Page 668 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Fluid Therapy with Macromolecular Plasma Volume Expanders 655

CLINICAL USES comparing dextran/hypertonic saline with isotonic saline
Support Of Intravascular Volume for fluid resuscitation of dogs suffering from gastric dila-
tation-volvulus syndrome 137 and trauma 138 did not
The principle use of colloids is for intravascular volume
reveal a consistent benefit with either approach.
expansion in patients with hypovolemic or distributive
shock. Colloids are generally considered to be more effec- Recommended Dose
tive for this purpose on a mL/kg basis than isotonic
crystalloids. However, given the many factors involved The recommended dosage for the high molecular weight
in the efficacy and persistence of colloid therapy and hydroxyethyl starches, the gelatins, and the dextrans is
the heterogeneous nature of the patient population in 20 mL/kg/day. Dependent on the patient’s status, this
which they are used, it is crucial to carefully assess the may be administered as one or more boluses with the
need for colloidal therapy and the clinical response of speed of bolus administration being dependent on the
the patient. Colloid therapy is not a panacea; rather it clinical status of the patient. Although higher dosages
106,150
represents one more group of drugs with specific have been used without apparent adverse effects,
indications, contraindications, benefits, and risks. The deleterious effects on coagulation (see later discussion)
treatment of critically ill human patients with colloid occur more commonly at and above this dosage. The
solutions recently has been questioned in several meta- newer low molecular weight hydroxyethyl starches avail-
analyses of randomized clinical trials in human patients. able in Europe may be used at higher doses of up to
17,35,116,139,171 50 mL/kg/day. 89 A dosage of 20 mL/kg represents
Despite the limitations of randomized
clinical trials and meta-analyses, 128 all showed a trend one quarter of a dog’s blood volume, and if repeated
toward increased mortality when colloids were used to doses are required to maintain perfusion, the underlying
resuscitate human trauma patients. Subdivision of the reason should be pursued aggressively. Cats seem to be
patients in one study 171 demonstrated that in trauma much more likely to develop volume overload than dogs,
patients there was a 12.3% difference in mortality rate at least in part due to their smaller blood volume as a per-
in favor of crystalloid therapy, and when data from studies centage of body weight. The suggested dose in cats is
that used nontrauma patients were pooled, there was a 5 mL/kg. Lastly, colloid solutions may not contain a bac-
7.8% difference in mortality rate in favor of colloid treat- teriostat and such formulations are therefore intended for
ment. The authors concluded: single-dose usage.

“in patients with trauma who are septic and in whom the COLLOID THERAPY IN
capillary leak syndrome leads to adult respiratory distress PULMONARY DISEASE
syndrome, it may be assumed that colloid resuscitation
would be no better than crystalloid resuscitation. Many pulmonary diseases result in accumulation of excess
In this study the meta-analysis of published data showed fluid in the interstitium alone or in the interstitium and
that this form of treatment is deleterious. In patients who
are nonseptic or having elective surgery, however, the alveoli. This increase in so-called extravascular lung
water is synonymous with pulmonary edema. The lung
basement membrane is intact, and meta-analysis of data
in this setting showed that treatment with colloids would is relatively resistant to the edemagenic effects of
be efficacious.” hypoproteinemia, 182 and the two most important
mechanisms by which pulmonary edema occurs are an
The likely explanation of these results is that if vascular increase in pulmonary hydrostatic pressure and an increase
leak is sufficiently severe to allow significant colloid in pulmonary microvascular permeability. 153 High-pres-
extravasation then colloids may worsen outcome com- sure edema may occur secondary to left-sided heart failure
pared with crystalloids. A meta-analysis that was designed or volume overload, whereas increased permeability
a priori to investigate resuscitation after trauma showed a edema may be caused by conditions such as pneumonia,
lower mortality rate associated with the use of crystalloid toxic lung injury, and systemic inflammatory response
fluids. 35 syndrome. In some clinical settings, the pathogenesis of
Similar large scale studies do not yet exist within the pulmonary edema may be unclear or include both
veterinary field. In experimental dogs given standard components (e.g., neurogenic and reexpansion edema).
boluses of isotonic saline (80 mL/kg) or hetastarch The pulmonary endothelium is relatively permeable to
170
(20 mL/kg), volume expansion was initially significantly protein compared with other tissues, and albumin and
86
greater with isotonic saline, was not significantly different HES equilibrate more rapidly with the interstitial space
30 minutes following administration, and was greater, even in a normal lung. Consequently, the effective COP
although not significantly so, in the hetastarch group gradient that can be generated between the intravascular
147
after 4 hours. Hetastarch was more effective than crys- space and the pulmonary interstitium is lower than in
talloid in reversing isoflurane-induced hypotension in other tissues. Therefore the lung must rely more on
1
healthy experimental beagles. Two small clinical studies increased lymph flow than interstitial COP dilution to