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Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • Fluid therapy consists of oral or IV fluids administered for treatment of shock, fluid replacement, or fluid maintenance
  • This chapter will focus on IV fluid therapy in the foal, although in less debilitated foals fluid requirements should be supplied by nursing or enteral feeding of mare's milk

Pathophysiology!!navigator!!

  • Neonates distribute fluids to the interstitial space rapidly owing to a high capillary filtration coefficient. Because of this filtration as well as immature renal function, neonates do not handle large fluid volumes as well as adults. Sepsis and hypoxia may exacerbate leakage of fluids into the interstitial space
  • Neonatal foals have low urinary fractional excretion of sodium, and this normal physiologic sodium conservation is well suited to the low-sodium milk diet. However, the sodium in isotonic IV fluids will lead to sodium overload and retention of free water
  • Hypovolemia—a decrease in circulating blood volume will lead to decreased perfusion of tissues. If perfusion impairment is severe or prolonged, organ failure may result

Systems Affected!!navigator!!

  • Cardiovascular—hypovolemia can reduce cardiac output, ejection fraction, and end-organ tissue perfusion
  • Renal/urologic—hypovolemia and poor systemic perfusion will decrease renal blood flow and renal perfusion, leading to azotemia, and, if the insult is severe enough, acute kidney injury
  • GI—poor perfusion can result in loss of mucosal barrier function and secondary bacterial translocation

Genetics!!navigator!!

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Incidence/Prevalence!!navigator!!

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Geographic Distribution!!navigator!!

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Signalment!!navigator!!

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Signs!!navigator!!

Historical Findings

  • Decreased nursing or lack of nursing for 4 h or longer. Mare will have a full udder and may be streaming milk
  • Fluid losses though diarrhea or third-spacing in the intestinal tract or abdomen

Physical Examination Findings

  • Signs of dehydration include prolonged skin tent, sunken eyes, tacky mucous membranes, increased urine specific gravity, hypercreatinemia, and prolonged capillary refill time
  • Signs of hypovolemia include tachycardia, cold extremities, decreased urine production, depressed mentation, and poor pulse pressure

Causes!!navigator!!

Indications for Fluid Therapy

  • Correct dehydration
  • Increase perfusion, treat hypovolemia
  • Sepsis/septic shock
  • Diarrhea or other GI fluid losses
  • GI disease preventing enteral intake
  • Volume replacement after acute blood loss (e.g. umbilical bleeding)

Risk Factors!!navigator!!

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Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

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CBC/Biochemistry/Urinalysis!!navigator!!

  • Hemoconcentration (elevated packed cell volume and TP) is common with dehydration
  • Elevated blood lactate concentration may indicate poor perfusion or tissue hypoxia
  • Urine specific gravity in normal foals is usually <1.008. Urine concentration will increase with dehydration and hypovolemia, provided renal function is normal

Other Laboratory Tests!!navigator!!

Immunoglobulin G should be checked in the neonatal foal—if plasma transfusion is required, this will need to be accounted for in the fluid therapy plan.

Imaging!!navigator!!

Vessel appearance on thoracic radiographs, ultrasonographic imaging of the size of the right atrium and ventricle.

Other Diagnostic Procedures!!navigator!!

  • Central venous pressure
  • Blood pressure
  • Urine output measurements
  • Cardiac output

Pathologic Findings!!navigator!!

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Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

Replacement Fluids

  • Boluses up to 80 mL/kg crystalloid fluid may be needed for treatment of shock. Fluids can be administered as boluses of 10–20 mL/kg (0.5–1 L in a 50 kg foal), with reassessment after each bolus. A foal that has received 60–80 mL/kg fluid boluses and is persistently hypotensive should receive vasopressor/catecholamine therapy
  • Rehydration—volume needed can be estimated by the formula (% dehydration × weight (kg))

Maintenance Fluids

  • Fluids with lower sodium and higher potassium than that of plasma (e.g. Plasma-Lyte 56) are more appropriate for maintenance requirements. Half-strength saline (0.45% NaCl) with dextrose (2.5%) can be used as well
  • Daily requirements for maintenance fluid administration can be calculated using the Holliday–Segar formula:
    • 100 mg/kg/day for the first 10 kg body weight
    • 50 mL/kg for the second 10 kg body weight, and
    • 25 mL/kg for body weight above 20 kg
    • A 50 kg foal would therefore require 2250 mL/day. The use of this formula results in substantially lower volume delivered than with a more traditional estimate of 60–80 mL/kg/day
  • Fluids can be administered as a constant rate infusion or as boluses given every 1–4 h
  • Additional fluid losses (diarrhea, reflux) should also be considered when determining fluid rates
  • Enteral and parenteral nutrition should be considered—increasing volumes of nutrition will lower the IV fluid requirements

Appropriate Health Care!!navigator!!

IV fluids are generally administered as inpatient medical management. Foals with severe systemic disease or hypovolemic shock will require emergency inpatient intensive care management.

Nursing Care!!navigator!!

IV catheter care—over-the-wire flexible polyurethane 14- or 16-gauge catheters placed in sterile fashion are preferred for long-term fluid and medication administration. Over-the-needle catheters can be placed for emergency administration of fluids.

Activity!!navigator!!

Foals requiring IV fluids must be restricted to a stall or small pen in order to maintain the IV catheter and deliver fluids. Foals may need to be separated from the mare (by a divider or in a pen) if they are receiving continuous IV fluids.

Diet!!navigator!!

See chapter Nutrition in foals.

Client Education!!navigator!!

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Surgical Considerations!!navigator!!

