Update on fluid therapy in horses (Proceedings)

Fluid Plans

     •Replacement: Determining Rate

     • New : 'Fluid Challenge' Method:

     • Volumes are based on "fluid challenges" rather 'estimates' of deficits

     • Traditional method is with estimates of % of water loss

          o Riddled with errors....

"Fluid Challenge Method"

     • 20 mL/kg boluses of isotonic crystalloid over 30-60 minutes, then reassess for more

          o Repeat boluses until signs of shock abate or plateau, or until limits reached, indicating the need for vasopressors

          o 10 L for an average adult horse

          o 1 L for average neonatal foal

Fluid Challenge for Colloids

     • Lower rates because they stay within the vascular space

          o 3-10 mL/kg hetastarch

How much to give?

Base it on Clinical response

     • Mentation

          o Increase alertness

          o Foal that is kicking is rarely severely hypovolemic

     • Urination

          o In general, sufficient fluids have been given when the horse/foal begins to pass urine

     • Decrease heart rate

     • Improvement in membrane color or capillary refill

     • In hospital= blood pressure (> 60 mmHg in foal, 80 in adult)

Crystalloids vs. Colloids?

     • Crystalloids only contain electrolytes or glucose in water

     • Colloids contain large MW particles

          o Proteins or synthetic polysaccharides

     • Human studies fail to show an advantage of 1 over the other

          o Use together may be ideal

     • Isotonic crystalloids hydrate entire ECF

          o 25 % to plasma volume; 75 % to interstitium

     • Colloids expand the intravascular space only

     • Rapid expansion of plasma volume

     • Large particles stay within vessels

     • Colloids are better in horses concurrently hypovolemic and hypooncotic

Replacement Crystalloids

     • Choices:

          o Lactated Ringer's Solution (LRS)

          o Normosol-R

          o Plasma-Lyte 148 or A

          o Normal saline (0.9%)

Isotonic Crystalloids

LRS

     • Contains calcium

          o Not ideal when using blood products, sodium bicarbonate

     • Contains lactate

     • Contains potassium (4 mEq/L)

     • Chloride is relatively high (109 mEq/L) relative to sodium (130)

          o Na-Cl difference is 21 (ref: 40) – making this acidifying

     • Clinical Uses:

          o Botulism

          o Endurance horses

     • Do not use in:

          o Oleander cases

          o Not ideal in liver failure cases

Isotonic Crystalloids

Normosol R / PlasmaLyte 148 / PlasmaLyte A

     • Contain magnesium (3 mEq/L)– no calcium

     • Contain acetate/gluconate – no lactate

     • Contain potassium (5 mEq/L)

     • Sodium-chloride difference is optimal

          o Na=140

          o Cl=98

     • Can use with HCO3 or PO4 or blood products

     • Clinical Uses:

          o Oleander and arrhythmia cases

          o Brain injury cases

          o Liver failure cases

     • Do not use:

          o Botulism cases

Isotonic Crystalloids

Physiologic saline (0.9 %)

     • Contains only sodium and chloride

     • Compatible with blood products, sodium bicarbonate

     • No potassium

     • Increases chloride concentration relative to sodium concentrations in equine plasma

          o Mildly acidifying due to relative increase in chloride

Equine Plasma      Saline

Na = 130-140 mEq/L      154 mEq/L

Cl = 90-100 mEq/L      154 mEq/L

Normal Saline

Clinical Uses:

     • Do not use in acidemic cases

     • Not optimal fluid for most cases, although can be used

     • Good where potassium is not desirable

          o HYPP

          o Ruptured bladder

     • Good for hypochloremic cases with alkalosis

          o Some rhabdomyolysis cases

          o Endurance horses not heavily supplemented

Colloids

Solutions containing large molecular weight (> 5000 Da) proteins or polysaccharides

