Author

Stephen J. Birchard DVM, MS, Diplomate ACVS

Tuesday, November 18, 2014

Intravenous Fluids in Anesthetized Dogs and Cats: Are we giving too much?

Intravenous fluid therapy is one of the most important perioperative treatments veterinarians provide for their patients. Intravenous fluids are considered a necessary part of the anesthesia protocol because of hypotension and vasodilation that can occur due to the anesthetic drugs. 

All animals being prepared for anesthesia and surgery need to be assessed for hydration status and disorders that create fluid losses, e.g. vomiting and diarrhea. Intravenous fluid dosages will be influenced by the animal’s current hydration and ongoing fluid losses. Intravenous fluid dosages may also be affected by disorders that could predispose the animal to over-hydration such as cardiac or renal disease.

The traditional intravenous fluid rate for healthy animals under anesthesia has been 10ml/kg/hour.(1) In the recent AAHA/AAFP fluid therapy guidelines, this recommendation has been revised.(2) Table 4 from the paper describes current fluid therapy guidelines for anesthetized cats and dogs:

Table: Recommendations for Anesthetic Fluid Rates (from: 2013 AAHA/AAFP Fluid Therapy Guidelines for Dogs and Cats. Harold Davis, BA, RVT, VTS (ECC), Tracey Jensen, DVM, DABVP, Anthony Johnson, DVM, DACVECC, et.al., J Am Anim Hosp Assoc 2013; 49:149–159)

- Provide the maintenance rate plus any necessary replacement rate at <10 mL/kg/hr
- Adjust amount and type of fluids based on patient assessment and monitoring
- The rate is lower in cats than in dogs, and lower in patients with cardiovascular and renal disease
- Reduce fluid administration rate if anesthetic procedure lasts 1 hr
- A typical guideline would be to reduce the anesthetic fluid rate by 25% q hr
until maintenance rates are reached, provided the patient remains stable

Rule of thumb for cats for initial rate: 3 mL/kg/hr
Rule of thumb for dogs for initial rate: 5 mL/kg/hr

Note that not only are the initial fluid rates lower than the previously recommended 10ml/kg/hr, but a schedule for gradual reduction of fluid rates as the anesthetic period progresses is also recommended. These guidelines are considerably different from what was previously thought to be necessary fluid rates for anesthetized animals, but are based on carefully considered factors, evidence based medicine, and clinical experience of board certified specialists.

References

1. Ann Weil, DVM, DACVAA. Anesthesia reboot: Erase these myths and misconceptions. Veterinary Medicine, October 2014, pg. 318.

2. Harold Davis, BA, RVT, VTS (ECC), Tracey Jensen, DVM, DABVP, Anthony Johnson, DVM, DACVECC, et.al. 2013 AAHA/AAFP Fluid Therapy Guidelines for Dogs and Cats. J Am Anim Hosp Assoc 2013; 49:149–159.

Questions:

What are your thoughts or opinions about this change in recommended fluid dosage?

In private practice, in which anesthetized patients do you typically run intravenous fluids; in all animals or do you have some kind of selection criteria? In other words, what do you think the standard of care should be for fluid administration under anesthesia?

Please post comments either here on the blog site or on my facebook page:
Dr. Stephen Birchard, Veterinary Continuing Education

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