The most appropriate way to use fluid therapy in horses is far from well-understood, despite its frequent use, the authors of a just-published review have concluded.
“Many of the issues that plague equine clinicians mirror those encountered in human medicine,” Naomi Crabtree and Kira Epstein reported in the journal, Frontiers in Veterinary Science.
Despite the frequent inclusion of fluid therapy in the treatment of many conditions in horses, there are few studies available that provide evidenced-based, species-specific recommendations, they said.
“This significantly limits the ability to provide practitioners with evidence-based recommendations for fluid therapy in horses.
“Thus, equine fluid therapy is based on the application of physiology and extrapolation from evidence in other veterinary species and human medicine.”
The pair, with the University of Georgia College of Veterinary Medicine, said the physiologic principles that underlie the use of fluids in medicine are, at first glance, straightforward and simple to understand.
“However, in the past 20 years, multiple studies in human medicine have shown that creating recommendations based on theory in combination with experimental and/or small clinical studies does not consistently result in best practice.”
The authors traversed the current body of equine research into fluid therapy, connections to the controversies in human medicine and other veterinary species, and made recommendations for fluid therapy use in adult horses, based on available evidence.
They summarized their findings into six key points:
- Intravenous fluid therapy remains the most appropriate route for volume resuscitation, however, fluid administration via the stomach and rectally are effective and seemingly safe routes for correcting and maintaining systemic hydration and increasing fecal water content at rates that have been reported in the literature.
- Aggressive IV fluid rates (greater than twice maintenance) are likely to be no more effective at increasing fecal water than lower rates, despite significantly increasing the cost and increasing the risk of electrolyte abnormalities and volume overload.
- The use of non-sterile isotonic fluid options may be ill-advised due to the potential for mixing errors, bacterial and endotoxin contamination, and increased risk for catheter site complications.
- Normal saline has been repeatedly reported to result in hyperchloremic metabolic acidosis, which in other species has been associated with complications and possibly poorer outcomes. As such, balanced electrolyte solutions are likely preferable in most patients. Exceptions include situations in which these effects may be therapeutic (i.e., in cases of hypochloremic metabolic alkalosis). There are more debatable benefits in cases of hyperkalemia.
- While the proposed mechanism by which colloids exert their effects has been questioned, the equine literature to date does support their influence on colloid oncotic pressure and volume expansion.
- Synthetic colloid administration has been shown to exert some, albeit mild, effects on hemostatic parameters similar to those seen in people and small animal patients, particularly at higher doses. As such, it may be wise to limit their administration to lower doses. It is important to note that there is no data from which to evaluate the potential for additional side effects seen in other species.
The pair noted that most of the published research in the area of fluid therapy in horses has focused on the first two “Ds” — drug and dosing. Little has been evaluated with respect to duration or de-escalation (withdrawal), they said.
“Work in other species has shifted to consideration of how these factors influence outcome, with particular emphasis on concerns such as fluid overload.
“This has resulted in a move toward consideration of fluid therapy not as a sole treatment modality with a prescribed drug, dose, and route, but rather a therapeutic intervention with four phases: the resuscitation phase, the optimization phase, the stabilization phase, and the evacuation phase.
“Largely, to date, the average equine practitioner has likely considered the resuscitation and stabilization phases, but probably overlooked the later phases.”
However, some clinical research has recently been performed evaluating the possible implications of aggressive fluid therapy, such as its effects on intestinal hydration and the relationship between intravenous fluid administration and the development of post-operative reflux.
“It is encouraging to see a move toward this type of thinking and greater consideration of the implications of failing to reflect on these repercussions for the patient.”
Crabtree NE and Epstein KL (2021) Current Concepts in Fluid Therapy in Horses. Front. Vet. Sci. 8:648774. doi: 10.3389/fvets.2021.648774