August 2024

In this VETgirl online veterinary continuing education blog, Amanda M. Shelby, RVT, VTS (Anesthesia & Analgesia) summarizes updated changes in the 2024 AAHA Fluid Therapy consensus guidelines in dogs and cats. How does this impact fluid therapy in your veterinary clinic? Want to learn more? Check out Amanda’s July 2024 webinar on Understanding the 2020 AAHA Anesthesia and Monitoring Guidelines, Intraoperative Fluid Rate Recommendations HERE!

By Amanda M. Shelby, RVT, VTS (Anesthesia & Analgesia)

Updated Fluid Therapy Guidelines, What’s Changed?

The American Animal Hospital Association (AAHA) released the 2024 Fluid Therapy Guidelines for Dogs and Cats in July, 10+ years after the release of the 2013 guidelines for which AAHA collaborated with the American Association of Feline Practitioners (AAFP). Naturally veterinary professionals question what has changed within these revised guidelines and how will that affect current protocols. Below is a highlight of some of the differences or areas of interest, along with the associated page numbers if you would like to follow along. Upon review, I think you will agree that the overarching theme regarding changes in our use of fluids is centered around tailored, judicious, intentional fluid type, rate, and route selection.

Medicine is dynamic, ever-changing and as veterinary professionals, we have an obligation to our patients when we accept our respective veterinarian and veterinary technician oaths’ to uphold the “lifelong obligation [to] the continual improvement of my professional knowledge and competence”1 and to “furthering my knowledge and competence through a commitment to lifelong learning”.2 AAHA is a leading organization in developing widely accepted clinical practice standards and guidelines developed by expert task forces. Upon initial overview, several key differences from the 2013 guidelines are immediately noticeable. First and foremost, several points are emphasized:

  1. These are guidelines and recommendations, not AAHA standards of care.
  2. Patients should be individualized through initial assessment and repeat assessment during fluid administration.
  3. Fluids are drugs requiring a veterinarian’s prescription based on best “scientific evidence in conjunction with their own knowledge and experience”.3

So, what has changed? At a glance, the most instantly noticeable difference is the format of the 2024 guidelines. This edition is well organized into sections, figures, and tables so the reader can quickly reference an area of interest. Sections are dedicated to broadening the understanding of the physiology of body fluid dynamics and electrolyte balance to maintain homeostasis acknowledging the importance of a goal-directed, individualized fluid therapy prescription that is frequently reassessed and tailored to a patient’s on-going needs. The 2024 guidelines review criteria for the selection of a fluid type, rate and route of administration, and the assessment of patient response to fluid delivery. Emphasis is placed on correcting deficits—recognizing specifically where those deficits occur (i.e., the intracellular, interstitial, or vascular space), and avoiding fluid volume overload. There are sections dedicated to fluid therapy during anesthesia (my favorite) and practical strategies for patients with comorbidities. It’s rounded out with an FAQ section where the expert panel anticipated common questions and tried to address ongoing controversies.

If you were familiar with the 2013 guidelines, you might ask, “Where did the shock doses go?” The 2013 guidelines discuss the principle of a ‘standard crystalloid shock dose’, which represents a patient’s complete blood volume per body weight (or vascular component of the extracellular fluid space).4 When treating hypovolemia, the 2013 guidelines recommend giving percent increments (i.e., 25%) of a patient’s calculated crystalloid shock dose rapidly. Then reassess and repeat if the desirable response is not achieved. It stands to reason that rapid, large volumes of crystalloids in a hypovolemic patient may provide improved intravascular volume in the immediate period, however this could also result in hemodilution and place the patient at risk for fluid volume overload with little guidance on a defined desirable endpoint. The 2024 guidelines ask us to change our mindset and focus on three stages of fluid therapy: resuscitation (treating hypovolemia), rehydration (treating dehydration), and maintenance (meeting a patient’s ongoing needs). Thus, AAHA has improved upon this shock dose principle by suggesting when treating hypovolemia, within the resuscitation stage, veterinary staff begin with an intravenous or intraosseous buffered isotonic fluid at a rate of 5-10 mL/kg in cats and 15-20 mL/kg in dogs over 15-30 minutes.

Key fluid therapy differences for treating hypovolemia between 2013 and 2024 guidelines (Chart courtesy of Amanda Shelby, RVT, VTS)

Another noticeable change is the recommendation that crystalloid boluses be administered over 15 to 30 minutes when in a resuscitation phase (pg. 142 Table 9) or over 15 to 30 minutes when correcting hypovolemia (p. 138). The 2013 guidelines introduce the concept of the administration of fluid boluses slowly but do not suggest a time frame. Administering crystalloids over time has the potential to improve intravascular expansion, minimize distribution of fluid into the interstitial space, and reduce risk of edema.5 While the 2024 guidelines do not mention a maximum fluid volume limit or maximum number of boluses; instead, they state that boluses can be repeated in the event “desired hemodynamic and perfusion goals have not been achieved and the patient remains hypovolemic” (p.138), which is again reemphasized in Table 7 (p. 140) and Table 9 (p. 142) when endpoints including heart rate, CRT, blood pressure and mentation are not achieved.

