Subcutaneous Fluids

If your vet has prescribed subcutaneous fluids for your cat, you have almost certainly been given a quick demonstration and then left to figure the rest out yourself. This post is designed to fill in the gaps: which fluid to use and why, how to choose a needle, how to warm the fluids, the step-by-step technique for both giving set and syringe methods, how to know whether it is going well, and what to watch for that would mean calling your vet.

The idea of sticking a needle into your cat is frightening at first. Almost everyone feels that way. In a survey of 399 owners who gave subcutaneous fluids to their CKD cats at home, 85 percent described the experience as easy, somewhat easy, or acceptable for themselves, and 89 percent said the same for their cat. Most cats tolerate the procedure much better than their owners expect, and many cats that fight every other medication will sit calmly for fluids once they realize the fluids make them feel better. Give it a fair trial before concluding it is not working.

For background on why subcutaneous fluids are used, when to start them, and how much to give, see our companion page: Hydration

Your vet will provide your initial supplies. Once you are comfortable with the procedure, most owners source their own supplies to reduce cost.

For the giving set method (most common in the USA and Canada):

• Fluid bags (usually 1-liter bags of Lactated Ringer’s Solution or whichever type your vet has prescribed)
• IV administration sets, also called giving sets or venosets (tubing that connects the bag to the needle)
• Needles (see the needle section below)
• Somewhere to hang the bag so gravity can do the work, such as an IV pole, a coat hook, or a door handle at the right height

For the syringe method (common in the UK and used by some owners in the USA):

• Fluid bags
• Syringes (20 ml or 35 ml are practical sizes)
• Drawing-up needles (to pull fluid from the bag into the syringe)
• Winged infusion sets or butterfly needles (to inject the fluid into your cat)

For either method:

• A sharps disposal container
• A bowl or basin for warming the fluids
• Treats or a small amount of food to distract or reward your cat

A few optional items many owners find helpful: hanging kitchen scales for measuring how much fluid has been given (100 ml of fluid weighs 100 g), a thermometer to check fluid temperature, and a cat restraint bag or towel for cats who are more fidgety.

Your vet will prescribe the fluid type your cat needs, and you should only use what is prescribed. That said, understanding why one fluid is chosen over another helps you ask good questions and catch errors.

Lactated Ringer’s Solution (LRS), also called Hartmann’s Solution

LRS is by far the most commonly prescribed fluid for CKD cats giving home subcutaneous fluids, and it is the right choice for most. It is isotonic, meaning it has a sodium concentration similar to body fluids, so it does not sting on injection. It contains potassium, which is beneficial for CKD cats who tend toward low potassium levels. It also contains lactate, which is converted to bicarbonate by the liver and helps buffer the mild metabolic acidosis that accompanies CKD. The 2024 AAHA fluid therapy guidelines list LRS as a recommended fluid for subcutaneous use alongside Plasma-Lyte and Normosol-R.

Normosol-R / Plasma-Lyte A / Isolyte-S

These are sometimes prescribed as alternatives to LRS, typically when a cat has high calcium levels, liver problems, or lymphoma alongside CKD, since they do not contain lactate and use a different buffer system. However, they contain magnesium, which may not be appropriate for cats with elevated magnesium levels. They are also known to sting on subcutaneous injection in some cats and to cause twitching at the injection site, and some cats vomit after receiving them. If your cat is resisting fluids or vomiting afterward and you are using one of these fluid types, ask your vet about switching to LRS.

0.9% Saline (Sodium Chloride)

Saline is generally not a good choice for CKD cats for subcutaneous use. It is more acidic than LRS, lacks a buffer, does not contain potassium, and can sting on injection. The 2024 AAHA guidelines specifically note that 0.9% sodium chloride has a low pH and may be painful, and advise against its subcutaneous use. There are narrow situations where saline may be appropriate, such as when a cat has hyperkalemia (dangerously high potassium), but this would be managed in hospital with IV fluids rather than at home.

Fluids with dextrose (added sugar)

Do not use these for subcutaneous fluids at home. Dextrose-containing fluids promote bacterial growth and can cause abscess at the injection site. They are not appropriate for home subcutaneous use.

