Injection techniques for drug administration and methods of restraint

disposable
glass
cone
barrel
plunger
bevel
Gauge
11.1.2 Materials
11.1.2.1 Syringes
Injection syringes should be clean and sterile at all times. This is why disposable syringes are often
used. Re-usable (glass) syringes should be cleaned and sterilised after use. Re-usable syringes are
only cheaper in use if they are not broken too often! Disposable syringes exist in many sizes, from
1 to 50 ml. For larger volumes (250 ml), glass syringes may be used,
but often infusion with the aid of a fluid administration set is a better
solution. In syringes with a small volume, the outflow opening (cone)
is positioned centrally, while larger syringes (usually) have an eccentric
cone (Figure 11.1.). The cone is eccentric to allow the syringe (and
needle) to be held as parallel as possible to the blood vessel during
IV injections. The calibration marks on these syringes are printed on
the barrel opposite to position of the cone. When unwrapping the
disposable syringe, the cone should remain sterile. This is why the
wrapping should be opened at the side of the plunger - and not by
pushing the cone end through the wrapping!
11.1.2.2 Needles
Jos Ensink and Joris Robben 207
Figure 11.1. Disposable
syringes: a 2 ml syringe with a
central cone (left) and a 10 ml
syringe with an eccentric cone
(right)
Injection needles, too, should be clean and sterile and have a sharp and properly-shaped bevel
(needle tip). When whetting re-usable needles, the bevel should not be tapered in such a manner
that it will punch a piece of skin, as this will block the needle upon penetrating the skin. When
using disposable needles, one can be assured of a correct bevel shape. The size of the needle is
determined by its use. The thinner (and sharper) the needle, the less painful it will be. But the
smaller diameter will increase the injection time unacceptably if a large quantity or a viscous
solution is to be injected. For an IM injection, the needle should not be longer than the desired
injection depth to avoid too deep an injection. For SC injections too, a short needle will prevent
a too deep (IM) injection. The size of a needle is described by its diameter in mm (inches) or in
“Gauge” (G) and the length in mm (inches). Each size has its own colour code for easy recognition.
Unfortunately, this colour code is often different depending on the manufacturer. Below, some
common sizes are listed. For each needle size, the corresponding target species and injection
technique is given:
• 0.45 mm (26 G) x 12 mm;
• 0.6 mm (23 G) x 25 mm;
• 0.7 mm (22 G) x 30 mm;
• 0.8 mm (21 G) x 40 mm;
• 0.9 mm (20 G) x 30 mm;
• 1.2 mm (18 G) x 40 mm;
• 1.8 mm (16 G) x 40 mm;
• 2.1 mm (14 G) x 80 mm;
• 2.7 mm (12 G) x 80 mm.
In dogs and cats, 22-23 G needles are most commonly used. For injections of viscous solutions or
blood samples of large volume (e.g. 20 ml), 20 G needles are often used. For small quantities (1 ml,
e.g. vaccines), 26 G needles are used. Their short length is practical for SC injections. In horses,
18 G needles are commonly used for IM and IV injections. In cattle, 18 G needles may be used too,
but they can bend if the animal moves or resists during IM injections. This is why the thicker, 16 G
needles are more often used in cattle. For SC injections in the horse, 23 G needles usually suffice.
If more than one SC depot is required (for example for diagnostic anaesthesia of the lower limb),
the longer, 21 G needles may also be used. For IV infusions of horse and cattle, large-bore needles