Proceedings of the Annual Resort Symposium of the American Association of Equine Practitioners AAEP

Transcription

1 Proceedings of the Annual Resort Symposium of the American Association of Equine Practitioners AAEP Jan. 30-Feb. 1, 2012 Kauai, Hawaii, USA Reprinted in the IVIS website with the permission of the AAEP

2 Equine Medicine Field Tactics 103: Procedures and Therapies for Fluid Therapy Robert P. Franklin, DVM, Diplomate ACVIM Author s address: 1877 Mineral Wells Hwy, Weatherford Equine Medical Center, Weatherford, TX 76088l; rfranklin@weatherfordequine.com. Introduction IV fluid therapy in the field or in a limited staff clinic should be aimed at stabilizing patients in shock, treating mild dehydration and providing therapy for medical disorders. Maintenance fluids and replacing severe deficits in the field may be both infeasible and probably a time sump on the veterinarian and the horse. Knowing what service you can provide is as important as instituting it. Fluid Choices Colloids Hetastarch, Plasma, Whole Blood Crystalloids Hypertonic saline, Lactated Ringers Solution (LRS), Physiologic Saline Solution (PSS), Hartmann s Solution Replacement Hypertonic saline, Normosol- R, LRS, PSS, Hartmann s Maintenance 0.45% Saline w/ 5% dextrose, 0.225% Saline w/ 5% dextrose, Plasmalyte 56 w/ 5% dextrose Physiology of Fluid Distribution Colloids These protein-containing fluids when administered are restricted to the intravascular space and provide the best results for restoring cardiovascular function. Provision of antibodies, red blood cells and clotting factors are additional benefits some colloids contain. Colloids, liter for liter, provide 4 times the intravascular support compared to isotonic crystalloid fluids. Crystalloids 67

3 These are sodium-containing fluids that typically distribute to all the body s fluid spaces in varying degrees. They are indicated for rapid replacement of intravascular volume and maintenance depending on their sodium concentrations. Replacement These fluids contain equal or larger amounts of sodium as blood and are meant to provide for dehydration, gastrointestinal losses (reflux or diarrhea) or shock therapy. Their effects are limited to the intravascular (25%) and interstitial (75%) spaces because the sodium content prohibits the fluids from entering the cell (intracellular space: 2/3 of the body s water). Maintenance These fluids contain less sodium than blood and are balanced to isotonicity by the addition of dextrose. They are indicated for providing maintenance fluids to animals that are incapable of drinking or absorbing fluids from the gastrointestinal tract. Maintenance fluids effectively hydrate all of the body s fluid compartments. Fluid Calculations Fluid rates can easily be calculated when 3 factors are considered: maintenance, deficit and ongoing losses. Maintenance: Adults: 5% body weight Adolescents: 7.5% body weight Neonates: 10% body weight Deficit: Mild dehydration: 6% body weight Moderate: 8% body weight Severe: 10% body weight Ongoing losses: Diarrhea: Estimate losses Refluxing: Calculate losses Deficits should be replaced by administering ½ the volume quickly and then adding the rest to the 24-hour total. 24-hour total = Sum of Maintenance, Remaining Deficit, Ongoing losses. Important Note: This basic calculation should provide you with initial volume needs. This information should tell you what sort of impact your fluid therapy is having on the patient s needs and if you can actually meet these needs without getting the horse to your clinic or a referral hospital. 68

