Bleedingandintravenoustechniquesinpigs

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 correct point of venepuncture is illustrated in this picture. The needle should be directed caudo-dorsally, in this case perpendicular to the skin.

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.