Untangling Fluid Therapy

When you consider that 60% of the body is made up of fluid, it is no surprise that fluid therapy plays such an important part in all medicine, with the veterinary world being of no exception. The fluid within the body is used for many different functions and is utilised everywhere. Fluid is used to bathe and provide nutrients to every single cell in the body. It is used in synovial joints to aid our skeletal system to move smoothly and without damage, it is found in the cerebrospinal fluid that cushions, protects and supplies nutrients to the spinal column and the brain. It is found in the linings of the peritoneal, pericardium and pleural spaces and can be found in the bile duct and stomach. Of course, a lot of the fluid is used to make up plasma, which is the liquid portion of blood, and it is via blood, that the majority of nutrients, oxygen and waste products are transported around the body. The balance of fluid within the body is closely monitored and stabilised so that water distribution is achieved where it is needed.

The healthy patient

The normal healthy patient will intake fluid to match the fluid output of the body, thereby keeping a healthy balance. Intake is by food and drink and also by the metabolism of fats and carbohydrates. The output occurs naturally via the renal system, the gastrointestinal tract, the respiratory tract and also via the skin. These natural losses are called insensible losses.

The unhealthy patient

When a patient is experiencing illness or is compromised in some way, not only do you have to address the fluid deficits that may have occurred, but you also have to calculate for ongoing loss; both normal and abnormal, and maintain the fluid balance, especially if the patient is not able to do this himself by eating and drinking. You may also wish to give the patient fluid to support the body whilst it is healing and to deliver certain drug therapies or medications that should be administered intravenously.

Therefore, when addressing a fluid imbalance, it is pertinent to follow the guidelines of; Resuscitation, optimising and de-escalation.

Resuscitation: emergency replacement of a deficit of fluids and / or treating a disease or condition.

Optimising: Maintaining the correct fluid balance to address ongoing fluid losses and to maintain the patient whilst it remains compromised.

De-escalation: reducing the amount of fluids the patient is receiving once the body has healed sufficiently to be able to do this for itself.

Assessing the need for fluids.

Assessing the need for fluids in a patient will be done by a combination of the following:

  • Clinical observations / examination
  • Clinical history
  • Laboratory tests such as testing the SG of urine or the PCV /HCT of blood
  • Medication or drug requirements during the treatment or recovery period

As a general rule, for every 1% PCV increase in a blood sample, indicates a fluid loss of 10ml per kg of fluid, (however this can only be used if the patient has NOT experienced blood loss as the patient will have lost both blood and fluid so this method will not be accurate).

Fluids may also be given to prevent a fluid imbalance from occurring in the future. For example, preventing surgical or anaesthesia shock or to counteract dehydration due to having food and drink withheld, if the patient is nil by mouth.

Which fluid?

The choice of fluid used for fluid therapy will be entirely dependent upon the condition you are treating, the decision of which lies solely with the veterinarian or lead clinician in charge of the case, and your fluid choice should be prescribed as you would with any other drug you are administering.

There are 3 main groups of fluid to choose from:

Crystalloids, Colloids & Whole Blood

Crystalloids: These include Hartmann’s, Lactated Ringers and Saline.

Crystalloids are watery types of fluid that contain varying levels of electrolytes and sodium. Crystalloids are used to replenish the interstitial volume (fluid surrounding all cells) and also the intracellular volume (the fluid within all cells). Crystalloids are absorbed rapidly and distributed quickly by the body. Crystalloids are usually the first fluid of choice when addressing fluid loss and supportive therapy, with Hartmann’s and Lactated Ringers being considered to be the closest physiological match to the fluid found in the body.

Colloids: These fluids are gelatinous fluids consisting of larger molecules, that are unable to pass through cell membranes, remaining in the intravascular spaces. In this way, these fluids become plasma expanders, expanding the volume of blood that is present. Colloids can be manmade artificial plasma; fresh frozen plasma is also typically available from companies that supply whole blood. Plasma or plasma products are given to trauma patients, burn patients, those with liver disease or a coagulation deficiency, such as rodenticide toxicity.

Whole Blood: may be given when the patient has experienced a large loss of blood or if the body is incapable of providing viable Red Blood Cells also known as RBC’s. Whole blood can be obtained from a donor that is a suitable match for your patient or can be obtained from commercial companies that are available globally for this purpose. For additional information on animal Blood transfusions, please read our Blood article. [Please add www. Link to Millpledge.com blood article here]

Routes of administration.

Fluid therapy can be administered in one of two ways:

  1. Orally, by way of food and water, via the gastrointestinal tract, or
  2. Parenterally (by any other means). Parenteral fluids can be administered intravenously, subcutaneously, intraperitoneally and via intraosseous infusion. Subcutaneous and peritoneal fluids are slow to be absorbed and some fluids cannot be administered via the intraosseous route, therefore, the most common and convenient route of choice will be by peripheral intravenous access using Anicath™ IV catheters designed for veterinary use.
Image of dog receiving fluid therapy from a Vet Nurse

Calculating fluid requirements.

The aim of fluid therapy is to replace fluid deficit, to maintain the patient with normal fluid requirements and to address ongoing losses. When using crystalloids; once the overall requirement has been calculated, fluid replacement should be provided over a 24-hour period, so as not to overwhelm the body. In ECC cases, the deficit only can be given within 4 to 6 hours with the remaining maintenance amount being given over the remaining time period. Once the patient has been resuscitated and the fluid balance optimised, the lead clinician at the direction of a veterinarian can then de-escalate the fluids appropriately. This does not apply to the administration of whole blood or fresh plasma which needs to be administered differently.

