May 2023

In part 2 of a two-part VETgirl online veterinary continuing education blog, Dr. Garret Pachtinger, DACVECC, reviews fluid therapy in veterinary medicine, and what you need to know. From identifying dehydration on physical examination to treating your veterinary patients, read on to learn more! If you haven’t read part 1, check it out HERE before proceeding!

Fluid therapy is one of the most commonly used therapies for the small animal practitioner. Once immediate life-threatening fluid deficits are replaced, the focus then shifts to the patient’s dehydration level, maintenance level, and provisions for suspected ongoing losses.

The following chart is commonly used to asses patient dehydration characteristics:

Physical Examination Findings in Dehydrated Patients

Percent dehydration Clinical signs
<5 No detectable abnormalities
5-8 Decreased skin turgor, dry mucous membranes
8-10 Decreased skin turgor, dry mucous membranes, eyes may be sunken in orbits, slight prolongation of CRT
10-12 Severe skin tenting, prolonged CRT, dry mucous membranes, eyes sunken in orbits, possibly signs of shock
>12 All of the above plus signs of shock, often life threatening

Measurement of dehydration is subjective and is not expected to be detected clinically below 5%.

For patients with evidence of chronic dehydration on examination but stable cardiovascular parameters (i.e. no evidence of hypovolemia), fluid deficits are corrected over a 6-24 hour period, depending on the stability of the patience, the chronicity of disease, co-morbidities (e.g., cardiopulmonary disease), etc.

Following treatment of hypovolemia, the following formulas are used to create a fluid therapy plan:

  1. Dehydration fluid replacement (L) = Body weight (kg) x %dehydration x 1000
  2. Maintenance daily requirements = Body weight (kg) x 2–4 ml/kg/h.
  3. On-going losses = 3-4 ml/kg/vomit or diarrhea

Complications of fluid therapy
While fluid therapy is often considered a benign treatment, it is not without risk.  Complications to consider based on the individual patient characteristics include:

  • Pulmonary edema
    • Volume overload
    • Increased vascular permeability
  • Rapid sodium shifts
    • Neurologic signs
      • Obtundation
      • Cerebral edema
      • Seizures
    • Phelbitis
      • Use of hyperosmotic agents

What is the endothelial glycocalyx and why is it important?
The endothelial glycocalyx is a gel-like matrix that lines all vascular endothelial surfaces. It is composed of glycosaminoglycans, proteoglycans, and glycoproteins. It is a dynamic structure that has many functions, including hemostasis, inhibition of microthrombosis, regulation of adhesion and migration of leukocytes through endothelial cells, regulation of vascular tone and permeability, and regulation of fluid flux across endothelial cells. Why this has gained notoriety is that damage to the endothelial glycocalyx can lead to increased vascular permeability, capillary leakage and edema, a proinflammatory and hypercoagulable state, and altered vessel tone to name a few. At this time, there does not appear to be one particular therapy that is strongly recommended, nor is there any available research specific to veterinary medicine.  As such, judicious fluid therapy is recommended to avoid further damage to the endothelial glycocalyx.

Intravenous fluid therapy can be performed rapidly and can be life saving for the emergency patient.  A thorough history, physical examination, and preliminary diagnostics can be used to help differentiate disease processes which may be worsened by fluid therapy (i.e. cardiogenic shock), as well as help the clinician choice the best fluid type to improve the clinical condition.

TABLE: Colloids and their chemical properties.

Colloid Mean MW
5% Human albumin 69 N/A 23.2± 0.1
25% Human albumin 69 N/A > 200
Canine fresh frozen plasma 69 N/A 17.1± 0.6
6% Hetastarch in 0.9% NaCl 600 0.7 32.7± 0.2
6% Hetastarch in balance electrolyte solution–Hextend™ 670 0.75 37.9± 0.1
6% Voluven™ 130 0.4 37.1± 0.8
6% Vetstarch™ 130 0.4 40*
  • In vitro

TABLE: Common crystalloids and their chemical properties.

Solution LRS Plasmalyte A; Norm R 0.9% NaCl
Na 130 140 154
K 4 5 0
Ca 3 0 0
Mg 0 3 0
Cl 109 98 154
Gluconate 0 23 0
Lactate 28 0 0
Acetate 0 27 0
Osmolarity 270 294 310


References (Please note the references listed are for both Part 1 and 2):

  1. Barron ME, Wilkes MM, Navickis RJ. A systematic review of the comparative safety of colloids. Arch Surg 2004;139(5):552-63.
  2. Chan DL. Colloids: Current recommendations. Vet Clin No Amer Small Anim Pract 2008;38(3):587-93.
  3. Choi PT, Yip G, Quinonez LG, et al. Crystalloids vs colloids in fluid resuscitation: a systematic review. Crit Care Med 1999;27(1):200-10.
  4. Cohn LA, Kerl ME, Lenox CE, et al. Response of healthy dogs to infusions of human serum albumin. Am J Vet Res 2007;68:657-663
  5. Cornelius LM. Fluid therapy in small animal practice.J Am Vet Med Assoc. 1980;176:110.
  6. Cornelius LM, Finco DR, Culver DH. Physiologic effects of rapid infusion of Ringer’s lactate solution into dogs.Am J Vet Res. 1978;39:1185.
  7. Cunha MG, Freitas GC, Carregaro AB,et al. Renal and cardiorespiratory effects of treatment with lactated Ringer’s solution or physiologic saline (0.9% NaCl) solution in cats with experimentally-induced urethral obstruction. Am J Vet Res. 2010;71:840–846.
  8. DiBartola SP, Bateman S. Introduction to fluid therapy. In: DiBartola SP.Fluid, Electrolyte, and Acid Base Disorders in Small Animal Practice. 4th ed. St. Louis, MO: Elsevier; 2012:331–350.
  9. Gaudette S, Hughes D, Boller M. The endothelial glycocalyx: structure and function in health and critical illness. J Vet Emerg Crit Care (San Antonio). 2020;30(2):117-134. doi:10.1111/vec.12925
  10. Hansen B, DeFrancesco T. Relationship between hydration estimate and body weight change after fluid therapy in critically ill dogs and cats.J Vet Emerg Crit Care. 2002;12:235.
  11. Moore LE, Garvey MS. The effect of hetastarch on serum colloid osmotic pressure in hypoalbuminemic dogs. J Vet Intern Med 1996;10(5):300-3
  12. Rose RJ. Some physiological and biochemical effects of the intravenous administration of five different electrolyte solutions in the dog.J Vet Pharmacol Ther. 1979;2:279.
  13. Silverstein DC, Aldrich J, et al. Assessment of changes in blood volume in response to resuscitative fluid administration in dogs. Journal of Veterinary Emergency and Critical Care 2005;16(3):185–192.
  14. Trow AV, Rozanski EA, Delaforcade AM, et al. Evaluation of use of human albumin in critically ill dogs:73 cases (2003-2006). J Am Vet Med Assoc 2008;233(4):60

Only VETgirl members can leave comments. Sign In or Join VETgirl now!