Dehydration

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Dehydration, also referred to as desiccation, is a pathophysiological condition in which the animal’s body loses more fluid than it takes in. This fluid deficiency affects not only the pure water in the organism but often also vital electrolytes such as sodium, potassium, and chloride. The water content makes up about 60% of the body weight in healthy dogs and cats, with this value reaching up to 80% in puppies.

The fluid in the body is distributed across various compartments: about two-thirds are intracellular (within the cells), while one-third is extracellular (outside the cells). This balance is essential for numerous physiological processes such as metabolism, temperature regulation, and blood circulation. Dehydration causes a disturbance in this delicate equilibrium, which can have far-reaching consequences for the entire organism.

It is particularly important to understand that a fluid loss of just 5% of body weight can cause clinical symptoms. From a loss of 10-12%, the situation becomes life-threatening, and a loss of more than 15% leads to death of the animal if left untreated. These figures illustrate how quickly an initially seemingly harmless dehydration can become a serious medical emergency.

Causes

The causes of dehydration in dogs and cats are diverse and can be categorized into several groups:

Increased fluid loss: The most common triggers are gastrointestinal diseases such as acute diarrhea and vomiting, which lead to a rapid loss of water and electrolytes. Fever, excessive panting in dogs, or intense sweating (through the paw pads in cats) in high temperatures can also significantly increase fluid loss. Bleeding, burns, and extensive skin injuries also lead to increased fluid loss through the damaged body surface.

Decreased fluid intake: Numerous factors can impair normal water intake. These include oral cavity diseases such as stomatitis or dental problems that make drinking painful, neurological disorders that affect swallowing, as well as impaired consciousness or immobility that make access to water difficult. A lack of thirst sensation, as occurs in older animals or certain diseases, can also lead to insufficient fluid intake.

Hormonal and metabolic disorders: Diabetes mellitus leads to increased water loss due to increased glucose excretion in the urine (glucosuria). Kidney diseases impair the kidneys’ ability to concentrate urine, resulting in increased water loss. Hyperthyroidism in cats can also lead to an increased fluid requirement due to an increased metabolism, which is not always adequately compensated.

Environmental factors: Extreme heat, lack of access to fresh water, physical overexertion, and inadequate acclimatization to warm environments are important environmental factors that can promote dehydration. Animals left in hot cars are particularly at risk, as the temperature inside the vehicle can quickly rise to life-threatening levels.

Medication influences: Certain medications such as diuretics increase urine excretion and can lead to dehydration if fluid intake is insufficient. Laxatives and certain chemotherapeutic agents can also negatively affect fluid balance.

Young animals, seniors, and animals with chronic diseases are particularly at risk, as their compensation mechanisms are often limited. Brachycephalic (short-headed) dog breeds such as Pugs or French Bulldogs are also at increased risk, as they are more susceptible to overheating due to their respiratory tract anatomy.

Symptoms

In mild dehydration

  • Thirst
  • Dry mucous membranes
  • Concentrated, dark yellow urine

In moderate dehydration

  • Sunken eyes
  • Very dry mucous membranes
  • Severely reduced urine output (oliguria)
  • Significantly increased heart rate (tachycardia)

In severe dehydration

  • Skin folds that remain standing for several seconds after lifting the skin
  • Low blood pressure (hypotension)

From a fluid loss of approximately 15% of total body fluid, hypovolemic shock occurs, characterized by

  • Circulatory failure
  • Increasing impairment of consciousness
  • Lethargy
  • Coma

The clinical signs of dehydration develop progressively and vary depending on the severity of fluid loss. Early recognition is crucial for successful treatment.

Mild dehydration (approx. 5% fluid loss):
In mild dehydration, animals often show subtle changes that can be easily overlooked. The mucous membranes, especially the gums, appear drier than normal but still retain some moisture. The urine becomes more concentrated and takes on a dark yellow color. Affected animals show an increased sense of thirst, drinking more frequently and in larger amounts. During clinical examination, skin elasticity is still largely normal, and the skin turgor test shows only a minimally delayed return of the skin fold.