But what if crystalloids do not improve heart rate, CRT, blood pressure and mentation endpoints?

Perhaps the next steps to consider are an alternative fluid therapy (i.e., colloid, blood product, hypertonic solution) or use of a sympathomimetic (i.e., dopamine, dobutamine, ephedrine or norepinephrine), or to reassess your patient’s biochemical values such as glucose, calcium, potassium, magnesium, etc. Mentions of colloids, synthetic or natural (i.e., blood products, and hypertonic crystalloid solutions) are distributed throughout the work, making specific directives for those patients unresponsive to crystalloid therapy more involved for the reader. Fluid Therapy and Anesthesia (Section 4) suggests the use of a colloid as an option in persistent hypotension (Figure 9, p. 144), when blood products are unavailable during acute surgical blood loss, or the use of a colloid with crystalloids in patients with hypoproteinemia (p. 145). Colloid use is also discussed in Fluid Therapy in Ill Patients (Section 5, p. 147). Finally, colloids are mentioned in the FAQ section when addressing the common question, “Are synthetic colloids safe?” to which the summative answer is, ‘we really don’t know but perhaps proceed with caution in specific patient populations’ (p. 156) such as patients with sepsis, pre-existing azotemia, anemia and thrombocytopenia. This response has remained consistent because there is a lack of large-scale, prospective, blinded fluid therapy studies in veterinary medicine to provide us definitive recommendations for the administration of synthetic colloids and their safety.

Have there been any further changes to the anesthetic fluid rates?

The 2013 guidelines introduced the concept of reducing isotonic crystalloid fluid rates during anesthesia in healthy, euvolemic dogs (5 mL/kg/h) and healthy, euvolemic cats (3 mL/kg/h). Prior to the 2013 guidelines anesthetic rates were commonly recommended at 10 mL/kg/h. And while 10 mL/kg/h crystalloid rate is suggested (Box 4. p.145) to treat acute surgical blood loss temporarily during anesthesia, the 2024 guidelines continue to recommend that for healthy, euvolemic dogs crystalloid rates start at 5 mL/kg/h but have widened the suggested rate for healthy cats with normal cardiac and renal function to 3-5 mL/kg/h (p. 143). Likely the most significant difference is language stating that supporting anesthesia is a process. For optimal outcomes, an anesthetic fluid therapy strategy may require starting fluids before, providing fluids during, and continue fluids after the anesthetic event. The 2024 guidelines also suggest that fluids may not be necessary for all euhydrated, euvolemic, healthy patients undergoing short procedures using injectable anesthetics. Another area of guidance during anesthesia is the acknowledgement that hypotension is a common occurrence during inhalant anesthetic events. Treatment involves assessing anesthetic depth, ensuring an appropriate heart rate and body temperature, confirming appropriate balanced anesthetic/analgesic plan is in place, and using the recommended rate of balanced, isotonic crystalloids shown below. If hypotension persists, then crystalloid boluses, colloid administration, and/or inotropes or pressors can be considered (Figure 9, p. 144).

Current Recommendations from 2024 AAHA Guidelines (Photo courtesy of Amanda Shelby, RVT, VTS)

In summary, the 2024 Fluid Therapy Guidelines for Dogs and Cats offer us a thorough review of body fluid distribution and guidelines to assess patients for deficits and volume overload. It heightens our awareness that fluids are indeed drugs, which are often clinically beneficial but when misused, can be detrimental. Selection of the fluid type, rate, duration, and route of administration, or combinations of the beforementioned, is based on the patient’s individual need. The guidelines also recognize the limited availability of veterinary-based, large-scale, blinded, prospective studies upon which to base these recommendations. This emphasizes the importance of veterinary professionals remaining dynamic, engaging in ongoing conversations, initiating relevant investigations, and learning to make the best clinical judgements. The 2024 AAHA Fluid Therapy Guidelines are true to form in that they are organized in line with the principle that each patient should be individualized; no longer is there a blanket fluid rate for every patient. Veterinary professionals are encouraged to read the whole document and cross-reference sections specific to their patients’ needs underscoring the importance of downloading the open access article and individualizing a patient’s fluid therapy prescription.

Check out Amanda’s July 2024 webinar on Understanding the 2020 AAHA Anesthesia and Monitoring Guidelines, Intraoperative Fluid Rate Recommendations HERE!

References

  1. American Veterinary Medical Association Veterinarian’s Oath; https://www.avma.org/resources-tools/avma-policies/veterinarians-oath.
  2. National Association of Veterinary Technicians in America Veterinary Technician Oath https://navta.net/veterinary-technician-oath/.
  3. Pardo M, Spencer E, Odunayo A, et al. 2024 AAHA fluid therapy guidelines for dogs and cats. JAAHA. 2019;60(4):131-63.
  4. Davis H, Jensen T, Johnson A, et al. 2013 AAHA/AAFP fluid therapy guidelines for dogs and cats. JAAHA. 2013;49(3):149-59.
  5. Hahn RG. Understanding volume kinetics. Acta Anaesthesiol Scand. 2020;64(5):570-8.

 

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