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Obturator Nerve Block Using Ultrasound Guidance

Section Editor(s): Saidman, LawrenceFujiwara, Yoshihiro MD, PhD; Sato, Yutaka MD, PhD; Kitayama, Masato MD, PhD; Shibata, Yasuyuki MD; Komatsu, Toru MD, PhD; Hirota, Kazuyoshi MD, PhD

doi: 10.1213/01.ane.0000268517.37921.ef
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Department of Anesthesiology; Aichi Medical University School of Medicine; Yazako Nagakute, Aichi 480-1195, Japan; yyoshiff@aichi-med-u.ac.jp (Fujiwara)

Department of Anesthesiology; Goshogawara Municipal Hospital; Goshogawara, Aomori 037-8252, Japan (Sato)

Department of Anesthesiology; Hirosaki University School of Medicine; Hirosaki, Aomori 036-8562, Japan (Kitayama)

Department of Anesthesiology; Aichi Medical University School of Medicine; Yazako Nagakute, Aichi 480-1195, Japan (Shibata, Komatsu)

Department of Anesthesiology; Hirosaki University School of Medicine; Hirosaki, Aomori 036-8562, Japan (Hirota)

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To the Editor:

The traditional approach to obturator nerve block was first described by Labat (1). In 1993, Wassef introduced an interadductor approach to obturator nerve block for spastic conditions of adductor thigh muscles (2). Recently, ultrasound guidance has gained popularity in the field of peripheral nerve block, but there is no previous report about ultrasound-guided obturator nerve block.

As the anterior branch of the obturator nerve descends behind the pectineus and adductor longus muscle and in front of the obturator externus and adductor brevis muscles, identification of these muscles is key to success of this block. A high-frequency probe (12 MHz) is placed just distal to the inguinal ligament and medial to the femoral artery with an imaging depth of 4 cm (Fig. 1). Just medial to the femoral vein, pectineus, adductor longs, and adductor brevis muscles are easily identified. The obturator nerve is visualized as hypoechoic circles in a hyperechoic thick layer between the three muscles (Fig. 2). The needle is introduced superiorly to the probe via out-of-plane approach or medially via in-plane approach. Simultaneously, nerve stimulation is begun using a current intensity of 1 mA (2 Hz, 0.1 ms). The needle is slowly advanced to the nerve until the adductor twitch is elicited. We are able to recognize the twitch of muscles on real-time ultrasound image. After the initial twitch is obtained, the current intensity is gradually decreased until adductor twitch is elicited with current output of 0.5 mA. Then, 10 mL of 1% lidocaine is slowly injected (Fig. 3).

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

Using this technique we provided 23 blocks for patients having transurethral resection of a tumor on the posterolateral wall of the bladder and who had received spinal anesthesia. Although proof of a complete blockade of the obturator nerve is a dramatic decrease in adductor muscle strength, which could not be evaluated in this study because of motor blockade caused by spinal anesthesia, contraction of adductor muscle was not evoked by electroresection of the tumor in every patient. Furthermore, we found that the first attempt successfully resulted in twitch of adductor muscle in 21 patients (91%) and it took only 8 ± 3 s to obtain adductor twitch. We propose that ultrasound-guidance makes obturator nerve block much easier, faster and more reliable.

Yoshihiro Fujiwara, MD, PhD

Department of Anesthesiology

Aichi Medical University School of Medicine

Yazako Nagakute, Aichi 480-1195, Japan

yyoshiff@aichi-med-u.ac.jp

Yutaka Sato, MD, PhD

Department of Anesthesiology

Goshogawara Municipal Hospital

Goshogawara, Aomori 037-8252, Japan

Masato Kitayama, MD, PhD

Department of Anesthesiology

Hirosaki University School of Medicine

Hirosaki, Aomori 036-8562, Japan

Yasuyuki Shibata, MD

Toru Komatsu, MD, PhD

Department of Anesthesiology

Aichi Medical University School of Medicine

Yazako Nagakute, Aichi 480-1195, Japan

Kazuyoshi Hirota, MD, PhD

Department of Anesthesiology

Hirosaki University School of Medicine

Hirosaki, Aomori 036-8562, Japan

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REFERENCES

1. Labat G. Regional anesthesia, its technic and clinical application. Philadelphia: WB Saunders, 1928:286–7
2. Wassef MR. Interadductor approach to obturator nerve blockade for spastic conditions of adductor thigh muscles. Reg Anesth 1993;18:13–17
© 2007 International Anesthesia Research Society