Current Concepts in Fluid Therapy in Horses

Volume kinetics of lactated Ringer's solution in adult horses

BACKGROUND

Fluid therapy in horses is primarily empirical. Evidence-based quantification of the disposition of intravenous (IV) crystalloids used in clinical practice could enhance the effectiveness of fluid therapy.

OBJECTIVES

To determine the pharmacokinetics (i.e., volume kinetics: VK) and associated haemodynamic effects of IV lactated Ringer's solution (LRS) in adult euvolemic horses.

STUDY DESIGN

Unmasked multiple subjects, single baseline design.

METHODS

Thirteen healthy, euvolemic adult female horses were administered an IV bolus of LRS and monitored over 4 h. Haemoglobin, albumin and haematocrit concentrations were used to generate VK parameter estimates through a non-linear mixed effects model and stepwise covariate testing. Cardiorespiratory effects, hormonal parameters and urine output were monitored.

RESULTS

Administration of an IV bolus of LRS increased heart rate and systolic arterial pressure. Kinetic analysis was based on plasma albumin, as fluctuations in haemoglobin concentration suggested splenic recruitment of erythrocytes. Fluid disposition was best described by a two-volume fluid space model. Covariate analysis showed that a high systolic arterial pressure is associated with a decrease in urine output, and that haemoglobin recruitment was associated with the transfer of fluid from the central compartment, which was estimated to be 26.2 L, to a peripheral space. Kinetic constants showed rapid fluid distribution to the peripheral compartment and slow return to the central compartment, impeding fluid elimination from the body. Distribution of LRS from the central compartment was rapid but elimination from the body was slow.

MAIN LIMITATIONS

Limited sample size and sample collection duration may have influenced model selection and covariate identification.

CONCLUSIONS

Volume kinetics provides a method for quantitatively describing the volume expanding effects of administered fluids. Fluid infusion is associated with an increase in heart rate and arterial blood pressure. Volume kinetic analysis offers a context-dependent method for developing and refining more effective fluid infusion protocols.

Effects of Plasma and Hetastarch Administration on Colloid Oncotic Pressure and Coagulation Variables in Dairy Calves and Goats

BACKGROUND

Transfusion with fresh frozen plasma (FFP) or hetastarch 6% (HES) is an option for managing decreased colloid oncotic pressure (COP) associated with hypoproteinemia. The effectiveness of HES compared to plasma has not been reported in calves and goats.

HYPOTHESIS

Hetastarch increases COP to levels similar to FFP. There will be no significant adverse clinicopathological changes after administration of HES.

ANIMALS

Seven healthy preweaned calves and 7 juvenile goats from university herds.

METHODS

Cohort, clinical trial in a two-way crossover design. Hetastarch and FFP were administered intravenously at 10 and 20 mL/kg, respectively, once. Plasma COP was measured re-transfusion, at 0, 1, 2, 4, 6, 12, 24, 36, 72 h, and 7 days after each transfusion. Coagulation variables were analyzed pre-transfusion, at 0, 24, and 72 h after transfusion. The effects of treatment and time on COP and coagulation variables were determined by multivariate analysis of variance.

RESULTS

Transfusion with FFP and HES increased the COP in calves and goats, with FFP increasing the COP to a greater magnitude in calves (least square mean difference of 1.6 vs. 1 mmHg; p = 0.03) but not in goats (least square mean difference of 3.0 vs. 3.0 mmHg; p = 0.99). There were no significant changes (p > 0.05) in coagulation variables detected after transfusion with FFP or HES.

CONCLUSIONS AND CLINICAL IMPORTANCE

Hetastarch is an alternative colloid to FFP in calves and goats. Adverse changes were not observed in goats and calves after HES administration.

Bioreactance noninvasive cardiac output monitoring in euvolemic adult horses subjected with 7.2% saline and 6% hydroxyethyl starch (130/0.4) solution infusions

OBJECTIVE

To compare the ability of bioreactance noninvasive cardiac output (BR-NICO) with thermodilution cardiac output (TDCO) for the measurement of cardiac output (CO) in healthy adult horses receiving 2 different IV volume replacement solutions.

DESIGN

Prospective randomized crossover study from September to November 2021.

SETTING

University teaching hospital.

ANIMALS

Six university-owned adult horses.

INTERVENTIONS

Horses were randomly assigned to receive 7.2% hypertonic saline solution (HSS) or 6% hydroxyethyl starch (130/0.4) solution (HETA). BR-NICO and TDCO were measured simultaneously at baseline, 10, 20, 30, 40, 50, 60, 90, and 120 minutes before fluid administration and again at the same times after starting a bolus infusion of IV volume replacers. All solutions were administered within 10 minutes.

