Page 405 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Monitoring Fluid Therapy and Complications of Fluid Therapy 395

to occur with dextrans, hydroxyethylstarch, gelatin, and with corticosteroids. 58 Canine lyophilized albumin (Ani-
hyperoncotic albumin; therefore, no specific colloid solu- mal Blood Resources International) is now available and
tionofitselfisdirectlynephrotoxic.Asthisproblemhasbeen may also be beneficial in hypoalbuminemic patients.
identified predominantly in renal transplant patients and Species-specific blood products Transfusions of
those with sepsis, it is advised that careful consideration blood products may result in both acute or delayed
be given to the volume of colloid administered in conjunc- immune-mediated reactions. While these are relatively
tionwithanadequatevolumeofcrystalloidtomeetthemin- rare events, it is essential to be familiar with prevention
imum daily water requirement. 68 The frequency of renal and treatment (Chapter 24).
dysfunction associated with administration of synthetic
colloids in veterinary patients is not known; however, it is POTENTIAL COMPLICATIONS
wise to consider the human reports when administering ASSOCIATED WITH THE VOLUME
the various colloids to veterinary patients. OF FLUIDS ADMINISTERED
Diuresis and Electrolyte Losses
Pulmonary Edema
The volume of fluids administered tends to be empirically
Another potential complication that may occur is leakage
derived, and response to therapy must serve to guide
of the small molecules (<50,000 Da)—contained in the
ongoing requirements. Excessive administration serves
currently used synthetic colloid solutions (e.g., hetastarch
no therapeutic benefit and frequently results in patient
and pentastarch) —into the pulmonary interstitium when
morbidity. A mechanism conserved across species
administered to animals with capillary leak syn-
drome. 32,61 A review of fluid therapy in sepsis with capil- through evolution is the renal-body fluid system for arte-
rial pressure control. Urine output can double when
lary leakage concluded that additional studies, including
patients with specific diseases, considering various aspects intravascular volume and pressure increase even a few
of the colloids administered and with specific endpoints millimeters of mercury above normal, a response termed
for fluid resuscitation, should be conducted before defin- pressure diuresis. In addition to water loss, a concomitant
23
itive recommendations can be made for colloid adminis- sodium loss occurs. If this diuresis goes undetected, an
tration. 54 In the meanwhile, appreciating potential excess of all electrolytes is excreted in the urine because of
decreased reabsorption in the proximal and distal renal
adverse effects, selecting appropriate patients, and moni- 24
tubules. In some instances, resultant hypokalemia can
toring during treatment should reduce the morbidity
be quite profound, especially in cats.
associated with administration of these solutions.
The ability to concentrate urine relies on the high
As with other colloidal solutions, caution with adminis-
osmolarity of the renal medullary interstitial fluid, which
tration oftheHBOCs iswarrantedtoavoid complications,
provides the osmotic gradient necessary for water reab-
especially associated respiratory problems. A study of 72
sorption. Transport of sodium, potassium, chloride,
cats receiving a HBOC solution, developed pulmonary
edema (n ¼ 8) and/or pleural effusion (n ¼ 21). 20 It was and other ions into the medullary interstitium, along
with urea, maintains this osmotic gradient. Increased
concluded that this complication could potentially be
medullary blood flow, which can occur with excessive
associated with a rapid infusion rate and/or large volume
of infusion of approximately 14 mL/kg. 20 fluid administration, will wash out the hyperosmotic
interstitium, thereby reducing renal concentrating abil-
ity. 26 A vicious cycle then is established in which fluid loss
Immune-Mediated Reactions
occurs because of a lack of concentrating ability. When
Human serum albumin [HSA] Many critically ill vet-
this occurs, gradual fluid reduction is required to reestab-
erinary patients are hypoalbuminemic, and this frequently
lish the hyperosmotic gradient and maintain hydration.
contributes to morbidity and mortality as a result of inter-
stitial, pulmonary, and visceral edema, and the loss of
the many other physiologic functions of albumin. Edema
Administration of 25% HSA to these critically ill patients Administration of fluids can lead to interstitial and pulmo-
to reverse the adverse effects of hypoalbuminemia has nary edema when the patient’s illness is associated with
56
beenreported. Whileadministrationof25%HSAtoseri- inflammation,anuricoroliguricrenalfailure,cardiacinsuf-
ously ill animals has shown benefit, complications ficiency, hypoalbuminemia, or with administration of a
associated with immune-mediated adverse effects occur large overdose of fluids resulting in hypervolemia and a
when administered to healthy animals. 19 Therefore, care- subsequent increase in interstitial hydrostatic pressure.
ful consideration must be given before the administration
of 25% HSA, which should be restricted to severe Interstitial Edema
hypoalbuminic and seriously ill patients. In this setting Under normal conditions there is a slight negative pres-
the benefits will potentially outweigh the risks. Patient fol- sure ( 3 mm Hg) in most loose subcutaneous tissues of
low-up for up to 4 weeks is warranted to ensure early signs the body. This negative pressure holds the tissues together
of immune-mediated reactions are detected and treated and offers some resistance to fluid flux caused by the low