1 Fluid Therapy: Water Distribution and Fluid Choices

• Fluid therapy involves understanding water distribution in the body.
• Fluid therapy requires calculating fluid deficits and understanding electrolyte and acid-base abnormalities.
• Selection of appropriate fluid choices are required for fluid therapy.
• Fluid therapy requires the ability to calculate HCO3 and K+ deficits.

Fluid Choices

• When selecting fluid types, memorization of specific numbers is not necessary.
• Acidifying or alkalinizing properties should be considered when selecting fluid types.
• Sodium chloride richness should be considered when selecting fluid types.
• 0.9% NaCl is considered sodium chloride rich.
• 0.45% NaCl is considered sodium chloride poor.

Total Body Water

• Total body water (TBW) accounts for 60% of body weight (BW).
• Intracellular fluid (ICF) makes up 40% of BW and 66% of TBW.
• Extracellular fluid (ECF) makes up 20% of BW and 33% of TBW.
• Interstitial volume accounts for 12% of BW and 60% of ECF.
• Blood volume accounts for 8% of BW and 40% of ECF.

Fluid Deficits

• Volume needed can be calculated as % dehydration + maintenance + ongoing losses.
• Dehydration is the loss of total body water.
• Hypovolemia is a decrease in circulatory (blood) volume.
• An animal can be dehydrated without being hypovolemic.
• Animals can pull water from the interstitial space to maintain circulatory volume.

Assessing Hydration

• Mild dehydration, less than 5%, may not be clinically appreciable.
• Clinical findings of dehydration include tachycardia, reduced jugular fill, cold extremities, tacky mucous membranes, and sunken eyes.
• Reduction in body weight during hospitalization is a helpful indicator of hydration status.

Laboratory Estimates of Dehydration

• PCV/TP should be assessed when looking at dehydration.
• Splenic contraction or anemia can affect PCV/TP.
• Protein loss (GI, renal, or third spacing) impacts dehydration.
• High globulin with chronic disease affect dehydration.
• Creatinine levels can be used, however it is only valid when renal function is normal.

Laboratory Findings in Dehydration

• Urine specific gravity is very sensitive for dehydration if renal function is normal.
• Adult horses typically have a USG >1.030 when dehydrated.
• Young foals typically have a USG > 1.005 when dehydrated.
• Increased blood lactate, greater than 2.0, can indicate dehydration.
• Lactate increases with anaerobic metabolism, which can be caused by anemia or pneumonia (hypoxemia/hypoxia).
• Hypovolemia and dehydration lead to poor perfusion and reduced oxygen delivery, increasing lactate.

Estimating Dehydration

• You will need to make an estimate and constantly reassess hydration.
• Estimate that a 6% dehydrated animal will have a HR of 40-60, CRT of 2, PCV/TP of 40/7, and Creatinine of 1.5-2.0
• Estimate that an 8% dehydrated animal will have a HR of 60-80, CRT of 3, PCV/TP of 45/7.5, and Creatinine of 2.0-3.0
• Estimate that a 10% dehydrated animal will have a HR of 80-100, CRT of 4, PCV/TP of 50/8, and Creatinine of 3.0-4.0
• Estimate that a 12% dehydrated animal will have a HR of > 100, CRT of > 4, PCV/TP of > 50/8, and Creatinine of > 4.0

Maintenance Fluid Rates

• A horse requires about 60 ml/kg/day for maintenance.
• For a 450 kg horse, maintenance is about 27 L per day.
• Fluids typically come in bags of 5 L.
• Approximately 2.5 ml/kg/hr is another maintenance fluid rate.
• In a 450 kg horse, the maintenance fluid rate equals 1,125 ml/hr, or 1 L/hr.
• Catheters can be positional.
• Neonatal foals require a higher maintenance fluid rate than adult horses.
• Neonatal foals require approximately 80-120 ml/kg/day in fluids due to higher total body water.

Ongoing Losses

• Ongoing losses that need to be accounted for include nasogastric reflux, diarrhea, third spacing, and hemorrhage.
• Nasogastric reflux from post-op colic or anterior enteritis is relatively easy to measure.
• Diarrhea can be harder to measure.

Routes of Fluid Administration

• IV administration is necessary for severe dehydration, refluxing horses, or when administering large volumes.
• Oral administration via NG tube is the least expensive route and is suitable for large colon impactions, but not with refluxing horses.
• Subcutaneous fluid administration is not typically used.

