Giving a Good Needle: Resident Guide to Decreasing Injection Pain

Think back to a busy day and try to recall how many biopsies you performed. Chances are during that time you administered several dozen injections for various indications. Although we have become accustomed to performing injections through repetition, it may be the focus of many patient visits and may be the basis on which a patient judges his/her physician. There are various techniques and products available that can help decrease the physical and psychological burden of injections for patients, some that should be incorporated into a resident’s repertoire to be perfected before becoming an attending.

Factors Related to Anesthetics

The most frequently used local anesthetic in dermatology clinics is lidocaine (1% or 2%) combined with epinephrine 1:100,000. This premixed formulation relieves the burden of mixing for nurses; however, its low pH (4.2) contributes to stinging and burning with infiltration.¹ Buffering with sodium bicarbonate 8.4% in a 9:1 ratio (9 parts lidocaine-epinephrine to 1 part bicarbonate) more closely matches the neutral pH in human tissues and decreases injection pain.² Alkalinizing the anesthetic mixture also decreases the time of onset of its effects, as higher pH solutions convert lidocaine into its active unionized form. However, buffering the anesthetic does have the drawback of decreasing its shelf life, and many clinics no longer store buffered solutions for fear of spoilage. It can be useful to prepare a freshly buffered mixture prior to injecting a particularly needlephobic patient or when injecting in a difficult anatomic location.

In keeping with the philosophy that infiltrating with a solution that closely mimics physiologic parameters minimizes discomfort, a recent meta-analysis found that warming the anesthetic prior to injection led to less pain.³ In my experience, I have found that rolling the syringe between my hands prior to injection also decreases the patient’s sensation of “feeling the anesthetic going in.”

Preinjection Preparation

Properly positioning the patient is paramount to safe injection. Murphy’s Law should be anticipated, not discovered. A few moments spent adjusting the chair and lighting can pay dividends if a patient suddenly has a vasovagal episode. Unfortunately, it is difficult to predict which patients are prone to such attacks, as even a patient who may spend hours playing football in the summer heat could collapse at the sight of a needle. Aside from proper positioning of the patient, the biopsy tray should not be in the patient’s direct line of sight. Even those who tolerate the anesthesia well may become distraught at the sight of bloody gauze.

There are several options for topical anesthesia to decrease injection pain. Cream or gel preparations (ie, eutectic mixture of lidocaine and prilocaine, lidocaine cream, tetracaine gel) generally are cumbersome in a busy clinic setting, as they require at least 30 minutes of contact before anesthesia is achieved; a longer duration of exposure provides further anesthetization and may improve patient outcomes.⁴ However, these formulations may be useful in planned procedures. I have found much utility in utilizing ethyl chloride vapocoolant spray as a numbing agent with an immediate onset of action, a feature that makes this product useful in busy clinics.⁵ Ice is another excellent local coolant and is readily available in most offices at a negligible cost. Placing the ice in aluminum foil instead of a glove delivers more rapid cooling, and the ice is safe to use on areas where vapocoolant spray may be inconvenient or contraindicated, such as around the eyes, nose, ears, or mouth. Holding the ice in place for approximately 10 seconds prior to injection numbs superficial nerve endings and facilitates painless needle insertion.⁶

Injection Technique

Injection technique is arguably the most important factor in minimizing pain for patients and ensuring effective anesthesia in the field. It also is the factor that a patient will either praise or blame, depending on their perception of the injection.

An important point is that the initial injection should be done perpendicular to the skin. The superficial skin has the highest concentration of nerve endings, which branch repeatedly from larger stems in the deeper dermis and subcutaneous fat. Tangential injections disrupt a relatively larger number of nerve endings as the needle tracks through more superficial skin. By injecting perpendicularly, you minimize damage done during the needle’s plunge.²

Anesthetic should initially be deposited into the subcutaneous fat and continued as the needle is withdrawn. Injection directly into the dense dermis leads to pain with hydrodissection, while deeper placement is less painful due to the malleability of fat and a decreased concentration of nerve endings.⁷

Subsequent injections should be strategically placed. Ideally, the initial injection should be the only one that the patient feels, with widening of the anesthetic field achieved by slowly infiltrating lidocaine through skin that is already numb. The needle should be inserted into the wheal and advanced slowly with continuous pressure on the plunger; special attention should be paid to avoid advancing the needle tip past the leading edge of the wheal and into skin with intact sensation (areas of skin that have not yet been numbed by anesthesia and therefore are still capable of sensing pain from injection).⁸ This method of delivering anesthesia with only one initial prick experienced by the patient has been coined the “hole-in-one” technique and has proven to be not only efficacious in minimizing injection discomfort but also easy to learn, even for amateur injectors.⁹