4 Electrolytes Horses that are unable or unwilling to eat, or horses that have specific electrolyte derangements require supplementation. Calcium Deficiency in calcium can cause symptoms of weakness, excitation and ileus. 1 ml/kg of calcium gluconate in IV fluids is used to address hypocalcemia. This dose may be added to a single dose of fluids. Routine addition of calcium to anorexic patients is done at a rate of: Adult - 20 gm/day (approximately 1 liter of calcium gluconate 23% or Calcium/Magnesium/Phosphorus/Potassium (CMPK) solution), Lactating or pregnant mare- 50 gm/day (approximately 2.5 liters calcium gluconate 23% or CMPK solution), Weanlings and yearlings- 30 gm/day (approximately 1500 ml calcium gluconate 23% or 1500 ml of CMPK solution, Foals - 2 ml/kg/day calcium gluconate 23% or CMPK, divided up into daily fluids. The use of CMPK in foals must be monitored due to potassium content- maximum rate of potassium 0.5 meq/kg/hr). Potassium Hypokalemia is common in cases of digestive disturbances. Supplementation of potassium chloride is given at a maximum rate of 0.5 meq/kg/hr, only during constant rate infusions. Extreme cases (potassium <1.5 mmol/l) require faster rates of 1 meq/kg/hr. Horses that are not able to consume a normal diet will require potassium supplementation. Potassium chloride (2 meq/ml) is added at 20 meq/l of fluids, not to exceed administration rate of 0.5 meq/kg/hr. Spiking fluids with potassium chloride in foals should only be done with maintenance to twice maintenance fluid rates. Do not spike fluids with potassium chloride that are to be ed. A good rule of thumb is to consider the patient size and only putting as much potassium chloride as could safely be ed, in case the fluid rate is inadvertently changed: 50 kg foal, 1 liter bag is safely spiked with 20 meq/l, 500 kg adult is safely spiked with up to 250 meq/5 L. I routinely add 500 ml CMPK in 10 L of fluids to colicky horses on first arrival. Magnesium Magnesium derangements may be more common than initially thought in colic cases. Clinical signs of low magnesium include weakness, muscle fasciculations and ileus. Fluids (10 liters) can be spiked with 5 grams of magnesium sulfate (500 mg/ml) in adult cases suspected to be hypomagnesemic. Daily requirements are approximately 5 mg/kg. Therefore, magnesium supplementation should be performed in horses that are unable to consume normal amounts of feed (5 ml of 500 mg/ml magnesium sulfate or 1000 ml CMPK). Bicarbonate Metabolic acidosis is common in foals, and occasionally adults with diarrhea. Be very suspicious of a foal that is remaining depressed after a few days of otherwise successful 69

5 management of diarrhea. Pull a venous blood gas sample or make sure you at least are getting a TCO 2 level with your chemistry. Make sure your patient is adequately volume restored prior to giving bicarbonate as many times mild acidosis improves with isotonic fluid administration. Base deficit is easily calculated by subtracting bicarbonate (or TCO 2 ) levels from the normal of 25. Example: Bicarbonate level of 10, Base Deficit= 25 (normal) 10 (measured bicarbonate) = 15 meq base deficit. I recommend supplementing patients with ph <7.25 and base deficit levels >10. Traditional administration of bicarbonate dictates that one-half of the calculated dosage should be given over several hours followed by a reassessment of ph and base deficit. Experience has suggested that horses and foals with severe diarrhea and metabolic acidosis may be given their entire deficit in order to correct the derangement. Some risks exist with bicarbonate infusions. Extreme caution should be used in patients with hypokalemia as bicarbonate administration will worsen this syndrome and potentially lead to fatal arrhythmias. Thus, hypokalemia should be corrected before bicarbonate administration and concomitant administration of potassium should occur during treatment of patients predisposed to hypokalemia. Bicarbonate infusions will generate excessive amounts of carbon dioxide. Foals with central nervous disorders, such as neonatal encephalopathy, will not respond appropriately to this rise in carbon dioxide and a respiratory acidosis will be generated. Bicarbonate infusions will also contain high sodium loads. This may lead to osmolarity problems and hypernatremia. Bicarbonate should not be given with calcium or lactate containing fluids due to the risk of precipitate development. Bicarbonate infusions are available as hypertonic sodium solutions in either 5% or 8.4%. 5% sodium bicarbonate contains 0.6 meq bicarbonate per ml whereas 8.4% sodium bicarbonate contains 1 meq bicarbonate per ml. Each gram of sodium bicarbonate contains 12 meq sodium and 12 meq bicarbonate. Isotonicity may be achieved by adding 4.6 ml sterile water to each ml of 8.4% sodium bicarbonate. You may also just add the bicarbonate to non-calcium/lactate containing fluids, such as PSS, Normosol-R. Persistently acidemic foals may also require the administration of oral bicarbonate in the form of baking soda. One tablespoon, equal to 15 ml, of baking soda contains 62.5 meq bicarbonate. Experience suggests that two tablespoons, 30 ml, can be given every 12 to 24 hours. Bicarbonate status should be monitored during this course to adjust dosing. Energy Adult horses that are not refluxing nor consuming adequate feed should be tube fed with either a slurry of a complete pelleted feed or Purina s new WellSolve Gel product. Most enteral feeding preparations contain far too many soluble carbohydrates and too little fiber to avoid diarrhea, so I choose not to use them. You may also elect to provide a small dose of energy in the form of dextrose if you are ing fluids 2-3 times a day to a patient on the farm. In this case you can add 500 ml of 50% dextrose to a 5 L bag of fluids. The addition of B-vitamins (10 ml B-12, 10 ml B-complex) to the fluids may also be of benefit to the anorectic horse. 70

