Page 717 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

704 SPECIAL THERAPY

is effective at eliminating high-molecular-weight, protein- diffusion to the pores in the interior of the carbon. The
bound, or lipid-soluble toxins or drugs that are cleared combination of hemodialysis for small solute removal
poorly, if at all, by hemodialysis (i.e., diffusion and convec- and hemoperfusion for removal of larger, protein-bound,
tion). Toxic indications include mushroom poisoning or lipid-soluble molecules provides a broad spectrum of
(amanitin toxins and phalloidin), herbicides, insecticides, blood purification in animal poisonings 61 (Figure 29-12).
overmedication, hepatic failure, and sepsis. 79,152,161 Despite the theoretical benefits, decisions to initiate
Candidate toxins include barbiturates, salicylates, extracorporeal therapies for patients with acute
antimicrobials, antidepressants, chemotherapeutics, and intoxications remains problematic. The current availabil-
NSAIDs that historically have been regarded as poorly ity of experienced programs is limited, and the established
removed by either hemodialysis or hemoperfusion. benefits of extracorporeal therapies for known toxins are
Hemoperfusion represents an important extension of poorly defined. Extracorporeal therapy is generally
the extracorporeal therapies that can be provided at indicated if the clinical signs of intoxication are progres-
regional hemodialysis programs for the management of sive or deteriorating and if the toxin can be cleared faster
intoxications for which there are no effective or efficient with the intervention than by endogenous clearance. For
therapeutic alternatives. an intoxicant such as ethylene glycol, experience with
Typical adsorbents used for hemoperfusion contain a hemodialysis is extensive, documented, and effective;
vast and complex network of interstices and pores of treatment decisions are easily justified. Hemodialysis is
varied shape and size. Toxic solutes interact by electro- the most efficient and cost-effective means to clear this
static and hydrogen bonds within the pores in the sorbent toxin (and its metabolites) from the animal and to prevent
becoming entrapped and thus cleared from the blood. the renal and extrarenal consequences associated with the
Selection of the adsorbent is critical for effective and safe intoxication. It can be recommended and justified above
hemoperfusion and must meet the following general all other treatments. For other toxins, documentation of
criteria: (1) high adsorptive capacity for the drug(s) or efficacy and outcome is limited, but the window and
toxin(s) to be removed; (2) nontoxic and opportunity for possible benefit is finite and decreases
hemocompatible; (3) minimal adsorptive selectivity for hourly following exposure.
normal blood constituents; (4) sterile, free of endotoxins, The goals for extracorporeal therapies (hemodialysis
and noncarcinogenic; and (5) compositional stability and hemoperfusion) are to eliminate the toxin and its
when exposed to blood (free of leachables).
Activated charcoal has been the adsorbent used most
commonly to eliminate endogenous and exogenous (1.3 g/mL)
toxins in vivo. 27,152,161 Toxic substances are cleared
according to their molecular size and affinity for the char-
coal, concentration in extracellular fluid, distribution vol-
ume, degree and affinity of protein binding, and lipid HD 81%
solubility. Activated carbons can remove solutes with a
molecular mass ranging from 60 to greater than
21,000 Da. 27,185 93% (6.7 g/mL)
Activated charcoal has a robust adsorptive capacity
2
approaching 1000 m /g but generally is nonselective in HP 62%
its solute binding. It can be manufactured with pore sizes
˚
˚
ranging from <10 A to greater than 100 A to control the (17.8 g/mL)
selectivity of solute removal. The larger the pore size, the
larger the molecules that can be removed. With small
˚
pores (<10 A), there is less concern about depleting Figure 29-12 Combined hemoperfusion (HP) and hemodialysis
molecules such as albumin, which would jeopardize (HD) for the treatment of enrofloxacin overdose in a uremic cat. A
safety. To prevent the release of fine residuals that could neonatal extracorporeal circuit was modified to include a 50-mL
embolize in the kidneys, spleen, or lungs, most activated Clark biocompatible HP system (Clark Research and Development
charcoals used for hemoperfusion are enveloped in an Inc., Folsom, La.) activated charcoal cartridge upstream to a Cobe
ultra-thin surface coatings (albumin-cellulose, cellulose, 100HG hemodialyzer (Gambro Renal Products, Lakewood, Colo.).
This combined blood purification technique resulted in a marked
dextran) to prevent the release of residuals and improve decrease in the blood enrofloxacin concentration (numbers in
biocompatibility and hemocompatibility without undue parentheses) through the extracorporeal circuit from 17.8 to 6.7
compromise to their adsorbent efficiency. The surface mg/mL (D62%) across the HP cartridge and from 6.7 to 1.3 mg/mL
membrane has little influence on solutes with low molec- (D81%) across the hemodialyzer and 93% reduction across both
ular mass such as creatinine, uric acid, hippuran, indoles, devices at 10 minutes of treatment. Combined HD/HP provided a
and vitamin B 12 . For solutes with higher molecular mass safe and effective additional route of clearance for enrofloxacin in
(>3,500 Da), however, the surface membrane limits this cat with renal compromise.