Page 472 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

460 FLUID THERAPY

Factors Influencing Albumin Homeostasis
↓ Albumin Synthesis ↑ or Normal Albumin Synthesis
Nutritional Effects Nutritional Effects
Starvation Adequate protein/calorie intake
Malnutrition Branched chain amino acids
↓ Protein intake (especially tryptophan)
↓ Protein: ↑ calorie intake Hormonal Effects
↓ Branched chain amino acids Insulin Thyroxine
Glucocorticoids
Lack of negative feedback
Hepatocellular CA
Hormonal Effects ↑ Distribution
↓ Thyroxin
↓ Insulin ↓ Plasma colloidal osmotic pressure
↓ Glucocorticoids ↑ 3rd space fluid accumulation:
↓ Catecholamines
edema/pleural and abdominal effusions
↑ Glucagon
↑ Loss
Other Systemic Influences Protein losing enteropathy (PLE)
Interleukin 1 and 6: Acute phase 1 gut disease, vasculitis, lymphatic disease
↓ Functional hepatic mass portal or lymphatic hypertension
↑ Perisinusoidal oncotic pressure
colloid infusion, hyperglobulinemia Protein losing nephropathy (PLN):
amyloid, glomerulonephritis
Severe cutaneous losses: burns, exudative dermatitis

Altered Rates of Albumin Degradation Therapeutic centesis: ascites, repeated large volume
↑ Degradation ↓ Degradation
Albumin infusion ↑ Synthesis ↑ External loss
Colloid infusion Starvation Severely ↓ hepatic mass
Glucocorticoids Malnutrition
Figure 19-3 Factors and conditions influencing albumin synthesis and degradation.

of Disse by exocytosis. It then diffuses into the hepatic of distribution and numerous mechanisms influencing
sinusoids, where it mingles with the systemic circulation. the synthesis, distribution, and catabolism of albumin,
It then is dispersed into the interstitial space, returning to serum albumin concentration does not accurately reflect
the systemic circulation via lymphatics and the thoracic contemporary changes in total body albumin resources or
duct. In normal animals, 50% to 70% of albumin is located its hepatic synthesis.
extravascularly, with the largest amounts in interstitial The strong net negative charge of albumin ( 17)
spaces in skin and muscle. 132 Normal transcapillary explains its important contribution to the strong ion dif-
escape approximates 5% per hour, but inflammation ference (SID) and allows it to bind weakly and reversibly
may increase this several fold. This phenomenon com- with a variety of ions. In this capacity, albumin functions
monly contributes to the “negative-acute-phase” effect as a circulating depot and transport molecule for many
that modestly lowers serum albumin concentrations in ions (e.g., Ca 2þ ,Mg 2þ ,Cu 2þ ) and metabolites (e.g., fatty
inflammation. acids, thyroxine, bilirubin, bile salts, amino acids). 136
Catabolism of albumin probably occurs within or adja- Albumin accounts for most of the plasma thiol content
cent to vascular endothelium of tissues. 241 The half-life of (i.e., sulfhydryl bonds) and provides protection against
plasma albumin is 7 to 10 days in dogs and 6 to 9 days in oxidative stress. 175 Albumin also provides antioxidant
68,69,79
cats. The rate of albumin catabolism is highly vari- activity by binding reactive transition metals (e.g.,
able, but its fractional catabolic rate is directly propor- Cu 2þ ) that catalyze free radical generation. 136 Other
tional to the plasma albumin concentration and pool important effects of albumin involve anticoagulant,
size. 104 In conditions that cause hypoalbuminemia, the antithrombotic, and antiinflammatory effects.
fractional and absolute rate of albumin catabolism Oxidized and glycosylated forms of albumin occur in
decreases. The rate of albumin catabolism increases after human patients with cirrhosis, 231 and these forms
albumin or synthetic colloid transfusion. Thus transfu- increase in concentration as total serum albumin concen-
sion of albumin or infusions of synthetic colloids may tration decreases. The increase in the oxidized form of
potentiate endogenous hypoalbuminemia by two sepa- albumin reflects its role as a scavenger of reactive oxygen
rate mechanisms. As a consequence of the large space species. Glycosylation of albumin influences its binding