MEASUREMENTS AND MAIN RESULTS

BR-NICO and TDCO were strongly correlated (Pearson r2 = 0.93; P < 0.01). Regression analysis showed the relationship between TDCO and BR-NICO was BR-NICO = 0.48 × TDCO + 0.6. For the corrected BR-NICO values, the Bland-Altman agreement mean bias and lower/upper limits of agreement were -0.62 and -5.3 to 3.9 L/min, respectively. Lin's concordance (95% confidence interval) between methods was 0.894 (0.825-1.097). Compared with baseline, HSS increased the CO at 10 and 20 minutes (TDCO and BR-NICO). Compared with baseline, HETA decreased the CO at 10 and 20 minutes (TDCO and BR-NICO) and increased the CO at 90 (TDCO only) and 120 minutes (TDCO and BR-NICO).

CONCLUSIONS

BR-NICO strongly agreed with TDCO in the measurement of CO in healthy unsedated adult horses. HSS administration significantly increased CO in the first 30 minutes, while HETA initially decreased CO at 10 minutes but increased CO to above baseline values by 90 minutes.

Medical management and positive outcome after prolonged recumbency in a case of equine herpesvirus myeloencephalopathy

A 17-year-old mare presenting with acute fever, weakness and bladder dysfunction was diagnosed with equine herpesvirus myeloencephalopathy (EHM). The mare become transiently recumbent, underwent parenteral fluid therapy, plasma infusion, steroidal/nonsteroidal anti-inflammatory drugs (SAID/NSAIDs) and bladder catheterization. After 10 days the mare was hospitalized. Neurological evaluation revealed ataxia and proprioceptive deficits mainly in the hind limbs. The mare was able to stand but unable to rise from recumbency or walk. Secondary complications included Escherichia coli cystitis, corneal ulcers and pressure sores. A full-body support sling was used for 21 days. Medical treatment included systemic antimicrobials, NSAIDs, gradual discontinuation of SAIDs, parenteral fluid therapy and bladder lavage. The mare tested positive for Varicellovirus equidalpha 1 (EHV-1) DNA in nasal swab and blood samples on day 13 and in urine samples on days 13 and 25 after the onset of fever. Neurological signs improved over a period of 34 days and the mare was discharged with mild hind limb weakness/ataxia. Secondary complications resolved within 2 weeks. At the eight-month follow-up, marked improvement in locomotory function had been achieved.

Fluid Therapy in Exotic Animal Emergency and Critical Care

Many new concepts are emerging in the understanding of fluid therapy in human and mammalian medicine, including the role of the glycocalyx, increased understanding of fluid, sodium, and chloride overload, and the advantages of colloid administration in the form of albumin. None of these concepts, however, appear to be directly applicable to non-mammalian exotic patients, and careful consideration of their alternate physiology is required when formulating fluid plans for these patients.

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.

Advanced Strategies of Drug Delivery via Oral, Topical, and Parenteral Administration Routes: Where Do Equine Medications Stand?

While the global market for veterinary products has been expanding rapidly, there is still a lack of specialist knowledge of equine pharmaceutics. In many cases, the basic structure of the gastrointestinal tract (GIT) and integumentary system of the horse shares similarities with those of humans. Generally, the dosage form developed for humans can be repurposed to deliver equine medications; however, due to physiological variation, the therapeutic outcomes can be unpredictable. This is an area that requires more research, as there is a clear deficiency in literature precedence on drug delivery specifically for horses. Through a careful evaluation of equine anatomy and physiology, novel drug delivery systems (NDDSs) can be developed to adequately address many of the medical ailments of the horse. In addition to this, there are key considerations when delivering oral, topical, and parenteral drugs to horses, deriving from age and species variation. More importantly, NDDSs can enhance the duration of action of active drugs in animals, significantly improving owner compliance; and ultimately, enhancing the convenience of product administration. To address the knowledge gap in equine pharmaceutical formulations, this paper begins with a summary of the anatomy and physiology of the equine gastrointestinal, integumentary, and circulatory systems. A detailed discussion of potential dosage-form related issues affecting horses, and how they can be overcome by employing NDDSs is presented.

Acute Kidney Injury and Renal Failure in Horses

Nephrotoxic and hemodynamically mediated disorders are the most common causes of acute renal failure (ARF) in horses and foals. Leptospira spp. is the most common infectious cause of ARF. Initial treatments for ARF include elimination of nephrotoxic drugs, correction of predisposing disorders, and fluid therapy to promote diuresis. Horses and foals with polyuric ARF often have a good prognosis, while those with oliguric or anuric ARF have a guarded to poor prognosis. When fluid therapy is unsuccessful in improving urine production, various drugs treatments have been used in an attempt to increase urine production, but none are consistently effective in converting oliguria to polyuria.