Avian fluid therapy (Proceedings)

Article

When developing a fluid therapy protocol it is incumbent upon the veterinarian to understand what the best products to use are and why in order to achieve the best physiologic response. Unfortunately, there is a paucity of scientifically based information regarding the underlying assessment parameters for fluid therapy protocol in individual avian species.

Goals of Fluid Therapy

  • Administer the least amount of fluids needed by the patient

  • Restore perfusion and hydration without volume overload

  • Have a treatment goal

  • Assess clinical response toward treatment goal

  • Early intervention

Assessment of a Fluid Therapy Protocol

When developing a fluid therapy protocol it is incumbent upon the veterinarian to understand what the best products to use are and why in order to achieve the best physiologic response. Unfortunately, there is a paucity of scientifically based information regarding the underlying assessment parameters for fluid therapy protocol in individual avian species. Therefore fluid therapy has been administered based on extrapolation from other animals and avian species and anecdotal clinical reports. Reference ranges, calculated using the robust method, were 288-324, 308-345, 223-369 mOsm/kg in African grey parrots, Hispaniolan Amazon parrots, and red-fronted macaws, respectively. Means ± SD were  306 ± 7, 327 ± 7, 304 ± 18 mOsm/kg in African grey parrots, Hispaniolan Amazon parrots, and red-fronted macaws, respectively. Comparisons with osmolality values in mammals and values previously reported for psittacine species suggest that plasma osmolality is slightly higher in parrots than in mammals, species-specific differences exist, and differences between reported values occur. Overall, fluids with an osmolarity close to 300-320 mOsm/L, such as Normosol-R, Plasmalyte-R, Plasmalyte-A, and NaCl 0.9%, can be recommended in parrots for fluid replacement therapy when isotonic fluids are required.

The dynamics of body fluids between compartments and across membranes depend on many factors and are based on the composition and osmotic pressure of each compartment. Osmolality is defined as the concentration of solutes in moles per kilogram of solvent (mOsm/kg). Osmolarity, on the other hand, is the concentration of solutes per liter of solution (mOsm/L). Osmolality and osmolarity are considered equal in biologic fluids and can be used interchangeably.

Fluid Therapy

If it is determined the patient can withstand the stress of handling and treatment then fluid therapy may be initiated.  Normosol or Lactated Ringers Solution can be administered through the following routes: subcutaneous, intravenous, intraosseous, orally and through the cloaca.  Anatomic sites commonly used for IO catheter placement include the distal ulna (larger birds), proximal ulna, proximal tibiotarsal bone and lateral femur (young and small birds).  Placement of the IO catheter begins with proper site preparation, similar to epithelial preparation for an IV catheter.  A 22-gauge, 1½” spinal needle is the catheter of choice in most psittacine cases although any size needle may be used, provided that a stylet is inserted into the needle prior to placement of the IO catheter into the medullary cavity of the bone.  When the IO catheter is placed in the distal ulna, the distal wing tip is flexed and the needle is inserted at a 45 to 60° angle, and this angle is reduced once the catheter enters the cortex. The needle should be advanced to the hub, stylet removed and the catheter flushed with heperized saline.  The catheter is capped with a PRN and managed as an IV catheter.  Intraosseous catheters require more maintenance than an IV catheter and should be flushed 6 to 8 times a day to maintain patency. Subcutaneous fluid therapy is not an effective method of rapid restoration of circulatory fluid volume..  Adding hyaluronidase (Wydase, Wyeth-Ayerst Pharmaceuticals, Philadelphia, PA) to lactated Ringer's solution (LRS) for SC fluid administration has been recommended as a method to increase the absorption rate of the fluid into the circulatory system.

