Systemic, renal, and colonic effects of intravenous and enteral rehydration 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.

Intake, digestibility, and behavior of horses fed açaí kernel (Euterpe oleracea Mart.) as a substitute of Mombaça grass (Megathyrsus maximus)

In this study, we analyzed the effects of including açaí kernel, in the experimental diets fed to horses on the intake and digestibility of their nutrient and the resultant effects on the behavior of horses. The experiments were conducted in Federal Rural University of Amazonia. Five mares with no defined breeds, were allocated to five treatments (the replacement of Mombaça grass (Megathyrsus maximus) with crushed açaí kernel at 0, 18.75, 37.50, 56.25, and 75% levels of dry matter), in a 5 × 5 Latin square design. The animals were housed in covered stalls with concrete floors, equipped with individual troughs and drinkers, and fed 80% roughage and 20% concentrate. The inclusion of açaí kernel altered the intake and digestibility of a few nutritional components and the feeding behavior of mares. Increasing levels of the substitution of Mombaça grass with crushed açaí kernel in the experimental diets increased the nutrient intake and digestibility of neutral detergent fiber, total carbohydrates, and non-fibrous carbohydrates (P < 0.05) while reducing the time spent on feeding by the animals. Crushed açaí kernel can, therefore, be included as a substitute for Mombaça grass at up to 37.5% in equine diets.

Critical Care of the Colic Patient: Monitoring, Fluid Therapy, and More

A successful outcome to management of the critical colic patient is highly dependent on how the patient is monitored and treated, particularly, in the perioperative period. In this article, we will provide an update on monitoring techniques, advances in fluid therapy, nutrition management and pharmacotherapeutic agents, inclusive of pain monitoring and management, prokinetics, and management of systemic inflammatory response syndrome and the hypercoagulable state.

Repeat Celiotomy-Current Status

Repeat celiotomy can be lifesaving in horses with a surgically treatable postoperative obstruction, although guidelines for its use are lacking, except for uncontrollable postoperative pain. Overdiagnosis of ileus as the cause of postoperative obstruction could delay a second surgery so the disease progresses beyond a manageable level of severity. Although many horses respond favorably to repeat celiotomy, complications can be severe and life threatening, such as incisional infection and adhesions. Repeat celiotomy does not seem to exacerbate postoperative ileus, despite additional surgical manipulation. An important benefit of repeat celiotomy is termination of hopeless cases, thereby reducing cost and suffering.

Basic Postoperative Care of the Equine Colic Patient

The 3 time periods around colic surgery (preoperative, operative, and postoperative) are all critical to successful outcomes. Although much focus is often paid to the first 2 time periods, the importance of sound clinical judgment and rational decision-making in the postoperative period cannot be overstated. This article will outline the basic principles of monitoring, fluid therapy, antimicrobial therapy, analgesia, nutrition, and other therapeutics routinely used in patients following colic surgery. Discussions of the economics of colic surgery and expectations for normal return to function will also be included.

Oral Electrolyte and Water Supplementation in Horses

Horses that sweat for prolonged periods lose considerable amounts of water and electrolytes. Maintenance of hydration and prevention of dehydration requires that water and electrolytes are replaced. Dehydration is common in equine disciplines and can be avoided, thus promoting equine wellness, improved performance and enhanced horse and rider safety. Significant dehydration occurs through exercise or transport lasting one hour or more. Oral electrolyte supplementation is an effective strategy to replace water and electrolytes lost through sweating. The stomach and small intestine serve as a reservoir for uptake of water and electrolytes consumed 1 to 2 h prior to exercise and transport. The small intestine is the primary site of very rapid absorption of ions and water. Water and ions absorbed in the small intestine are taken up by muscles, and also transported via the blood to the skin where they serve to replace or augment the losses of water and ions in the body. Effective electrolyte supplements are designed to replace the proportions of ions lost through sweating; failure to do so can result in electrolyte imbalance. Adequate water must be consumed with electrolytes so as to maintain solution osmolality less than that of body fluids in order to promote gastric emptying and intestinal absorption. The electrolyte supplement should taste good, and horses should be trained to drink the solution voluntarily prior to and during transport, and prior to and after exercise.

Polyuria and Polydipsia in Horses

Polyuria and polydipsia are rare, but significant, manifestations of several different diseases of horses. Causes can be endocrine, iatrogenic, psychogenic, infectious, or toxic in nature and can also be due to primary renal disease or diseases of other organs, such as the liver. Although numerous causes of polyuria and polydipsia in horses exist, the most common conditions include chronic kidney disease, pituitary pars intermedia dysfunction, and psychogenic polydipsia with secondary polyuria. Additional testing is dictated by history, other clinical signs, and the results of blood work and/or urinalysis. Prognosis for horses with polyuria and/or polydipsia varies significantly based on the underlying cause.

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.

Effect of Feed Intake on Water Consumption in Horses: Relevance to Maintenance Fluid Therapy

Maintenance fluid therapy is challenging in horses that cannot drink or are denied feed and water because of concerns about gastrointestinal tract function and patency. Intravenous fluid delivery to meet water needs based on current recommendations for maintenance requirements were obtained in fed horses and therefore might not apply to horses that are not being fed. This is a critical flaw because of the interdependence between intestinal tract water and extracellular water to support digestion while preserving water balance, a concept explained by the enterosystemic cycle. Because horses drink less when they are not eating and hence have lower water needs than fed horses, maintenance water requirements need to be adjusted accordingly. This article reviews this topic and identifies benefits of adjusting maintenance fluid therapy to meet lower demands from gastrointestinal function, such as reduced volumes, lower cost, avoidance of overhydration.

