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1228 Plasmapheresis in Renal Disease

  • Guidelines for Plasmapheresis in Renal Disease

    Definition

    Apheresis is of Greek origin and means to "take away". Plasmapheresis therefore means removal of plasma.

    Plasma constitutes 55% of circulating blood volume. The other 45% is formed elements, such as RBC's, WC's and platelets. The components of plasma include:

    • Water 
    • Plasma proteins-albumin, fibrinogen, globulin
    • Antibodies
    • Hormones 
    • Minerals  
    • Gases Nutrients  
    • Enzymes 
    • Organic waste products 
    • Drugs

    Therapeutic Plasma Exchange (TPE) occurs when the removed plasma is replaced or exchanged with a replacement fluid, usually 4% albumin, FFP, or a combination of both. The removal of autoantibodies, immune complexes, inflammatory mediators and cytokines is the intended benefit of the procedure in the renal unit.

    Indicators for Plasma exchange in Renal Disease

    • Goodpasture's syndrome 
    • Systemic vasculitis with crescentic nephritis
    • Haemolytic Uraemic Syndrome/ TTP 
    • Lupus Nephritis 
    • Allograft rejection

    TPE may be used for a variety of other non renal diseases with Haematological and Neurological involvement.

    Methods of Plasma Exchange

    Separation of plasma and whole blood may be performed by filtration or by centrifugation.

    The Fresenius 4008 haemodialysis machine is used here at the Royal children's Hospital, Melbourne, with adaptation and filters specific to plasma exchange. The filters have pore sizes up to 0.5 micrometers allowing the passage of immune complexes.

    Exchange Volume Calculation

    A single plasma volume is approximately 50ml/kg. Therefore a double exchange, which is most common, is 100 ml/kg. The volume can also be calculated as follows:

                         TBV x (I-haematocrit (Hct)).  (TBV=80ml/kg)

    Circuit

    As in Haemodialysis, the extracorporeal blood circuit volume should not exceed 8% of the total blood volume, calculated at 80 ml/kg. Blood prime will be required in some circumstances, especially in small children (<20kg).

    Blood line volumes for the Fresenius machine are

    Adult: 170mls

    Paediatric: Arterial 59ml Venous 46ml

    Filter Sizes and priming volumes are:

    • PSu 1s-0.3m2 SA, 36ml priming volume.
    • PSu 2s-0.6m2 SA, 70ml priming volume.
    • LF-030-00 0.3m2 SA, 30ml priming vol
    • LF-050-00 0.45m2 SA, 50ml priming vol
    • PF 1000 N 0.15m2 SA, 23 ml priming vol
    • PF 2000 N 0.35m2 SA, 41 ml priming vol                                              

    Investigations

    • Ionised Calcium level should be >1mmol/L pre exchange. If not, a calcium gluconate infusion should commence and run during treatment. An ionized calcium test should be taken 30-40 min into procedure as well to ensure level doesn't fall below 1 mmol/L. At risk groups for hypocalcaemia include those receiving FFP replacement  (high citrate content) and those with liver disease (impaired capacity to metabolise citrate).
    • Coagulation profile
    •  FBE
    • U&E
    • Others according to disease process eg LDH, anti-GBM Ab, ANCA, dsDNA.
    • Urine for microscopy and Pr:Cr monthly

    Anticoagulation

    Initial Dose

    Patient Weight

    Units of Heparin /Kg

    Total initial dose

    5-15

    30-50

    150-750

    15-25

    30-50

    450-1000

    25-35

    30-50

    750-1000

    35-55

    30-50

    1000

    >55

    30

    1000

    Maintenance Dose

    • 15-20 units/kg/hr

    The above dosage guidelines may need to be exceeded in patients with a low haematocrit or when the plasmafiltration rate is high.

    Rate of Exchange

    Filtration rate should commence slowly- .2 ml/kg/min grading up to no more than .5 ml/kg/min when using FFP.

    When using 4% albumin, a faster rate of isovolaemic exchange can be undertaken (eg 3 litre exchange over 2 hours).

    The limitation to rate of exchange when using FFP is due to the presence of 17% ACD, which is only around 4% in albumin replacement.

    Replacement Fluid

    4% Albumin is the most commonly used replacement fluid, with FFP x1 or 2 units at the end of therapy to minimize the risk of bleeding.

    PICU uses an electrolyte balanced replacement solution produced by RCH pharmacy - this is generally not necessary for plasma exchange in the ambulatory care unit, but may be prescribed in special circumstances at the discretion of the renal consultant.  

    IVIG may be ordered for administration at the end of the exchange procedure.

    Some disease such as HUS and TTP are more effectively treated by using FFP as the replacement fluid.

    Reactions to Albumin and FFP are not uncommon, and it is recommended that patients known to react receive Hydrocortisone and/or Promethazine or cetirizine hydrochloride at the beginning of treatment.

    All patients should have a PRN dose written up at the bedside in case of a reaction.

    Refer to Pharmacopeia for dosage.  

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