What is a pudendal nerve block?

From the Guidelines

Pudendal nerve block is suggested for patients with retained anorectal foreign body and failure of bedside extraction, as it can improve chances of transanal retrieval. This recommendation is based on the World Journal of Emergency Surgery guidelines from 2021 1. The procedure involves injecting local anesthetic near the pudendal nerve, providing pain relief to the perineum, external genitalia, and lower rectum.

Key Points to Consider

• The pudendal nerve block can be performed using either a transvaginal or transperineal approach, with ultrasound guidance increasingly used to improve accuracy and safety.
• Potential complications include vascular injection, hematoma formation, infection, and nerve injury, though these are rare when performed by experienced practitioners.
• The block is particularly useful for procedures in the perineal region, allowing patients to remain conscious with minimal systemic effects.
• In patients with retained anorectal foreign body, it is also suggested to perform a proctoscopy or flexible sigmoidoscopy after foreign body removal, to evaluate bowel wall status 1.

Clinical Considerations

• The choice of local anesthetic, such as 0.5% bupivacaine or 1-2% lidocaine, can affect the onset and duration of the block, with typical onset within 5-10 minutes and duration of 1-4 hours.
• The pudendal nerve originates from sacral nerve roots S2-S4 and provides sensory innervation to the perineum and motor function to the external anal sphincter, making this block particularly useful for procedures in this anatomical region.
• In patients with signs of hemodynamic instability or perforation, transanal extraction is not recommended, highlighting the importance of careful patient selection and monitoring 1.

From the Research

Pudendal Nerve Block Techniques

• Ultrasound-guided pudendal nerve block at the entrance of the pudendal (Alcock) canal is a technique that minimizes the risk of sacral plexus blockade and anesthetizes all 3 branches of the pudendal nerve before they ramify in the ischioanal fossa 2.
• Transsacral S2-S4 nerve block is an option for successful relief of pain due to pudendal nerve injury, and can be used as a diagnostic and therapeutic option for pudendal neuralgia 3.
• Real-time ultrasound guidance can be used to perform pudendal nerve block, allowing for easy identification of anatomical structures and local anesthetic spread 4.
• A new technique of ultrasound-guided transperineal approach for pudendal nerve block in children has been described, which improves the safety of the technique by providing real-time visualization of anatomical structures and local anesthetic spread 5.
• An ultrasound-guided technique for pudendal nerve block has also been developed in cat cadavers, which could be proposed to provide peri-operative analgesia in clinical patients undergoing perineal urethrostomy 6.

Efficacy and Safety

• The ultrasound-guided technique for pudendal nerve block at the entrance of the pudendal (Alcock) canal has been shown to be effective in alleviating pain in patients with chronic perineal pain, with no affection of the sacral plexus nerve branches 2.
• Transsacral S2-S4 nerve block has been shown to be effective in treating pudendal neuralgia, with significant reduction in pain scores in patients who underwent the procedure 3.
• Real-time ultrasound guidance for pudendal nerve block has been shown to be safe and effective, with easy identification of anatomical structures and local anesthetic spread 4.
• The new technique of ultrasound-guided transperineal approach for pudendal nerve block in children has been shown to have a good success rate, with real-time visualization of anatomical structures and local anesthetic spread improving the safety of the technique 5.
• The ultrasound-guided technique for pudendal nerve block in cat cadavers has been shown to be feasible, with homogeneous spread of the tracer around the pudendal nerve sensory branches 6.