Dorsal Penile Nerve Block

Anatomy and Physiology

The innervation of the penis is derived from sacral nerve roots S2 through S4 via the pudendal nerve, which runs in the pudendal canal with the pudendal artery. The pudendal nerve divides within the pudendal canal to give terminal branches, the dorsal penile nerves, and the perineal branch. The dorsal nerve on each side passes under the inferior ramus of the pubis, deep to the suspensory ligament, and each lies in its own space, which rarely communicates. These then continue directly within Buck’s fascia on the penis next to the dorsal vessels. The frenulum of the penis, in addition to receiving supply from the dorsal penile nerves, also receives innervation from a branch of the perineal nerve.

Indications

A dorsal penile nerve block is a useful technique in the following situations:

• Circumcision: Performed under local anesthesia or for postoperative analgesia after a general anesthetic procedure
• Dorsal slit procedure
• Paraphimosis reduction
• Repair of penile laceration
• The release of trapped penile skin (zipper injuries)

Contraindications

Skin/soft tissue infection at the injection site and allergic reaction to local anesthetic agents are the most common absolute contraindications. Bleeding diathesis, uncooperative patients, or patients with needle phobia are also relative contraindications depending on circumstances.

Equipment

Most practitioners develop their preference regarding the equipment and local anesthetic agent they prefer to use; however, a minimal list is outlined below:

• Skin prep: Chlorhexidine or povidone-iodine solution
• Disposable drape
• Gauze swabs 4 x 4
• Two 10-mL syringes
• Needles: A 19- or 21-G syringe for deeper infiltration of local anesthetic if required, a 25-G syringe for administering a local anesthetic to the skin, and an 18-G syringe for drawing up local anesthetic
• Local anesthetic solution without adrenaline/epinephrine

Personnel

A dorsal penile nerve block can be safely performed by an individual trained in the prescribing and administration of a local anesthetic. With proper prior preparation, the procedure does not require an assistant; however, for those performing the procedure for the first time, the assistance of a colleague experienced in local anesthetic blocks is recommended. Assistants can also be helpful if items are dropped or forgotten, enabling them to quickly replace them without interrupting the procedure. Clinicians should talk with the patient to reduce anxiety and improve the performance of the block.

Preparation

The required equipment should be gathered and laid out systematically so that each item is readily available and can be removed from its packaging. Consent should be obtained for the local anesthetic block and any subsequent procedure. The patient’s weight should be established or estimated in kilograms. Your local anesthetic agent of choice should be selected, its expiry checked, and the maximum dose calculated for your patient, based on their weight, the anesthetic agent, and the available concentration. Dosing should be based on your department's local anesthetic policy; if no such policy exists, you should use the standard dosing regimens outlined here.[1][2]

Drug Concentration mg/mL (Maximum Dose [mg/kg])

• Lidocaine 1% 10 mg/mL (3 mg/kg)
• Lidocaine 2% 20 mg/mL (3 mg/kg)
• Levobupivacaine 0.25%: 2.5 mg/mL (2 mg/kg)
• Levobupivacaine 0.5%: 5 mg/mL (2 mg/kg)

It is important to calculate the maximum safe dose accurately. This cannot be overstated, and if the healthcare professional is unfamiliar with this process, they should not perform the local anesthetic block. The patient should be positioned supine in a comfortable position with his genitalia exposed. The area should be cleaned of any gross contamination or debris. The skin prep should be applied generously to cover the suprapubic region, penis, and scrotum. Sterile disposable drapes should be applied to the area to maintain sterility.

Technique or Treatment

A dorsal penile nerve block is typically achieved through either a ring block at the base of the penis or a dorsal penile nerve block at the level of the pubic symphysis, or a combination of the 2.[3][4] Both techniques are outlined below.

Dorsal Penile Nerve Block

The objective of this technique is to inject sufficient local anesthetic into the bilateral spaces deep to the fascia on either side of the suspensory ligament. Begin by injecting a small volume of local anesthetic at the skin at the dorsum of the base of the penis with a small-gauge needle to raise a "bleb" or wheal of local anesthetic. Switch to a larger-gauge needle, if required, which is inserted via the anesthetic bleb and advanced until it touches the pubic symphysis, which allows the practitioner to gauge the depth required.

The needle is then withdrawn slightly and redirected to pass below the pubic symphysis, slightly laterally and approximately 3 to 5 mm deeper to enter the appropriate space; the syringe is aspirated to ensure there is no flashback indicating the needle tip lies in an artery/vein, and the local anesthetic is infiltrated. The procedure is repeated for the contralateral space, taking care to withdraw the needle to prevent inadvertent damage to the suspensory ligaments and the dorsal venous structures.

Different practitioners advocate different approaches. Some reduce the number of needle passes by performing the entire block through a midline approach, angling the needle to avoid midline structures and to reach the left and right dorsal nerves below the symphysis. Others, to minimize risk, repeat the procedure entirely lateral to the midline to avoid damage to midline structures, but at the expense of requiring multiple injections to achieve the block.

Due to the innervation of the frenulum of the penis, a dorsal nerve block often does not achieve total anesthesia. In these circumstances, it is advisable to instill further anesthetic at the base of the ventral penis or a partial ventral ring block.

Ring Block

A minimum of 2 injection sites is required for an effective ring block. Injections are typically positioned laterally to allow them to circumscribe the entire penis with the local anesthetic. Care must be taken not to infiltrate too deeply or injure any vasculature or the urethra, leading to a penile hematoma.

Complications

The most common complication is a patient complaining of pain during any subsequent procedure. This may represent an incomplete block, the patient experiencing tactile sensation, or insufficient time for the block to take full effect (typically 10 to 15 minutes). Pain during injection can be reduced by slowing the rate of injection of the local anesthetic.[5] Bleeding and hematomas are common and can usually be controlled with pressure and dressings. Local anesthetics with adrenaline/epinephrine should never be used, as this has been associated with tissue damage and ischemia.[6]

Clinical Significance

Dorsal penile nerve blocks are an effective clinical tool. They provide a rapid onset of anesthesia, allowing treatment of penile conditions in both elective and emergency settings. When used judiciously, they can prevent the need for general anesthesia and enable prompt treatment in the emergency department. Primary care providers who wish to perform a dorsal penile nerve block should be familiar with the anatomy of the penis to avoid complications.

A meta-analysis provides level I evidence that dorsal penile nerve block is more effective for analgesia than an eutectic mixture of local anesthetics block, with a small incidence of failure (4%-8%) and hematoma (5%).[7]

Enhancing Healthcare Team Outcomes

An interdisciplinary team comprising the clinician performing the procedure and an experienced nurse assistant yields the best clinical outcomes. During the procedure, the nurse can provide instruments and communicate with the patient to reduce their anxiety.