Application of the sodium dilution principle to calculate extracellular fluid volume changes in horses during dehydration and rehydration

Changes in electrolyte concentrations and hydration status in endurance horses following transport and an overnight stay prior to competition

OBJECTIVE

To evaluate changes in electrolyte concentrations and hydration status that take place in endurance horses prior to the start of a competition and determine whether these changes would be associated with elimination.

ANIMALS

19 horses entered in the 2016 Tevis Cup 100-Miles (160 km) One-Day Western States Trail Ride.

PROCEDURES

Heparinized blood samples were collected at 5 time points: prior to transport to the ride (T0), during check-in the day before the ride (T1), 1 to 2 hours before the start of the ride (T2), at the 15-km mark (T3), and at the 55-km mark (T4). Packed cell volume and plasma sodium, potassium, chloride, urea nitrogen, glucose, bicarbonate, and total protein concentrations were determined and compared across time points and between finishers and nonfinishers.

RESULTS

Signif icant differences were detected among plasma sodium, potassium, and urea nitrogen concentrations measured prior to the start of the ride (ie, T0, T1, and T2). For all variables except chloride and bicarbonate concentrations, significant differences were detected between values obtained prior to the start of the ride and values obtained during the ride (ie, T3 and T4). Only bicarbonate concentration at the 15-km mark of the ride was significantly associated with finishing status.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that significant changes in plasma sodium, potassium, and urea nitrogen concentrations can occur in endurance horses during transport to a competition and when horses are stabled overnight before an event. Additionally, a lower bicarbonate concentration following a steep climb early during the ride was associated with subsequent elimination.

Determining dehydration and its compartmentation in horses at rest and with exercise: a concise review and focus on multi-frequency bioelectrical impedance analysis

Multi-frequency bioelectrical impedance analysis (MFBIA) has been, and likely will increasingly be, used to rapidly and non-invasively assess the time course of volume losses and recovery in horses. Dehydration in performance horses is frequently the cause of health and performance problems, and presently used techniques for objectively quantifying optimum hydration are time consuming and challenging to perform accurately. Dehydration can take a number of different forms, with a balanced loss of water and electrolytes from both extra- and intracellular fluid compartments, or a primarily extracellular or intracellular dehydration. This review summarises the current state of knowledge regarding the quantification of dehydration, losses of water and electrolytes from extra- and intracellular fluid compartments. The effects of dehydration on exercise performance, muscle function, cardiovascular function, thermoregulation and feeding are briefly summarised. The review provides a quantitative description of the magnitude and time course of compartmental fluid losses and recovery in horses in response to feeding and due to exercise at different intensities and durations representing the endurance horse to the track race horse. Effective rehydration requires knowledge of the losses from the main body fluid compartments, which is now possible using MFBIA technology. The present review outlines the key approaches that have been used to assess dehydration in horses, including the new technique of MFBIA.

Systemic, renal, and colonic effects of intravenous and enteral rehydration in horses

BACKGROUND

Intravenous (IV) and intragastric (IG) administration of fluid therapy are commonly used in equine practice, but there are limited data on the systemic, renal, and enteric effects.

HYPOTHESIS

IV fluid administration will increase intestinal and fecal hydration in a rate-dependent manner after hypertonic dehydration, but will be associated with significant urinary water and electrolyte loss. Equivalent volumes of IG plain water will result in comparatively greater intestinal hydration with less renal loss.

ANIMALS

Six Thoroughbred geldings.

METHODS

Experimental study. 6 by 6 Latin square design investigating constant rate IV administration at 50, 100, and 150 mL/kg/d over 24 hours in horses dehydrated by water deprivation. Equivalent volumes of IG plain water were administered by 4 bolus doses over 24 hours.

RESULTS

Water deprivation resulted in a significant decrease in the percentage of fecal water, and increases in serum and urine osmolality. IV fluids administered at 100 and 150 mL/kg/d restored fecal hydration, but increasing the rate from 100 to 150 mL/kg/d did not confer any additional intestinal benefit, but did result in significantly greater urine production and sodium loss. Equivalent 24-hour volumes of plain water resulted in greater intestinal water and less urine output.

CONCLUSIONS AND CLINICAL IMPORTANCE

IV polyionic isotonic fluids can be used to hydrate intestinal contents in situations where enteral fluids are impractical. IV fluids administered at three times maintenance are no more efficacious and might be associated with adverse physiological findings after withdrawal. Bolus dosing of IG water can be used to restore intestinal water with minimal adverse effects.

