Page 439 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Perioperative Management of Fluid Therapy 427

protect against vascular leakage is supported by a study equal to or approximately 10% less than the volume
showing that HES 200/0.5 did not appear in cerebrospi- infused; hence there is little risk of volume overload. Of
nal fluid in patients with an impaired blood-brain the infused volume, approximately 50% was present in
barrier. 51 the circulation after 4 to 5 hours, although it has been
HES administration increases plasma volume by 71% stated that the plasma half-life is approximately
to 172% of the administered volume and generally 8 hours. 117 The plasma half-life of oxypolygelatin is
increases plasma volume by at least the volume 2 to 4 hours. The majority of the gelatin is excreted by
administered. 171 The degree of expansion depends the kidneys, with 71% of the urea-linked gelatin and
largely on the concentration of HES. Greater blood vol- 62% of the succinylated gelatin being found in the urine
ume expansion (e.g., 130%) is seen with 10% as compared in people within 24 hours. In chimpanzees, 66% of a dose
with 6% solutions. In this regard, HES is about equivalent of oxypolygelatin was found in the urine within 24 hours.
to dextran 70 but has a slightly longer duration of action. Mechanisms for the metabolism of the remaining
In one study in dogs, 25 mL/kg of dextran 70 or HES molecules are not well defined, but it is thought that they
450/0.7 gave an almost identical increase in plasma vol- are metabolized by proteolytic enzymes in the liver with
ume compared with the volume infused (approximately some of the end products being excreted in the feces
140%), but at 12 hours the dextran effect had decreased (approximately 15% of the total dose). 117
to 18%, whereas the HES effect had decreased to 38%. By Anaphylactoid reactions to gelatin solutions are rare.
24 hours, the dextran effect had further decreased to 1%, It is uncertain whether these reactions represent an
whereas HES still caused a 16% increase in plasma volume immunologic response or are caused by histamine release.
compared with the volume infused. 182 Greater expansion An overall incidence of allergic reactions to gelatins was
of blood volume occurs when HES is used to maintain reported to be 0.115%, with the highest incidence
blood volume in the face of ongoing loss as compared reported for oxypolygelatin (0.617%). 149 In this report,
with trying to expand blood volume in the normovolemic it was also noted that the severity of the reactions was
patient. In the former situation, the volume effect can be greater with the gelatins than with other colloids
up to 80% of the dose administered as compared with 40% (0.038% vs. 0.008% for dextrans and 0.006% for HES).
in the latter situation. 33 The incidence of anaphylactoid In a study of the release of histamine associated with
reactions with HES use in people is similar to that use of urea-linked gelatin in anesthetized patients, a
recorded for dextrans. Whereas antibodies to dextrans 26% incidence of histamine release was reported with
have been found in humans, no antibodies to HES have 4 of 57 patients exhibiting life-threatening signs. 116
been found in dogs, cats, or humans even after chronic Patients with malignant disease were twice as likely to
use. The frequency of life-threatening reactions appears release histamine and were seven times more likely to have
to be lower for HES than for other colloids. 171 No ana- a life-threatening episode. Pretreatment of patients with
phylactoid reactions to HES have been reported in dogs histamine blockers (H 1 and H 2 ) reduced the incidence
or cats. of clinical signs to zero. 116 The gelatin solution
(500 mL) in this study was given over 20 minutes
GELATIN SOLUTIONS (approximately 20 to 25 mL/kg/hr), and it has been
Gelatin solutions are prepared by degradation of bovine recommended that these solutions be administered
collagen and come in several forms. The process involves slowly.
exposure of the raw material to hydrochloric acid for sev- In the early reports of gelatin infusion, minimal effects
eral days, to saturated calcium hydroxide for several on coagulation were identified. 117 However, subsequent

weeks, and finally to a temperature of at least 138 C. studies showed that the effects are somewhat similar to
The three currently used preparations are oxypolygelatin those observed with other colloids but of lesser magni-
(Vetaplasma/Geloplasma, Institut Merieux Benelux, tude. An increase in bleeding time was recorded in
Brussels, Belgium), succinylated gelatin (Gelofusine, B healthy people and in trauma victims and was attributed
Braun Medical, Bethlehem, Pa.), and urea-linked to a decrease in von Willebrand’s factor activity. 48,57 In
gelatin (Haemaccel, Intervet, Milton Keynes, UK). studies using thromboelastography to measure the
Oxypolygelatin was available in the United States, and dynamics of clot formation, dilution with gelatins
the other two forms have been used extensively in resulted in more rapid onset of clot formation, more rapid
Europe. The main advantages of these solutions are that strengthening of the clot, and some decrease in the maxi-
they have lower molecular weights than the other colloids mal strength obtained. 56,127 In both of these studies, gel-
(and hence are excreted rapidly), they appear to be mini- atin was compared with hydroxyethyl starch, and the
mally antigenic, and they have minimal effects on coagu- latter induced greater changes than did the gelatin solu-
lation. 117 In one report, the use of more than 79,000 tion. In one study, 50% dilution with dextran 40
units of succinylated gelatin in humans was prolonged most coagulation parameters to such an extent
summarized. 117 The infusion of a solution of succinylated as to be unmeasurable. 127 In a clinical study examining
gelatin was associated with an increase in plasma volume the use of gelatin as a priming solution before