Which of the following muscles is a possible site for intramuscular injections?

Indications

Although indications have not been well established, generally this procedure is beneficial formigraine, tension-type, posttraumatic, andcervicogenic headaches.

Relative and Absolute Contraindications

Secondary headache disorders are a relative contraindication (seeTable 11.1).

Treatment of the headache should not interfere with treatment of the underlying condition. Although allergy to local anesthetics is very rare, especially allergy to the amides (lidocaine, bupivacaine, and mepivacaine), such an allergy is a contraindication. (SeeChapter 5, Local Anesthetics.)

Editor’s note: Theparabens preservatives are used to prolong shelf life in multidose vials of amide anesthetics and may induce sensitivity reactions similar to those seen with the ester group of local anesthetics (procaine, tetracaine). In fact, parabens are the most likely cause of any “allergy” ascribed to the amides. Fortunately, the incidence of parabens allergy is also quite low. There is also no cross-reactivity between the amide and ester anesthetics.

Equipment and Supplies

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Bupivacaine 0.5% 3 mL (1.5 mL injected bilaterally)

Syringe with 25-gauge, 1.5-inch needle

Ethyl chloride (Gebauer) or Frigident (Ellman Cynosure) (optional vapocoolant sprays to minimize injection discomfort)

Precautions

As with all injections, a sterile technique is essential. Inject slowly to minimize the risk of a vasovagal reaction. It is probably better for the patient to not see the needle nor observe the medication being drawn up into the syringe prior to the injection for the same reason.

Technique

SeeFig. 11.1.

Have the patient seated with the neck flexed, chin toward chest. The forehead can rest on crossed forearms.

Identify the T1 spinous process by finding the superiormost rib. Walk your fingertips medially to the spinous process and move up one or two levels to the C6 or C7 level. Identify the areas for injection bilaterally, 2 to 3 cm lateral to the selected spinous process (two fingerbreadths approximates 3 cm for many people).

Insert the needle, all the way to the hub, angled perpendicular to the cervical spine, and toward the anterior neck.

Once fully inserted to the needle’s hub, aspirate, and if there is no return of blood, inject all of the bupivacaine slowly in one spot. After all of the bupivacaine is injected, withdraw the needle and apply an adhesive strip (Band-Aid) at the site of the injection.

Repeat the injection on other side.

The injection may be repeated once in 20 to 30 minutes if the headache has not resolved.

Publisher Summary

This chapter describes intramuscular drug administration. In contrast to intravascular administration, other parenteral dosing procedures, such as intramuscular administration, often cause the formation of a drug depot. Intramuscularly injected drug solvent distributes rapidly in the fascial planes or connective tissue surrounding the muscles. The spreading of aqueous systems is completed almost directly after injection; oily solutions continue to spread from 1 to 5 min before they become to some degree fixed in position. The solvent water spreads more extensively than oily solutions. The injection water is usually taken up by the hyaluronic acid gel; oils localize in the connective tissue spatia in artificial lacunae. In both the cases, the formed depots take a flat shape similar to a pod. The only slowly cleared oil depots certainly continue to change in shape and distribution with time. Deep, firm massage of muscle tissue following an intramuscular injection favors the spread of the depot over a wider tissue area so favoring the absorption rate.

Intramuscular Access

Intramuscular injection involves inserting a needle under ultrasound guidance into a fetal extremity or buttocks (Video Clip 38-1, Coming Soon). Unlike umbilical cord injection, a noxious stimulus to the fetus is provided at the time of intramuscular injection, thereby stimulating the fetal stress response. Although the bleeding risk from intramuscular injection is less than that with intravascular injections, there is still a risk of bleeding and injury from the needle itself. Furthermore, if the fetus is already stressed, blood will be diverted away from muscle (the site of drug administration) and toward the fetal heart and brain. In this case, it may be impossible to estimate how much drug has been absorbed from the intramuscular site.

Intramuscular Injection

Intramuscular injections are one of the most common routes of administering drugs to nonhuman primates. The use of a squeeze cage makes this technique the method of choice for delivering drugs that are available in intramuscular injection form. Small nonhuman primates may be restrained by physical means. Typically either muscles of the caudal thigh, cranial thigh, deltoid, or the longissimus of the back are used. One must be familiar with the normal anatomy of the primate and avoid injecting the intramuscular injection into an area where a blood vessel is located, where a bone is located near the skin surface, or near a nerve, e.g. the sciatic nerve must be avoided when injecting into the caudal thigh muscles especially in small nonhuman primates (Brady, 2000). One author (Line, 1993), quoting the human literature, suggests limiting the volume for intramuscular injection at one site to 0.5 ml in a nonhuman primate up to approximately 3 kg or 1.0 ml in a nonhuman primate up to approximately 13 kg as a means of lowering the risk of sterile abscess formation, muscle contractures, and vascular compression injuries. The tip of the needle is placed deeply into the muscle. The syringe is aspirated to ensure that the needle is not in a blood vessel. If blood is seen, the needle is withdrawn and discarded. When placement is correct, the liquid is injected slowly to allow the muscle fibers to stretch.

Intramuscular Route

Intramuscular administration relies upon the high vascularity of muscle tissue to achieve a moderately rapid onset of action, usually within 5 to 10 minutes. When properly administered, intramuscular injection provides a more rapid onset and offset as compared with enteral techniques (see Fig. 17-4, B). As with enteral techniques, practitioners are limited to a single dose of medication; however, the onset of sedation is more predictable than is the onset of oral techniques. For pediatric dental sedation, injections are typically performed in the vastus lateralis or deltoid muscle. Aqueous solutions are well absorbed following intramuscular injection. Care should be taken to prepare the solution in a volume that is appropriate for the size of the injected muscle because excessive volume may cause pain and/or tissue damage and hinder absorption. The most common error in the delivery of intramuscular injections is failure of the injected solution to be deposited deep in the muscle bed, where maximum absorption can take effect. Misplaced or superficial injections result in deposition of the solution in fascia or subcutaneous tissue, resulting in slower, less predictable onset.

As with local anesthetic techniques, knowledge of the anatomy of the injection site is mandatory for safe and effective delivery. The vastus lateralis muscle on the ventral thigh is often preferred due to its larger size and relative easy access in small children. The upper outer quadrant of the gluteus maximus muscle and the middle of the deltoid muscle are other acceptable sites as long as muscle development is adequate. Once the medication has been injected, if the desired effect is not achieved within 25 to 30 minutes, termination should be considered. As with oral agents, additional intramuscular injections are not advisable, and may create unintended sequelae for a prolonged period of time.