Injection techniques for drug administration and methods of restraint

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loose-needle technique over-the-needle catheter 11.1.3.2 Intravenous injections Jos Ensink and Joris Robben 211 For IV injections, the vein is raised and the needle is inserted through the skin at an angle of around 30°, with the bevel (needle opening) turned away from the animal (so that the person injecting “looks into the needle”). As soon as the tip of the needle reaches the vein, blood becomes visible at the cone. Then, the needle is pushed in further, parallel to the vein. The compression of the vein is lifted only after the needle has been advanced further to prevent slipping off the needle of the collapsing vein and to reduce the risk of puncturing the vein wall from the inside. The needle may be turned 180° over its longitudinal axis to avoid puncturing the opposite wall while advancing the needle into the vein (see Figure 11.5.). While giving the IV injection, the vein is no longer raised, as the purpose is to dilute the solution directly into the streaming blood. There are two ways to establish the correct position of the needle in the lumen of the vein. A loose needle may be used, so that, once the needle punctures the vein, blood drips from the cone. A continuous blood flow from the needle should be apparent while it is advanced further in the vein. But the needle can also be connected to the syringe prior to injection. Negative pressure is applied to the syringe (by slightly pulling the plunger) once the skin has been penetrated. Figure 11.5. Schematic drawing of a venipuncture. In the drawing on the left, the needle is inserted at an angle of 30°, with the bevel (needle opening) turned away from the animal. On the right, during insertion, the needle is twisted 180° over its longitudinal axis to avoid puncturing the opposite wall of the vein. Blood appears in the syringe the moment the vessel wall is punctured. The “loose-needle” technique is easiest but often causes the hair coat and hands to become soiled with blood. Using an attached syringe prevents blood spillage but maintaining negative pressure requires some dexterity. Also, the 180°-twist of the needle is not possible with this technique. The loose-needle technique is rarely used in companion animals. When giving an IV injection, a little blood is aspirated immediately before the injection is given to check whether the needle is still in the vein. Also during injection, for example after an animal has moved, position should be checked again. At the end of the injection, blood can be aspirated once more to avoid that the (potentially irritating) solution infiltrates the subcutaneous area when the needle is withdrawn. Sometimes, the vein needs to be raised for the aspiration of blood. After needle withdrawal, the injection site is compressed to avoid a haematoma. If the solution (particularly if it is irritant) ends up in the perivenous area, this may lead to inflammation or even necrosis. To prevent this from happening, the perivenous depot of the solution should be diluted as soon as possible. For dilution, a sterile saline solution containing mucopolysaccharidase (e.g. Thiomucase ® ) is used, which improves the passage through the interstitial area, thereby leading to a more rapid absorption of the solution. Following this, a special ointment can be applied several times daily, containing substances that improve diffusion through the interstitial area (e.g. Lasonil ® , a heparinoid/hyaluronidase ointment) but this is less effective than dilution by injection. An over-the-needle catheter is inserted as follows. The skin is clipped and disinfected, and the vein is raised. The catheter is inserted until blood
212 horse cattle pig Chapter 11 Injection techniques for drug administration and methods of restraint appears in the transparent chamber, and is moved a little further into the vessel to make sure that the tip of the catheter, which is slightly shorter than the needle, is also inside the vein. The needle is now held in this position (and certainly not withdrawn), while the catheter is advanced further into the vein. Then the needle is fully withdrawn and the catheter is flushed and capped if not immediately connected to an administration or extension set. The catheter is secured to the skin and protected with a bandage if possible. Catheters are placed towards the heart, firstly to avoid turbulence of the inflowing fluid, and secondly because the catheter can only pass the venous valves in the direction of the heart. Sometimes, resistance is encountered while the catheter is inserted. This could indicate that the catheter is no longer inside the vessel lumen and could crinkle if advanced any further. In this situation, the needle should never be re-inserted into the catheter, as the needle might puncture the catheter. It even may cut off part of the catheter that will remain inside the patient after catheter removal. When encountering problems with catheter advancement, the compression of the vein should be lifted and both needle and catheter should be removed. To prepare for a second attempt, the needle can be carefully re-inserted into the catheter (if still completely intact). If the bottle or bag is left to be emptied completely, depending on the venous pressure, blood may flow into the catheter, causing it to block (e.g. animal in lateral recumbency), or air may flow into the vein, with a risk of air embolism (e.g. standing horse with an IV drip in the external jugular vein). Therefore, someone needs to be present when the bottle or bag is nearly empty, in order to disconnect the administration set or to replace the bottle or bag. In horses, the external jugular vein is most commonly used for IV injections. At about one third between head and shoulders (measuring from the head), the risk of puncturing the carotid artery is minimal, as it runs a little deeper here and is covered by the omohyoid muscle. An assistant slightly lifts the horse’s head up and away from the person injecting. Restraint methods are rarely necessary and will cause the horse to tense up its neck muscles, causing the vein to become less visible. With a hand placed around the front base of the neck, the vein can easily be compressed using a thumb. The vein raises slowly, however, and is not always clearly visible. By sudden release of the compression, the vein can be seen to deflate fast. This action is valuable in establishing the location of the vein. Horses rarely resist venipuncture, especially if the needle is inserted through the skin calmly. If the external jugular veins cannot be used (e.g. damage due to previous injections), the superficial thoracic, cephalic or lateral saphenous veins may be used. Beware of being kicked if using these veins. In cattle, IV injections can also be given into the external jugular vein. Cattle tend to resist more than horses to venipuncture. It is therefore wise to control the head with the use of a rope and/or halter, so that the neck is stretched. A jugular vein clamp or neck tourniquet is recommended. Both skin and venous wall are thick and sturdy in cattle. This means that the needle sometimes needs to be “thrust in” to attain the vein. In cattle, also the subcutaneous abdominal (“milk”) vein can be used for IV injections. This vein is always raised. A disadvantage is that leakage of irritating solutions (e.g. calcium-containing solutions) may lead to extensive inflammatory lesions. When using the subcutaneous abdominal vein, attention should be paid to possible forward kicking of the cow. For blood sampling, the median caudal vein of the tail is often used, as the animal hardly needs to be restrained. This site is less suitable for IV injections, as the vein can only be punctured at an angle of 90° and the needle cannot be advanced very far into the vein. This means that part of the liquid is likely to arrive in the perivenous area by extravasation of the tip of the needle. In pigs, the cranial vena cava at the thoracic inlet or the external jugular vein just cranial of this inlet are suitable for blood sampling but less so for IV injections, as the veins are reached at an angle of around 90° and the needle cannot be advanced very far into the vein. For blood sampling, pigs are restrained as follows: in a standing position large animals are restrained with a noose over the upper jaw; smaller individuals are placed in lateral or dorsal recumbency, or upside-down with the forelimbs held back. An auricular (“ear”) vein is usually chosen for IV injections. The animal is restrained and the base of the ear is clamped by hand or with a tourniquet. For venipuncture, a thin needle or catheter is used, which is secured to the ear with adhesive tape or a clamp to prevent it from dislodging if the animal moves its head.
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