Invasive procedures can cause significant anxiety in patients both young and old, much of which is related to fear of the associated pain. Topical anesthesia has been shown to decrease pain and anxiety surrounding procedures such as lumbar puncture, intravenous access, and laceration repair.1 This chapter will discuss topical anesthetic agents and the range of techniques that are available for delivery of these agents.
Mechanical, thermal, and chemical stimuli are detected by nerve endings called nociceptors. These pain receptors are located in the skin, specifically in the dermis and the epidermis, below the stratum corneum (Figure 124-1). 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 transverse the stratum corneum to be delivered to the terminals of cutaneous sensory nerve fibers. 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. Refer to Chapter 123 for the complete details regarding the direct injection of local anesthetic solution. This chapter will discuss techniques for enhancing passive diffusion and needle-free administration of local anesthetic agents, collectively known as topical anesthesia.
Cross section of skin with underlying sensory nerve endings.
Topical anesthesia is commonly utilized in the Emergency Department in two situations. The first is the patient experiencing pain from an injury such as a laceration, abrasion, or contusion. The second is in the patient who will undergo a painful procedure such as venipuncture, lumbar puncture, abscess incision and drainage, or laceration repair.
Topical anesthetic agents offer several potential advantages over local infiltration anesthesia. They are less painful to apply, do not distort the wound margins, and decrease the need for sedation.2 The major limitations of topical anesthesia have been the extended time required to achieve anesthesia and the lack of sufficient analgesia in many clinical situations 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.
There are very few contraindications to the use of topical anesthetics. The topical anesthetic agent is typically not systemically absorbed to any significant degree. However, they can cause local adverse reactions and should not be used in patients who are allergic to the medication or its components (such as preservatives). Use care when applying topical anesthetics to mucous membranes, as absorption is typically more rapid and efficient than through skin and more substantial systemic absorption can occur. A relative contraindication to using topical anesthetic agents are patients taking ...