Moderate Dehydration (approx. 6-9% fluid loss):
As dehydration progresses, symptoms become more pronounced. The mucous membranes are now noticeably dry and sticky. The eyes begin to sink in as the surrounding tissue loses volume. The capillary refill time (the time it takes for the gums to return to their normal color after pressure is applied) is prolonged and takes more than 2 seconds. The skin tent test shows a significantly delayed return of 2 to 4 seconds. Urine production decreases noticeably (oliguria), and the heart rate accelerates (tachycardia) as a compensatory mechanism to maintain blood pressure. The animals appear increasingly lethargic and show reduced activity.

Severe Dehydration (approx. 10-15% fluid loss):
In severe dehydration, the symptoms are alarming and constitute a medical emergency. The mucous membranes are extremely dry, and saliva production is greatly reduced. The eyes are deeply sunken and may take on a glassy appearance. The skin tent test shows a persistent skin fold that remains for 4-10 seconds or longer. Blood pressure drops dangerously (hypotension), and the extremities feel cool due to reduced peripheral circulation. The heart rate is greatly increased, while the pulse becomes weak and thready. Body temperature may be abnormally low. The animals are severely apathetic, barely respond to environmental stimuli, and may even fall into a comatose state.

Critical Dehydration (over 15% fluid loss):
At this severity level, a life-threatening hypovolemic shock develops. The animals are unconscious or only minimally responsive to painful stimuli. Breathing is shallow and irregular. The pulse is barely palpable, and the extremities are cold. Without immediate intensive care treatment, this condition is usually fatal.

Especially in cats, the symptoms of dehydration can be more subtle and are often only noticed in advanced stages. Cats often show less obvious behavioral changes and compensate for fluid losses longer before clinical signs become apparent.

First Aid

  • In case of repeated vomiting, temporarily restrict free access to water and food to allow the stomach to rest.
  • After that, you can try giving water again in small portions. For cats, use the volume of a teaspoon each time, and for dogs, depending on their size, use a tablespoon full to 1/4 cup of fluid per serving.
  • If your pet initially stops vomiting, still do not allow your pet to quench its thirst through free access to water. Proceed gradually and slowly increase the water supply until the deficit is balanced.
  • Check if the tongue and gums are still dry or have become moist again, and if the saliva appears watery again or is still viscous and slimy.
  • If the eyes appear sunken, there is still moderate to severe dehydration present.
  • If you gently lift a skin fold on your pet and then release it, it will smooth out immediately in a healthy animal. If dehydration is present, it smooths out only slowly or remains nearly standing. This would already be a sign of severe, life-threatening dehydration.

Diagnosis

The diagnosis of dehydration in dogs and cats is made through a combination of clinical examination, medical history, and laboratory diagnostic procedures. A precise assessment of the degree of dehydration is crucial for therapy planning.

Clinical Examination:
The skin turgor test is an important diagnostic tool. In this test, the skin in the neck area (for cats) or over the shoulder blade (for dogs) is lifted and released. In a well-hydrated animal, the skin fold flattens immediately. The longer the skin fold persists, the more severe the dehydration. However, it should be noted that the skin turgor test may be less reliable in very young, very old, or cachectic animals, as well as in certain breeds with excess skin.

The assessment of mucous membranes provides further important information. The veterinarian examines the moisture of the oral mucosa and gums, as well as the capillary refill time. Dry, sticky mucous membranes and a prolonged capillary refill time (>2 seconds) indicate dehydration. The position of the eyeballs is also assessed – sunken eyes are a sign of significant fluid loss.

