How can we perform a purely landmark-guided obturator nerve block for transurethral resection of bladder tumor (TURBT) when a nerve stimulator is unavailable?

Landmark-Guided Obturator Nerve Block for TURBT Without Nerve Stimulator

When a nerve stimulator is unavailable, perform a blind anatomical landmark-guided obturator nerve block using the pubic tubercle as your primary reference point, injecting 10-20 mL of local anesthetic 2-2.5 cm lateral to the pubic tubercle and 2 cm deep to the superior pubic ramus, which achieves successful block rates of 94-97% in preventing obturator reflex during lateral bladder wall tumor resection.

Anatomical Landmarks for Needle Placement

Primary landmark approach:

• Identify the pubic tubercle by palpation - this is the most reliable and least variable landmark for obturator nerve localization 1, 2
• Insert the needle 2.0-2.5 cm lateral to the pubic tubercle on the sagittal plane 1, 2
• Advance the needle perpendicular to the skin to a depth of approximately 2.0 cm beyond the superior ramus of the pubis 2
• The nerve consistently lies at this depth relative to the bony landmark 2

Alternative reference points if needed:

• The obturator nerve exit point is located approximately 5.1-5.4 cm lateral to the pubic symphysis 2
• The inguinal ligament serves as another reliable landmark with low anatomical variability 1

Technical Procedure Details

Equipment and medication:

• Use a 22-gauge spinal needle for the block 3
• Inject 10-20 mL of local anesthetic (lidocaine 1-2% or prilocaine 1%) 4, 3
• The procedure typically takes 5-6 minutes to perform 4

Step-by-step technique:

• Position the patient supine after spinal anesthesia has been administered 4
• Palpate and mark the pubic tubercle as your primary landmark 1, 2
• Insert the needle 2-2.5 cm lateral to the pubic tubercle 1, 2
• Advance until you contact the superior pubic ramus, then advance an additional 2 cm deeper 2
• Inject the local anesthetic in a fan-like distribution to account for anatomical variability 4

Expected Success Rates and Outcomes

Clinical effectiveness:

• Blind anatomical approach achieves 94-97% success rate in preventing adductor muscle spasms during TURBT 4, 3
• Leg jerking occurs in only 6.3% of patients with landmark-guided technique compared to 34% without block 4
• This success rate is comparable to nerve stimulator-guided techniques, which show 94.2% success 4

Morbidity prevention:

• The obturator nerve block prevents bladder perforation caused by sudden adductor spasms during lateral wall resection 3
• It allows complete tumor resection without surgical interruptions in the vast majority of cases 5
• No local anesthetic systemic toxicity was reported in a series of 159 patients receiving this block 6

Critical Safety Considerations and Pitfalls

Anatomical variability:

• High anatomical variability exists in obturator nerve localization, which explains occasional block failures 1
• Using the pubic tubercle minimizes this variability as it shows the lowest standard deviation from the nerve exit point 1
• A skin entry point at 2.3 cm from the pubic tubercle is associated with very low risk of vascular puncture 2

Common pitfalls to avoid:

• Do not rely solely on the anterior superior iliac spine as a landmark - it shows greater variability 1
• Avoid injecting too superficially - the nerve lies 2 cm deep to the superior pubic ramus 2
• Do not skip the block for lateral wall tumors - bladder perforation risk is significantly higher without it 3
• If adductor spasms occur despite the block during deep resection, stop the procedure immediately to prevent perforation 3

When Block May Be Insufficient

Recognize limitations:

• In approximately 2-3% of cases, minimal adductor jerks may still occur during very deep tumor bed resection 4, 3
• If high-intensity adductor jerks persist despite proper technique, consider converting to general anesthesia rather than risking bladder perforation 5
• The block is most critical for lateral bladder wall tumors where obturator nerve stimulation risk is highest 4, 3

Comparison to Nerve Stimulator Technique

Evidence shows equivalence:

• A randomized study demonstrated no statistically significant difference in success rates between blind anatomical technique (93.7%) and nerve stimulator-guided technique (94.2%) 4
• The blind technique is actually faster to perform (5.2 minutes vs 6.7 minutes) 4
• Both techniques are equally safe with no reported complications of local anesthetic toxicity 4, 3