Supertrochlear Nerve Block

Anatomy and Physiology

Providers must possess adequate knowledge of the regional anatomy involved in this block to achieve analgesia. The supratrochlear nerve is a division of the trigeminal nerve, specifically the V1 (ophthalmic) branch. The trigeminal nerve divides into the ophthalmic (V1), maxillary (V2), and mandibular (V3). Furthermore, the ophthalmic branch divides into the supraorbital nerve and the supratrochlear nerve. The supratrochlear nerve emerges 3 mm medial to the vertical line drawn from the apex of the lacrimal caruncle along the supraorbital margin.[1] The nerve innervates the paramedian aspect of the forehead and occasionally the part of the eyebrow and internal angle of the orbit.[2]

Indications

The supratrochlear nerve block indications include local anesthesia as needed for procedures or temporary pain relief in the following:

• Migraine headaches[3]
• Laceration repairs
• Procedures (i.e., cosmetic, nerve decompression, etc.)
• Burns
• Rashes (i.e., herpes zoster)
• Trigeminal neuralgia

Contraindications

Contraindications for the supratrochlear nerve block include:

• Allergy to the anesthetic
• Patient/power of attorney/guardian (if the patient is a minor) refusal
• Distorted landmarks/anatomy
• Evidence of infection (i.e., cellulitis) over the site of injection

Equipment

To perform the supratrochlear nerve block, the required equipment includes:

• 3 to 10 mL syringe
• 25 to 30 gauge hypodermic needle
• The local anesthetic choice depends on the desired time of anesthesia and patients’ allergies (i.e., lidocaine, bupivacaine, diphenhydramine, etc.)
• Skin preparing agent, i.e., alcohol or chlorhexidine wipes
• Lipid emulsion for the systemic overdose of local anesthetic (although it is unlikely to be needed as the amount required for the block is orders of magnitude less than what is generally thought to cause overdose)

Preparation

Providers need to discuss the risks and benefits of the procedure and document informed consent from the patient or alternative decision-maker/authority (i.e., the patient’s parent or guardian). Proper preparation includes having all necessary equipment and medication at the bedside. Providers, especially those new to this technique, may also find it helpful to review and map out or even mark the appropriate landmarks prior to infiltrating the anesthetic agent.

Technique or Treatment

The following steps are used in performing the supratrochlear nerve block:

• First, identify landmarks as presented and discussed above in the anatomy section.
  • 3 mm medial to the vertical line drawn from the apex of the lacrimal caruncle along the supraorbital margin
• Use an aseptic solution to cleanse the area in preparation for the injection of the anesthetic. Aseptic solutions may include but are not limited to alcohol, chlorhexidine, or betadine. Betadine, especially on the forehead, can be more irritating than other options noted.
• Next, draw up the desired amount of anesthetic into a syringe, using a 25 gauge (in adults) or a 30 gauge (in pediatrics) hypodermic needle. For most patients, we recommend having 3 to 5mL of anesthetic available for the procedure. Please note, however, that care is necessary when treating pediatric patients, especially infants with this procedure, and it requires attention regarding weight-based toxic dose for the various anesthetic agents.
• We recommend inserting the needle at the site where the supratrochlear nerve emerges. After inserting the needle just under the dermis, the provider should perform a test aspiration to ensure no vascular structures have been breached. Following confirmation of proper positioning, the provider should continue to inject 0.5 to 1.0 mL of anesthetic and create a wheal.
• Next, the provider should advance the needle closer to the supratrochlear nerve. Perform a second test with aspiration and continue to inject another 1.0 to 3.0 mL of anesthetic.
• Lastly, the needle should be removed and pressure applied to avoid bleeding complications. Providers can also gently massage the area to aid in hemostasis and dispersing the anesthetic, respectively.

Complications

Complications vary in frequency, but may include:

• Bleeding/hematoma/ecchymosis
• Infection
• Transection or injury of the supratrochlear nerve and/or supraorbital nerve (given proximity)
• Local anesthetic systemic toxicity (LAST) - symptoms of which can include central nervous system changes, arrhythmias, seizure, respiratory arrest, and coma[4]
• Allergic reaction to the anesthetic

Puncture of angular vein causing hematoma has been described in literature.[5]

Clinical Significance

The supratrochlear nerve block can help anesthetize a large area of the forehead without distorting the tissue, as would be the case with local infiltration. Moreover, it is an alternative to opioids or other pain medications.

The supraorbital nerve block is also frequently used to anesthetize the forehead and, as it innervates a larger portion of the forehead, involves a larger total area, including the periphery of the forehead/face. Performing a supratrochlear nerve block can help anesthetize the paramedian region of the forehead and, in conjunction with a supraorbital nerve block can anesthetize the entire hemi-forehead extending posteriorly to include the anterior portion of the scalp.

Enhancing Healthcare Team Outcomes

Interdisciplinary teams are essential to healthcare. Each member of the healthcare team should cooperate, and the team should operate seamlessly with each member knowing their role and working together to provide the best and highest level of care for each patient.

In many healthcare settings, nurses have the most face to face contact with the patient from triage/introduction to discharge. They can ensure that informed consent was obtained before any procedure. Nurses are often the first to notice abnormal vital signs, allergic reactions and medication side effects including rashes or changes in mental status and can take proactive action by placing them on appropriate monitors (i.e., cardiac or pulse oxygenation), double-checking the patient’s known allergies as well as whether the medication ordered was ordered with the appropriate dose. Their assistance before, during, and after nerve blocks is imperative to minimize adverse effects and complications from any procedure.

Likewise, pharmacy staff can be crucial to provide aid in the selection of alternative agents due to allergies and dosing of less commonly used medications or treatments, such as lipid emulsion, especially in the case of adverse events such as local anesthetic systemic toxicity (LAST). The amount of local anesthetic used, particularly in small regional nerve blocks like the supratrochlear nerve, is so little that concern for LAST is quite minimal.

Nurse practitioners and provider assistants are usually the members of the healthcare team who will perform the supratrochlear nerve block and any related procedures (i.e., laceration repair) if necessary depending on the indication. They are ones who will be held primarily responsible for any significant complications or adverse events. Good communication practices between providers, team members, patients, and the patients’ families are essential for optimal patient outcomes and promote a culture and commitment to patient and provider safety.