Alkalinizing effect of NaHCO₃ with and without glucose when administered orally to euhydrated neonatal dairy calves

The use of oral rehydration solutions (ORS) is well established as an effective treatment to correct water-, electrolyte-, and acid-base balance in diarrheic calves. The main ingredients of a commercial ORS are Na, glucose, and alkalinizing agents, such as NaHCO3. Particular importance is attributed to the combination of glucose and Na at a specific ratio to optimize intestinal sodium, and thereby water uptake, through the sodium-glucose co-transport. Enhancing intestinal Na absorption by combining glucose and Na in an ORS has the potential to improve the alkalinizing effect of an ORS according the strong ion theory. The objective of this study was to investigate the effect of glucose on the alkalinizing effect of NaHCO3 when administered orally. Nine healthy neonatal Holstein-Friesian calves underwent 3 oral treatments with 2-L solutions of NaHCO3 (150 mmol/L), glucose (300 mmol/L), and glucose + NaHCO3 (300 mmol/L + 150 mmol/L, respectively) in randomized order. Arterial and venous blood was obtained before treatment and in 30-min intervals thereafter for blood gas analysis and determination of plasma protein and electrolyte concentrations. Urine was collected volumetrically to determine urine volume, osmolality, pH, net acid excretion, and renal Na excretion after treatment. Plasma volume changes were extrapolated from plasma protein concentration changes. Treatment and time effects were tested with repeated measures ANOVA. Only subtle differences between oral administration of NaHCO3, with and without glucose, were observed for the change of the standard HCO3 concentration relative to baseline. No differences in plasma Na, plasma volume expansion, renal Na, net base excretion, urine volume, or pH could be identified between animals treated orally with NaHCO3 with and without glucose. Similarly, no differences in blood glucose concentration, plasma volume expansion, urine volume, or renal glucose excretion were observed in the 8h after treatment when comparing oral glucose treatment with and without NaHCO3. Our results indicate that combination of NaHCO3 with glucose in a hypertonic ORS only had a minor effect on the alkalinizing effect of NaHCO3, which is unlikely to be of clinical relevance. The combination of NaHCO3 and glucose neither improved Na, glucose, nor water absorption in euhydrated neonatal dairy calves, questioning the relevance of a specific ratio between Na and glucose in ORS for calves.

Clinical, hematologic, and electrolyte changes with 0.9% sodium chloride or acetated fluids in endurance horses

OBJECTIVE

To describe the clinical and laboratory changes associated with the use of IV0.9% sodium chloride and a commercially available acetated fluid (CAF) to treat endurance horses requiring emergency medical treatment.

DESIGN

Randomized, controlled clinical trial from 2007 to 2010.

SETTING

Emergency treatment centers of the Western States 100-mile (220 km) endurance ride.

ANIMALS

Twelve horses requiring emergency medical treatment in the form of IVfluids completed the study.

INTERVENTIONS

Horses were assigned to either the 0.9% sodium chloride group (6 horses) or CAF group (6 horses) and received a total of 20 L of fluid. Clinical, hematologic, and electrolyte data were collected prior to and during fluid therapy.

MEASUREMENTS AND MAIN RESULTS

As compared to results prior to fluid therapy, horses treated with 0.9% sodium chloride had a decrease in heart rate (P < 0.01), PCV (P < 0.001), total plasma protein (TPP) (P < 0.001), and the sodium-chloride difference (P < 0.05). These horses also had an increase in plasma chloride (P < 0.01) and sodium (P < 0.01) concentrations. Horses treated with CAF showed a decrease in PCV (P < 0.01) and TPP (P < 0.001).

CONCLUSIONS

These findings should aid in the design a larger clinical trial to provide further clarification on the effects of type of fluid therapy on clinical and biochemical parameters in endurance horses. The use of 0.9% sodium chloride may not be ideal for the emergency management of endurance horses as it was associated with an increase in plasma chloride concentration.

A comparison of hypertonic (7.2%) and isotonic (0.9%) saline for fluid resuscitation in horses: a randomized, double-blinded, clinical trial

BACKGROUND

Hypertonic saline solution (7.2%) (HSS) can quickly replace intravascular volume deficits. HSS more recently has been advocated in the treatment of traumatic brain injury, but its use in dehydrated patients remains controversial.

HYPOTHESIS

Hypertonic saline solution will show a significant improvement in both clinical and laboratory hydration parameters as compared to isotonic (0.9%) saline solution (ISS).

ANIMALS

Endurance horses eliminated from the 2009 Western States 100-mile (220-km) endurance ride and requiring IV fluid therapy were eligible for enrollment in the study.

METHODS

Twenty-two horses were randomly assigned to receive 4 mL/kg of either HSS or ISS along with 5 L lactated Ringer's solution (LRS). After this bolus, horses were treated with additional LRS in varying amounts. Blood and urine samples were collected before, during, and after treatment. Data were compared using 2-way ANOVA with repeated measures.

RESULTS

As compared to ISS, HSS horses showed greater decreases in PCV (P = .04), total protein (P = .01), albumin (P = .01), and globulin (P = .02) concentrations. HSS horses showed greater increases in sodium and chloride (P < .001) as compared to ISS horses. Horses receiving HSS had a shorter time to urination (P = .03) and lower specific gravity (P < .001) than those receiving ISS.

CONCLUSIONS

Results of this study indicate that HSS may provide faster restoration of intravascular volume deficits than ISS in endurance horses receiving emergency medical treatment. More marked electrolyte changes should be expected with HSS, however, and additional fluids after HSS administration likely are needed.