Colloid Choices

     • Natural colloids

          o Plasma

          o Whole blood

     • Synthetic colloids

          o Hetastarch

          o Dextrans

Indications for Colloids

Hypovolemia with concurrent hypoproteinemia

     • Examples:

          o Colitis

          o Lawsonia foals

     • Crystalloids distribute among the entire ECF potentiating edema

     • Colloids are restricted to the intravascular space, (assuming endothelial integrity)

          o Less likely to cause edema

Hetastarch

     • Large molecular weight synthetic pss in solution

     • May have advantages over plasma during endotoxemia or sepsis with endothelial compromise

          o Fraction with MW > 100,000 may be retained within vessels

          o Smaller fractions and albumin may extravasate

     • More cost effective than plasma on a per unit oncotic pressure basis

Hetastarch - Adverse Effects

Dose-dependent hemostatic alterations

     • Induces a von Willebrand like state

          o Prolongation of PT and PTT

     • Coats platelet surface

          o Alters platelet function

     • May not want to use in pre-surgical case

     • Don't use in bleeding cases

Hetastarch Doses

Suggested doses

     • 10 mL/kg/day

          o Safe, but do not exceed

Plasma

     • Great colloid for foals

     • Has antibodies for FPT, R. equi, other diseases

     • Has clotting factors, antithrombin

     • 40 ml/kg for foals whenever possible for FPT

          o (2 L for average sized foal)

     • Adult horses 2-3 L

Hypertonic Saline (7 %)

     • Sodium: 1200 mEq/L

     • Chloride: 1200 mEq/L

     • Dose: Small volumes = 4 mL/kg

     • Rapid, transient plasma volume expansion

          o Borrows' water temporarily – increases blood volume and CO transiently

          o Shifts water from interstitium and ICF until osmolarity equilibrates

Advantages

     • Other potential advantages:

          o Improvement in cardiac contractility (CO)

          o Antiinflammatory

          o Reduces endothelial and RBC edema Reduces neutrophil activation and endothelial adhesion

          o Neurologic – reduces glutamate release, decreases intracellular calcium accumulation

Potential Adverse Effects of HS

     • Potential adverse effects:

          o Hypernatremia and hyperosmolarity

Contraindications

     • Severe dehydration (8-10 %) – no water to borrow

          o Provide initial isotonic fluids, then follow with HS

     • Judicious use in the neonatal foal

     • Uncontrolled hemorrhage – may cause more bleeding

Additives

     • Potassium

     • Calcium

     • Magnesium

     • Phosphorus

Potassium

     • Hypokalemia most common

          o Anorexia

          o Diuresis

          o Stress (excess corticosteroids and aldosterone)

          o Loss in diarrhea

Treat

     • Empiric supplementation:

          o If K < 2.7 add 40 mEq/L KCl or KPO4

          o If K 2.8-3.3 add 20 mEq/L KCl or KPO4

          o If K 3.4-3.5 add 10 mEq/L KCL or KPO4

          o Maximum: 0.5 mEq/kg/h

Hypokalemia

     • Oral supplementation:

          o g/kg KCl per day, divided into 4 treatments per day

     • If hypokalemia is refactory to treatment:

          o Supplement with magnesium

3 mEq/L MgSO4

Calcium

     • Ionized Hypocalcemia

          o Anorexia

          o Loss in sweat (endurance horse)

          o Parathyroid dysregulation (endotoxemia, SIRS)

     • Treat: < 1.1 mmol/L (4.4 g/dL)

     • Treat: 0.5-1 mEq/kg 23% calcium gluconate

          o Slow, dilute

          o If refractory: supplement with magnesium

Magnesium

     • Hypomagnesemia

          o Anorexia

          o GI disease, ileus

          o Diuresis – most fluids are devoid of Mg

          o Excessive sweating

          o Treat: 3 mEq/L (up to 10 mEq/L)

          o Normosol and PlasmaLyte contain this amount

          o Provides 3 mEq/L, or 30 mg/dL of MgCl2

          o If clinical signs present: 8-32 mg/kg, not to exceed 50 mg/kg at 2 mg/kg/min

Phosphorus

     • Not routinely supplemented unless hypophosphatemic or anorexic for > 1-2 d

          o mmol/kg/h of sodium (or potassium) phosphate, administered for 8-24 h per day as needed

          o Requirement: 28 mg/kg orally

     › 35 % absorption efficiency:

     › Translates to 10 mg/kg/d IV requirement

     › 0.013 mmol/kg/h