Reinventing IM and Procedural Injections: The Sota Omoigui Short Needle Technique
Intramuscular and procedural injections are common practice in modern medicine and are used by virtually all clinical specialists. Millions of injections are administered worldwide every year for curative and preventive purposes.
In intramuscular (IM) injections, one of the most common routes of administration, medication is injected directly into a muscle, where it may be absorbed into the bloodstream quickly or gradually, depending on the viscosity and formulation of the medication, local blood supply, and depth of the injection. Principal injection sites are the deltoid muscle of the arm, the vastus lateralis muscle of the leg, and the ventrogluteal and dorsogluteal muscles of the buttocks. Needles used for IM injections generally are 1 to 1.5 inches long and 19- to 22-gauge in size.
Procedural injections (eg, nerve blocks, pain site injections, trigger point injections into the cervical, thoracic, or lumbar paraspinal muscles, epidural and facet injections) incorporate insertion of a needle through the skin, subcutaneous tissue, and muscle into deeper structures. Needles used for these injections generally are 1 to 3 inches long and 19- to 25-gauge in size.
A complication that may be associated with these injections is nerve trauma arising from needle contact with a nerve. Such complications can be minimized by the use of shorter, higher-gauge (smaller-bore) needles.
Factors Influencing the Injection Process
There are multiple factors that influence the selection of injection type as well as the injection process, including patient characteristics (size and weight), the site of the injection, and needle characteristics (length and gauge).
The skin has multiple layers of ectodermal tissue and guards the underlying muscles, bones, ligaments, and internal organs. For the average adult, the skin has a surface area of between 1.5 and 2 square meters (16.1- 21.5 square feet), with most being between 2 to 3 mm (0.10 inch) thick.1 The various sites used for injections also have differing amounts of muscle and can affect the injection. Gibney et al used ultrasound to measure skin and subcutaneous adipose layer thickness at sites used for insulin injections in adult subjects (18-85 years) with diabetes and Basic Metabolic Indices between 19.4-64.5 kg/m2 (Table 1).1
The appropriate choice of injection site helps prevent complications—for example, dorsogluteal injection should be avoided in obese patients and to prevent any nerve injury. Review of the literature found that injury to the sciatic nerve is associated with use of the dorsogluteal site for injection.2 Therefore, when giving gluteal injections, it is safest to use the upper outer quadrant (ventrogluteal site).
Another safe alternative site is injecting into the lateral thigh (vastus lateralis), which avoids accidental sciatic nerve injection. The uptake of drugs from the thigh region is slower than from the arm (deltoid muscle) but faster than from the buttock, thus facilitating better drug serum concentrations than is possible with the gluteal muscles.3 In fact, the vastus lateralis site can hold up to 2 mL of fluid. It can be used in patients administering their own medication and also in children.
The thickest part of the deltoid muscle is 2.5 to 5 cm below the lower edge of the acromion process of the scapular. The deltoid site is used especially in outpatient setting. However, caution is needed because of the close proximity of the radial nerve, brachial artery, and bony processes.
The ventrogluteal site provides the greatest thickness of gluteal muscle (consisting of both the gluteus medius and gluteus minimus), and is free of penetrating nerves and blood vessels, and has a narrower layer of fat of consistent thinness than is present in the dorsogluteal site.4 This site may be the best choice for very thin patients.
The route of injection is dependent on the site to be injected and the nature of the medication to be injected.5 For example, injecting vaccines into the layer of subcutaneous fat may result in slow mobilization and processing of antigen because there is poor vascularity compared to the muscular layer. When compared with IM administration,6 subcutaneous injection of hepatitis B vaccine leads to significantly lower seroconversion rates and more rapid decay of antibody response.7
Administration of IM Injections
For IM injections, the current approach requires that a needle used to administer medication intramuscularly should be long enough to reach deep into the target muscle without penetrating the structures underneath. A slender individual with very little fatty tissue may need a 1-inch long needle, whereas someone heavier will need a 1½- to 3-inch needle.8
When administering an IM injection to the buttocks, the total depth from the skin to the muscle layer would be an average of 17.8 mm. Therefore, a 30 G, 1-inch (25-mm) needle will pass through the skin and subcutaneous tissue and penetrate only 7.2 mm into the muscle whereas a 25 G, 1½-inch (37.5-mm) needle will penetrate 19.7 mm.
Complications of IM injections include bleeding, soreness, redness at the site, allergic reaction to the medication, infection, abscess, hematoma, pain at the injection site, nerve injury, numbness, and tingling.9 However, serious reactions to IM injections are rare.
In one series of 26,294 adults, of whom 46% had received at least one IM injection, only 48 (0.4%) had a local adverse reaction.7 Muscle is probably spared the harmful effects of substances injected into it because of its abundant blood supply.2
In contrast, subcutaneous injections can cause abscesses and granulomas.3,5 Adipose tissue, having much poorer drainage channels, retains injected material for much longer and is, therefore, also more susceptible to its adverse effects.
At the L.A. Pain Clinic, we routinely perform IM and ultrasound-guided procedural injections to alleviate inflammation and relieve pain. During ultrasound guidance for spinal procedures, we have observed that a clear solution of lidocaine 2% injected from a 30-G, 5/8-inch (15.6-mm) needle using a 3-mL syringe and inserted just lateral to the spinous process into the paraspinal muscles travels a distance of 4 to 6 cm (Figure 1).
Insertion of the needle this distance was sufficient to allow the medication to travel down to the vertebral lamina and produce anesthetic block to relieve radicular pain from the nerve roots within minutes.