Phlebotomy (blood drawing) in a rabbit
Esther van Praag, Ph.D.
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Rabbits are easily startled and may start scratching the manipulating person or jump from the examination table during the clinical examination or a blood sample. They often jerk in response to venipuncture in the marginal vein of the ear, when the skin has not been anesthetized beforehand. As a result, rabbits should therefore be restrained in a towel, bag or laboratory coat.
For a pictorial demonstration of restraint in a towel, see: Safe immobilization of a rabbit in a towel (“rabbit burrito”)
The amount of blood needed for a blood test will determine the location where the sampling will be done. Veins are used (venipuncture (blood from the vein is used), some rare tests nevertheless require blood from the artery. Arteries, should, however, be avoided as this procedure is painful and can lead to damage and necrosis of the arterial vessel.
Amounts up to 5 ml of blood can be safely drawn from the auricular marginal vein, using a 23- to 25-gauge needle or a 23-gauge butterfly attached to a syringe or tube. It is also possible to place a catheter-over-needle.
The preparation of the skin is identical, independent of the collection method used. Before starting the sampling, the fur on the ear is shaved, and the skin is cleaned with alcohol. As the skin on the ear is very sensitive it is recommended to anesthetize the skin locally with e.g. a lidocain containing cream (e.g. EMLA®).
The creamed spot is wrapped with a plastic sheet and a protective adhesive bandage. After 45 min., the full thickness of the skin is numb. The anesthetic effect remains effective for the next 60 min.
Dilation of the vessel can be obtained by massage of the ear, approach of a heat source near the rabbit ear or by using blood vessel dilating agents, e.g. acetylpromazine (0.25 ml, SC).
After occlusion of the vein, the needle is carefully inserted and blood can be withdrawn. The procedure must be done slowly, in order to avoid hemolysis of the red blood cells (erythrocates), but should be fast enough to avoid the formation of blood clots. After removal of the needle, a cotton gauze is firmly applied on the site of venipuncture, during at least 1 minute, or until bleeding has stopped, in order to prevent the formation of hematomas and blood clots. The use of alcohol-impregnated gauze should be avoided; alcohol causess vasodilatation and prevents hemostasis.
Stain of blood on the ear can be removed with hydrogen peroxide
The rabbit should remain under observation over the next hours to ensure that hemostasis is complete.
The jugular vein can be used to collect a fairly big amount of blood. The dewlap of female rabbits does not represent a hindrance. The rabbit can be placed in several positions, in order to collect blood from the jugular vein:
- sternal recumbency, with the neck extended upwards and the front limbs hanging over the end of the examination table;
- dorsal recumbency, after safely restraining the rabbit in a towel, and extending the neck in order to expose the jugular vein;
- lateral recumbency, with the neck extended out and the front legs pulled downward.
The jugular vein should be avoided for blood collection if the rabbit suffers from a respiratory problem or shows respiratory distress. It may become cyanotic during the procedure.
Alternate sites for blood collection are the cephalic and the lateral saphenous veins. Their locations are the same as in dogs and cats. These veins are fragile, and a hematoma is easily formed.
Collection of blood from the central artery must be avoided, unless higher volumes of blood need to be collected. This site is painful and often leads to subsequent distal ischemia, due to impairment of blood supply to the pinna after the formation of a hematoma or due to blood vessel damage (arterial trauma with thrombosis). A collapse of the vessel may, furthermore, occur when excessive pressure is exerted. If the use of the central artery cannot be avoided, the 21-gauge needle should be inserted as distally (tip of the ear) as possible into the artery. The blood should start to flow immediately in the syringe.
Thanks are due to Akira Yamanouchi (Veterinary Exotic Information Network), for the permission to his photograph.
Thanks are also due to my rabbits Grijsje, Flora and Stampi, for their patience.
Mc Guill, M.W. and Rowan, A.N. (1989) Biological effects of blood loss: implications for sampling volumes and techniques. ILAR NEWS 31, No. 4, 5-18.
Exotic Companion Medicine Handbook for Veterinarians, Cathy Johnson-Delaney and Linda Harrison
Mader DR. Rabbits - basic approach to veterinary care. In: Hillyer EV, Quesenberry KE (eds.): Ferrets, Rabbits, and Rodents - Clinical Medicine and Surgery. Philadelphia, WB Saunders, 1997: 160-168.
Paul-Murphy J, Ramer JC. Urgent care of the pet rabbit. In: Rupley AE (ed.): Vet Clin North Am (Exotic Anim Pract). Philadelphia, WB Saunders, 1998: 127-152.