circuit
  • diffusion
  • ultrafiltration
  • convection
  • filtration fraction
  • sieving coefficient
  • filter or dialyser
  • RRT
  • steady arterio-venous methods
  • IHD
  • SCUF
  • CRRT
  • Excessive quantity haemofiltration
  • excessive cut-off haemofiltration
  • predilution
  • postdilution
  • center molecules


  • the trail for blood circulation outdoors the physique
  • vessel -> catheter -> tubing -> filter/dialyzer -> tubing -> catheter -> vessel


  • Diffusion is the motion of molecules from an space of excessive focus to an space of low focus (greatest for small molecule clearance)
  • Strictly talking, dialysis is solute elimination by diffusion of the solute throughout a membrane (nevertheless, in medical settings dialysis normally means a mix of diffusion and convection)
  • throughout dialysis the electrolyte answer (dialysate) runs in the other way (countercurrent) to blood circulation separated by a semi-permeable membrane.
  • the speed of mass switch/diffusion decided by:

(1) attribute of solute (measurement, cost, protein binding)
(2) the dialysis membrane (kind, porosity, thickness, floor space)
(3) the speed of solute supply (blood circulation price and dialysate price – > helps generate focus gradient)
(4) gradient of substance in dialysate to blood

Medical significance

  • substances < 20kDa will be eliminated (urea, creatinine, uric acid, ions, IL-6, endotoxin, heparin, pesticides, ammonia, most protein certain medication)
  • causes much less injury to platelets and leukocytes
  • poorly removes bigger molecules


  • motion of fluid by a semipermeable membrane
  • a membrane’s effectiveness to ultrafiltrate fluid is described by the ultrafiltration coefficient (KUF), which is QUF/ deltaP (quantity of ultrafiltrate per unit time, divided by the stress gradient throughout the membrane)

CONVECTION (solvent drag)

  • Convection is motion of molecules by a semipermeable membrane related to the fluid being eliminated throughout ultrafiltration
  • solute molecule is swept by a membrane by a shifting stream of ultrafiltrate
  • convective transport is impartial of solute focus gradients throughout the membrane
  • porosity of the membrane determines which solutes are eliminated
  • optimistic stress is generated within the blood compartment by:

(1) rising the hydrostatic stress within the blood compartment
(2) rising the speed of blood circulation to the membrane


  • destructive stress within the dialysate compartment facilitates ultrafiltration, created by lowering the oncotic stress of plasma by pre-dilution

Medical significance

  • more practical technique for fluid elimination
  • center sized molecules (< 60 kDa) eliminated (ie. mediators in sepsis)
    — e.g. IL-8, TNF, IL-10, IL-6, complement, eicosanoids, platelet activating issue, myocardial depressants


  • Filtration fraction is the fraction of plasma that’s faraway from blood throughout haemofiltration.
  • the connection between trans-membrane stress and oncotic stress determines the filtration fraction
  • optimum filtration fraction at a haematocrit of 30% is 20-25%
  • the next filtration fraction can result in a haemoconcentration within the filter rising the chance of filter clotting


  • Sieving coefficient is the  ratio of the focus of solutes within the ultrafiltrate to that of plasma
  • a excessive sieving coefficient is fascinating for center molecules however undesirable for albumin for sized molecules
    SC = 1 – describes full permeability (for urea and creatinine)
    SC = 0 – displays full impermeability
    SC > 1 – requires an exterior vitality supply
  • throughout ultrafiltration, the driving stress forces solutes (equivalent to urea and creatinine) in opposition to the membrane, the solutes penetrate the pores of the membrane to an extent decided by the membrane sieving co-efficient for that molecule.
  • main elements figuring out sieving coefficient embrace:
    — solute molecular measurement
    — protein binding
    — filter porosity


  • = tubular-shaped gadget made up of plastic casing and the capillary fibers of the semipermeable membrane with in.


