Chapter 15: Medicines optimization: ensuring quality and safety
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Subcutaneous injection
Definition
Subcutaneous injections are given beneath the epidermis into the loose fat and connective tissue underlying the dermis and are used for administering small doses of non‐irritating water‐soluble substances such as insulin or heparin (Downie et al. [82]).
Related theory
Subcutaneous tissue is not richly supplied with blood vessels and so medication is absorbed more slowly here than when given intramuscularly. The rate of absorption is influenced by factors that affect blood flow to tissues, such as physical exercise and local application of hot or cold compresses (Ostendorf [277]). Other conditions can prevent or delay absorption due to impaired blood flow, so subcutaneous injections are contraindicated in conditions such as circulatory shock and occlusive vascular disease (Ostendorf [277]).
Evidence‐based approaches
Injection sites recommended are the abdomen (in the umbilical region), the lateral or posterior aspect of the lower part of the upper arm, the thighs (under the greater trochanter rather than midthigh) and the buttocks (Downie et al. [82]) (Figure 15.28). It has been found that the amount of subcutaneous tissue varies more than was previously thought; this is particularly significant for administration of insulin, as inadvertent intramuscular administration can result in rapid absorption and hypoglycaemic episodes (King [156]). Rotation of sites can decrease the likelihood of irritation and ensure improved absorption. If using the abdominal area, try to inject each subsequent injection 2.5 cm from the previous one (Chernecky et al. [39]). Injection sites should be free of infection, skin lesions, scars, birthmarks, bony prominences, and large underlying muscles or nerves (Ostendorf [277]).
Figure 15.28 Sites recommended for subcutaneous injection. Source: Adapted from Perry et al. ([282]) with permission of Elsevier.
The skin should be gently pinched into a fold to elevate the subcutaneous tissue, which lifts the adipose tissue away from the underlying muscle (FIT [95]). The practice of aspirating to ensure a blood vessel has not been pierced is no longer recommended as it has been shown that this is unlikely to occur (Ostendorf [277], Peragallo‐Dittko [279]). The maximum volume tolerable using this route for injection is 2 mL and drugs should be highly soluble to prevent irritation (Downie et al. [82]).
Pre‐procedural considerations
Equipment
Subcutaneous injections are usually given using a 25 G needle. There is no clinical reason to recommend needles longer than 8 mm in adults (FIT [95]). Where a needle is 6mm or shorter, it may not be necessary to lift a skin fold, unless injecting into slim limbs or the abdomen (FIT [95]). When using a needle of 6 mm length or less, insulin injections should be given at an angle of 90° in adults (FIT [95]). Needles of 6 mm or less should be used in children and adolescents; a skin fold should be lifted, unless a smaller needle (4 mm) is being used, in which case this is not usually required. An angle of 90° is recommended for most insulin injections when using a 4 mm needle (FIT [95]). If the medication is presented in a pre‐filled syringe, do not transfer it into another container or delivery system.
Specific patient preparation
Skin preparation
There are differences of opinion regarding skin cleaning prior to subcutaneous or intramuscular injections. It has been stated that it is not necessary to use an alcohol swab to clean the skin prior to administration of injections providing the skin is socially clean (FIT [95]). Further studies have suggested that cleaning with an alcohol swab is not always necessary, as not cleaning the site does not result in infections and may predispose the skin to hardening (Dann [51], Koivistov and Felig [159], Workman [376]).
In a study over a period of 6 years involving more than 5000 injections, Dann ([51]) found no single case of local and/or systemic infection. Koivistov and Felig ([159]) concluded that while skin preparations do reduce skin bacterial count, they are not necessary to prevent infections at the injection site. Some hospitals accept that if the patient is physically clean and the nurse maintains a high standard of hand hygiene and asepsis during the procedure, skin disinfection is not necessary (Workman [376]). There is no recent research currently available on what is appropriate skin preparation prior to a simple intramuscular or subcutaneous injection (Wolf et al. [375]).
In immunosuppressed patients, consideration may be given to skin preparation as such patients may become infected by inoculation of a relatively small number of pathogens (Downie et al. [82]); however, advice on this subject will vary between healthcare providers as there is minimal evidence available. The practice at the Royal Marsden Hospital is to clean the skin prior to injection in order to reduce the risk of contamination from the patient's skin flora. The skin is cleaned using an alcohol swab (containing 70% isopropyl alcohol) for 30 seconds and then allowed to dry. If the skin is not dry before proceeding, skin cleaning is ineffective and the antiseptic may cause irritation by being injected into the tissues (Downie et al. [82]).
Procedure guideline 15.17
Medication: subcutaneous injection
Post‐procedural considerations
Education of the patient and relevant others
Patients often have to administer their own subcutaneous injections, for example insulin for diabetics. The nurse must teach the patient how to prepare and administer self‐injection, including aspects such as equipment, storage, hand washing, injection technique, rotation of sites, and safe disposal of equipment and sharps (FIT [95], Ostendorf [277]).
Complications
If medications collect within the tissues, this can cause sterile abscesses, which appear as hardened, painful lumps (Ostendorf [277]). In rare cases, lipohypertrophy (wasting of the subcutaneous tissue at injection sites) can develop (FIT [95]). The nurse must monitor and report these, and avoid using these areas for further injections (FIT [95]).
