Fluid therapy involves the intravenous or subcutaneous administration of fluid to an animal. This is typically done to replace fluid that has been lost either due to injury or disease. Vets use fluid therapy often, as it is a key part of treating some of the most common medical problems that owners will bring their pets to a clinic for.

Fluids are commonly administered to cat intravenously (through a vein), or subcutaneously (under the skin).

To begin intravenous (IV) fluid therapy, the vet will shave the area around the vein being targeted for injection. This will both allow the vet to easily locate the vein and make it more straightforward to attach the IV drip to the cat. The next step is to clean the skin and insert a catheter using a hypodermic needle and tape it in place before attaching the drip. The drip is then connected to a bag of fluid (normally a saline solution), which is elevated above the cat so that it can drain via gravity at a steady pace into the cat's body. Fluid pumps are often needed so we can control the rate of fluid adminstration. When the bag is sufficiently depleted, the fluids are replaced or, if the cat is well again, the catheter is removed.

A subcutaneous fluid administration procedure is similar to IV administration, but rather than inserting a catheter into a vein, a needle is used to deliver fluid under the cat’s skin near the spine. The procedure is performed in-office by vets, but is also commonly recommended for at-home administration for cats with chronic health issues, such as kidney disease. It is far less effective than IV fluids and cannot deliver the same amount of fluids. It is not appropriate for those who have acute kidney failure or severe dehydration.

After having undergone intravenous fluid therapy, the cat should show improvement within a couple of hours. That said, if there is a serious underlying condition it will take time for the cat to fully regain its health, as fluid therapy in this context should be thought of as a management strategy and not a form of treatment. Intravenous fluid replacement therapy is much faster and more efficient than oral replenishment (i.e. simply drinking the water), as it enters directly into the bloodstream with no waiting period.

Following the procedure, there will be a period during which the cat is much more alert and energetic than before the fluid therapy. It is important for owners to remember that this is still a recovery stage and they should limit the activity of the cat as much as possible, lest their symptoms return. In the case of injury especially, extra care should be taken to make sure the cat does not re-open their wounds either by biting (which is fixable with an e-collar) or by vigorous activity (which can be mitigated by keeping them indoors). The vet will also most likely want to schedule further visits in order to check the progress of recovery and refill any prescriptions for medication or painkillers. The vet might also wish for the cat to undergo fluid replacement at home, in which case they will provide the owner with instructions and equipment to carry out the procedure themselves.

Owners will be pleased to know that the price for fluid therapy can be quite low, with many clinics charging around $100 inclusive of materials and diagnosis. However, fluid therapy is often administered as just one component of a larger treatment plan. Kits for at-home fluid therapy cost roughly $30.

Although most fluid therapy procedures go off without a hitch, cat owners should be aware that there are some potential downsides. Pain and general discomfort is the first problem.Much like humans who have injections or give blood there will be residual pain and numbness after the procedure. There is also a slight risk of limb swelling and pain, as if the needle misses or over penetrates the vein, it will deliver the fluids into the surrounding tissues. Although not usually a life-threatening problem, this can be very uncomfortable for the patient. Infection is another risk, as needles that come into contact with dirt and grime can spread bacteria and viruses extremely easily. Fortunately, a competent vet will use a fresh, sterile needle and will takes steps to lessen the risk of an outside infection by cleaning the injection site.

Despite many causes of kidney failure being hereditary and therefore almost impossible to avoid, owners can always strive to lessen the risk of their cat becoming dehydrated. Making sure to always have accessible fresh water (especially in summer) and not constantly relying on dry food will keep a cat's fluid intake at a healthy level. If the classic symptoms of dehydration do start to appear (e.g. dry gums, lethargy,  and infrequent urination), then taking the cat straight to the vet will help prevent more serious conditions from gaining a foothold.