Stephen Cital RVT, SRA, RLAT
United Veterinary Specialty and Emergency, Oakland Zoo, San Francisco Zoo
For more visit www.stephencital.com
Blood transfusions are an ever-growing therapy in small animal practice. Transfusions offer patients a lifesaving option by giving us time to treat the underlying disease or correct hemodynamic imbalances. However, did you know you could use most of the same methods used in cats and dog blood transfusions in other species? Exotic animals suffer from anemia or require transfusions due to acute blood loss just like any other animal. However, transfusions are often overlooked in these species because of unfamiliarity and practicality.
Whenever transfusing a patient, many constants exist. Donor availability is always trickier when it comes to more exotic species, while donor selection is also very important. Selecting a healthy donor from the same species is ideal. It is ideal if the donor is from the same home to reduce the risk of cross infection for a number of diseases. A stressed donor with a release of cortisol can be avoided with light to moderate sedation. Midazolam is a generally safe and effective drug choice in mammals, birds and reptiles. It is recommended that, if sedation is used in the donor animal – and in most cases it will be needed – all the anesthetics/sedatives should be chosen with the recipient’s health status in mind. Residual effects have been described in recipient animals from medications given to the donor from still circulating medications.
Blood substitutes are still available outside of the USA and have been used in many species with success. These products (Oxyglobin™, Hemopure™, Dextran-Hemoglobin™) may offer an advantage to the practitioner by allowing a constant supply and not having to rely on the time for collection, stress, risk factors and accessibility of a donor animal.
Monitoring and transfusion rate guidelines during a transfusion do not change among species. Although slight variances occur, many guidelines have all vital signs (including mentation) being recorded every 5-15 minutes for the first 30 minutes. The starting transfusion rate is 0.25 mL/kg for the first 30 minutes and can be increased to a rate that would make the whole transfusion completed within 4 hours when using blood products. After the first 30 minutes of the transfusion with no adverse reaction, the monitoring frequency can be decreased to every 15-30 minutes. Remember, guidelines are merely guidelines! Patients may need more or less attention based on their clinical status.
In many of the species discussed below, in particular the non-mammals, blood compatibility is less of a concern, especially if this is the patient’s first transfusion. The lessened concern stems from the lack of identified blood groups in bird and reptilian species. However, it is still encouraged to perform a major and minor crossmatch when samples allow.
Reptilian and amphibian blood transfusion
Reptiles and amphibians are one of the least common species one will have to perform a blood transfusion on. These species have amazing regenerative attributes and can tolerate some pretty inhospitable environments. These attributes also hold true for their survivability of medical conditions. Few studies and just as few clinical write-ups have been done on transfusions in these species. Most of the literature leans away from transfusing an amphibian all together, but rather treat the underlying condition and hope for the best.
Reptilian blood transfusions, on the other hand, are a more feasible therapy. A general guideline for most species suggests transfusions when the PVC drops below 20%. This is a good guideline, but a careful clinical evaluation should be made before jumping to a blood transfusion.
The morphology of reptilian and amphibian red blood cells include a nucleus in an oval shaped cell. The erythrocyte size is also one of the largest in the animal kingdom, which explains a lower PCV compared to mammals.
Setup and precautions are the same as with mammal transfusions, but IV access poses a bigger challenge. In many reptiles, cut downs are often necessary for basic indwelling IV catheters. Common sites for IV catheterization include the jugular vein for chelonians (which can be done percutaneously), ventral tail vein, dorsal tail vein in chelonians and in large lizards cephalic or saphenous veins. In more critical and non-ambulatory lizards the ventral abdominal vein is a useful site.
Collection sites from a donor include all of the before mentioned, but also include the heart in certain reptiles such as snakes. A more practical means of administration and easier accessibility in reptiles is by using an intraosseous catheter. In lizards, the preferred site is the tibial crest. Sites such as the proximal humerus, femur and ulna can also be used. Snakes obviously are not candidates for IO catheters. Reptile and bird blood can clot quickly and using a heparinized syringe with sodium citrate may be indicated instead of using CPD, CPDA or ACD. *Heparin can cause RBC lysis in chelonian blood
Although, not ideal cross-species transfusions has been described in the literature. More rapid cell death often occurs, and the potential for cross-reactions is greater. Because normal reptilian erythrocytes have a long life span, 600-800 days, a quicker die off of heterologous transfusions may need to be repeated, increasing a patient’s chance for reaction, stress and infection.
When transfusing ANYTHING, a blood filter for clots is vital! One study on alligator blood determined that the 18-micron filter did not lead to hemolysis or a decrease in PCV with smaller quantities of blood, suggesting the efficacy of the filter in other reptilian species.
