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What are Intravenous Fluids?

When to Use Intravenous Fluids

Where to Use Intravenous Fluids

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Home > Fluid Therapy > Intravenous Fluids



  • "Intravenous" means the fluids are given into a vein.

  • As with humans, this treatment is usually only used in a hospital setting.

  • Intravenous fluids are therefore normally reserved for acute situations. In the case of a CKD cat, this would often be when a cat is severely dehydrated ("crashing").

  • They may also be used for cats with pancreatitis, or kidney stones or kidney infections, or before and during surgery.

What are Intravenous Fluids?


Intravenous (IV) fluids are a form of fluid therapy whereby the fluid is administered via a drip feeding into a vein (intravenous). If you've ever been a patient in hospital, you were probably on intravenous fluids, which are sometimes referred to as "a drip."


The fluid used is not simply water because you cannot simply inject ordinary water into the body, you need to use a fluid which is compatible. One commonly used fluid type is lactated ringers solution (LRS), which is isotonic, i.e. it has the same sodium concentration as body tissues.


Cornell University College of Veterinary Medicine has a video showing a cat on IV fluids and what it entails (click on Part 5 Diuresis and Hospitalization).


Management of chronic renal failure: beyond the can (2001) Wallace M Presentation to the Atlantic Coast Veterinary Conference explains when and how to use IV fluids.


Fluid therapy for critically ill dogs and cats (2005) Schaer M Presentation to the 30th World Small Animal Veterinary Association World Congress discusses the use of IV fluids. This is a rather technical presentation for the layperson.


Long Beach Animal Hospital discusses IV fluids in an easy to understand way.


Intravenous fluids: balancing solutions (2017) Hoorn EJ Journal of Nephrology 30(4) pp485-492 discusses the types of fluid used for intravenous fluid therapy.


Where to Use Intravenous Fluid Therapy


This is a skilled form of treatment, and great care needs to be taken to ensure the rate of fluid flow is correct for the cat. Too fast a flow can be dangerous (it can overtax the heart), but too slow a flow may not rehydrate the cat quickly enough.


Because of this, IV fluids are usually only given at the vet's office, where the cat can be carefully monitored. If you are giving fluids at home, you are probably giving subcutaneous fluids, not IV fluids.


When to Use Intravenous Fluid Therapy


IV fluids are used to support cats who are sick for a variety of reasons. Introduction to fluid therapy (2008) DiBartola SP Idexx Laboratories FAQ states "The intravenous route is preferred when the patient is very ill, when  fluid loss is severe, or when fluid loss is acute."


Critically Ill Cats

As explained on the Fluid Therapy page, intravenous fluids are often used to treat acute problems e.g. to stabilise a critically ill animal who has lost a life-threatening amount of body fluids, perhaps following a road traffic accident, or a cat who has been poisoned.


They are also used to treat cats who are critically ill for other reasons, such as our George on the left who was extremely ill at this time with liver disease.


CKD Cats

IV fluids are commonly used for severely dehydrated cats. Since CKD cats are prone to dehydration because of their increased urination, which may be compounded by the cat not eating and/or drinking enough, it is not uncommon for CKD cats to become dehydrated enough to require IV fluids. This is sometimes referred to as crashing, and may well be the first sign that your cat has CKD.


In most cases, cats in this situation will have high bloodwork with creatinine over 6-7 mg/dl (US) or 550-650 µmol/l (international). The IV fluids are employed as a flushing through of the kidneys to correct an acute crisis situation of severe dehydration and any resulting electrolyte imbalances, and to remove toxins from the blood. Increasing urine production in this way is known as diuresis.


IV fluids are also used for cats who have suffered an acute insult to the kidneys (acute kidney injury), such as a kidney infection or kidney stones. In some cases, IV fluids may succeed in flushing out kidney stones.