A note on the DEHP issue

Some fluid bags are made with a plasticizer called diethylhexyl phthalate (DEHP). Some owners prefer to avoid these, and DEHP-free bags are available at higher cost. Regulatory bodies including the FDA have concluded that DEHP exposure from crystalloid IV fluids represents little or no meaningful risk, and this is a personal choice rather than a safety requirement. If DEHP-free bags are available and affordable for you, there is no harm in using them, but if you cannot find them or they are cost-prohibitive, this should not stop you from giving fluids.

The needle you use makes a bigger difference to your cat’s comfort than almost anything else in this process. The right needle slides in smoothly; the wrong one drags. Owners who switch from standard needles to better ones frequently describe it as transformative.

Gauge (thickness). Needle gauge is counterintuitive: the higher the number, the thinner the needle. A 19-gauge needle is thicker than a 21-gauge needle. For subcutaneous fluids in cats, needles between 18 and 21 gauge are most commonly used. The tradeoff is speed versus comfort: thicker needles (18 or 19 gauge) allow the fluids to flow faster, which means less time for your cat to sit still, but they are marginally less comfortable on insertion. Thinner needles (20 or 21 gauge) are more comfortable but flow more slowly.

Most owners find 19 or 20 gauge to be the best practical balance. If your cat tolerates fluids well and time is not a concern, 20 or 21 gauge is fine. If your cat gets impatient and the quicker you can finish the better, 18 or 19 gauge reduces the session time considerably.

Terumo thin-wall needles. Terumo thin-wall needles (previously marketed as ultra-thin wall or UTW) have a larger inner bore relative to their outer diameter compared to standard needles, meaning they flow faster than a standard needle of the same gauge. They are also exceptionally sharp, which reduces the force needed on insertion and the discomfort for the cat. Many experienced owners will not use anything else. In the USA, look for Terumo TW needles in 18, 19, or 20 gauge. In the UK and Europe, these are sold under the Neolus or Agani names. Nipro Flomax needles are an alternative that some owners rate positively, though most find them slightly less sharp than Terumo.

Never reuse needles. A needle used once is immediately blunter than a new one, and the distortion at the tip is significant enough to make the next insertion noticeably more painful. Needles are inexpensive in bulk; around US$10 for 100 online. Buy enough to use a fresh needle every time.

Needle length. Most needles come in 5/8 inch or 1 inch lengths. The 1-inch length gives a little more room to maneuver once inserted. The shorter length carries a slightly lower risk of going through the tent of skin and out the other side. Both work well and it is a matter of personal preference.

This is the most common method in North America. The fluid drips from a suspended bag through a length of tubing and into the needle under the skin, driven by gravity. It takes a little longer than the syringe method but is easier to manage alone because both hands are free once the needle is in place.

Setting up

1. Warm the fluid bag (see the warming section below).
2. Close the roller clamp on the administration set before you begin.
3. Remove the protective cap from the spike end of the administration set and the port cap from the fluid bag.
4. Push the spike firmly into the bag port with a twisting motion. This requires more force than most people expect.
5. Hold the bag upright and squeeze the drip chamber several times until it is about half full of fluid.
6. Open the roller clamp briefly to run fluid through the tubing until no air bubbles remain, then close the clamp again. This is called priming the line.
7. Attach a fresh needle to the end of the tubing. If your administration set has a luer lock, screw it snug.
8. Hang the bag at a reasonable height. The higher it hangs, the faster the flow. Many owners use a coat hook, a towel rail, or a simple IV pole. Something between 1 and 2 meters above where your cat will sit works well for most needle gauges.

Giving the fluids

1. Position your cat comfortably. Many owners do this on a lap, a table, or a countertop. If your cat is calmer on a particular surface or in a particular room, use that.
2. With one hand, form a tent of loose skin by gently pinching and lifting the skin over the saddle area (see the saddle area section below).
3. Hold the needle bevel-up (the angled cut should face upward) and parallel to your cat’s back.
4. Insert the needle smoothly through the base of the skin tent, directing it slightly forward toward the cat’s head rather than downward. One clean, steady motion works better than a hesitant one.
5. Release the skin tent and check that the needle tip is under the skin and not sticking out the other side. If it has gone through, you will see or feel fluid leaking onto the fur almost immediately.
6. Open the roller clamp fully to start the flow. You will see the fluid level in the bag begin to drop and a soft lump will start to form under the skin.
7. Hold the needle gently in place or use a small piece of tape to secure the line. Keep your cat calm and still.
8. When the right amount has been given, close the roller clamp, withdraw the needle, and gently press or massage the injection site for about a minute to minimize leaking.
9. Replace the needle on the end of the line with a capped fresh needle for next time, to keep the line sterile.