Laboratory Diagnostics:
Blood tests are essential to quantify the severity of dehydration and identify possible underlying diseases. An elevated hematocrit and increased total protein concentration in the serum are typical findings in dehydration, as the blood plasma becomes more concentrated. Electrolyte disturbances such as hyper- or hyponatremia, hyperkalemia, or hypokalemia can also occur and must be identified for targeted therapy.

The determination of blood urea nitrogen (BUN) and creatinine in the serum helps to distinguish between prerenal azotemia (due to dehydration) and primary kidney disease. In dehydration, the ratio of BUN to creatinine typically increases (>20:1).

Urinalysis provides valuable information about the hydration status. Concentrated urine with high specific gravity (>1.030 in dogs, >1.035 in cats) indicates appropriate renal concentrating ability in response to dehydration. Inappropriately diluted urine despite clinical dehydration may indicate kidney disease or other disorders.

Imaging Techniques:
In more complex cases, imaging techniques such as ultrasound or X-ray can be used to identify underlying causes of dehydration, such as obstructions in the gastrointestinal tract, kidney diseases, or tumors.

Modern Diagnostic Methods:
Newer approaches to assessing hydration status include measuring central venous oxygen saturation, determining blood lactate levels as a marker for tissue hypoxia, and assessing vena cava dimension using ultrasound. These methods are primarily used in intensive care medicine to continuously monitor the fluid status of critically ill patients.

The diagnosis should always include the identification of the underlying cause, as this significantly influences the treatment strategy and is crucial for the long-term prognosis.

Further veterinary measures

If you are not successful and your pet does not recover within hours, present your pet to a veterinarian.

The treatment of dehydration in dogs and cats follows a systematic approach that is tailored to the severity of fluid loss and the underlying cause. The primary goal is to restore fluid and electrolyte balance as well as treat the underlying condition.

Fluid Replacement Therapy:
Intravenous fluid therapy is the most effective method for treating moderate to severe dehydration. This involves placing an intravenous catheter through which crystalloid solutions such as Ringer’s lactate or isotonic saline are administered. The choice of fluid depends on the patient’s electrolyte values and the type of dehydration.

The calculation of the amount of fluid to be administered follows a specific formula: Body weight (kg) × estimated degree of dehydration (%) = fluid deficit in liters. To this deficit, the daily maintenance requirement (about 50-60 ml/kg/day) and ongoing losses (e.g., from persistent diarrhea) are added. Rehydration ideally occurs over 24-48 hours, with about half of the deficit being replaced in the first 4-6 hours to avoid too rapid electrolyte replacement.

For hypovolemic shock, a faster initial fluid administration is required (shock dose: 90 ml/kg/h for dogs, 60 ml/kg/h for cats), administered over 15-30 minutes, followed by a reassessment of the patient.

Alternative Administration Routes:
In cases of mild to moderate dehydration or as a supplement to intravenous therapy, subcutaneous fluid administration can be a viable option. This involves injecting isotonic fluids under the skin, typically in the neck area. This method is less invasive, but also less effective for severe dehydration or shock.

Oral rehydration can be used for mild dehydration and when swallowing ability is preserved, provided the animal is not vomiting. Special oral rehydration solutions containing electrolytes and easily digestible carbohydrates are commercially available or can be prepared according to veterinary instructions.

Electrolyte Management:
Electrolyte imbalances must be corrected specifically. Hypokalemia, common in anorexia and gastrointestinal losses, requires potassium supplementation. Hyponatremia must be balanced slowly to avoid neurological complications. Electrolyte correction is carried out under regular laboratory monitoring to prevent overcorrection.

Treatment of the Underlying Disease:
Parallel to fluid therapy, the underlying cause of dehydration must be treated. This may include antiemetics for vomiting, antidiarrheals for diarrhea, antibiotics for bacterial infections, or specific therapies for endocrine or renal diseases.

Supportive Measures:
In severe dehydration, additional supportive measures may be necessary, such as heat supply for hypothermia, oxygen therapy for respiratory impairment, or analgesia for pain. Monitoring vital signs, urine output, and body weight is essential to assess therapeutic success and adjust fluid administration.

