Page 582 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Shock Syndromes 569

administered for resuscitation. A mixture of one part decrease perfusion to many tissue beds. In pigs subjected
hypertonic saline (23.4% NaCl) with two parts dextran to hemorrhagic shock with or without traumatic brain
70 or hetastarch will make a 7.5% saline mixture. There injury, HBOC-21 was able to restore cardiovascular
are limited veterinary studies supporting the beneficial and cerebral recovery better than hetastarch or isotonic
use of this mixture for traumatic shock, endotoxic crystalloid administration. 67,69,74,86,106,118 However,
shock, hemorrhagic shock, pyometra, and gastric dilata­ Driessen et al showed that the administration of
tion-volvulus in dogs. 5,43,62,101,113,114,125,126,141,152,161 Oxyglobin to dogs with experimental hemorrhagic shock
led to severe vasoconstriction and a decrease in cardiac
HEMOGLOBIN-BASED OXYGEN output, despite apparent normalization of the typical
CARRIERS physical examination parameters. 34 Further studies have
Hemoglobin-based oxygen carriers (HBOC), such as found that microvascular perfusion and oxygen transport
Oxyglobin, have been the object of much study and inter­ are ameliorated following Oxyglobin therapy, how­
est for several years now. Although advanced scientific ever. 32,34,35,74 Although Oxyglobin can be lifesaving in
research is still lacking in animals, the solution contains specific animals (i.e., severe, acute anemia as seen with
many attractive characteristics. HBOCs improve the massive blood loss or hemolytic diseases), there are some
delivery of oxygen to the tissues by increasing both hemo­ medical concerns with the safety of this product and it is
globin content and preload. However, hemoglobin con­ not superior to natural blood products (and is more
centration may not increase due to the dilutional effects expensive). The recommended dose is 10 to 30 mL/kg
of the fluid. Although Oxyglobin is the only approved (dogs), and it is important to remember that this product
HBOC for use in small animals, its future availability is a colloid and can easily contribute to IV volume over­
is uncertain. load (especially in cats). Although the product’s safety
Oxyglobin is a sterile, ultrapurified, stroma-free, and efficacy have not been studied in cats, there are
polymerized bovine hemoglobin solution that is an alter­ two retrospective reports of its use in this species. 33,50
native oxygen carrying solution. It is nonantigenic and
therefore does not require blood typing or crossmatching BLOOD PRODUCTS
before administration. Oxyglobin has an MW of 200,000 The need for blood products in the shock patient is
Da and a COP of 40 mm Hg. The hemoglobin concen­ dependent on the patient’s disease process. Most previ­
tration is 13 g/dL and it is suspended in a modified ously normal patients can tolerate acute hemodilution
lactated Ringer’s solution with an osmolarity of to a hematocrit of less than 20%, although it is
300 mOsm/L and a pH of 7.8 (see Table 23-5). The recommended that the hematocrit be kept above 24%
half-life ranges from 18 to 43 hours, depending on the in critically ill humans patients to ensure adequate oxygen
dose administered (10 to 30 mL/kg, respectively). delivery. 155 In shock patients that are unresponsive to
It can be stored at room temperature for up to 2 years, fluid therapy alone, the hematocrit target may be
but an open bag must be used within 24 hours. It is pur­ increased to greater than 30% to maximize oxygen carry­
ple in color and will cause a yellow-orange discoloration ing capacity. Excessive increases in hematocrit should be
to the animal’s skin, urine, serum, sclera, and mucous avoided because this will increase blood viscosity.
membranes. Following administration of Oxyglobin, Most animals can tolerate an acute loss of 10% to 15%
the animal’s hemoglobin must be measured to estimate of blood volume without requiring a blood transfusion.
oxygen carrying capacity because the hematocrit of the Acute hemorrhage exceeding 20% of the blood volume
animal is unaffected (or diluted) by Oxyglobin. Several often requires transfusion therapy in addition to crystal­
laboratory parameters are invalidated due to discolor­ loid and colloid therapy (as discussed previously). In
ation of the serum. The oxygen dissociation curve for animals with acute blood loss requiring transfusion ther­
Oxyglobin is right-shifted, so oxygen is unloaded from apy, fresh whole blood or packed red blood cells and fresh
the red blood cells to the tissues more easily, and the frozen plasma should be used to stabilize clinical signs of
nonlaminar flow of the solution increases contact shock, maintain the hematocrit above 24%, and keep the
between the hemoglobin polymer and the endothelium clotting times within the normal range. Packed red blood
to further enhance the off-loading of oxygen. The hemo­ cells and fresh frozen plasma are administered at a dose of
globin may serve to perfuse areas that red blood cells can­ 10 to 15 mL/kg and fresh whole blood at a dose of 20
not reach. The nitric oxide (NO) scavenging effects of to 25 mL/kg (see Chapter 24 for further details on
Oxyglobin may be good or bad. On the one hand, the transfusion therapy).
combination of reactive oxygen species and NO produces The administration of 25% human albumin has gained
cytotoxic peroxynitrite and peroxynitrous acid that might recent popularity, although its potential adverse effects
be prevented by a NO scavenger, such as Oxyglobin. On have also been recognized. Because it is clearly a function­
the other hand, the vasoconstrictive effects of a nitric ally important blood component and accounts for 80% of
oxide scavenger will serve to increase afterload and the plasma oncotic pressure, animals with severe