6 Providing energy to foals can be lifesaving. Hypoglycemia, glucose <100 mg/dl, is common in the neonate and causes signs of depression, lethargy, hypothermia or seizures. Treatment goals are to correct hypoglycemia and to regulate glucose levels of mg/dl thereafter. Bolus infusions of glucose, especially hypertonic doses of 50%, should be discouraged due to the chance of CNS damage and rebound hypoglycemia. Instead, an infusion of 10% dextrose is recommended. Most patients are also hypovolemic and require replacement fluid therapy. One liter of Lactated Ringers Solution is supplemented with 200 ml of 50% dextrose to achieve a 10% solution and is given slowly over minutes. Regulation of glucose levels then requires the use of a dextrose infusion. At this point a 5% dextrose solution, either maintenance fluid containing dextrose or replacement fluid supplemented with 100 ml 50% dextrose per liter (not plain 5% dextrose in water), is given until the foal is either able to nurse successfully or until it has arrived at a hospital facility. A slow drip of such infusion will preserve the glucose levels once the foal has had a rescue dose of dextrose. Neonatal foals that are unable to nurse or have severe diarrhea and cannot be sent to a hospital setting, can be given a crude version of intravenous nutrition. A 5 L bag of replacement fluids is spiked with 1 L 50% dextrose, 1 L of 10% amino acids (Aminosyn II 10%, Hospira) and 1 ml/kg CMPK (you can get all of this into a 5 L bag of Normosol-R) and is then administered at a maintenance rate using a gravity flow regulator or by calculating drip requirements. This setup will typically provide about 36 hours of partial parenteral nutrition. I routinely use this fluid setup to maintain foals with severe neonatal diarrhea to allow the gut time to rest. Blood Blood transfusions are easy to do in the field and are life saving. You will need 4 L blood collection bag (J-520F, Jorgensen Laboratories) and sodium citrate (J-521, Jorgensen Laboratories). Dispense 500 ml of the sodium citrate solution into each 4 L blood collection bag and then hook the collection bag up to a donor s IV catheter (10 or 12 gauge catheter works best for donor instrumentation). Gravity will feed the system once it is primed. A 10 or 12 ga catheter works best for donor instrumentation. Foals with neonatal isoerythrolysis can be given separated red blood cells from the mare at a dose of 40 ml/kg if referral for washed red cells is not an option. To perform this crude washing process simply collect the blood from the mare and allow it to sediment out over minutes. Then run only the cells into the foal leaving a comfortable buffer of 1-2 cm before reaching the plasma before turning the infusion off. Do not exceed 40 ml/kg to avoid hypertension. Adult horses, especially mares with ruptured uterine arteries, can be given blood from a donor gelding at a dose of 8 L per adult horse (they often need more but this is the most you should take from a donor). Summary Colic with low calcium and magnesium on the farm or at admission to clinic 500 ml calcium gluconate 23% with 10 ml of magnesium sulfate (500 mg/ml) in 10 liters of fluids, or 500 ml CMPK in 10 liters of fluids. 71

