Invasive procedures can cause significant anxiety in patients both young and old, much of which is related to fear of the associated pain. Noninvasive anesthesia has been shown to decrease pain and anxiety surrounding procedures (e.g., lumbar puncture, intravenous access, and laceration repair).1,2 This chapter will discuss topical anesthetic agents, noninvasive anesthetic agents, and the range of techniques that are available for delivery of these agents. Not discussed are many of the nonpharmacologic techniques to decrease pain and anxiety except oral sucrose.3-10
ANATOMY AND PATHOPHYSIOLOGY
Mechanical, thermal, and chemical stimuli are detected by nerve endings called nociceptors. These pain receptors are in the dermis and the epidermis of the skin (Figure 154-1). Nociceptors are free nerve endings that have their cell bodies outside the spinal column in the dorsal root ganglia. The intact stratum corneum, the outer layer of cornified epithelial cells of the skin, is an effective barrier to the outside environment. Local anesthetics must traverse the stratum corneum to be delivered to the terminals of cutaneous sensory nerve fibers. The local anesthesia can block or reduce the action potential of the nerve fibers and prevent depolarization of the nerve ending. The three methods by which the stratum corneum can be bypassed to deliver a local anesthetic are direct injection, passive diffusion, and needle-free drug delivery strategies. This chapter will focus on the techniques for enhancing passive diffusion and needle-free administration of local anesthetic agents, collectively known as topical anesthesia.
Cross-section of skin showing cornified stratum corneum surface with underlying sensory nerve endings.
Topical anesthesia is commonly utilized in the Emergency Department. The patient experiencing pain from an injury (e.g., a laceration, abrasion, or contusion) can benefit from the application of topical anesthesia. The use of topical anesthesia is beneficial in the patient who will undergo a painful procedure (e.g., venipuncture, lumbar puncture, abscess incision and drainage, or laceration repair).11,12
Topical anesthetic agents offer several potential advantages over local infiltration anesthesia. They are less painful to apply, overcome aversions toward needles, do not distort the wound margins, decrease the infection rate, are easy to use, and decrease the need for sedation.2 The major limitations of topical anesthesia have been the extended time required to achieve anesthesia (Table 154-1) and the lack of sufficient analgesia that often requires supplemental infiltration anesthesia. These constraints have limited the use of topical anesthesia in the Emergency Department. Several new agents and delivery techniques have addressed these limitations with some success, offering the Emergency Physician more options for providing anesthesia.
TABLE 154-1Characteristics of Topical Anesthetic Agents