This method is more common in the UK and is preferred by some owners who want more precise control over exactly how much fluid is delivered. It requires slightly more preparation but each injection is faster once underway.

Setting up

1. Warm the fluid bag.
2. Attach a drawing-up needle to each syringe.
3. Insert the drawing-up needle into the bag port and pull back on the plunger to draw fluid into the syringe. Tilt the bag to minimize air in the syringe.
4. Remove the drawing-up needle, lay the filled syringe on a clean surface, and repeat until you have enough syringes for the full dose (for example, five 20 ml syringes for a 100 ml dose).
5. The same drawing-up needle can be used for all syringes as long as it only contacts the bag port and nothing else.

Giving the fluids

1. Attach a winged infusion set (butterfly needle) to the first syringe.
2. Squeeze a tiny amount of fluid through the butterfly needle to clear the air.
3. Form a skin tent, insert the butterfly needle bevel-up through the base of the tent, and begin squeezing the syringe steadily.
4. There should be slight resistance as you push the fluid in. If it feels too easy, the needle may have come through the other side of the tent.
5. When the first syringe is empty, keep the butterfly needle in place and swap to the next syringe. This takes some practice to do smoothly with one hand.
6. Repeat until the full volume has been given, then withdraw the needle and press the site gently.

Cold fluid is uncomfortable, even if the needle itself causes no distress. A cat’s normal body temperature is around 38.5 degrees Celsius (101.5 degrees Fahrenheit), and room temperature fluid can feel quite cold going under the skin. Warming the fluid to approximately body temperature makes a real difference for many cats.

Place the sealed fluid bag in a basin of hot water for 10 to 15 minutes before the session. The water should be warm to hot but not boiling. Check the temperature by placing the bag against your wrist or inner arm before using it: it should feel comfortably warm, not hot.

Alternatively, some owners use a heating pad on a low setting to warm the bag, or wrap it in a towel that has been warmed briefly in the dryer.

Do not warm fluid in a microwave. Microwaves heat unevenly and it is easy to create hot spots in the bag that could burn your cat.

If you are using the giving set method, run a little fluid through the line before inserting the needle to ensure any cool fluid sitting in the tubing does not reach your cat first.

A small number of cats actually prefer fluids at room temperature. If your cat seems unfazed and tolerates fluids well without warming, that is fine too.

Many people are told to give fluids only at the scruff of the neck, but this is not necessary and giving the fluids at the same spot every session will eventually cause scar tissue to build up, making injections harder and less comfortable. You have a much larger area to work with.

Think of the area that would be covered by a riding saddle on a horse: from roughly the shoulders back to the hips, excluding the spine itself. This entire region of loose skin over the back and sides is fair game. Moving around within this area, even slightly, each session distributes the injections and reduces the chance of scar tissue developing.

Some cats have a clear preference for one side over the other. Pay attention to whether your cat is consistently more relaxed when you inject on the left versus the right. Rotate injection sites systematically, for example giving fluids a little further along each session as if moving around a clock face, or alternating left and right sides.

Do not inject over the spine itself. The skin is thinner there and there is less subcutaneous space.

Routine helps more than almost anything else. If you give fluids at roughly the same time each day, in the same location, your cat will come to know what is happening and will often remain calmer because the rest of the day is entirely predictable and safe. Cats that are startled or caught unawares during the rest of the day because you approach them unexpectedly are harder to work with.

Tell your cat what is happening. Many owners use a specific phrase or word that signals to the cat that fluids are coming. Over time, the cat learns that this word means the session, and everything outside that word is safe. It sounds anthropomorphic but in practice it works well.

Distraction and reward. Offering a small amount of food during or immediately after the session gives the cat something to focus on other than the needle, and creates a positive association over time. A little wet food, a lickable treat, or a small amount of tuna water works well. Avoid feeding a large meal immediately before a session as this makes some cats less interested in treats during it.