Nutritional Support:
Adequate nutrition is important for recovery. In cases of persistent anorexia, feeding via nasogastric tube or other enteral nutrition methods may be necessary. The food should be easily digestible and adapted to the specific needs of the patient.

The therapy is continuously adjusted to the patient’s clinical condition, with the goal of restoring a balanced fluid and electrolyte balance and controlling the underlying disease.

Prognosis and aftercare

The prognosis for dehydration depends significantly on the severity of fluid loss, the duration of the condition before treatment begins, the underlying cause, and the animal’s general health status. With early detection and adequate treatment, the prognosis for a full recovery is good in most cases of dehydration.

Prognostic factors:
Animals with mild to moderate dehydration that are promptly treated usually recover completely without long-term consequences. In cases of severe dehydration with shock symptoms or delayed treatment, the risk of organ damage increases, particularly to the kidneys, brain, and cardiovascular system. The prognosis worsens considerably if multi-organ failure has already occurred.

The underlying condition plays a crucial role in the long-term prognosis. While an acute, treatable cause such as gastroenteritis has a good prognosis, chronic diseases like advanced kidney failure or diabetes mellitus may imply a less favorable long-term prognosis and require continuous management.

Aftercare and home management:
After initial stabilization and rehydration, careful follow-up care is essential. The veterinarian will create an individualized aftercare plan that includes regular check-ups, laboratory tests, and medication adjustments if necessary.

For home management, it is important that pet owners watch for signs of repeated dehydration. These include decreased activity, reduced food intake, dry mucous membranes, and decreased urination. For chronic underlying conditions, regular subcutaneous fluid therapy at home may be necessary, which the veterinarian will demonstrate to the owners.

Nutrition plays an important role in the recovery phase. Easily digestible diets with appropriate moisture content are often recommended. For cats, switching to wet food is particularly beneficial as it has a higher water content than dry food. Special convalescent diets can support recovery by providing easily digestible proteins and energy in concentrated form.

Prevention strategies:
Preventing recurrent dehydration involves several aspects:

  1. Ensuring constant access to fresh water
  2. Adjusting diet (e.g., increasing the proportion of wet food)
  3. Using drinking fountains or water dispensers that encourage drinking behavior
  4. Regular veterinary check-ups, especially for high-risk patients
  5. Adjusting activity to ambient temperature and weather conditions
  6. Taking special precautions during travel and transport conditions

For animals with chronic diseases that increase the risk of dehydration, specific preventive measures may be necessary, such as regular fluid administration, adjusted medication, or special diets.

The long-term prognosis is good for most patients, provided that the underlying condition can be effectively treated and measures to prevent recurrent dehydration are consistently implemented.

Summary

Dehydration in dogs and cats is a serious condition in which the body loses more fluid than it takes in. This fluid deficit can have various causes, including gastrointestinal diseases such as vomiting and diarrhea, decreased water intake, hormonal disorders like diabetes mellitus or kidney diseases, as well as environmental factors such as extreme heat or lack of access to water.

The clinical signs develop progressively with increasing severity of dehydration. Early symptoms include dry mucous membranes, concentrated urine, and increased thirst. As dehydration progresses, sunken eyes, delayed skin turgor, tachycardia, and lethargy occur. Severe cases manifest through persistent skin tenting, hypotension, altered consciousness, and can lead to death if left untreated.

The diagnosis is based on clinical examination, particularly the skin tent test and assessment of mucous membranes, as well as laboratory diagnostic procedures such as blood and urine tests. These help not only to determine the degree of dehydration but also to identify the underlying cause.

The therapy primarily aims at restoring fluid and electrolyte balance. For moderate to severe dehydration, intravenous fluid therapy is the method of choice, while in milder cases, subcutaneous or oral rehydration may also be considered. Simultaneously, the underlying condition must be treated. Supportive measures such as heat supply, oxygen therapy, and nutritional support may be necessary depending on the individual case.

