Page 710 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice
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Hemodialysis and Extracorporeal Blood Purification  697


              There are four common alternatives for “no heparin”  Regional Anticoagulation with Heparin and
            hemodialysis. In many circumstances, a “no heparin”  Protamine
            protocol really means drastically reduced heparin or  This procedure introduces heparin into the arterial blood
            regional heparin rather than a complete absence of hepa-  line to anticoagulate the extracorporeal circuit and
            rin use. In cases where there is a severe, life-threatening  reverses (antagonizes) the actions of heparin with prot-
            potential for bleeding (i.e., CNS hemorrhage, uremic  amine in the venous outflow before returning the blood
            lung), the risks for any degree of anticoagulation may  to  the  patient.  Regional  anticoagulation  avoids
            be too extreme for any use of heparin.              anticoagulating the patient while permitting effective
                                                                anticoagulation  of  the  dialysis  circuit.  Although
            Reduced Heparin                                     conceptually attractive, it is rarely performed because of
            Most treatments are performed with some heparin deliv-  the difficulty of precisely regulating the balance of
            ery to the extracorporeal circuit. If the predialysis ACT is  anticoagulation and antagonism.
            already increased or within the standard target range, the
            heparin prime usually can be eliminated. In most animals  Regional Citrate Anticoagulation
            (even those with increased ACT measurements) some   In another regional approach to anticoagulate, only the
            heparin is delivered to the extracorporeal circuit to pre-  extracorporeal circuit uses the sequential administration
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            vent overt clotting (especially in treatments employing  of citrate and calcium. Trisodium citrate is infused into
            slow blood flow rates). This may be on the order of 10  the arterial blood path to chelate calcium, decrease ion-
            U/hr (cats) or 10 U/kg/hr (dogs) up to 100 or 200   ized calcium, and prevent activation of the coagulation
            U/hr in small and large dogs, respectively. Clotting  cascade while blood is circulated in the extracorporeal cir-
            occurs preferentially in the venous header of the dialyzer  cuit. On the venous side, calcium is reinfused to normal-
            followed, in order of frequency, in the venous drip cham-  ize ionized calcium and reestablish normal coagulation
            ber, the fiber bundle, the arterial header of the dialyzer,  before blood is returned to the patient. Regional citrate
            and in the arterial drip chamber. The drip chambers are  anticoagulation is used routinely in a variety of extracor-
            particularly prone to clotting if the blood flow rate is  poreal therapies, including CRRT and apheresis, but is
            <20 mL/min as there is little stirring at these flows,  not used commonly in intermittent hemodialysis.
            and the chamber volume remains static. Under these  Although this represents an attractive approach, there
            conditions, the heparin infusion can be split and delivered  are a variety of predictable complications that require
            directly into both the arterial and venous chambers.  careful monitoring and procedural fine tuning. The bal-
            It also is helpful during slow treatments to pause the  ancing of citrate and calcium infusions is critical and often
            treatment every 20 to 30 minutes by placing the system  problematic. If the citrate infusion is inadequate, the sys-
            in bypass and increasing the blood flow to dislodge  tem is predisposed to clotting. If it is excessive, the patient
            accumulating thrombin aggregates and clots.         is predisposed to hypocalcemia and metabolic acidosis. If
                                                                the calcium supplementation is inadequate or excessive,
            No Heparin                                          the patient develops hypocalcemia or hypercalcemia,
            Truly no heparin treatments can be performed, but they  respectively. Other  possible  complications  include
            demand considerable attention. The extracorporeal cir-  hypernatremia from the trisodium citrate infusion and
            cuit usually is recirculated with heparin during the setup  metabolic alkalosis from metabolism of excessive citrate
            to promote binding of heparin to the plastic surfaces. This  or returned calcium-citrate complexes. This may become
            procedure had merit for some membranes (i.e.,       amorestandardizedprocedureforhemodialysisinanimals
            Hemophan), which could bind heparin covalently. It is  as greater experience is gained with the variety of extracor-
            uncertain if this procedure is rational with newer syn-  poreal techniques in which it is used more routinely.
            thetic membranes, which may not bind heparin. Before   Real-time monitoring of “no heparin” treatments is
            starting the treatment, the excessive heparin is removed  critical to their success and to prevent overt clotting
            from the circuit by a saline rinse (refresh) that is at least  complications. The goals of monitoring are to adjust
            three times the volume of the circuit. No heparin prime  intradialytic procedures to minimize progressive clotting
            or maintenance dose of heparin is provided during the  in the system and to abort the treatment before cata-
            treatment. The risk of clotting can be minimized by  strophic clotting causes loss of the entire extracorporeal
            maintaining the blood flow rate as high as possible,  blood volume (Figure 29-9). The presence of clotting
            keeping the treatment time to less than 2.5 hours, and  often can be predicted by visual inspection of the extra-
            flushing the extracorporeal circuit with 25 to 50 cc of  corporeal circuit and measurement of dialyzer perfor-
            saline every 15 to 30 minutes. Saline flushing dislodges  mance throughout the treatment. The most subtle
            accumulating thrombin aggregates and clots, and permits  evidence of potential clotting is often seen in the arterial
            visual inspection of the dialyzer for clotting. The excessive  and/or venous drip chambers as sticky fibrin tags or a film
            volume associated with flushing can be removed by   on the surface of the chambers. Visible clots in the
            ultrafiltration if necessary.                       headers of the dialyzer can be recognized as dark shapes
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