The dorsal penile nerve block is an effective technique for gaining regional anesthesia of the penis with small volumes of a local anesthetic. The technique is essential for all practicing urologists and desirable for those who work in emergency departments who see acute presentations such as paraphimosis.
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.
A dorsal penile nerve block is a useful technique in the following situations:
Skin/soft tissue infection at the site of injection and allergic reaction to local anesthetic (LA) agents are the most common absolute contraindication.
Bleeding diathesis, uncooperative patients, or patients with needle phobia are also relative contraindications depending on circumstances.
Most practitioners will develop their preference regarding the equipment and local anesthetic agent they prefer to use; however, a minimal list is outlined below:
A dorsal penile nerve block can be safely performed by an individual who is trained in the prescribing and administration of local anesthetic.
With proper prior preparation it does not require an assistant, but for those performing the procedure for the first time, the assistance of a colleague experienced in performing local anesthetic blocks is recommended.
Assistants can also be useful if any items are dropped or forgotten so that the assistant can quickly replace them without stopping the procedure. Clinicians should talk with the patient to reduce anxiety and improve the performance of the block.
The equipment required should be gathered and laid out methodically so that each item is readily available and 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, expiry checked, and the maximum dose calculated for your patient: based on their weight, the anesthetic agent and the concentration available. Dosing should be based upon your departmental local anesthetic policy, but if no such policy exists, you should utilize standard dosing regimens outlined here.
Drug Concentration mg/mL (Maximum Dose [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, then 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.
A dorsal penile nerve block is typically achieved through either 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. Both techniques will be outlined below.
Dorsal Penile Nerve Block
The objective of this technique is to inject a sufficient amount of local anesthetic into the bilateral spaces deep to the fascia 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 and angle the needle to avoid midline structures and reach the left and right dorsal nerves below the symphysis. Others, to minimize risk, will repeat the procedure entirely just lateral to the midline to ensure no damage to midline structures but at the expense 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.
A minimum of 2 injections sites is required for an effective ring block. Injections are typically positioned laterally to allow it to circumscribe the entire penis with the local anesthetic. Care must be taken not to infiltrate too deeply or to injure any vasculature or the urethra which can lead to a penile hematoma.
The most common complication is a patient complaining of pain during any subsequent procedure. This can either represent an incomplete block, the patient feeling the sensation of touch or typically not enough time being left for the block to take full effect (which is typically 10 to 15 minutes). Pain during injection can be reduced by slowing the rate of injection of local anesthetic.
Bleeding and hematomas are common, and most can be controlled with pressure and dressings.
Local anesthetic with adrenaline/epinephrine should never be used as this has been associated with tissue damage and ischemia.
Dorsal penile nerve blocks are an effective clinical tool. They provide a rapid onset of anesthesia allowing treatment of penile conditions in both the elective and emergency setting. When used judiciously they can prevent the need for a general anesthetic and for patients to be promptly treated in the emergency department. Nurse practitioners or 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 in providing analgesia than a eutectic mixture of local anesthetic (EMLA) block with a small incidence of failure (4% to 8%) or hematoma (5%).