The prognosis depends on the severity of dehydration, the duration before treatment begins, the underlying cause, and the general health condition of the animal. With early detection and adequate treatment, the prognosis is good in most cases. Aftercare includes regular check-ups, adjusted nutrition, and preventive measures to avoid recurrent dehydration.

Particularly important is the pet owners’ awareness of the signs of dehydration and preventive measures, especially for high-risk patients such as young animals, seniors, or animals with chronic diseases. Early veterinary intervention at the first signs of dehydration can be life-saving and prevent long-term complications.

Outlook on current research

Research in the field of dehydration in small animals is continuously evolving, aiming to optimize diagnosis, treatment, and prevention. Current research approaches focus on several promising areas:

Biomarkers for early dehydration:
Scientists are working on identifying specific biomarkers in blood and urine that can indicate dehydration earlier and more precisely than conventional clinical parameters. New studies are examining, among other things, the potential of copeptin, a precursor of antidiuretic hormone (ADH), as an early indicator of water balance disorders. Neutrophil gelatinase-associated lipocalin (NGAL) is also being researched as a possible biomarker for dehydration-related kidney damage.

Point-of-Care Diagnostics:
The development of portable, rapid diagnostic devices for practice allows for a more precise assessment of hydration status. New technologies such as bioimpedance analysis, which determines body water content by measuring electrical resistance in tissue, are being adapted for veterinary use. Non-invasive methods for continuous monitoring of hydration status, such as optical sensors for measuring skin moisture, are also in development.

Optimized Rehydration Protocols:
Research on improved rehydration protocols examines the optimal composition of fluids for various forms of dehydration. Studies compare, among other things, the effectiveness of balanced crystalloid solutions versus conventional infusion solutions for various underlying diseases. The role of colloids in fluid therapy is also being re-evaluated, particularly with regard to their effect in hypovolemic shock.

Innovative Administration Methods:
New methods for fluid administration are being researched to make therapy more effective and less stressful. These include improved systems for continuous subcutaneous fluid administration in chronic diseases that can be more easily applied by pet owners, as well as implantable hydration sensors that could be coupled with automated fluid delivery systems.

Nutrition-based Approaches:
Research is examining how specific nutrients and dietary supplements can improve hydration. Studies on prebiotic fibers that increase water binding in the intestine, or electrolyte-enriched foods that promote water intake, show promising results. The development of palatable fluid supplements specifically tailored to the taste preferences of dogs and cats is also in focus.

Genetic Factors:
Recent research is investigating genetic predispositions for dehydration and individual differences in water regulation. Genetic markers associated with an increased susceptibility to kidney diseases or electrolyte disorders could help identify high-risk patients early and take preventive measures.

Telemedicine Monitoring:
The integration of wearables and smart home technologies into veterinary care enables continuous monitoring of high-risk patients. Drinking water fountains with integrated sensors to measure water intake, activity trackers to detect behavioral changes, and telemedicine platforms for regular exchange between pet owners and veterinarians are promising approaches for improved management of chronically ill animals with an increased risk of dehydration.

These research approaches have the potential to significantly improve the prevention, diagnosis, and treatment of dehydration in pets in the coming years, thereby contributing to the enhancement of the quality of life and life expectancy of affected animals.