Feliway. Some owners find that a Feliway diffuser in the room where fluids are given, or a spray applied to the area a few minutes beforehand, helps cats that are anxious about the session.

Restraint. Some cats do better with gentle restraint; others become more resistant when held. Cats that generally dislike being held are usually better managed with minimum restraint and maximum distraction. A cat restraint bag or a light towel wrap can help with cats that are truly difficult, but use minimum necessary restraint and check whether your cat is more cooperative without it before assuming restraint is needed.

If your cat is very resistant. Do not give up after one or two bad sessions. It often takes several weeks for both cat and owner to settle into a rhythm. A session that goes badly can be stopped and tried again later the same day or the next day. If your cat is consistently very distressed, talk to your vet about whether there are adjustments to technique, needle type, or fluid temperature that might help, or whether anti-anxiety support is appropriate.

During. Your cat may flinch slightly when the needle goes in. This is normal and usually passes in a moment. Some cats show no reaction at all; others flinch every time but then settle immediately. If your cat yelps or pulls away sharply, try a fresh needle: occasionally a needle is slightly flawed and sharper ones make a real difference.

A soft lump or pouch of fluid will form under the skin as the fluids go in. This is normal and expected. The fluid will move around over the next few hours as it disperses through the tissue, sometimes migrating toward the front legs or chest. This is also normal and not a concern.

After. Most cats feel better within a few hours of receiving fluids and may show increased alertness, more interest in food, and more willingness to move around. Some cats are a little quieter for an hour or so after fluids, which is generally not a concern. If a cat becomes persistently lethargic after every session or loses appetite afterward, let your vet know, as this can occasionally indicate that the cat has a concurrent heart problem or is not tolerating the fluid volume well.

A small amount of fluid leaking from the injection site when you withdraw the needle is normal. Pressing the site for a minute or so reduces this.

A small amount of blood occasionally appears at the needle site when you withdraw. This means a tiny vessel was nicked, which is harmless and needs no treatment.

Giving the right amount matters. Too little and the hydration benefit is reduced; too much and you risk overhydration.

Bag markings. Most 1-liter bags are marked in increments of 100 ml. In the USA, these are usually numbered 1 through 9 or 10, with the number indicating how many 100 ml units remain. The marks are not always perfectly accurate, particularly toward the end of the bag.

Hanging scales. Many owners find this the most practical method. Weigh the bag before and after the session using a kitchen scale or hanging scale. Because 100 ml of fluid weighs approximately 100 g, the difference in grams equals the amount given in milliliters.

Syringe method. If you are drawing fluid into measured syringes, you know exactly how much you are giving because you controlled the volume when filling.

Counting drops. Administration sets are rated in drops per ml, usually 10 or 15 drops per ml. If you count the drops for a measured time period you can calculate the total volume, though this is tedious and most owners prefer the scale method.

Fluid is not flowing or is flowing very slowly. Check that the roller clamp is fully open. Check that the bag is hung high enough (lowering the bag slows the flow significantly). Check whether the needle may have become blocked by moving against tissue: a slight adjustment of angle or a small rotation can restore flow. If none of these work, the needle may need to be replaced.

Fluid is leaking onto the fur. The needle has most likely gone through the far side of the tent of skin. Withdraw the needle and try again with a fresh one in a slightly different spot. This is common when learning and becomes less frequent with practice.

The cat seems uncomfortable during the session. Check the fluid temperature: cold fluid is the most common cause of discomfort during an otherwise well-executed session. Also check whether you are using Normosol-R or Plasma-Lyte, which are known to sting in some cats. If you have eliminated temperature and fluid type as causes, try a different needle gauge or brand.

The pouch of fluid has not been absorbed by the next session. Do not give more fluid until the previous amount has been absorbed. If the pouch is consistently taking longer than 8 to 10 hours to absorb, or if it is still present the next day, contact your vet. Slow absorption can indicate overhydration, heart problems, or that the amount being given is more than the cat needs.

Your cat vomits after fluids. This sometimes happens with Normosol-R, Plasma-Lyte, and similar fluid types. It can also happen if the fluid was too cold. If vomiting after fluids is consistent, mention it to your vet so the fluid type or temperature can be reviewed.