Cats with Other Ilnesses or Concerns

IV fluids may also be used for cats who need additional support for some other reason. Cats with pancreatitis often require IV fluids when first diagnosed. Cats with severe diarrhoea or vomiting may become dehydrated and need IV treatment, as may cats who are not eating or drinking for some reason other than CKD.


Cats Receiving Anaesthesia

Cats who are undergoing anaesthesia are often also placed on IV fluids. Anaesthesia can reduce blood flow through the kidneys and cause falls in blood pressure, which may damage the kidneys, but giving IV fluids to the cat during the procedure reduces this risk.


CKD cats should definitely be placed on intravenous fluids for a few hours before, during and after any surgery. Most vets will place cats on IV fluids during and sometimes after surgery, but not every vet wishes to place a CKD cat on IV fluids before anaesthesia. However, this is very important for your cat's safety. In Chronic kidney disease (2007) Polzin DJ Delaware Valley Academy of Veterinary Medicine, Dr Polzin (a kidney specialist) states "It appears that the medical prophylaxis most likely to be effective is related to pre-intervention fluid support. Pre-loading patients with fluids before potential ischemic or nephrotoxic interventions has thus far been shown to be the most effective therapy. Other options that have been investigated include diuretics, vasodilators, and some forms of metabolic support. However, none have thus far proven to be superior to support with a saline-based fluid. Usually, fluids should be administered in sufficient volume to induce diuresis."


Goals of Intravenous Fluid Therapy for CKD Cats


In terms of CKD patients, the primary aim of IV fluids is usually to rehydrate a severely dehydrated cat. Dehydration is very unpleasant and can make cats look and feel very ill, but they usually look and act much better once dehydration is under control.


As a side effect, the cat's kidney bloodwork should improve. The goal is not to lower the bloodwork values as such, but this usually will happen, because the dehydration is making the bloodwork look artificially elevated.


Other goals may include flushing out kidney stones (which may or may not be successful), or supporting the kidneys during anaesthesia.


Speed and Length of Intravenous Fluid Therapy


How much intravenous fluid to give each day and the drip rate (how fast the fluid flows into your cat) is a complex calculation, based on various factors such as your cat's weight and the degree of dehydration. Your vet is trained to do this.


Most CKD cats need to stay on IV fluids for 2-4 days. For a severely dehydrated cat, the first 2-4 hours are used to rehydrate the cat i.e. the severe dehydration is quickly corrected. This is known as the replacement phase. Cats stay on IV for longer than this though, usually for several days: this is the maintenance phase which is designed to give the cat a chance to stabilise. The different phases are discussed on the Fluid Therapy page.


IV fluids should not be stopped suddenly, but should be reduced gradually in order to give the cat's kidneys time to adapt. If IV fluids are being given to a severely dehydrated CKD cat, most vets will start this weaning process once there are no longer any improvements in the cat's bloodwork. This tends to be measured over 1-2 days, so if a cat's creatinine level is unchanged on Day 3 from Day 2, that is when the vet would start gradually reducing fluids with a view to discharge probably on Day 4 if the cat remains stable. Managing fluid and electrolyte disorders in renal failure (2008) Langston C Veterinary Clinics Small Animal Practice 38 pp677–697 says "When serum creatinine concentration reaches a baseline value (ie, when it no longer decreases despite IV fluid therapy), fluids should be tapered in preparation for patient discharge. After a period of intensive diuresis, fluid administration should be tapered gradually over approximately 2 to 3 days."