*polychromasia is not uncommon in shedding reptiles
*EDTA can cause hemolysis in some reptile and bird species. Lithium heparin is recommended instead for hemograms
Avian blood transfusion medicine is nearly the same as reptilian. The morphology of the avian erythrocyte is almost identical to the reptile RBC but is a bit smaller. The transfusion guideline of a PCV below 20% also applies to avian species. Birds are more tolerant of lower PCV’s especially if chronically acquired. One author has even described seeing patients with PCV’s ranging from 7-12%! They also describe not transfusing the patient if the bird is bright, alert and reactive. In studies with ducks, the investigator found hypovolemic shock only occurred after 60% acute blood loss. In another study, 50% loss of total blood volume was corrected without blood product resuscitation, but instead with crystalloid and colloid fluids.
As with any species, homologous transfusions are preferred, but pigeon to raptor transfusions have been successful, although erythrocyte life was short. Erythrocyte life span is only 28-45 days in birds, couple this with a small spleen that does not act as an RBC reservoir, and avian patients can become anemic again quickly. Unlike the reptile, erythrocyte genesis can occur rapidly, and reticulocytes can occur within hours. With varying degrees of anemia more pronounced, RBC size variances might occur; cell size has a normal “cell distribution width” of 10-11%. Even with an increased erythrocyte size compared to mammal’s one study in chickens concluded the 18-micron filter does not cause significant hemolysis.
*Poikilocytosis (variable cell shape) is most commonly seen with systemic disease that affects bone marrow or is an artifact error.
Blood groups among birds have not been thoroughly studied among many species. However, in chickens twenty-eight different blood group antigens have been described. Multiple other blood groups have been discovered in other common species such as turkeys, pheasants, quail and ducks. Sedation or light anesthesia is more than likely going to be needed for blood collection from a donor and is often the safest and least stressful approach. As with any species choosing sedatives that will have minimal effects on the donor and the recipient is ideal. Collection and transfusion sites in the bird include the right jugular (careful attention should be paid so that the adjacent air sacs are not cannulated), ulnar vein, brachial vein and the medial metatarsal vein. The recommended volume collection is 1-2% of the patient’s body weight. Sodium citrate is the recommended anticoagulant in birds; however ACD, CPDA and CPD are also compatible. Heparin has also been described at 0.25ml (1000U/ml Heparin) to 10ml of whole blood. Intraosseous catheters maybe indicated in severely hypovolemic patients. The humerus and femur should be avoided for any IO catheter in the avian patient as they are pneumatic, and one can drown the patient if fluids are given through these sites. Commonly IO catheters are placed in the tibiotarsus or distal ulna with appropriate anesthesia/ analgesia.
Other Indications for transfusions
Coagulopathies in reptiles and birds do happen. However, treatment is limited to treating the underlying inflammatory response. Accurately estimating clotting times in reptile and avian species is still being studied. The literature has described methods such as PT and PTT as possible reliable clotting indicator tests. Methods such as ACT and whole blood clotting times are more reliable at this time. Blood component transfusions in theory are possible, but can prove impractical in most settings.
Protein imbalance disorders are also not uncommon disorders. Reliable tests for determining true serum or plasma protein levels are still evolving. Thankfully present research has shown refractometry is fairly accurate and is a device most practices already have. It should be noted plasma protein will be higher in bird and reptile species due to the presence of circulating fibrinogen. Hyperproteinemia can be associated to egg production in both birds and reptiles. Other etiologies for hyper and hypoproteinemia seen in mammals are also causative factors in both special species.
Total protein levels in the reptile range from 3-7 g/dL and 3-4g/dL in birds. Birds of prey usually have a slightly higher plasma protein compared to their non-carnivorous cousins.
Exotic small mammals
There are relatively few differences between methods used in cat and dog transfusion medicine to exotic mammal transfusion medicine. The biggest differences exist with the overall accessibility of donor animals and feasibility of the transfusion in practice. Acute blood loss of 30-40% total blood volume will lead to shock and fluid resuscitation is warranted. When more than 40% total blood loss occurs immediate volume resuscitation is warranted. If the corrective actions do not lead to appropriate tissue oxygenation an immediate blood transfusion or blood substitutes need to be considered. A benefit of blood substitutes like Oxyglobin™ includes a smaller molecule size giving it the ability to better access micro capillaries for improved perfusion. It also has a 10 fold better resuscitative effect in hypovolemic shock than actual blood because of vasoconstricting properties, therefore, requiring less volume to be infused.
The average RBC lifespan of a small exotic mammal is relatively short (22-55 days) in comparison to a dog (100-120 days).
*Howell-Jolly bodies are normal in the rabbit and do not indicate cellular regeneration as seen in the feline patient
Sedation is also a common practice is the exotic mammal to reduce stress, injury and hormone release. Intravenous and intraosseous catheterization is well described for many species of small exotic mammals.
Micro hemofilters used in small animal practice are effective and recommended in the exotic small mammal.
Little research has been done into defining different blood groups in many small exotic mammal species. A major and minor crossmatch should be performed before any transfusion with special attention to the more important major cross match.
*It should be noted that volatile anesthetic gasses, such as isoflurane and sevoflurane, have been associated to a significant drop in hemoglobin and hematocrit levels in ferrets.
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