The skin feels tough or hard at the injection site. This can indicate dehydration (the skin is less elastic when dry) or, over time, scar tissue forming from repeated injections in the same spot. Rotating your injection site around the saddle area reduces the risk of scar tissue developing.

You accidentally stab yourself. This happens to almost everyone eventually. Wash the area with soap and water. If the area becomes red or painful, or if you have an immunocompromising condition, seek medical advice. Keep your tetanus vaccination up to date.

Giving too much fluid, or giving fluid when the cat does not need it, can cause fluid to accumulate where it should not. This is not a common problem when fluids are given in the amounts recommended in the companion post, but it is worth knowing what to watch for.

Contact your vet promptly if you see any of the following:

• Rapid unexplained weight gain over one to two days
• Coughing, increased respiratory rate, or labored breathing
• Clear watery discharge from the nose
• Swelling around the legs, face, or jaw
• The fluid pouch from the previous session has not been absorbed by the time the next session is due
• Your cat seems generally worse rather than better after starting or increasing fluids

Coughing and breathing changes are the most urgent signs and warrant same-day veterinary attention. Overhydration can cause fluid to accumulate in the chest cavity (pleural effusion) or the lungs (pulmonary edema), which is a serious and rapidly worsening condition. When in doubt, call your vet rather than waiting.

Weigh your cat regularly on a consistent scale to track trends. A stable weight over weeks is reassuring; a gradual downward trend suggests the cat needs slightly more fluid or is not absorbing it well; a sudden upward spike suggests fluid may be accumulating.

Fluid bags do not need to be refrigerated before opening. Store them at room temperature away from direct sunlight and check the expiration date before use. Never use a bag that has passed its expiration date.

Once a bag has been opened (the spike has been inserted), it should ideally be used within 10 days. If you are giving fluids daily and the bag is lasting around 10 days, this is straightforward. If you are giving fluids less frequently and the bag will last longer, err on the side of caution and discard and open a new bag at 10 days. Some owners extend this to 14 days without apparent problems, but given that CKD cats have compromised immune systems, 10 days is a reasonable limit.

Before each session, check that the fluid inside the bag looks completely clear. If it appears cloudy or has visible particles, do not use it.

Needles and administration sets should be kept in their sealed sterile packaging until use. Keep the end of the administration set capped and sterile between sessions. Most owners change the administration set every two or three bags.

Used needles are clinical waste and cannot simply be placed in the household trash in most jurisdictions. Options include:

• Purchasing a sharps disposal container (a rigid plastic container designed for this purpose) from your vet or pharmacy. When full, return it to the vet or pharmacy for disposal.
• A firm, puncture-resistant plastic container such as a laundry detergent bottle with a screw-on lid, sealed and labeled “sharps,” may be acceptable in some areas for household waste disposal. Check local regulations first.
• SafeNeedleDisposal.org allows you to search for drop-off locations in the USA by zip code.

Never place loose uncapped needles in the trash or recycling.

• 2024 AAHA fluid therapy guidelines for dogs and cats (2024). Pardo M et al. Journal of the American Animal Hospital Association 60(4), pp131-163.
• ISFM consensus guidelines on the diagnosis and management of feline chronic kidney disease (2016). Sparkes AH et al. Journal of Feline Medicine and Surgery 18, pp219-239.
• Survey of owner subcutaneous fluid practices in cats with chronic kidney disease (2018). Cooley CM, Quimby JM, Caney SMA and Sieberg LG. Journal of Feline Medicine and Surgery 20(10), pp884-890.
• Managing fluid and electrolyte disorders in renal failure (2008). Langston C. Veterinary Clinics Small Animal Practice 38, pp677-697.
• 2013 AAHA/AAFP fluid therapy guidelines for dogs and cats (2013). Davis H et al. Journal of the American Animal Hospital Association 49(3), pp149-159.
• Introduction to fluid therapy (2008). DiBartola SP. IDEXX Laboratories FAQ.
• International Cat Care. How to give subcutaneous fluids to your cat (updated November 2025). icatcare.org.
• Polzin DJ (2007). Chronic kidney disease. Delaware Valley Academy of Veterinary Medicine.