Subcutaneous fluid is given to patients to prevent or treat dehydration. Though less common than fluids administered intravenously, this treatment is common in elderly patients, who may have collapsed or hidden veins. This method of administering fluids is also used in veterinary medicine.
In order to administer subcutaneous fluid, a needle is inserted into the area just beneath the skin. In humans, where the skin is attached to the fat layer underneath, the best places to administer fluids are the thighs, abdomen and scapula. In animals such as dogs and cats, the skin is easily lifted from the flesh underneath at the scruff of the neck, which makes administering fluid in this region relatively easy. The needle is attached to a plastic tube which runs from the fluid bag. In humans, fluids can be administered at a rate of 0.5 gallons (2 liters) per day. Animals of different sizes and different dehydration levels require specialized dosing.
Subcutaneous fluid consists primarily of about 95% water and usually has 5% dextrose and 0.8% saline added. Fluids with dextrose and saline are known as electrolyte solutions. Though the infusion of solutions without electrolytes has led to shock and cardiovascular problems, there are few side effects associated with the use of subcutaneous hydration if electrolytes are added.
In human and animal patients, subcutaneous fluid is often given to patients that cannot drink enough water to properly hydrate themselves. This may be because of illness, gastrointestinal problems, or because of problems with the kidneys. Patients who arrive at a hospital dehydrated may be given this treatment.
Fluids that are administered too quickly into the veins can pose health risks for patients. Excess subcutaneous fluid, on the other hand, is simply not absorbed until the subcutaneous layer can take more fluids in. Though either method of rehydration can pose a health risk if patients are given too much fluid, patients given a proper amount of subcutaneous fluid too quickly are not at any risk. A patient can be given hyaluronidase to increase the speed of absorption.
Humans are rarely given medication along with subcutaneous fluids. Though this method of drug administration is largely untested, some medical practitioners are looking at it as a way to administer antibiotics, making the need for injections or intravenous lines unnecessary. Veterinarians commonly administer antibiotics in this manner.