When determining the dehydration deficit of a psittacine patient, the veterinarian must estimate the percentage of deficit prior to calculating replacement fluid volumes. Parameters applied to measure dehydration status in psittacine species include skinfold elasticity, corneal moisture, appearance of the globe and packed cell volume.  Dehydrated psittacine chicks have wrinkled and reddened skin, with a sunken face and prominent eyes. It is generally believed that in most cases of severe trauma or disease a 5% to 10% dehydrated status should be estimated for the avian patient.  The estimated deficit should be replaced over a 48 – 72 hour period. The recommended daily fluid maintenance formula for psittacine species is 100 ml/kg/day, and baby birds consume 2 to 3 times the maintenance fluid levels as adult patients but may range between 50 – 150 ml/kg/day depending on species of bird being treated.  Recent recommendations to compensate for tissue fluid loss are a crystalloid  (e.g. LRS) 10 ml/kg + colloid (eg, hetastarch) at 5 ml/kg increments.  The crystalloid/colloid combination given at 1 to 2 bolus infusions will generally raise the blood pressure to greater than 90 mm Hg systolic. Fluids should be warmed before administration and bolus fluids can be given with relative safety IO or IV over a 3 – 5 minute period.  Once the fluid deficit is replaced and the bird is eating and drinking normally for 2 or 3 days, the maintenance hydration therapy can be discontinued.

Fluids therapy may be replaced through subcutaneous, intravenous or intraosseous administration.  Subcutaneous fluid replacement can be achieved using a 26 or 25 gauge needle attached to a syringe filled with a warmed crystalloid or colloidal agent.  The sites usually preferred for subcutaneous administration are the featherless inguinal and/or axillary regions of most avian species.  Intravenous catheters are placed in the jugular vein of larger birds and median metatarsal of smaller companion avian species.  The distal ulna and proximal tibiotarsal bone are the recommended sites for IO catheter placement.  Although IO catheter placement is easier in smaller birds, these catheters require more maintenance to prevent plugging.  Intraosseous catheters have a similar delivery to IV catheters and are much easier to place, especially in smaller species.

Lactated Ringer's solution (LRS), 2.5% dextrose in 4.5% saline, and 0.9% saline comprise the commonly used isotonic crystalloid solutions administered to avian species.  The necessity for continuous fluid administration is based on the fact that only 25% of the fluids administered to a bird remains in the vascular compartment 30 minutes after it enters the blood stream.9  Since the patient that presents in shock is often suffering from metabolic acidosis and lactate is metabolized to bicarbonate in the liver, LRS is the fluid of choice.  Lactated Ringer's solution can be supplemented with potassium chloride (0.1 – 0.3 mEq/kg to a maximum dose of 11 mEq/day) if the plasma potassium and sodium levels are low in the patient due to vomiting or diarrhea.9 If a patient is hyperkalemic due to severe tissue injury, a catabolic state, or renal dysfunction, LRS is not contraindicated and calcium gluconate (0.5 ml/kg facilitates the movement of potassium across the cell membranes.  In cases of hydropericardium, pulmonary edema, or increased intracranial pressure without hemorrhage is present hypertonic saline may be useful.

Plasma, dextrans, and hetastarch are large molecules that do not cross the vascular endothelium and are called colloids. These products replace lost protein and help to maintain plasma oncotic pressure and reestablish circulatory volume. Caution is advised when considering the use of synthetic colloids in patients diagnosed with congestive heart failure or anuric/oliguric renal failure because they are excreted by the kidney.10 The recommended dose for hetastarch is 10-15 ml/kg IV for 1 to 4 treatments over a 24 hour period. Remember to reduce the volume of crystalloid administration by the volume of hetastarch used to prevent fluid overload.

References

Beaufrere H, Acierno M, Mitchell M, et al. Plasma osmolality reference values in African grey parrots (Psittacus erithacus erithacus), Hispaniolan Amazon parrots (Amazona ventralis), and red-fronted macaws (Ara rubrogenys), submitted for publication J Avian Med Surg 2010.

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Wellman M, Dibartola S, Kolm C. Applied physiology of body fluids in dogs and cats. In: Dibartola S (ed): Fluid Electrolyte and Acid-Base Disorders in Small Animal Practice.  St. Louis, Missouri: Saunders/Elsevier 2006; 3 - 25.

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