IV Fluids in Cats, Potential Problems, and Their Causes
IV fluids in cats, potential problems, and their causes
IV fluids directly into the blood vessel system are an indispensable tool in small animal medicine for treating dehydration, electrolyte imbalances, and administering medication. Special care is required for cats, as they have an increased risk of overhydration (hyperhydration), which can cause serious complications.
Physiological basis of fluid balance
Fluid balance is maintained through a complex interplay of hydrostatic (simply: pressure in the blood vessel on the vessel wall) and colloid osmotic pressure (simply: pressure in the blood vessel due to proteins contained) as well as hormonal regulation. The kidneys play a central role in the excretion of excess water and electrolytes, while the cardiovascular system is responsible for the distribution of fluids.
Pathophysiology of overhydration
• Volume overload and increased hydrostatic pressure
An excessive supply of fluid increases the volume in the blood vessel system (intravascular volume). This leads to an increase in hydrostatic pressure in the small blood vessels in the tissue, causing fluid to be filtered out of the vessels into the tissue. The result is edema, potentially also a life-threatening pulmonary edema.
Symptoms: Respiratory distress, Panting, moist crackling sounds.
• Impaired cardiac function
Cats have a relatively small functional reserve of the cardiovascular system. Acute volume overload can lead to overexertion (decompensation) of the heart. The resulting Heart failure (cardiac insufficiency) worsens the fluid accumulation in the tissue or in body cavities such as the abdomen.
The Congestive heart failure in turn leads to a further increase in pressure in the large venous blood vessels, which in turn increases the risk of pulmonary edema.
Symptoms: Increased heart rate, general weakness (lethargy), exacerbation of impaired lung function.
• Reduced colloid osmotic pressure
In poorly eating cats, a protein deficiency in the blood (hypoproteinemia) can easily occur, which reduces the colloid osmotic pressure in the blood. This also promotes the fluid shift from the blood vessel system into the tissue.
Symptoms: Diarrhea and Vomiting due to mucosal edema in the intestine
• Renal insufficiency
With impaired kidney function, the ability to excrete excess fluid is reduced, which worsens the volume overload.
• Electrolyte imbalances
Excessive fluid intake can lead to shifts in electrolyte levels, including a deficiency of sodium (hyponatremia). This results in a shift of water into the cells, leading to swelling of the cells. Cell swelling in the brain is associated with neurological Symptoms:
Symptoms: General weakness (lethargy), Drowsiness, Disorientation, Gait instability, Convulsions
• Influence of hormones
A special hormone (ADH) regulates water reabsorption in the kidneys. Stress can affect this hormone and inhibit water excretion via the kidneys.
Therapeutic measures
Therapeutic measures can only be taken by a veterinarian after appropriate diagnostics. These include:
• Drug-induced promotion of urinary excretion (furosemide)
• Oxygen administration in case of impaired lung function
• Drug-induced dilation of the venous blood vessels in the body periphery to reduce blood flow to the heart (venodilators, nitroglycerin).
• Treatment of the underlying disease
Prevention of overhydration
• Individual fluid planning
Consideration of body weight, state of water balance, and organ functions when determining the infusion plan.
• Continuous monitoring
Regular monitoring of simple parameters such as heart rate, heart rhythm, respiratory rate, body temperature, and some neurological functions as well as urine formation and body weight makes it possible to monitor vital functions and detect complications early.
• Use of infusion pumps
Infusion pumps allow precise control of the infusion rate to avoid incorrect dosages. The pet owner must be clear that correct infusion therapy takes some time.
Conclusion
Overhydration from intravenous infusions in cats is a complex problem. The fluid dynamics in the body, regulatory mechanisms, and possibly limited organ functions due to pre-existing conditions such as Congestive heart failure or kidney disease must be taken into account. Individual therapy planning, careful veterinary monitoring, and early intervention can minimize potential complications and increase patient safety.
