Injection techniques for drug administration and methods of restraint

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small ruminants dog and cat sphinx position Jos Ensink and Joris Robben 213 In small ruminants, IV injections can be given in the external jugular vein. In fat animals, this vein is poorly visualised and in sheep this area needs to be clipped or shorn. For this reason, the cephalic vein is often used (for the technique, see below). In dogs and cats, the antebrachial part of the cephalic vein is preferred for IV injections as the animal accepts this with minimal restraint, and the vein is easy to locate. The animal is preferably placed on a table in the so-called “sphinx position” (a sitting or standing position is preferred by some animals and can therefore be more successful, but unexpected movements of the animal are more difficult to control). With one hand, the assistant restrains the head of the animal, turning it away to prevent the animal from biting the face of the person injecting. With the arm over the back of the animal, the other hand of the assistant grasps the opposite forelimb of the animal, at elbow level. In large dogs, the assistant thereby leans on the back of the animal, preventing it from sitting or standing up. The assistant compresses the vein with the thumb. In doing so, the entire hand is rotated outward: this causes the slightly medially running cephalic vein to be pulled “on top” of the forelimb, for a better presentation to the person injecting. To prevent the animal from pulling back its limb, the hand and lower arm is kept in contact with the tabletop. In cats, a second assistant may be necessary to control the hind limbs. The forelimb is grasped at the carpus (wrist) by the person injecting (right limb in left hand and vice versa), whereby the thumb is positioned parallel to the cephalic vein to prevent lateral movement of the blood vessel. The person injecting should not grasp the limb too tightly in an effort to extend the limb (this should be performed by the assistant), as this compresses the peripheral part of the cephalic vein, impeding circulation in the vessel. In preparation of the actual injection, the connection of the needle to the syringe should be checked, the calibration markings visible, the eccentric cone placed against the skin and the inside of the bevel visible. The needle is then advanced through the skin, into the blood vessel at an angle of 20-35°. The blood vessel can be punctured directly or the skin next to the blood vessel can be penetrated first, followed by puncture of the vein. The latter method prevents flattening of the vein at the time of skin penetration, which leads to an increased risk of puncturing the opposite venous wall. Once the needle has penetrated the skin, the plunger of the syringe is pulled slightly backward to create slight negative pressure in the barrel, so that blood is aspirated the moment the needle punctures the vein. At this moment, the needle is advanced slightly further into the vessel to ensure that the needle does not slip out when the venous compression is released. Securing the syringe against the ball of the thumb after venipuncture allows the absorbtion of any unexpected limb movements. After releasing the compression (but not the limb!), the solution is slowly injected. After the injection, the skin is pulled taut over the injection site by the assistant after the needle is withdrawn, and kept in this position for a minute. The injection site may also be compressed with a bandage for 5 to 15 minutes. An alternative location for IV injections is the saphenous vein in the hind limb. In dogs, the lateral, in the cat the median saphenous vein is routinely used. The dog is placed in lateral recumbency and the assistant restrains the upper hind limb at the stifle. The thumb is positioned over the patellar tendon, with the fingers around the popliteal area. Increased pressure of the hand will raise the lateral saphenous vein. The vein is better visualised than the cephalic vein, but is more difficult to puncture as proper fixation to reduce lateral movement is harder. In cats, the uppermost limb is held away by the assistant and the femoral vein is compressed in the inguinal area of the opposite (lower) limb. The median saphenous vein is clearly visible through the thin, nearly hairless skin. The external jugular vein is mainly used in small animals if (a large volume of) blood needs to be sampled, or if the injectable substance is too irritant for peripheral injection. For an IV injection in the external jugular vein, the animal is placed in the sphinx or in a sitting position. The assistant stretches the neck by lifting the head, turning it slightly to the contralateral side of which the jugular vein will be used. If this is done slowly and the neck is not overstretched, this generally leads to little resistance. In cats and small dogs it may be necessary to restrain the forelimbs, bringing them in a straight line with the head and neck, so that the person injecting has sufficient room to place the needle and syringe more parallel to the vein. The forelimbs may be restrained by holding them from the back in one hand, with a finger between the limbs. For this, the arm is placed over the back of the animal to the other side and brought