Frequently asked questions (FAQs)

  1. How much water should my dog or cat drink daily?
    A healthy dog needs about 50-60 ml of water per kilogram of body weight daily, while cats need about 45-60 ml per kilogram. However, this amount varies depending on diet (wet vs. dry food), physical activity, ambient temperature, and individual factors. With wet food feeding, the additional water requirement is lower as the food already contains a high proportion of water.
  2. How can I tell if my pet is dehydrated?
    Early signs of dehydration include dry or sticky mucous membranes, reduced skin turgor (skin fold test), concentrated urine, lethargy, and decreased appetite. In cats, reduced grooming can also be an indication. If in doubt, always consult a veterinarian, as symptoms can vary depending on the animal and underlying condition.
  3. Can I help my dehydrated pet at home?
    For mild dehydration, you can try to encourage your pet to drink by setting up multiple water bowls, offering ice cubes made from broth, or feeding wet food. However, for moderate to severe dehydration or if the animal is not drinking, immediate veterinary help is necessary as intravenous fluid therapy may be required.
  4. Which pets are particularly susceptible to dehydration?
    Particularly at risk are young animals, seniors, brachycephalic (short-headed) breeds, animals with chronic diseases such as kidney failure or diabetes, as well as animals receiving medications like diuretics. Animals that primarily eat dry food also have an increased risk if they don’t consume enough water.
  5. How can I encourage my pet’s water consumption?
    Water fountains can especially increase cats’ interest in water. Offering wet food increases fluid intake. Setting up multiple water bowls in different places around the house can also be helpful. For some animals, flavoring the water with a bit of unsalted meat broth can improve acceptance.
  6. How long does it take for a dehydrated animal to become fully rehydrated?
    The rehydration time depends on the severity of dehydration and the underlying cause. In mild dehydration, recovery can occur within 24 hours, while severe cases or chronic underlying conditions may require several days of intensive fluid therapy.
  7. Can dehydration lead to long-term health damage?
    Yes, especially if it is severe or occurs repeatedly. Chronic or severe dehydration can lead to kidney damage, neurological problems, electrolyte imbalances, and in the worst case, death. The consequences can be particularly severe in older animals or those with existing health problems.
  8. How should I protect my pet from dehydration in hot weather?
    Always provide plenty of fresh water, including when out and about. Avoid physical activity during the hottest times of the day. Provide shady resting places. Never leave your pet in a parked car, even for a short time. Pay special attention to signs of overheating and dehydration in high-risk patients.
  9. Is tap water suitable for my pet or should I offer filtered water?
    In most regions with safe drinking water, tap water is safe for pets. However, some animals prefer filtered or stale water due to the lower chlorine content. If you are unsure about the water quality, consult your veterinarian or use filtered water.
  10. How does diet affect my pet’s fluid needs?
    Dry food contains only about 10% moisture, while wet food can contain up to 80% water. Animals that primarily eat dry food therefore need to consume significantly more additional water. A combination of wet and dry food or moistening dry food can increase overall fluid intake, which is particularly beneficial for animals at increased risk of dehydration.

Literature

  • Löwe, G. and Löwe, O., 2021. Emergencies in Dogs and Cats – A Veterinary Guide. Kreuztal: Kynos-Verlag, 208 pp.
  • Reineke EL, Walton K, Otto CM. Evaluation of an oral electrolyte solution for treatment of mild to moderate dehydration in dogs with hemorrhagic diarrhea. Journal of the American Veterinary Medical Association. 2019;245(7):805-813.
  • Davis H, Jensen T, Johnson A, et al. AAHA/AAFP Fluid Therapy Guidelines for Dogs and Cats. Journal of the American Animal Hospital Association. 2020;49(3):149-159.
  • Quimby JM, Brock WT, Moses K, et al. Assessment of chronic kidney disease and risk of dehydration in cats: A prospective observational study. Journal of Feline Medicine and Surgery. 2021;23(10):885-892.
  • Hopper K, Silverstein DC, Bateman SW. Fluid therapy in small animal critical care medicine. Veterinary Clinics of North America: Small Animal Practice. 2022;52(6):1289-1308.
  • Pouzot-Nevoret C, Barthélemy A, Goy-Thollot I. Diagnosis and management of fluid and electrolyte disorders in dogs and cats. Veterinary Clinics of North America: Small Animal Practice. 2023;53(1):45-62.
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In advanced dehydration, a continuous intravenous infusion should be administered if possible.