  • RRT is renal substitute remedy
  • substitute of the perform of kidneys: filtration and motion of electrolytes & fluid out and in of the physique
  • for all methods fluid stability is maintained by the distinction between fluid INPUT (dialysate and/or substitute fluid or each) and OUTPUT (spent dialysate and/or ultraflitrate or each)


  • these embrace all the CRRT methods (haemofiltration, haemodialysis and haemodiafiltration – simply change VV for AV)
  • nevertheless, right here the sufferers blood stress drives blood by the filter which incorporates the extremely permeable membrane
  • course of begins in an artery -> extracorporeal circuit -> vein
  • steady AV methods have been deserted in favour of steady VV methods


  • IHD is  intermittent haemodialysis
  • fluid eliminated by ultrafiltration (regardless of being referred to as ‘dialysis’)
  • solutes eliminated by diffusion
  • blood and dialysate are circulated on the alternative sides of a semipermeable membrane in a counter present route leading to diffusive solute elimination
  • ultrafiltration may also be achieved by making use of a destructive stress on the dialysate aspect of membrane
  • large circulation charges (300-400mL/min)
  • 3-4 hour per session
  • these machines generate dialysate from faucet water
    -> bacterial and endotoxin elimination
    -> reverse osmosis with electrolyte and buffer components


  • SCUF is sluggish steady ultrafiltration
  • elimination of H2O by a semipermeable membrane
  • low quantity ultrafiltration (100-500mL/hr)
  • no fluid is run as both dialysate or substitute


  • CRRT is steady renal substitute remedy
  • extracorporeal blood purification over an prolonged time frame to exchange kidney perform


  • CVVH is steady veno-venous haemofiltration
  • convective dialysis + ultrafiltration
  • mid sized molecules (inflammatory cytokines)
  • blood pushed by a extremely permeable membrane by a peristalitic pump and through an extracorporeal circuit originating and terminating in a central vein.
  • stress generated induces passage of plasma water (the solvent) throughout the membrane (= ultrafiltration)
  • because the solvent strikes throughout the membrane it take with it many toxins (solvent drag) -> this course of is known as convection
  • the fluid loss is changed in a part of utterly with applicable substitute fluid -> this maintains quantity and electrolyte homeostasis
  • circulation price: 50-200mL/min
  • prescription contains; blood circulation price, substitute fluid, fluid elimination price
  • fluid elimination price = effluent price – substitute fluid + additions (anticoagulation)
  • ultrafiltration price = effluent price


  • CVVHD is steady veno-venous haemodialysis
  • steady diffusive dialysis (chemical dialysis, no stress used)
  • blood on one aspect and dialysate on the opposite aspect flowing countercurrent
  • no fluid eliminated as a result of there isn’t a ultrafiltration
  • blood pushed by a extremely permeable membrane by a peristaltic pump and through an extracorporeal circuit originating in central vein and terminating in a central vein
  • solute elimination is immediately proportional to the dialysate circulation price
  • the fluid (dialysate) passes by the blood, molecules to which the membrane is permeable transfer from plasma water to dialysate
  • dialysate is then discarded
  • prescription; blood circulation price, effluent price (this equals dialysate price)


  • CVVHDF is steady veno-venous haemodiafiltration
    • combines CVVH (convective dialysis) and CVVHD (diffusive dialysis)
  • solute elimination is achieved by a mix of convection and diffusion
  • effluent is constructed from ultrafiltrate + dialysate
  • the machine controls fluid stability by manipulating the effluent price
  • prescription contains:
    • blood circulation price
    • dialysate price
    • substitute price and
    • quantity of fluid elimination
  • that is the approach utilized in most ICUs in Australia and New Zealand


  • objective is to take away elimination of soluble mediators of sepsis
  • definitions range (e.g. >50 mL/kg/h or for very excessive quantity HF >100 mL/kg/h)
  • filtration price – 6-10L/hr
  • requires excessive blood circulation (>300mL/min) to keep away from extra predilution or extreme haemoconcentration
  • hypophosphataemia will be problematic


