How can a landmark‑guided obturator nerve block be performed in an adult patient undergoing transurethral resection of bladder tumor when ultrasound is unavailable?

Landmark-Guided Obturator Nerve Block for TURBT

When ultrasound is unavailable, use the inguinal approach for obturator nerve block, inserting the needle at the midpoint between the femoral artery and the inner margin of the adductor longus muscle, 0.5 cm below the inguinal crease, using a nerve stimulator to confirm proper placement. 1

Why Obturator Nerve Block is Necessary

During transurethral resection of lateral or posterolateral bladder wall tumors under spinal anesthesia, electrical resection can trigger violent adductor muscle contraction (obturator reflex), potentially causing bladder perforation, bleeding, or incomplete tumor resection. 2, 3 Obturator nerve block is therefore mandatory to prevent this complication. 1

Landmark-Guided Technique: Inguinal Approach (Preferred)

Patient Positioning and Preparation

• Position the patient supine with the leg slightly abducted. 1
• Perform the block after establishing adequate spinal anesthesia. 2, 1

Anatomical Landmarks and Needle Insertion

• Identify the femoral artery by palpation at the inguinal crease. 1
• Locate the inner margin of the adductor longus muscle by having the patient adduct the thigh or by palpation. 1
• Insert the needle at the midpoint between these two structures, 0.5 cm below the inguinal crease. 1
• Advance the needle perpendicular to the skin or slightly cephalad. 1

Nerve Stimulator Guidance

• Use a nerve stimulator set at 1-2 mA initially, then reduce to 0.3-0.5 mA once adductor contraction is elicited. 3, 1
• Confirm proper placement by observing adductor muscle twitches (thigh adduction). 3, 1
• The obturator nerve has anterior and posterior branches; block both by redirecting the needle slightly after the first successful stimulation. 3

Local Anesthetic Administration

• Inject 5 mL of 0.5% bupivacaine for each branch (anterior and posterior), totaling 10 mL per side. 3
• For bilateral lateral wall tumors, perform bilateral blocks using 20 mL total. 2
• Aspirate before injection to avoid intravascular administration. 3

Alternative Landmark Approach: Classic Pubic Approach

If the inguinal approach fails or anatomical landmarks are unclear, use the classic pubic approach as a backup. 1, 4

Technique

• Insert the needle at a point 1.5 cm lateral and 1.5 cm inferior to the pubic tubercle. 1
• Advance the needle perpendicular to the skin until nerve stimulation produces adductor contraction. 1
• Inject 5 mL of 0.5% bupivacaine per branch. 1

Important Caveat

The classic approach has a higher risk of vascular injury compared to the inguinal approach, as the obturator nerve is deeper and closer to vascular structures. 1, 4 The inguinal approach is technically easier with a higher success rate (96.1% vs. 84.0%). 1

Success Criteria and Troubleshooting

Defining Block Success

• Successful block: No adductor muscle contraction during tumor resection. 2, 3
• Mild jerk: Minimal contraction that does not preclude safe resection (acceptable). 2
• Failed block: Significant obturator jerk requiring conversion to general anesthesia (occurs in approximately 8-10% of cases). 2

If Block Fails After 3 Attempts

• Do not exceed 3 needle insertion attempts per side to minimize tissue trauma and patient discomfort. 1
• Convert to general anesthesia with muscle relaxation if the block fails. 2

Safety Considerations and Monitoring

Expected Motor Block Onset

• Motor block onset occurs within 6-12 minutes after injection. 3
• Wait at least 10-15 minutes before starting resection to ensure adequate blockade. 3

Complications to Monitor

• Vascular injury: Higher risk with the classic pubic approach; aspirate before injection. 1, 4
• Local anesthetic systemic toxicity: No toxicity was observed in a series of 159 patients, but continuous vital sign monitoring is essential. 5
• Bladder perforation: If perforation occurs despite the block, immediately insert a large-bore urethral catheter (20-24 Fr) with continuous drainage. 5
• Neurovascular injury: Rare but possible; avoid excessive needle manipulation. 2

Fluid Management During the Procedure

• Administer 500 mL isotonic saline preload before spinal anesthesia to reduce hypotension risk. 5
• Maintain intraoperative crystalloid infusion at 1-4 mL/kg/hr. 5, 6
• Give goal-directed fluid boluses of 200-250 mL if stroke volume decreases by ≥10%. 5, 6
• Avoid fluid overload in patients with cardiac or renal comorbidities. 5, 6

Key Pitfalls to Avoid

• Do not skip nerve stimulator confirmation: Landmark-only techniques without nerve stimulation have lower success rates. 3
• Do not use excessive local anesthetic volumes: Stick to 5 mL per branch to minimize toxicity risk. 3
• Do not proceed with resection if block adequacy is uncertain: Test for adductor contraction before starting surgery. 2
• Do not ignore patient anatomy: In obese patients or those with difficult landmarks, consider converting to general anesthesia rather than risking multiple failed attempts. 1