Page 436 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Perioperative Management of Fluid Therapy 425

C6 ratio (Table 17-3). 51 In the literature, the molecular in 30 hypoalbuminemic dogs, there was an increase in
weight and substitution ratio usually are used to define colloid osmotic pressure with the administration of 7.7
the product. For example, HES 200/0.5 represents to 43.9 mL/kg, but this effect lasted less than 12 hours.
HES with an average molecular weight of 200 kDa and It was suggested that maintenance of colloid osmotic
a molar substitution ratio of 5 hydroxyethyl groups per pressure would require additional HES or administration
10 molecules of glucose. It would be preferable to include of other colloids. 125
the C2:C6 ratio of the molecule because HES 200/0.5 As with dextrans, there has been concern about the
with a substitution ratio of 13.4:1 behaved very differ- effect of HES on coagulation. 176 In early experiments
ently than HES 200/0.5 with a C2:C6 substitution ratio in dogs, infusion of 10 mL/kg was not associated with
of 5.7:1. 183 The original commercially available prepara- increased blood loss or any change in bleeding time. With
tion of HES has an average molecular weight (M w ) of 450 infusions of 20 to 30 mL/kg, however, bleeding time and
kDa with a number molecular weight (M n ) of 69 kDa. quantity of blood lost increased. These effects were more
This solution was made up in normal saline. A newer high pronounced with dextrans than with HES 450/0.7. 101
molecular weight HES (Hextend, BioTime, Inc., Factor VIII complex consistently is decreased after
Emeryville, Calif.) is made up in a balanced electrolyte HES 450/0.7 administration, and it is advised that
solution so that infusion is less likely to be associated with HES 450/0.7 not be given to dogs with known or
hyperchloremic acidosis, and the presence of calcium may suspected von Willebrand’s disease. 171 In a study in
reduce the occurrence of clotting abnormalities. How- which very large doses (110 to 120 mL/kg) of HES
ever, this solution, at a dosage of 20 mL/kg administered 450/0.7 were used, prolonged bleeding times were
over 1 hour had an effect on platelet function for at least 5 identified. Platelets appeared swollen and shiny and had
169 114
hours and in some individual dogs up to 24 hours. The decreased adhesion. Clots were friable and had weak
newer HESs have even lower molecular weights, and tensile strength. These effects were presumably caused
HES 130/0.4 (Voluven, Fresenius Kabi Norge AS, by more than just hemodilution, and these findings
Holden, Norway, and Hospira Inc., Lake Forest, Ill.) is should be borne in mind when using HES 450/0.7 at
thought to have close to ideal properties because it does the time of surgery. Studies in humans undergoing sur-
not remain in plasma as long as bulkier molecules, but it gery have not documented any increase in blood loss
also does not interfere with coagulation as much. In any associated with the administration of HES 450/
of these solutions, the smaller molecules (molecular 0.7. 13,188 The lower molecular weight HES is associated
weight, <59 kDa) are excreted by the kidneys or pass with fewer alterations in coagulation. HES 130/0.4
through the vascular endothelium into the interstitial causes fewer effects on coagulation than HES 200/0.5
space. Molecules that reach the interstitial space are taken and may reduce the need for blood transfusions in human
up by macrophages and are slowly metabolized by cellular orthopedic patients. 110 I have not seen increased bleed-
lysozymes. The larger molecules are slowly broken down ing tendency in dogs given HES 450/0.7, but the dosage
by a-amylases. Dogs have approximately three times as used has not exceeded 20 mL/kg.
much amylase as do humans, and HES 450/0.7 is broken Other concerns with HESs are their effects on renal
down faster. In dogs, 31.5% of administered HES was and hepatic function. Renal function appears to be mini-
excreted in urine, and 38% remained in plasma after 24 mally affected if it was normal initially, but septic patients
hours. 182 The half-life of HES 450/0.7 in humans varies may be at increased risk for renal injury after HES admin-
with time after administration and dose (e.g., the half-life istration. 26,161 Hepatic failure has been noted in some
is 1.5 to 3.6 days during the first 3 days after administra- human patients who have had repeated infusions of high
tion and 13 to 17 days between 7 and 42 days after molecular weight HES, but such usage does not appear
administration). After three consecutive daily doses, the to be a major risk factor in the perioperative period in vet-
36
excretion of 41% to 46% of this HES took 168 hours com- erinary patients. Serum amylase concentrations are
pared with 48 hours after a single dose. This dependence expected to increase after the use of HES. Pruritus is
on time and dose has not been demonstrated in dogs. 171 another consequence of HES infusion and appears to
In hypoalbuminemic dogs, the administration of HES be related to dose rather than HES type. If pruritus
450/0.7 was associated with an increase in colloid occurs, it can be of major concern to the patient and is
osmotic pressure and a reduction in peripheral edema refractory to treatment. 11
in most treated patients. There was no apparent correla- HES may be beneficial to the patient by reducing the
tion between the dose of HES 450/0.7 or the change in inflammatory response to surgery. In human patients
colloid osmotic pressure and resolution of edema. A few undergoing abdominal surgery, concentrations of inter-
dogs showed prolongation of APTT and a decrease in leukin-6 and -8 and intercellular adhesion molecule-1
platelet numbers, but it was unclear whether this effect were lower when HES 130/0.4 was used for intravascular
was caused by the HES treatment. Some dogs with volume replacement instead of LRS. 109 The effect on
abnormal hemostasis before treatment actually became adhesion molecules also may alter the capillary leak that
normal after treatment. 170 In another trial using HES can occur in trauma and sepsis. The idea that HES may