Example Case - QH Mare

• 18 year old QH mare presented at 8 AM.
• The mare weighs 500 kg.
• The presenting complaint was a 3 day history of anorexia & colic.
• The horses temperature was 102 F and her heart rate was 80 bpm.
• The mare had small intestinal distention and no NG reflux.
• Further Bloodwork results include: PCV = 50%, TP = 8.0 g/dl and Creatinine = 3.0 mg/dl, USG > 1.035.
• The horse had a WBC = 1,600 cells/ul with neutropenia and elevated AG and lactate.
• The problem list included that the horse was 10% dehydrated, colic, fever, leukopenia, and azotemia.
• Differential diagnoses included anterior enteritis and prerenal azotemia.
• A 500 kg horse is dehydrated, and is greater than mild dehydration (< 5%), approximately 10% or 50 L.
• The horse is also hypovolemic
• Maintenance fluids = 30 L over 24 hours.
• 60 ml/kg/day * 500 kg = 30 L.
• Total fluids = 50 + 30 or 80 Liters in 24 hrs with constant reassessment.
• If giving 80 L in 24 hrs, the rate of fluids should be 3.3 L/hr or 10-20 ml/kg as a bolus.
• The shock dose is 60-80 ml/kg/hr = 24-32 L in 1 hr but is now used anymore.
• You then reassess the patient and can add rest of fluids over 24 hrs
• After giving 10 L at admission the total to give is 80 L.
• Seeing clinical improvement the, 80 L-10 L = 70 L left to give.
• Plan on 70 L over 24 hours or 3 L/hr.
• This is a goal of 14 of the 5 L bags in 24 hrs.
• If after treatment the horse has an HR = 52, PCV = 39%, TP = 5.3 g/dl, and Creatinine = 1.8 mg/dl and is still refluxing 70 L in 24 hrs the volume needed over 24 hrs is 30 L + 70 L or 90-100 L per day.

Example Case - Mini Stallion

• 11 year old Mini stallion weighing 100 kg presented with a 2 day history of colic and anorexia.
• The pony’s temperature was 100 F (normal 100-101 F) and his HR = 44 bpm (normal) and RR = 20 bpm (normal).
• The pony had mild colic and were GIT- decreased.
• Blood work: PCV = 38 %; TP = 5.4 g/dl, Albumin = 2.4 gm/dl, and Creatinine = 1.8 mg/dl.
• The pony had no clinical signs but with impaction the blood work showed that his TP and albumin was low causing a mile dehydration.
• The stallion is not hypovolemic and will be treated with "2x maintenance" or 12 L/day.
• Treating mild dehydration is the goal with impaction- with over-hydration which will get fluid into impaction.

Approach to Fluid Therapy

• The approach is typically the same for the clinical Case.
• Determine the estimated % dehydration
• Determine maintenance needs.
• Account for any ongoing losses
• Calculate the rate of fluid administration.
• Continually Reassess the patient

Considerations

• The pony can be give intravenous or oral fluids.
• Oral or IV routes (colon impaction) should work depending on the ability to administer.
• 12 L will be given in 24 hours total.
• Goal 12 L in 24 hours: Giving 6 L oral and 6 L IV.
• Oral fluids are Least Expensive given via NG tube every 4 hrs
• Typically, 4 L q 30-60 minutes is given to a 450 kg horse.
• For 100 kg ~ so gave less (1 L).
• Oral fluids can be administered as a Continuous Rate Infusion, and are Not typically indicated for large volumes, animals in shock.
• Oral is a valid route for Mild Dehydration not hypovolemia. Oral is better for impactions and Cost issues.
• However, Oral fluids would not work in a Anterior enteritis horse.

Fluid Types

• Types of Fluids to Give depends on Crystalloids (several).
• Choice dependent on: Replacement (treating dehydration), Maintenance, and Electrolyte & Acid-Base.
• Lactated Ringers Solution: Alkalinizing, mOsm/L: 273, Na: 130 mEq/L, Cl: 109 mEq/L, K 4 mEq/L, Ca: 3 mEq/L and Lactate anion metabolized to HCO3 in liver
• 0.9% NaCL: Acidifying mOsm/L 308, Na 154 mEq/L and CI 154 mEq/L
• Plasmalyte A- Alkalinizing, mOsm/L 298 Na 140 mEq/L Cl: 98 mEq/L, K 5 mEq/L, Mg 3 mEq/L and Acetate: anion metabolized to HCO3 in plasma
• 0.45% NaCl- Acidifying, BUT HYPOTONIC Can add 2.5% dextrose to make isotonic and Used in some patients that develop hypernatremia on IV fluids (foals)
• 5% dextrose: Isotonic, but only dextrose
• 5% or 8.4% NaHCO3: Commercially available but very hypertonic, We dilute to 1.3% (isotonic)
• Hypertonic saline: Will use in select situations
• Lactic Acidosis is Common in dehydrated animals/poor perfusion, however you will still use LRS in these patients provided no liver failure.

Approach to Lactic Acidosis

• Rehydrate and reassess as the initial approach.
• If it is No longer dehydrated and metabolic acidosis we will give NaHCO3

Fluid Therapy in Foals (Hope)

• This 48 hr QH filly with Diarrhea of 24 hrs duration that is Anorexic, weak, and depressed that weighs 50 kg could be a case in the decision making process.
• The foal could present as Recumbent, weak, Temp 100 F, HR 150 bpm, with Bloody Diarrhea, Sunken eyes, and No urine production.
• A foal that is Dehydrated 10% (50 kg x.1 = 5 L) should Give 20ml/kg or 1 L LRS over 2 hrs, and then Waiting on blood

Fluid Volume

• Provide Further correction of dehydration (4.0 L) with Maintenance fluids: Foals have higher TBW
• 100 ml/kg/day will work or 5 L/day
• Consider any Ongoing losses from diarrhea
• 9 L/day = 375 ml/hr can be given as "2x maintenance" (10 L a day)
• However, Fluid restricted formula should be used if the foal has euvolemic related to Maladjustment- concerns of brain edema
• 2.25 L in 24 hrs should is the fluid restriction volume to use if there are concerns for brain edema.

