How Dehydration Affects Dogs
Dehydration causes an abnormal reduction in the volume of circulating blood. This has a number of adverse consequences, many of which are related to imbalances in the levels of electrolytes in fluids that normally are contained inside and outside of cells (intracellular and extracellular fluids). Electrolytes are natural chemical substances which, when dissolved in water or melted, dissociate into electrically charged particles called “ions”. Ions can be negatively or positively charged and can conduct electrical currents. The key positively charged ions in a dog’s body fluids (“cations”) are calcium, magnesium, potassium and sodium. The primary negatively charged ions (“anions”) are bicarbonate, chloride and phosphate. The concentration of electrolytes is carefully regulated, because electrolytes are critical to the normal metabolic activities and functions of all cells in the body.
When a dog becomes dehydrated, the relative concentration of electrolytes in its cells, blood and other body fluids becomes imbalanced. This can affect virtually any organ or system, including the kidneys, bones, gastrointestinal tract, nerves, muscles, blood pressure, heart function and respiratory tract, among others.
Symptoms of Dehydration
The observable signs of dehydration in dogs can include one or more of the following:
- Excessive skin tenting/decreased skin turgor (the skin stays “stuck together” for a prolonged period of time after being gently lifted and pressed between two fingers. Normal skin pliability depends in large part upon hydration status. Obesity and emaciation can alter the results of this test.)
- Loose skin (loss of elasticity)
- Wrinkled skin (due to dryness)
- Lack of appetite (inappetance; anorexia)
- Weight loss (may be rapid in onset)
- Excessive volume of urine production and output (polyuria)
- Lethargy; listlessness
- Excessive drooling/salivation (ptyalism)
- Tacky, dry gums and other mucous membranes
- Elevated heart rate (tachycardia)
- Weak pulse quality/strength
- Prolonged capillary refill time (this is a simple test done by pressing on the dog’s gums with a fingertip and assessing how long it takes for the spot to return to its normal pink color; the normal canine capillary refill time is less than 2 minutes.)
- Sunken eyes (enophthalmos; usually bilaterally symmetrical/affecting both eyes equally)
Dogs at Increased Risk
Small dogs have an increased risk of becoming dehydrated, because they have a high body surface area-to-volume ratio. Anything that adversely affects thirst or appetite, or that diminishes water or food intake, can predispose a dog to dehydration. For example, dogs housed outdoors in exceptionally hot weather, and dogs whose water supply is frozen in the dead of winter, commonly have decreased water intake and become dehydrated. Dogs with some systemic diseases – especially those that cause vomiting, diarrhea, appetite loss or excessive urine production and output - are also predisposed to dehydration.