Page 710 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

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
7
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