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Intrathecal

Medications can be administered intrathecally if they have poor lipid solubility and therefore do not pass the blood–brain barrier (Downie et al. 2003). Only medication specially prepared for the intrathecal route should be used; doses should be carefully calculated and are usually much smaller than would be given by intramuscular or intravenous injection. Water-soluble antibiotics are administered by the intrathecal route to achieve adequate concentrations in the cerebrospinal fluid (CSF) in the treatment of meningitis. Other medicines administered via this route include antifungal agents, opioids, cytotoxic therapy and radiopaque substances (used in the diagnosis of spinal lesions) (Downie et al. 2003) (see Chapter 11).

Preprocedural considerations

Equipment

Ampoules

Ampoules (Figure 13.18) are single-dose glass containers although plastic ampoules are now used for certain products (Downie et al. 2003). They have a wide-ranging capacity and are sealed by heat fusion to exclude any contamination. They have a thin wall which allows rupture of the glass to expose the contents of liquid or powder. There is a narrow constriction leading to the neck which is often marked with a white ring which indicates the place where the neck can be snapped off (Downie et al. 2003). Ampoule opening devices of various designs are available. They are available in several sizes from 1 to 20 mL (Perry 2007).

Figure 13.18 Ampoules.

Vials

Vials (Figure 13.19) are glass containers which have a rubber closure which can be penetrated to allow the addition of a vehicle to dissolve powder contents and to allow the withdrawal of a dose via the needle. The exposed rubber surface is usually covered by a protective pull-off metal or plastic cap which prevents tampering or damage but does not provide sterility (Downie et al. 2003, Perry 2007). The vials may be packaged with a specific transfer needle, and the nurse should follow the manufacturer’s instructions in these instances.

Figure 13.19 Vials.

Syringes

Syringes are commonly plastic and disposable, although some medicines must be administered via glass syringes. They consist of a graduated barrel and a plunger and a tip. It is the tip that classifies the type of syringe as Luer-Lok or Luer-Slip (see Figure 13.20). Syringes come in various sizes from 1 to 60 mL. The choice of syringe is made according to the volume of medication to be administered so it is important to choose the smallest syringe possible to ensure accuracy (Downie et al. 2003, Perry 2007). Luer-Lok requires the needle to be twisted onto the tip and ‘locked’ into position. This provides security and these syringes are recommended for use with intravenous medicines, especially cytotoxic medications and any medicines administered via a syringe pump. Luer-Slip syringes tend to be used for intramuscular and subcutaneous injections. Insulin syringes are low-dose syringes and are often calibrated in units and are only used for insulin administration (Downie et al. 2003, Perry 2007). There are now a number of pre-prepared syringes that contain 0.9% sodium chloride specifically for flushing or ready to administer medicines often used in emergency situations.

Figure 13.20 Syringes: Luer-Lok and Luer-Slip.

Needles

A needle is composed of three parts (see Figure 13.21):

the hub which fits onto the tip of a syringe

the shaft which connects the hub

the bevel or slanted tip or eye of the needle (different bevels are required depending on use of needle).

Needle sizes are known as gauges, for example 19 G, 21 G (used for IM injections), 23 G (subcutaneous injections) and 25 G (intradermal injections). This indicates their diameter. The higher the gauge, the finer the needle and selection is made depending on the viscosity of the liquid to be injected (Downie et al. 2003, Perry 2007). Needles vary in length from 10 to 16 mm and selection of length will depend on the size and weight of patient, and the type of tissue into which the drug is to be injected, for example