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Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

IV Fluids

  • Crystalloids
    • Lactated Ringer's, 0.9% saline, Plasma-Lyte 148, and Normosol-R are isotonic crystalloid solutions that can be used for fluid replacement. Normal saline is acidifying due to the high chloride concentration (154 mEq/L), and is generally preferred only if a potassium-free crystalloid is needed for resuscitation (as with uroperitoneum)
    • Plasma-Lyte 56 and Normosol-M are crystalloid maintenance solutions that are more appropriate for long-term fluid therapy. These solutions may not be readily available, but maintenance solutions low in sodium (40–80 mEq/L) and high in potassium (13 mEq/L) can be made using 0.45% saline or a combination with 2.5% dextrose in water with potassium supplementation
  • Colloids
    • Hetastarch 6% (3–10 mL/kg) is an example of a synthetic colloid that will remain in the vasculature for a longer period of time due to the large molecule size. There is no evidence of superiority of colloid fluids for resuscitation, but colloids are indicated when colloid oncotic pressure is low and volume resuscitation is needed
  • Plasma
    • Plasma is a natural colloid and is the most commonly used colloid in neonatal foals due to the frequent need for immunoglobulin supplementation
  • Whole blood
    • It should not be a first-line fluid for resuscitation unless hemorrhagic shock is present

Fluid Supplementation

  • Glucose—start with a rate of 4–8 mg/kg/min (in a 50 kg foal, ≈250 mL/h of a 5% dextrose solution) if enteral or parenteral feedings have not been initiated. Dextrose solution should not exceed 10%. Blood glucose should ideally be <150 mg/dL and >80 mg/dL. If hyperglycemia persists, treatment with insulin may be needed
  • Potassium—supplementation of a maintenance fluid may range from 10 to 40 mEq/L. The rate of potassium administration should not exceed 0.5 mEq/kg/h
  • Bicarbonate—should not be used routinely to correct metabolic acidosis since lactic acidosis may resolve readily with fluid resuscitation. If pH < 7.2 or there is significant loss of bicarbonate, a combination of IV and oral supplementation may be needed. Formula for bicarbonate supplementation: base deficit × 0.3 × body weight (kg), with half the calculated amount given initially, then blood gas reassessed
  • Calcium and magnesium supplementation should be guided by ionized values. Systemic inflammatory response syndrome appears to produce hypocalcemia and hypomagnesemia; therefore, septic neonates may require supplementation

Contraindications!!navigator!!

  • Hypertonic saline is generally not recommended for use in neonatal foals, since it causes rapid changes in osmolarity and foals have less ability to handle large sodium loads resulting in fluid retention and a hyperchloremic metabolic acidosis
  • Bicarbonate is contraindicated with hypoventilation/abnormal respiratory function because the CO2 produced cannot be eliminated

Precautions!!navigator!!

Hetastarch can prolong clotting times at doses ≥20 mL/kg. Once Hetastarch has been administered, TP is no longer a good estimate of oncotic pressure, so colloid oncotic pressure should be directly measured with a colloid osmometer.

Possible Interactions!!navigator!!

Bicarbonate- and calcium-containing solutions are incompatible.

Alternative Drugs!!navigator!!

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Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Volume and perfusion status—monitor for improvement in mentation, return of peripheral pulse and warmer extremities, urine production, and improvement in mucous membrane color and capillary refill time. Monitor blood work every 4–24 h, and adjust fluid composition and rate accordingly
  • Catheter complications—examine IV catheter site at least daily for any heat, swelling, pain, discharge, phlebitis, or kinking/pulling out of the catheter
  • Body weight every 24 h to estimate fluid balance and adequate nutrition

Prevention/Avoidance!!navigator!!

Frequent nursing is imperative for maintenance of normal hydration in neonatal foals. Any foal that has not been seen to nurse during a period of 4 h is at high risk of dehydration. Careful monitoring of nursing behavior and fluid losses (e.g. diarrhea) may help to prevent life-threatening hypovolemia.

Possible Complications!!navigator!!

  • Fluid overload
  • Hypernatremia
  • Thrombophlebitis

Expected Course and Prognosis!!navigator!!

  • Foals with uncomplicated dehydration should respond rapidly to fluid therapy, although they may require continued fluid replacement if there are ongoing fluid losses or reduced intake
  • Prognosis depends on the underlying disease

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Age-Related Factors!!navigator!!

Neonatal foals (<2 weeks old) have a large interstitial fluid reserve and altered handling of sodium loads compared with adults.

Zoonotic Potential!!navigator!!

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Pregnancy/Fertility/Breeding!!navigator!!

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Synonyms!!navigator!!

  • Rehydration
  • Fluid resuscitation

Abbreviations!!navigator!!

TP = total protein

Suggested Reading ⬆ ⬇

Buchanan BR, Sommardahl CS, Rohrback BW, Andrews FM. Effect of a 24-hour infusion of an isotonic replacement fluid on the renal clearance of electrolytes in healthy neonatal foals. J Am Vet Med Assoc 2005;227:1123–1129.

Magdesian GE. Fluid therapy for neonatal foals. In: Fielding CL, Magdesian GE, eds. Equine Fluid Therapy. Ames, IA: Wiley Blackwell, 2014:279–298.

Palmer JE. Fluid therapy in the neonate: not your mother's fluid space. Vet Clin North Am Equine Pract 2004;20:63–75.

Author(s) ⬆

Author: Eric L. Schroeder

Consulting Editor: Margaret C. Mudge

Acknowledgment: The author acknowledges the prior contribution of Margaret C. Mudge.