Bleeding and intravenous techniques in pigs
Tore Framstad, Øystein Sjaastad and *Rolf A. Aass
Norwegian School of Veterinary Science and *Norwegian Independent Meat Association, Oslo
For more resources about planning animal research and testing, please see the PREPARE guidelines.
A paper on this subject has been published previously in Norwegian:
Framstad T., Sjaastad Ø. and Aass R.A. (1988): Blodprøvetaking på gris. Norsk Veterinærtidsskrift 100(4): 265-272.
Most of the pictures are also available on loan as a slide collection from the Library at the Norwegian University of Life Sciences, Veterinary Campus, in Oslo. This presentation was prepared for the Internet by Adrian Smith.
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The ear veins
The marginal ear veins are the only veins that are easily visible on pigs of any size. Usually there are three prominent veins. The lateral or central vein is usually the largest of these. The ear veins are branches of the caudal auricular vein and the superficial cervical vein. Their pattern, anastomoses and relative sizes vary from pig to pig.
The pig in the picture weighs about 7 kg. An assistant holds the pig across his lap and at the same time raises the vein. The illustration shows the use of a 22 gauge needle. Sometimes it may help if the finger used to raise the vein gently pumps the vessel.
Pigs cannot sweat and blood circulation through the ears is important for temperature regulation. In a warm environment the veins are more dilated and blood collection is facilitated.
When the vein has been punctured, the emerging blood can be collected directly by capillary action into appropriate tubes. This technique is suitable for measurement of haematocrit and haemoglobin levels, and for making blood smears. Tubes used to collect blood for haematocrit measurement must be coated with an anticoagulant. The tubes most often used for haemoglobin measurements (20 microlitres) are not treated in this way. The dilution fluid used for haemoglobin measurement must therefore be available at hand so that the blood can be blown into that fluid immediately after collection.
It is possible to undertake intravenous injections using the ear veins even on newborn piglets. These are held in the same way as was illustrated on the two previous pictures. Very thin needles, such as 25 gauge, must be used on the very smallest pigs. The pig on this photograph is larger, and a 23 gauge needle is in use. The veins are thin-walled and are easily perforated. It can prove difficult to fasten the syringe to the needle once it is in place in the vein. The syringe should therefore be fastened to the needle before venepuncture, and the operator should gently aspirate as the needle is inserted. The operator will see and feel the needle in the vein. It is a good idea to begin on the peripheral part of the vein. Then it is possible to try again nearer the head if the first attempt is unsuccessful.
The needle and ear are fixed between the operator's thumb and forefinger. When this has been done, the assistant can stop raising the vein and the injection can begin. For practical reasons, the injection should be performed relatively quickly, and the amount that can be injected is therefore somewhat limited.
Infusion sets are also commercially available, consisting of a tube connected to a needle. These 'butterfly needles' must be fastened to the skin using adhesive tape or a louse. Their great advantage is the flexibility of the tubing. These sets are available in a variety of sizes, such as 19 and 21 gauge.
This picture shows the central ear vein (the intermediate auricular vein) on a young sow. The animal has been given azaperone as a sedative. This compound has the added advantage of causing peripheral vasodilatation, making the vein more readily accessible.
A venous catheter equipped with a stiletto (Braunule, 18 gauge) has been inserted into the vein. The stiletto is retained completely within the needle until blood appears. It is then partially withdrawn and the catheter is inserted into the ear vein. The catheter illustrated has a 'wing' that aid handling. It may be seen on the picture between the operator's forefinger and thumb. A similar wing is mounted on the stiletto. A suitable size catheter for slaughter pigs and young sows is 18 gauge. On larger sows 16 gauge catheters may be used. This latter size is also useful on sick animals in urgent need of intravenous fluids.
The catheter has been inserted right up to the wing. It must now be fastened, for example by a louse. This grasps the end of the catheter at the junction with the wing and also grips the skin. This method ensures that the catheter remains in place even if the animal shakes its head relatively violently.
The external jugular vein
Blood samples from adult pigs are most commonly taken from the external jugular vein. The animal must be held using a snout rope and the neck must be stretched well upwards. This is best achieved if the pig stands on all four legs. The rope is placed behind the canine teeth so that it does not slip off so easily or move rostrally towards the nasal cartilage, an area that clearly is uncomfortable for pigs. The animal will try to move backwards and in that way tighten the rope suficiently. It is therefore not necessary to prevent the pig from moving forwards.
The picture is a close-up view of the neck of the same sow, taken from the side. The correct puncture site is in the deepest point of the jugular groove formed between the medial sternocephalic and lateral brachiocephalic muscles. This site is marked on the picture by a black dot. Right-handed operators will usually find it easiest to use the animal's right jugular vein.
A vacuum tube has been connected, and the needle inserted in its full length. This is important, since these needles are really slightly too short for large sows, and the adipose tissue above the vein must therefore be compressed somewhat. Blood is seen entering the glass tube.
This picture shows the same situation as in the previous illustration, but the picture has been taken diagonally from in front. The jugular groove is easily seen. In order to illustrate the technique as well as possible, the needle holder is only held in place on this picture and the previous one by the operator's forefinger. In reality this holder should be held more firmly.
It is vital that the needle holder is held firmly if the operator wishes to change vacuum tubes. This picture shows a good method of doing this. The blood sample is being taken in the right external jugular vein. The operator holds the needle holder with his left hand, at the same time pressing it gently against the sow's neck. He uses his right hand to change tube.
