The effect of colloid formulation on colloid osmotic pressure in horses with naturally occurring gastrointestinal disease

Potomac Horse Fever

Potomac horse fever (PHF) is a common cause of equine colitis in endemic areas. Until recently, the only causative agent known to cause PHF was Neorickettsia risticii. However, N. findlayensis has been isolated from affected horses. Horses typically become infected upon ingestion of Neorickettsia spp.-infected trematodes within aquatic insects. The most common clinical signs include diarrhea, fever, anorexia, lethargy and colic. The diagnostic test of choice for PHF is PCR of blood and feces. Tetracyclines remain an effective treatment. Supportive care, including fluid therapy, colloid administration, NSAID and anti-endotoxin medication, and digital cryotherapy, is also necessary in some cases.

Current Concepts in Fluid Therapy in Horses

Despite the frequent inclusion of fluid therapy in the treatment of many conditions in horses, there are limited studies available to provide evidenced-based, species-specific recommendations. Thus, equine fluid therapy is based on the application of physiology and extrapolation from evidence in other veterinary species and human medicine. The physiologic principles that underly 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. As a result, there are ongoing controversies in human medicine over fluid types, volumes, and routes of administration. For example, the use of 0.9% NaCl as the replacement fluid of choice is being questioned, and the theoretical benefits of colloids have not translated to clinical cases and negative effects are greater than predicted. In this review, the current body of equine research in fluid therapy will be reviewed, connections to the controversies in human medicine and other veterinary species will be explored and, where appropriate, recommendations for fluid therapy in the adult horse will be made based on the available evidence. This review is focused on the decisions surrounding developing a fluid plan involving crystalloids, synthetic colloids, and plasma.

Hydroxyethyl starches in equine medicine

OBJECTIVE

To review and discuss the use of hydroxyethyl starches (HES) in equine veterinary medicine, and to provide recommendations for its use.

DATA SOURCES

Veterinary and human peer-reviewed medical literature including scientific reviews, meta-analyses, and original research articles.

HUMAN DATA SYNTHESIS

Increasing evidences on adverse effects after HES use and decreasing support for beneficial effects with regards to volume expansion and colloid osmotic pressure (COP) support in critically ill subjects have led to a recent guideline to limit the use of HES in critically ill people.

EQUINE VETERINARY DATA SYNTHESIS

The rationale for HES use in horses is mainly extrapolated from human medicine, and very limited studies in horses are available. There is limited evidence suggesting a superiority of volume expansion effects of HES over crystalloids. The potential for HES to increase and maintain COP is well supported, but there is no evidence that maintaining or increasing plasma COP influences outcome, tissue edema formation, or rates of complications that potentially relate to edema formation. HES induce dose-dependent changes in coagulopathic parameters, but there is no evidence that HES causes clinical coagulopathies. Insufficient data are available on other adverse effects such as acute kidney injury, or mortality in horses. The use of HES should be restricted in septic patients, but may still have some use in cases of hemorrhagic shock resuscitation, hypoalbuminemia, or perioperative fluid replacement.

CONCLUSION

The evidence supporting the use of HES in horses is weak due to lack of species-specific investigations. Acknowledging species differences, the use of HES should be judicious, yet with some recognition of its benefits in particular cases. More research is necessary to improve knowledge on use of HES in horses and to establish better future recommendations.

Plasma transfusions in horses with typhlocolitis/colitis

The outcome of treatment of horses with plasma for typhlocolitis/colitis at the Ontario Veterinary College-Health Sciences Centre was evaluated. Horses with typhlocolitis/colitis that received a plasma transfusion had higher odds of dying than did non-transfused horses. The clinical usefulness of transfusing plasma to hospitalized hypoproteinemic horses is questioned.

Diagnosis and Treatment of Undifferentiated and Infectious Acute Diarrhea in the Adult Horse

Acute, infectious, diarrhea in adult horses is a major cause of morbidity and is associated with numerous complications. Common causes include salmonellosis, clostridiosis, Coronavirus, and infection with Neorickettsia risticii (Potomac horse fever). Treatment is empirical and supportive until results of specific diagnostic tests are available. Supportive care is aimed at restoring hydration, correcting electrolyte imbalances, and limiting the systemic inflammatory response. The mainstays of therapy are intravenous fluid therapy, electrolyte supplementation where necessary, nonsteroidal anti-inflammatory agents, and nutritional support. Specific therapies include colloid oncotic support, antibiotics, hyperimmune plasma, polymyxin B, pentoxifylline, probiotics, binding agents, gastroprotectants, laminitis prevention, and coagulation prophylaxis.

Effect of infusion of equine plasma or 6% hydroxyethyl starch (600/0.75) solution on plasma colloid osmotic pressure in healthy horses

OBJECTIVE To compare the effects of equivalent volumes of equine plasma and 6% hydroxyethyl starch (600/0.75) solution (hetastarch) administered IV on plasma colloid osmotic pressure (pCOP) and commonly monitored clinicopathologic variables in horses. ANIMALS 6 healthy mares. PROCEDURES In a randomized, crossover study, horses were administered hetastarch or plasma (both 10 mL/kg, IV) 18 months apart. The pCOP and variables of interest were measured before (baseline), immediately after, and at intervals up to 96 or 120 hours after infusion. Prothrombin and activated partial thromboplastin times were measured before and at 2 and 8 hours after each infusion. RESULTS Prior to hetastarch and plasma infusions, mean ± SEM pCOP was 19.4 ± 0.5 mm Hg and 19.4 ± 0.8 mm Hg, respectively. In general, hetastarch and plasma infusions comparably increased pCOP from baseline for 48 hours, with maximum increases of 2.0 and 2.3 mm Hg, respectively. Mean Hct and hemoglobin, total protein, and albumin concentrations were decreased for a period of 72, 96, or 120 hours after hetastarch infusion with maximum decrements of 8.8%, 3.2 g/dL, 1.2 g/dL, and 0.6 g/dL, respectively. Plasma infusion decreased (albeit not always significantly) hemoglobin concentration and Hct for 20 and 24 hours (maximum changes of 1.5 g/dL and 6.6%, respectively) and increased total solids concentration (maximum change of 0.6 g/dL) for 48 hours. Platelet count and coagulation times were minimally affected. CONCLUSIONS AND CLINICAL RELEVANCE Overall, the hetastarch and plasma infusions comparably increased pCOP in healthy horses for up to 48 hours. Hetastarch induced greater, more persistent perturbations in clinicopathologic variables.