Whether we're treating small animals, exotics, large animals, or equines, you need fluid therapy in your veterinary practice. It's more than just water and salt; it's about understanding the science and art behind it to deliver optimal patient care. The purpose of this article is to help you and your practice make informed decisions about fluid therapy protocols. Book mark it for reference, or use it as a refresher or training guide for your staff.
The Art and Science of Fluid Therapy
The need for fluid therapy is often a two-part harmony: restoring the patient’s intravascular volume (ICF) and replenishing extravascular fluid (ECF). However, there’s a lot of debate about which fluid type is the best to use for treatment or resuscitation. Well, the truth is, it all depends on the patient’s needs and the underlying disease process. That’s why it’s important for practices to have a variety of fluids ready on hand.
Diagnosing the drip: Which type of fluid is the best to use?
There are 4 types of hypoperfusion commonly recognized in vet practice: hypovolemia, maldistributive/septic, cardiogenic, and obstructive. When a patient is hypoperfused, it’s vital to ‘diagnose the drip’. This means figuring out which type of hypoperfusion is present so the right treatment plan – both initial and long term – can be given.
When it comes to fluid replacement, isotonic crystalloids seem to be the go-to or the drip of choice. Isotonic crystalloids are intravenous (IV) fluids that have the same osmolality as blood plasma. This means that when they are infused into the bloodstream, they do not cause any fluid to move between the intravascular (blood) and extracellular (outside the blood cells) compartments. Common crystalloids veterinarians have on their shelf include Lactated Ringer’s, Normosol-R, and Plasma-Lyte 148.
Isotonic crystalloids are used to:
- replace fluid losses caused by vomiting, diarrhea, or sweating
- treat dehydration
- expand blood volume
- flush IV lines
Synthetic colloids, such as Hetastarch, Vetstarch®, and dextrans, are also effective options in improving perfusion in hypovolemic patients. But they’re not without risks –leading to complications such as heart failure and allergic reactions, not to mention its cost – so they should only be used when necessary. But here are some situations where synthetic colloids might be a good option:
- when crystalloids are not effective in improving or maintaining blood volume
- peripheral edema develops
- in support of colloid osmotic pressure
- capillary permeability problems
- total protein < 3.5 g/dL
- albumin < 1.5 g/dL
Besides the two mentioned, hypertonic saline is used in patients that have a normal hydration status and is contraindicated in patients that are dehydrated or hypernatremic. In addition to osmotic effects, hypertonic saline is theorized to have other potential benefits including:
- improved myocardial contractility
- activation of a neurogenic reflex leading to peripheral vasodilation
- improvement of microcirculatory flow by preventing capillary collapse
- reduction of endothelial cell swelling
- alterations in function of polymorphonuclear cells (PMN) and endothelial cells
However, hypertonic saline can have various risks such as bradycardia, bronchoconstriction, sodium fluctuations, fluid overload and pulmonary edema, phlebitis, and ventricular arrhythmias. To prolong the effects of fluid resuscitation, Dr. Garret Pachtinger suggests a combination of hypertonic saline and synthetic saline.
The initial goal of fluid therapy is to replace the patient’s immediate life-threatening fluid deficits. Once this has been achieved, the focus shifts to maintaining the patient's hydration level and preventing further losses. In fact, the severity of dehydration cannot be accurately assessed by clinical signs alone, and it is not usually possible to detect dehydration below 5%.
Patients with chronic dehydration but with stable cardiovascular parameters can be rehydrated over a 6-24 hour period, depending on the patient’s stability, the severity of their dehydration, and any underlying medical conditions.
Fluid therapy formulas: How to calculate the right amount of fluids for your patient
By calculating the right amount of fluids for your patient, you can help to ensure that they receive the treatment they need. Dr. Pachtinger recommends using the following formulas:
- Dehydration fluid replacement (L) = Body weight (kg) x %dehydration x 1000
- Maintenance daily requirements = Body weight (kg) x 2–4 ml/kg/h
- On-going losses = 3-4 ml/kg/vomit or diarrhea
Some additional things to keep in mind when calculating fluid therapy:
- patient’s age, sex, and underlying medical conditions
- type of fluid that is being used
- the route of administration (intravenous, oral, etc.)
- patient’s response to fluid therapy
Fluid therapy should be carefully monitored and adjusted to avoid excessive fluid administration, which can damage the endothelial glycocalyx, leading to a number of complications, including fluid overload, impaired blood clotting, and increased risk of infection. Thus, it is important to use judicious fluid therapy in patients who are at risk of endothelial glycocalyx damage.
The correct amount of fluids at the correct rate: Tools for your fluid therapy dream team!
Fluid therapy is about delicate balance – too much or too little fluid can be harmful to the patient. Fret not! Infusion and syringe pumps allow practices like yours to switch or customize the fluid therapy to the patient's individual needs.
If you are looking for a secure and reliable fluid delivery that is within your budget, look no further than our patient-ready used IV pumps! We stock many certified and recalibrated infusion pumps – from Baxter, Smiths Medical/ Medfusion, and Abbott/ Hospira – ready to be shipped to you same-day to meet your infusion pump needs.
In addition, AIV Vet’s easy-to-use VetroCRI syringe pump is designed for controlled continuous administration of IV fluids and does not require software to operate. Battery-powered, VetroCRI is the most convenient and flexible solution for your practice.
What are you waiting for? Upgrade your tools now!
As Dr.Pachtinger put it, fluid therapy is not just ‘set it and forget it’. It’s an ongoing process with no one-size-fits all approach. It is critical to reassess the patient’s perfusion parameters after each fluid bolus to ensure that the patient is responding well to the therapy and that there are no complications. If their infusion parameters are not improving, there might be a need to give them booster shots of fluid. And if there is still no improvement after that, there might be a need to switch gears and give them a different type of fluid.
Sources:
Pachtinger, G. (2023). Fluid Therapy: More Than Just Water and Salt: Part 1 with Dr. Garret Pachtinger | VETgirl Veterinary Continuing Education Blog
Pachtinger, G. (2023b). Fluid Therapy: More Than Just Water and Salt: Part 2 with Dr. Garret Pachtinger | VETgirl Veterinary Continuing Education Blog. VETgirl.