Bleeding techniques for smaller pigs
This picture depicts the venous drainage in the neck of piglets.
A: the cephalic vein. This drains into:
B: the external jugular vein
C: the internal jugular vein
B and C anastomose and form the communal jugular vein
D: the end of the sternum (manubrium), marked in black
In pigs weighing less than 50 kg it is an advantage to collect blood further caudally (and more medially) in the jugular groove, nearer the manubrium. Depending upon the puncture site, angle and depth of penetration, blood will be collected from one of the vessels depicted in the previous picture. It is difficult to say with certainty which vessel is punctured. An assistant can hold pigs up to about 20 kg on their lap. The assistant holds the forelegs in one hand, and the animal's head in the other. The manubrium and puncture site are marked in black.
For pigs of this size it is a good idea to use a syringe and needle. The needle is fastened and filled with anticoagulant. For piglets, needles of 23 gauge should be used, while 22 gauge needles can be used on slightly larger pigs. When the needle has penetrated the skin, the operator should aspirate as he gentlly pushes the needle forwards. Blood should be apparent after 10-25 mm, depending on which vessel is punctured. As soon as blood flows into the needle, it should be held firmly to avoid further movement. The operator can place his hand on the pig as shown to steady the needle.
This picture shows venepuncture on a smaller pig, photographed from the side. The pig lies between the assistant's thighs, and only the head and forelimbs are held. The head must not be stretched too far backwards, as this impairs air flow through the throat region.
Pigs weighing between 20 and 50 kg can either be held on their backs in a 'trough' or immobilized with a snout rope as shown on the picture. This pig weighs about 40 kg. The manubrium is marked in black.
The cephalic vein can be used for blood collection in newborn piglets and weanling animals. It will only be possible to withdraw small amounts of blood from animals weighing less than 10-15 kg. When they weigh 20-50 kg, it is possible, with some training, to withdraw blood nearly as quickly as with the other methods described here. The pig is laid on its back in a 'trough'. The forelimbs are extended backwards and slightly out from the animal. This position allows the vein to extend in more of a straight line and it becomes more accessible. The vein and manubrium are marked in black.
The milk vein
The milk vein (the subcutanous abdominal vein) is easily visible lateral to the teats on smaller pigs. The animal in the photograph weighs about 30 kg. The vein travels subcutaneously on the lateral part of the abdominal musculature. The vein can often be palpated as a groove in this muscle.
For blood sampling a vacuum tube and a 20 gauge needle is used. The needle is inserted where the vein is most visible. On the picture it has been inserted in a cranial direction just lateral to the second teat. The vein appears larger in this photograph because of a small haematoma. The vein fills maximally during expiration, a wave of blood is often seen as expiration begins. It is often an advantage to bend the needle slightly at the point where it joins the plastic needle holder, so that the holder remains above the skin. In this way the operator avoids sticking too deeply.
Pigs weighing more than 50 kg must be immobilized as described earlier using a snout rope. The vein is palpated and the skin is punctured at the point where the vein is felt most clearly. The vacuum tube is then connected and the needle is carefully moved around until the vein is punctured. The photograph shows a young sow. The operator is standing on the animal's right side and inserts the needle rostrally. This is usually considered to be the best position for right-handed operators. On the animal's left side it is usually easiest to insert the needle caudally.
This photograph shows an old sow after weaning. The vein is punctured between the mammary glands. This is where the milk vein is easiest to palpate. The vein may be hidden by the glands on sows with well-developed udders. In pigs from about 5 months of age and upwards it has been stated that it is possible, with training, to obtain enough blood for serological investigations in about 90% of cases. The technique has the advantage of being relatively easy to learn, and the operator is slightly further away from the noise source! In some sows it is possible to collect blood using this technique without any form of immobilization while they are lying down or standing in their pen.
The tail vein
The medial caudal vein lies in a groove under the tail, next to the artery. The operator raises the tail with one hand and punctures the vein with the other. Vacuum tubes and 20 gauge needles are used. The puncture site is at the first freely movable tail joint. This is around the fifth tail vertebra. In adult pigs the needle should be inserted at an angle of 45 degrees to the skin. In smaller pigs it is recommended to hold the tail nearly horizontally and to stick the needle in nearly parallel to the skin.
This photograph shows a close-up of blood collection in the medial caudal vein. It is difficult to obtain large amounts of blood even in large pigs. The artery lies right next to the vein, and arterial blood is not uncommonly collected instead. There is, however, no undue risk in taking blood from this site.
In experiments where it is necessary to take frequent blood samples, it may be desirable to insert a permanent venous catheter. This may be placed in the external jugular vein. The catheter is inserted under general anaesthesia, and is tunnelled dorsocaudally to the neck, using a metal rod. The catheter is led out through the skin via a small incision. It is then possible to take blood samples without disturbing or stressing the animal.
The end of the catheter can be hidden in a small bag sewn onto the skin. The bag can be opened and closed as required (the bag is homemade). After blood withdrawal the catheter is rinsed with a heparin solution. The catheter can also be used for injections or infusions.
This picture, kindly supplied by Dr. William Campaigne at Lone Star Laboratory Swine, Sequin, Texas, USA, demonstrates the use of the tail vein for blood collection.
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