One day on IV fluids is unlikely to be sufficient for most cats to restore hydration and some degree of balance; so I am concerned by the number of vets I hear about who offer just one day on IV, say the cat's numbers have not improved sufficiently after that short stint, and recommend euthanasia. In most cases this is inappropriate in my opinion (and is not what Dr Langston recommends in the previous paragraph). Yes, not every CKD cat can be saved; but euthanasia is an irrevocable decision so you need to be very sure, and for most people that means giving their cat every chance. For a severely ill cat, one or two days on IV are simply not going to be long enough, so I would recommend that you make sure that your cat is given a reasonable stint on IV of 3-4 days if you can afford it. Conservative medical management of chronic renal failure in cats (2012) DiBartola SP Metropolitan New Jersey Veterinary Medical Association says "Don't pass judgement on a lethargic dehydrated cat with markedly abnormal laboratory results. 2 to 3 days of conscientious intravenous fluid therapy can produce remarkable results." If your cat's bloodwork is still improving, your cat may stay on IV even longer, occasionally cats are on IV for as long as a week. IV catheters can usually remain in place for 72 hours before there is any risk of infection; after this, a catheter can be placed in the other paw if necessary.


If Bloodwork Does Not Improve With Intravenous Fluids


Don't be too despondent if your cat's bloodwork does not improve after a few days on IV fluids. In fact, sometimes the bloodwork actually worsens after 1-3 days on IV. This can happen with BUN in particular, because BUN can be found in other tissues as well as the bloodstream, and as the BUN is removed from the bloodstream via diuresis, it may flow into the blood from the other tissues, so it may still appear high.


Some vets may recommend euthanasia if this occurs, but don't feel obliged to agree to this, especially if you are in the USA where your cat is probably receiving IV fluids in the ER. Vets in the ER are usually emergency medicine specialists who are used to dealing with acute situations; they often have a lot less experience of cats with chronic diseases and may not realise that further improvement may occur. This may not even necessarily occur while the cat is in hospital but may gradually happen once you take your cat home and use sub-Q fluids.


Thomas is a good example of a cat who did not respond dramatically to IV fluids, but they did help stabilise him, and he continued to improve once he came home. Initially Thomas was on IV fluids for four solid days and nights, and only began to eat a little on day 3. He had urea of 89 µmol/L (BUN: 241 mg/dl) at diagnosis, and it did not actually improve after four days and nights of IV fluids either. But he was rehydrated and acting better in himself by the end of the four days, so we took him home. He had his good and bad days, which were influenced in particular by his severe anaemia, but with home sub-Qs and an ESA and other treatments over a number of weeks he improved and began to enjoy life again. Eventually his numbers reduced to urea 27 (BUN: 76) and creatinine 316 µmol/L (US: 3.57 mg/dl), where they stabilised for some months.


Monitoring Cats on Intravenous Fluids


Cats on IV fluids need close monitoring to ensure they do not become overhydrated, which is a strain on the heart. The cat should be checked once an hour, and heart and lungs should be checked every 3-4 hours. The cat should be assessed by a vet at least once every twelve hours and weighed regularly. The following should be routinely monitored:

  • the weight of the cat

  • blood pressure

  • electrolytes, such as potassium and sodium levels

  • chest sounds

  • fluid output (urination)

Unfortunately many American vet offices do not have anybody present at their premises overnight, so some of these tests cannot be performed for several hours, which is potentially very risky. 2013 AAHA/AAFP fluid therapy guidelines for dogs and cats (2013) Davis H, Jensen T, Johnson A, Knowles P, Meyer R, Rucinsky R & Shafford H Journal of the American Animal Hospital Association 49(3) pp149-159 state "Patients with a high risk of fluid overload include those with heart disease, renal disease, and patients receiving fluids via gravity flow."


I personally would not feel at all comfortable leaving a cat on IV fluids unattended. If your vet recommends IV fluids for your cat, but s/he would be left alone overnight, a possible compromise is for your cat to be on IV fluids at the vet's office during the day, but to come home (with catheter still in place) overnight. Ideally though, your cat should be on IV fluids continuously but under supervision.


The vet may add treatment for nausea to the IV fluids. Ask if this is being done because if it is not, your cat may need oral medication instead.


Helping Your Cat on Intravenous Fluids


If you agree to have your cat put on IV fluids, ask for him/her to be put in a quiet area as far away as possible from any canine in-patients. Leave a blanket or an old item of clothing with your smell on it in the cage to comfort your cat.