Electrolye Abnormalities

• When presented and blood work is complete, the findings could show that the foal has: PCV 50% TP 8.5 gm/dl (all high), Creatinine 3.9 mg/dl (high), Hyponatremia = 121 mmol/L (135-144), Hypochloremia = 89 mmol/L (95-105), and Hypocalcemia = 4.0 (ionized)
• Evaluate blood gas levels show: pH = 7.25 (rr 7.4), HCO3 = 12 mEq/L (rr 24), PCO2 = 39 mm Hg (rr 35-45), and Increase in Anion Gap 22 mEq/L (rr 10-17) and Lactate = 5 mmol/l
• You can define the pH by: < 7.4 acidosis or > 7.4 alkalosis
• The pH is now 7.25 = acidosis
• Assesment of HCO3 would show: If an animal has a HCO3 of < 24 mEq/L they have metabolic acidosis where if they have an HCOL3 >24 mEq/L they have metabolic alkalosis
• Assesment of > 45 mm Hg = respiraotry acidosis while < 35 mm Hg = respiraotry alkalosis
• Hope has : HCO3 = 15 mEq/L & normal PCO2 = therefore has metabolic acidosis
• Anion Gap can be assessed with : (Na + K)-(Cl + HCO3) which should be 10-17 should be evaluated
• AG increase- unmeasured anion results in lactic acid metabolic acidosis due to Lack of perfusion resulting in anaerobic metabolism.

Fluid Choices for Metabolic Acidosis

• LRS and 5% dextrose is not used alone.
• 5% NaHCO3 is possible and has some Ca.
• Metabolic Acidosis Rx rules: Correct dehydration and then reassess and HCO3- not before volume expansion with lactic acidosis
• 5% dextrose should not be used because it would worsen low Na, Cl and Ca
• Saline- mildly acidifying is another option.

Considerations with LRS

• Increased production causes Tissue hypoxia (dehydration and Liver which metabolizes lactate resulting in HCO3.
• Watch out for Liver failure which would make it problematic to use LRS.
• Common electrolyte abnormalities would be Hyponatremia, hypochloremia caused Common with colitis as well as Hypocalcemia caused by Common with Gl disease.
• You may Need to add more calcium at 20 ml/L Calcium gluconate.
• Later on the blood work shows a pH = 7.4, HCO3 = 20 (rr 24), and Improved Na, Cl, Ca
• This later turns around and is a pH = 7.2 with a HCO3 = 14 mEq/L and Lactate = 0.8 mmol/L resulting in Metabolic acidosis and normal AG.

Supplement HCO3

• HCO3 deficit is given by (24-14) x 0.5 x 50 kg = 250 mEq with a Volume of Distribution (0.3 to 0.6)
• In this case only Replace ½ deficit and rest over 12-24 hrs and Dont use with Ca++ fluids
• 5% NaHCO3 has 595 mEq/L HCO3 with a But hypertonic 1190 mOsm/L.
• 1.3% NaHCO3 has = 156 mEq/L HCO3 is Isotonic.
• Hopes deficit: 250 mEq HCO3 which is the total deficit so Use 800 ml of 1.3 % = 125 mEq the 1.3 % NaHCO3: 800 ml over 30 minutes with 1.3% = 156 mEq/L that 800 ml Provides 125 mEq HCO.
• Give additional 270 ml q 8 hours or if they dont want to use a 1.3 % then you can oral administer Easy by using 1 gm NaHCO3 = 12 mEq HCO3 and Divide into doses for 24 hrs

Example Case - Sue

• Sue is a 10 yr old QH mare that is Lame and was treated with Bute for 3 weeks and now she has Anorexia, Diarrhea at 500 kg
• Temp = 102 F, HR = 72 bpm, RR = 24 bpm, and PCV = 50% TP = 3.5 g/dl with Albumin = 1.0 g/dl.
• Also, shows with a WBC = 3,000 cells/ul
• With that the Most likely diagnosis = NSAID toxicity and Estimate dehydration 8-10%
• The best approach for a 500 kg horse is to Initially Administer 10 L of LRS and then to Sue after administeration.
• After reevaluation she may need fluids Discontinuation due to concerns of overhydration.
• Consider recommending plasma or Administer LRS- 70 L, or Hypertonic saline
• Sue- fluid choices depend on Increase oncotic pressure with Plasma or Hetastarch to Help increase oncotic pressure to Help increase oncotic pressure and Maintain circulatory volume with Plasma to get albumin > 1.5 gm/dl although it will cost $$$ to give a needed 3-5 L at a time.