214 horse cattle pig small ruminant dog and cat Chapter 11 Injection techniques for drug administration and methods of restraint behind the forelimbs. In particular in fractious cats and dogs, the “stretching” of the head and forelimbs improves the grip, as it is more difficult for the animal to use its muscles in defence when stretched. It is advisable to restrain the hind limbs separately or to restrain the hindquarters by pressing them with the arm holding the forelimb to the assistant’s upper body.The external jugular vein runs from the base of the ear to the thoracic inlet. By pressing a thumb flatly across the base of the neck, the vein can be raised over the whole length of the neck. There are three methods for locating the vein: releasing compression of the vein will show a deflating vein; compressing and releasing the compression while feeling for the deflating vein with a finger; flicking a finger against the neck while the vein is raised: if the vein is hit, a pulsation can be felt by the thumb compressing the vein. Often, a combination of methods is used. Once the vein has been located, the thumb is positioned just below the middle of the lower neck, so that the thumb can act as support for the needle (after prior disinfection of the thumb with alcohol) and to better prevent the vein from moving sideways. The needle is then inserted just above the thumb at an angle of around 30°. For the rest of the technique, see under cephalic vein. During anaesthesia, the sublingual vein may be used to administer substances or to draw blood. 11.1.3.3 Intramuscular injections In IM injections, the injectable solution should not enter the blood stream as certain substances (e.g. procaine-penicillin suspension in the horse) may cause shock. Prior to injection, the syringe should be briefly aspirated to check whether the needle has not accidentally penetrated a vein. In horses, the pectoral muscle (pectoralis descendens) and the hamstring (biceps, semitendinous and semimembranosus) may be used. An injection in the pectoral muscle will often cause a visible (but benign) swelling; the hamstring is covered by a fascia, making the swelling invisible. When injecting in the hamstring, the operator should stand as close as possible to the shoulder of the horse to avoid injury if the horse kicks. When injecting in the hamstring, restraint may be necessary. The semimembranosus muscle is difficult to reach safely because of its medial position and therefore rarely used. Many horses will tolerate IM injections without too much resistance, especially if the muscle of the injection site is relaxed. This may be obtained by “pounding” a few times on the muscle with the side of the fist, needle in hand, before turning the hand and inserting the needle in the muscle. The injection is carried out as close as possible to the muscle belly, not too close to the insertion on the bone (e.g. ischial tuber for the semimembranosus). After injecting 20 ml, the needle is usually repositioned 10 cm apart for the next 20 ml. In horses, the neck muscles are avoided, as a possible abscess in this area is very difficult to treat: due to the vertical fascia, an abscess is more likely to extend vertically than to burst and drain sideways. If the horse owner insists that the injection is given in the neck (for fear of reduced performance due to pain after injection in the pectoral or hamstring muscles), he should be well informed of this risk. In cattle, the neck muscles are the preferred injection site as these muscles are economically not very important. The injection should be placed in the muscles cranial to the shoulder blade, well above the vertebral column. In animals that need to be given a large number of injections, the hamstring muscles may be used, as in the horse. Cattle will always resist being injected. “Pounding” of the muscles in preparation of needle insertion is of little use and restraint is usually necessary. In pigs, the neck muscles are also used. The needle is inserted in a medio-vertical direction about three fingers’ width behind the ear. Group injections (using revolver syringes) are best carried out at the feeding trough. Young pigs may also be injected in the (more expensive!) hamstring muscles. Care should be taken, not to insert the needle too deeply to avoid damage to the ischiatic nerve. In small ruminants, the triceps muscles may be used for IM injections (accessible in sheep through the hairless skin on the inside of the elbow) or the hamstring muscles. In IM injections of dogs and cats, quantities of 2 to 6 ml are considered acceptable depending on the size of the animal. In dogs and cats, a number of muscles can be considered for IM injections: behind the femur in the hamstring muscles (dog), in front of the femur in the quadriceps muscles (cat), the triceps muscles and the back muscles in the lumbar area (dog and cat). Traditionally, injections have been given in the hamstring muscles. But in this area, two major complications may arise, so that this site is no longer considered acceptable. First of all, there is a risk of severe damage
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