Summary
Edema is a general medical term that is often considered synonymous with swelling. As always, however, it’s more complicated than that. More precisely, edema refers to the accumulation of abnormally large volumes of fluid in the tissues between the body's cells. And when fluid accumulates in these tissues (called interstitial spaces), swelling is the most obvious result.
In the case of edema, either too much fluid moves from the blood vessels into the tissues, or not enough fluid moves from the tissues back into the blood vessels. This fluid imbalance can cause mild to severe swelling in one or more parts of the body.
A variety of factors can be responsible for this fluid imbalance. Consider these edema-causing conditions in pets:
Heart failure: If the heart can no longer pump blood adequately, the body’s normal fluid balance may be disrupted. Fluid can back up into the lungs or more superficial tissues (limbs, especially).
Kidney disease: If sodium and water can’t be normally excreted by the kidneys, fluid may be retained throughout the body.
Liver disease: The loss of normal liver function means that blood proteins are reduced. As such, fluid will leave the blood vessels and enter spaces in surrounding tissues throughout the body.
Gastrointestinal disease or malnutrition: Diseases where proteins are lost or too few proteins are taken in may result in fluid leaving the blood vessels.
The above factors tend to lead to generalized edema (of the whole body) while the following tend to lead to localized edema (of a specific location):
Infection: Inflammatory components enter an area when infection takes root there and blood flow to the area increases, leading to edema.
Trauma: As with infections, inflammation is the result of trauma after blood flow increases to help repair damaged tissues anywhere in the body. Even trauma to an eye, for example, will lead to edema of the cornea as the body attempts to bring healing factors to bear via increased blood flow.
Tumors: So, too, may inflammation and edema result when tumors take up space in tissues they’re wont to damage. By compressing vessels and lymphatic drainage they can also lead to fluid imbalances.
Some medications (such as corticosteroids), hormonal imbalances (such as thyroid hormone reductions), heat or immobility may also result in abnormal fluid balance and edema.
The problem, however, is that fluid imbalance isn’t always visible. Consider cerebral edema, which is what happens when a fluid imbalance affects the brain, or pulmonary edema when it affects the lungs. In both cases, too much fluid accumulates in the brain and lung tissues, respectively.
These manifestations of edema have so many unique features that they require treatment individually elsewhere in this library. See here and here. (Add links for pulmonary edema and cerebral edema.)
Symptoms and Identification
Animals and humans with edema can have specific areas of swelling (as with trauma and localized infections) or they can have the general appearance of puffiness, as when fluid tends to accumulate in their face and limbs.
While edema is readily identifiable, its underlying causes are not always so amenable to diagnosis. Blood tests, urinalysis, X-rays, ultrasound, echocardiogram, fecal examination, tissue biopsy, and CT scans are but a few methods commonly employed to pinpoint the cause of an animal’s edema.
Affected Breeds
Any breed of dog or cat is equally subject to the effects of edema.
Treatment
Treatment of edema depends entirely on its cause and effects. Righting the underlying cause of fluid imbalance is the ideal approach, however, sometimes this is impossible, as with end-stage heart, liver, or kidney failure. In cases like these, correcting the fluid imbalance through secondary means is often achievable with fluid therapy and medications. Diuretics are often employed for conditions that lead to generalized edema.
Veterinary Cost
The veterinary cost of edema will vary widely as some manifestations are so minor as to require no treatment whatever. Other cases, however, require everything from simple antibiotic therapy to chemotherapy, radiation therapy, long-term cardiac drug therapy, and even kidney transplant. The cost of edema, therefore, is impossible to estimate in general.
Prevention
Preventing edema is not always possible as certain conditions are genetically preordained and others impossible to predict (as with trauma or infection).
References
DiBartola SP. Applied physiology of body fluid in dogs and cats. In: Fluid, electrolyte, and acid-base disorders in small animal practice. 3rd ed. St. Louis, Mo: Saunders Elsevier, 2006;3-26.
DiBartola SP. Introduction to fluid therapy. In: Fluid, electrolyte, and acid-base disorders in small animal practice. 3rd ed. St. Louis, Mo: Saunders Elsevier, 2006;325-344.
Donohoe C. The technician's role in fluid therapy—from catheters to colloids, Part 2, in Proceedings. North Am Vet Conf, 2007. Available from the International Veterinary Information Service (www.ivis.org).
Fluid compartment deficits. In: Merck veterinary manual. Available at: www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/160403.htm. Accessed Dec. 13, 2009.
Goodwin JK, Strickland KN. The emergency management of dogs and cats with congestive heart failure. Vet Med 1998;93:818-822.
Hansen B, DeFrancesco T. Relationship between hydration estimate and body weight change after fluid therapy in critically ill dogs and cats. J Vet Emerg Crit Care 2002;12(4):235-43.
Muir WW, DiBartola SP. Fluid therapy. In: Kirk RW, ed. Current veterinary therapy VIII. Philadelphia, Pa.: WB Saunders Co, 1983;33.
Sisson D, Kittleson MD. Management of heart failure: principles of treatment, therapeutic strategies, and pharmacology. In: Fox PR, Sisson D, Moise NS, eds. Textbook of canine and feline cardiology. Philadelphia, Pa: WB Saunders Co, 1999.
Waddell L. Fluid therapy in the veterinary patient, in Proceedings. Western Vet Conf, 2009.
Wanamaker BP, Massey K. Therapeutic nutritional, fluid, and electrolyte replacements. In: Applied pharmacology for veterinary technicians. 4th ed. St. Louis: Mo.: Saunders Elsevier, 2008;298-324.
Ware WA, Bonagura JD. Pulmonary edema. In: Fox PR, Sisson D, Moise NS, eds. Textbook of canine and feline cardiology. Philadelphia, Pa: WB Saunders Co, 1999.