7 Adult, non-gravid, non-lactating, anorexic on fluids Add 500 ml CMPK to 10 L of fluids TWICE per day Foal 100 kg, diarrhea, already given fluids to rehydrate but still depressed, base deficit 15 Bicarbonate needs = 100 (bwt in kg) x 15 (base deficit) x 0.6 (or 0.3 in adults) = 900 meq bicarbonate. Add 1.5 L 5% sodium bicarbonate to 5 L Normosol-R. Administer over an hour. *Major rate limiting dose on CMPK is potassium levels. Each 500 ml bottle of CMPK has 205 meq KCl. An adult horse can safely receive this amount in an hour. Smaller horses and foals...double check that you aren t exceeding 0.5 meq/kg/hr. Not for dosing, the below formulas are for constant rate infusions of fluids only. Adult NPO on IV fluids at a maintenance rate of 1 L/hr Add 120 meq KCl, 200 ml Calcium gluconate, 1 ml magnesium sulfate, or 250 ml CMPK to a 5 L bag. If patient is on higher rate, only spike every 2 nd, 3 rd or 4 th bag for 2x, 3x, 4x maintenance rate Foal NPO on maintenance IV fluids Add 20 meq KCl, 1 ml/kg Calcium gluconate, 0.5 ml magnesium sulfate, or 1 ml/kg CMPK per liter bag Indications Indication Fluid Dose Note Acute Blood loss Hetastarch 10ml/kg IV Hetastarch should be given as an emergency treatment if donor blood is unavailable. Therapy will restore blood pressure quickly and stabilize for shipment. Doses >20ml/kg may cause Cardiovascular Shock Impaction colic Whole blood Hypertonic saline Hetastarch LRS LRS Adult horse: 8 L Other: Max 40 ml/kg 2-4 ml/kg IV 2-10ml/kg IV Replace ½ the deficit quickly L as needed coagulopathies. May take 1.6% of body weight from a donor (8L in 500kg horse) Follow with isotonic fluids and have fresh water available unless contraindicated (e.g. refluxing). Provides rapid support to intravascular volume. Most cases of shock are about 10% dehydrated: a deficit of 50 L in a 500kg horse, which would require rapid administration of 25 L of crystalloids. A horse with significant reflux or violent colic should not be managed in the field. Taking min to give 10 72

8 Mild diarrhea Rotavirus diarrhea Rhabdomyolysis Neonate unable to nurse or with severe diarrhea Failure of Passive Transfer LRS LRS Na Bicarbonate LRS, PSS Crude Partial Parenteral Nutrition Estimate deficit and give ½ IV Estimate deficit and give ½ IV Bicarbonate deficit (meq)= BW(kg) x base deficit (BD)x 0.6 Estimate deficit and give ½ IV Run at maintenance rate of 10% BWT per day L of LRS to a mare with a colon torsion is a bad use of time if transportation is ready. Give fluids in transit. Severe or protracted diarrhea cases should not be managed in the field. Severe or protracted diarrhea cases should not be managed in the field. Low bicarbonate is common with Rotaviral diarrhea and may require treatment. TCO 2 may be used to calculate base deficit. BD= 25-TCO 2. Supplement cases with BD>10. Myoglobinuria is a good indicator for fluid therapy. Monitor creatinine for pigment nephropathy. Add 1 L 50% Dextrose, 1 L 10% Amino Acids, 1 ml/kg CMPK to 5 L replacement fluids. Plasma ml/kg Partial FPT typically requires 1 L where total FPT foals greatly benefit from 2 or more L. Don t try to save the owner a few dollars with Serramune and similar products. A penny wise 73