Your cat will do better if s/he keeps his/her strength up by eating, so make sure your cat is fed during hospitalisation. Some vets will tell you that your cat is receiving nutrients and calories from the IV fluids, but a litre of lactated ringers solution contains only around 10 calories, which is not enough. They may also tell you that your cat is being fed, but they are simply placing food in front of the cat and do not ensure that the cat  actually eats the food. Ask them to assist feed your cat is necessary, or consider the use of a feeding tube. See Feeding Tubes for more information.


Some people believe that they should not visit their hospitalised cat because the cat may find it distressing. I don't agree with this, I think it is better for both the cat and the caregiver if regular visits take place, preferably daily. This also enables you to feed your cat yourself during your visits. The Persuading Your Cat to Eat page has tips on getting food into your cat.


I know it can seem very lonely at home while your cat is in hospital, but remember, you are doing this in order to help your cat. Try to focus on the positives: your cat is receiving professional care to give him or her the best chance possible; you can have a break from chasing your cat with plates of food, pilling sessions etc, and can recharge your batteries a little. Focus on resting, reading this website and obtaining the supplies you need, so you can offer your cat the best possible care when s/he returns home.


What to Expect After IV Fluid Therapy


When your cat comes home from a session on IV fluids in hospital, don't expect him/her to bounce back immediately. Most cats are exhausted—if you've ever been in hospital, you'll know how hard it can be to sleep well there—so fatigue and lethargy are normal. Your cat will probably not drink much either, because s/he will be well hydrated from the IV fluids. Many cats hide, which indicates they are not feeling 100%. Give them time. Most cats need a few days at home convalescing before they begin to act better. Appetite may take some time to return, or your cat may need a little help in this department, perhaps treatment for nausea and, if that is not sufficient, possibly an appetite stimulant.


Most CKD cats who have been on IV fluids will need sub-Q fluids at home if they are to avoid crashing again. You probably won't need to start sub-Qs as soon as you return home because your cat will be nicely hydrated from the IV fluids but you will probably need to start them a couple of days after returning home. Bring a few basic supplies home from the vet, and then check Obtaining Supplies Cheaply to find sources for obtaining the supplies you need more cheaply.


If your vet believes IV fluid therapy is the best treatment for your cat, you should give it very serious consideration - it really can be lifesaving.


When Not to Use Intravenous Fluids

IV fluids are not always a benign treatment, plus they are can be stressful for your cat and expensive for you. Therefore they should only be used when necessary. I occasionally hear of vets putting CKD cats with low or medium level numbers (creatinine around 3-3.5 mg/dl (US) or 260-300 µmol/l (international) on IV fluids. In most cases this is unlikely to be necessary, because most cats would not be dehydrated at this level. However, it may be appropriate if a cat is very dehydrated despite the low bloodwork, perhaps from vomiting or diarrhoea, or if there are other issues present, such as a kidney infection, kidney stones or pancreatitis.


IV fluids are not a suitable treatment for ongoing hydration purposes: they are too taxing on the kidneys and, since they increase GFR (see What is CKD?), they could accelerate the loss of kidney function if done for too long; plus of course they entail a stay in the vet's office, which many cats find very stressful and which is also very expensive.



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This page last updated: 30 June 2020


Links on this page last checked: 30 March 2020







I have tried very hard to ensure that the information provided in this website is accurate, but I am NOT a vet, just an ordinary person who has lived through CKD with three cats. This website is for educational purposes only, and is not intended to be used to diagnose or treat any cat. Before trying any of the treatments described herein, you MUST consult a qualified veterinarian and obtain professional advice on the correct regimen for your cat and his or her particular requirements; and you should only use any treatments described here with the full knowledge and approval of your vet. No responsibility can be accepted.


If your cat appears to be in pain or distress, do not waste time on the internet, contact your vet immediately.



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