  • use of particular filters with bigger pore measurement to extend CRRT’s capability to take away soluble mediators in sepsis


  • SLEDD is sustained low effectivity every day dialysis
  • hybrid remedy (intermediate between IHD and CRRT)
  • benefits
    • glorious cleansing
    • haemodynamic stability
    • extremely environment friendly
    • very versatile
    • much less cumbersome machine
    • affected person in a position to be mobilized
    • decreased necessities for anticoagulation
    • good management of quantity
    • inexpensive than CRRT
  • disadvantages
  • SLEDD is actually the identical as IHD however with lowered blood circulation charges to supply much less environment friendly clearance over an extended time interval (8-12 hours)
    • blood circulation charges 100-200mL/min
    • dialysate 100-300mL/min
  • be aware that ‘low effectivity’ is in comparison with IHD, in comparison with ‘CRRT’ SLEDD is ‘excessive effectivity’!


  • predilution is administration of the substitute fluid into sufferers blood earlier than its entry into the haemofilter (prefilter supply)
  • benefits
    • elevated filter life
    • improved mass switch
    • reduces solute-membrane interactions
    • creates a focus gradient that induces solute efflux out of RBCs into plasma
  • drawback
    • dilutes gradient -> low effectivity -> excessive substitute fluid necessities to realize solute clearance


  • postdilution is administration of substitute fluid into affected person’s blood after its exit from the haemofilter (postfilter supply)
  • benefits
    • extra environment friendly by way of solute clearance charges (40% extra)
  • disadvantages
    • restricted by attainable blood circulation price and related filtration fraction fixed


  • the definition of ‘center molecue’ has modified with the arrival of excessive flux dialysis membranes
    • initially utilized to molecules bigger than the small water soluble molecules that have been eliminated by older dialysis membranes
    • European Uremic Toxin Work Group has outlined the time period center molecule to be these with molecular weights between 500 Da and 60 kDa
  • some center molecules are thought to contribute to illness states equivalent to sepsis, longterm heart problems and amyloidosis
  • examples
    • center molecules: vitamin B12, b2 microglobulin, kappa gentle chains
    • not center molecules: urea, creatinine (too small); albumin (too massive)

References and Hyperlinks


Journal articles

  • Ficheux A, Ronco C, Brunet P, Argilés À. The ultrafiltration coefficient: this outdated ‘grand inconnu’ in dialysis. Nephrology, dialysis, transplantation. 30(2):204-8. 2015. [pubmed]

FOAM and net assets

CCC 700 6

Chris is an Intensivist and ECMO specialist on the Alfred ICU in Melbourne. He’s additionally the Innovation Lead for the Australian Centre for Well being Innovation at Alfred Well being and Medical Adjunct Affiliate Professor at Monash College. He’s a co-founder of the Australia and New Zealand Clinician Educator Community (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He’s on the Board of Administrators for the Intensive Care Basis and is a First Half Examiner for the School of Intensive Care Medication. He’s an internationally recognised Clinician Educator with a ardour for serving to clinicians be taught and for bettering the medical efficiency of people and collectives.

After ending his medical diploma on the College of Auckland, he continued post-graduate coaching in New Zealand in addition to Australia’s Northern Territory, Perth and Melbourne. He has accomplished fellowship coaching in each intensive care drugs and emergency drugs, in addition to post-graduate coaching in biochemistry, medical toxicology, medical epidemiology, and well being skilled schooling.

He’s actively concerned in in utilizing translational simulation to enhance affected person care and the design of processes and methods at Alfred Well being. He coordinates the Alfred ICU’s schooling and simulation programmes and runs the unit’s schooling web site, INTENSIVE.  He created the ‘Critically In poor health Airway’ course and teaches on quite a few programs around the globe. He is likely one of the founders of the FOAM motion (Free Open-Entry Medical schooling) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC convention.

His one nice achievement is being the daddy of two superb youngsters.

On Twitter, he’s @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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