To avoid confusion: You must follow local policies and procedures regarding technique, equipment used and documentation.

Introduction

Subcutaneous (SC) injection means injection of a medication into the subcutaneous tissue beneath the epidermis and dermis.

The subcutaneous tissue has a good blood supply but the blood vessels are relatively small and so the absorption rate of the drug will be slower than if given intramuscularly.

Subcutaneous injection is chosen when slow, continuous absorption of the drug is required.

The medicines most commonly administered by SC injection are insulin and low molecular weight heparin (anticoagulant). The maximum volume for SC injection is 2 mL although it is usually much less than that.

Low molecular weight heparins (e.g., enoxaparin and tinzaparin) come in prefilled syringes.

Unlike all other injections, the air in a heparin syringe is not expelled, but is designed to remain in the syringe, next to the piston.

When the small amount of drug is administered, the air fills the needle hub or the nozzle of the syringe and needle ensuring that all fluid has been expelled from the syringe.

This prevents the drug tracking back to the surface as the needle is withdrawn, which can cause skin irritation.

If there is a bubble present in the syringe, it must be adjacent to the plunger so that it follows the drug.

Definition

These 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. 2003).

Related theory

Subcutaneous tissue is not richly supplied with blood vessels and so medication is absorbed more slowly than when given intramuscularly. The rate of absorption is influenced by factors that affect blood flow to tissues such as physical exercise or local application of hot or cold compresses (Ostendorf 2012). Other conditions can prevent or delay absorption due to an impaired blood flow so in these conditions, subcutaeous injections are contraindicated, for example circulatory shock, occlusive vascular disease (Ostendorf 2012).

Evidence-based approaches

Injection sites

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. 2003) (Figure 12.25). 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 2003). Rotation of sites can decrease the likelihood of irritation and ensure improved absorption. If using the abdominal area then try to inject each subsequent injection 2.5 cm from the previous one (Chernecky et al. 2002). Injection sites should be free of infection, skin lesions, scars, birthmarks, bony prominences and large underlying muscles or nerves (Ostendorf 2012).

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 2011). 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 2012, Peragallo-Dittko 1997). The maximum volume tolerable using this route for injection is 2 mL and drugs should be highly soluble to prevent irritation (Downie et al. 2003).

Pre-procedural considerations

Equipment

Injections are usually given using a 25 G needle. To ensure medication reaches the subcutaneous tissue, the rule is: if you can grasp 2 inches of tissue, insert the needle at a 90° angle; for 1 inch, insert needle at a 45° angle (Chernecky et al. 2002, Ostendorf 2012). With the introduction of shorter needles (4–8 mm), it is recommended that insulin injections be given at an angle of 90° (FIT 2011, King 2003). The length of the needle should be selected by pinching the skin tissue and selecting a needle one-half the width of the skinfold (Chernecky et al. 2002, FIT 2011). Shorter needles should also be used at a 45° angle in children and underweight adults.

Specific patient preparation

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 2011). If unsure or in immunocompromised patients, the skin should be prepared using an antiseptic swab (Dann 1969, Downie et al. 2003, FIT 2011).

(Royal Marsden 2015)

The article below will consolidate knowledge = administering medication via the subcutaneous route.