Effect of feed deprivation on daily water consumption in healthy horses

BACKGROUND

Measurements of water consumed by fed healthy horses might not apply to horses that are unwilling or unable to drink or are not fed for any reason.

OBJECTIVE

To examine the effects of feed deprivation on voluntary water consumption compared with fed conditions.

STUDY DESIGN

In vivo experiment.

METHODS

Eight healthy adult Thoroughbred geldings were used in a randomised crossover design so that each horse served as its own control for fed vs feed-deprived conditions. Water intake, bodyweight, physical findings and vital signs were measured during 4 days of feeding and 4 days of feed deprivation. Daily measurements during the trial periods were PCV, TPP, electrolytes, osmolality and triglycerides. Plasma and extracellular fluid volumes were measured in the last 8 hours of the trial periods. Data were analysed with a two-way analysis of variance with repeated measures, and statistical significance was P ≤ .05.

RESULTS

Feed deprivation immediately and persistently reduced water consumption to ~16% of fed values, with laboratory evidence of mild dehydration on day 4.

MAIN LIMITATIONS

Changes in total body water and in water and electrolyte excretion or conservation through faeces and urine were not measured.

CONCLUSIONS

Feed consumption has a marked effect on water requirements in healthy horses. Because current guidelines for water needs were obtained in the fed state, they might not apply to horses that are denied feed for any reason or have reduced feed intake. This study provides new information on water consumption in horses that should apply to this essential nutrient in health and disease.

Prospective survey of veterinary practitioners' primary assessment of equine colic: clinical features, diagnoses, and treatment of 120 cases of large colon impaction

Background

Large colon impactions are a common cause of colic in the horse. There are no scientific reports on the clinical presentation, diagnostic tests and treatments used in first opinion practice for large colon impaction cases. The aim of this study was to describe the presentation, diagnostic approach and treatment at the primary assessment of horses with large colon impactions.

Methods

Data were collected prospectively from veterinary practitioners on the primary assessment of equine colic cases over a 12 month period. Inclusion criteria were a diagnosis of primary large colon impaction and positive findings on rectal examination. Data recorded for each case included history, signalment, clinical and diagnostic findings, treatment on primary assessment and final case outcome. Case outcomes were categorised into three groups: simple medical (resolved with single treatment), complicated medical (resolved with multiple medical treatments) and critical (required surgery, were euthanased or died). Univariable analysis using one-way ANOVA and Tukey’s post-hoc test, Kruskal Wallis with Dunn’s post-hoc test and Chi squared analysis were used to compare between different outcome categories.

Results

1032 colic cases were submitted by veterinary practitioners: 120 cases met the inclusion criteria for large colon impaction. Fifty three percent of cases were categorised as simple medical, 36.6% as complicated medical, and 9.2% as critical. Most cases (42.1%) occurred during the winter. Fifty nine percent of horses had had a recent change in management, 43% of horses were not ridden, and 12.5% had a recent / current musculoskeletal injury. Mean heart rate was 43bpm (range 26-88) and most cases showed mild signs of pain (67.5%) and reduced gut sounds (76%). Heart rate was significantly increased and gut sounds significantly decreased in critical compared to simple medical cases (p<0.05). Fifty different treatment combinations were used, with NSAIDs (93%) and oral fluids (71%) being administered most often.

Conclusions

Large colon impactions typically presented with mild signs of colic; heart rate and gut sounds were the most useful parameters to distinguish between simple and critical cases at the primary assessment. The findings of seasonal incidence and associated management factors are consistent with other studies. Veterinary practitioners currently use a wide range of different treatment combinations for large colon impactions.

Water intake, faecal output and intestinal motility in horses moved from pasture to a stabled management regime with controlled exercise

Reasons for performing study

A change in management from pasture to stabling is a risk factor for equine colic.

Objectives

To investigate the effect of a management change from pasture with no controlled exercise to stabling with light exercise on aspects of gastrointestinal function related to large colon impaction. The hypothesis was that drinking water intake, faecal output, faecal water content and large intestinal motility would be altered by a transition from a pastured to a stabled regime.

Study design

Within-subject management intervention trial involving changes in feeding and exercise using noninvasive techniques.

Methods

Seven normal horses were evaluated in a within-subjects study design. Horses were monitored while at pasture 24 h/day, and for 14 days following a transition to a stabling regime with light controlled exercise. Drinking water intake, faecal output and faecal dry matter were measured. Motility of the caecum, sternal flexure and left colon (contractions/min) were measured twice daily by transcutaneous ultrasound. Mean values were pooled for the pastured regime and used as a reference for comparison with stabled data (Days 1–14 post stabling) for multilevel statistical analysis.

Results

Drinking water intake was significantly increased (mean ± s.d. pasture 2.4 ± 1.8 vs. stabled 6.4 ± 0.6 l/100 kg bwt/day), total faecal output was significantly decreased (pasture 4.62 ± 1.69 vs. stabled 1.81 ± 0.5 kg/100 kg bwt/day) and faecal dry matter content was significantly increased (pasture 18.7 ± 2.28 vs. stabled 27.2 ± 1.93% DM/day) on all days post stabling compared with measurements taken at pasture (P<0.05). Motility was significantly decreased in all regions of the large colon collectively on Day 2 post stabling (-0.76 contractions/min), and in the left colon only on Day 4 (-0.62 contractions/min; P<0.05).

Conclusions

There were significant changes in large intestinal motility patterns and parameters relating to gastrointestinal water balance during a transition from pasture to stabled management, particularly during the first 5 days.