Animal specific fluid calculator apps are available to assist in calculating the deficit and maintenance volumes, we recommend the Millpledge Fluid Therapy Calculator – Animal IV.

Monitoring the patient.

All animal patients undergoing fluid therapy for whatever reason should be closely monitored, with regular patient checks performed throughout the infusion, until its completion. These regular checks should include;

  • TPR (Temperature, Pulse, Respiration)
  • MM (Mucous Membrane colour and feel)
  • CRT (Capillary Refill Time)
  • Peripheral oedema
  • Chemosis check.
  • Skin Turgor
  • Bodyweight fluctuations
  • Monitoring input of fluids
  • Monitoring output of fluids
  • Abnormalities such as Diarrhoea and vomiting
  • General demeanour
  • IV site is clean and dry.

The results of these checks should always be recorded in the patient’s hospital and fluid charts and then be kept alongside the patients’ other records to provide a complete clinical history. Traditionally, these observations have all been recorded manually and each check is completed when the Veterinary nurse, tech or assistant is able. With the use of the Anifusion® IV pump, each infusion can have scheduled patients checks throughout, and when each check is due, Anifusion® will alert you to this fact. After each check is completed, staff will need to enter these findings on the Anifusion® system, which in turn will be recorded on each patient infusion report. A great way to have all your clinical infusion results available electronically.

Errors in fluid therapy

The reason for patient checks is to ensure that the fluid imbalance is being correctly addressed and in such a way that the patient is coping well and is not overwhelmed. If the patient is under perfused, the patient will not have received enough fluid to correct the deficits and address maintenance requirements. This will mean that the patients’ health is not able to return to normal, and any fluid imbalance or illness will still be present. Continued imbalance can occur as a result of an error in calculation or an interruption to the fluid therapy due to equipment failure. The use of an Anifusion® IV pump in combination with Aniset-Anti-Kink® will ensure that accurate amounts of fluid are delivered and if there is any interruption to the therapy, the monitoring staff will be immediately alerted.

Over perfusion is where too much fluid has been given or too much fluid is present. This could be as a result of an error in a calculation, or that the fluid has been given too quickly. Often, if infusion pumps such as Anifusion® are not used, and fluid is given by gravity-assisted means only, a patients movement or user error can lead to inaccuracies and as a result, too much fluid being given in a short period of time. The use of an Anifusion® IV pump will ensure the fluid is infused at a controlled rate. Monitoring in all cases should be done thoroughly and regularly throughout any infusion. Failure to do so can result in pulmonary oedema, peripheral oedema, respiratory / cardia distress, hypothermia, shock, and death.

Optimising recovery, therapy and safety considerations.

As with any other type of treatment or therapy, it is important to not only meet the patient’s medical needs but to also meet the patients nursing needs as well. When a patient is receiving fluid therapy, it is recommended that the patient be placed in a quiet yet visible area, one where monitoring can be undertaken, optimise patient care when you combine the Anifusion® IV pump with the central cloud monitoring system, as not only will you be alerted to any alarms or scheduled therapy events, but an email and / or text notification can be sent to your phone as well.

The patient should be hospitalised in a large enough kennel or cage to allow enough movement that the patient can stand up fully, lay down completely stretched out and has easily accessible food and water bowls if provided. Cats should also have enough room and be able to reach a litter tray.

The cage / kennel should not be over large, as any excessive movement and stretching, will put stress on both the IV line and IV cannula, potentially causing the IV cannula to be pulled out completely. Too much allowable movement could also cause the IV line to become tangled up and risk occlusion. The use of Aniset Anti-Kink® is of great use here: no matter how much your patient moves around the kennel, and twists up the IV line, Aniset Anti-Kink® line will always allow the fluid to pass through, regardless!

UV light can negatively affect the fluids being infused into your patient. The use of the Aniset Anti-Kink® UV protected IV line should also be considered when using photosensitive drugs and fluids, using a purpose-built UV IV line that is designed to block out UV light will protect the drug from crystallising when exposed to UV light, preventing degradation of the potency of the drug or from crystals entering the patient’s bloodstream.

The clinician's safety is important too, working with animals as we all know has its moments and to protect ourselves from any further injuries and time away from the patient and our team for our own recovery can be avoided. Ensure that patient recovery and treatment areas are kept dry to avoid slipping, consider using a self-priming IV set that avoids any fluid waste or spillage. You should also consider using IV lines that have needle free injection ports or sites to prevent needle stick injuries from occurring and choose an IV set that has an injection site outside of the recovery cage closer to the upper portion of the IV set. Millpledge does offer a comprehensive range of Needle Free Aniset Anti-Kink® IV sets providing a more practical and safer solution for veterinary practices.

Patients can become very bored whilst undertaking their fluid recovery, take steps to ensure that your Anicath™ catheter, t-connectors and Aniset® IV line are protected and remain secure, try securing in place with a bitter tasting bandage such as Wrapz® Chewy No No or Wrapz® Alert bandages or spraying the iv line with a bitter tasting fluid such as Chewy No No™ spray. Ensure that your injection sites remain accessible when protecting your equipment.


Fluid therapy plays an important role in the successful treatment of patient’s and patient recovery times in every veterinary practice and is performed several times a day / 7 days a week. A fluid infusion is not something that should be undertaken without experience, and planning and continual monitoring is vital to ensure success. The essential need for fluid, the correct choice of fluid and complete monitoring throughout, should be addressed for an individual patient and their respective condition, on a case-by-case basis. Accurately calculating rates, VTBI and duration accompanied with the use of quality, reliable equipment such as Aniset Anti-Kink® IV lines and the Anifusion® IV pump, will greatly increase the success of your fluid therapy whilst at the same decreasing the likelihood of interruptions.

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