Determining the Maximum Tolerable Concentration of Ropivacaine to Maintain Sensation of the Nerve Root in Percutaneous Endoscopic Transforaminal Lumbar Discectomy: Can Epidural Anaesthesia Achieve Pain-Tactile Separation Block to Avoid Nerve Injury?

Abstract

Introduction

Nerve injury is a serious complication of percutaneous endoscopic transforaminal lumbar discectomy due to nerve root contact. The maximum tolerable concentration (MTC) of ropivacaine concentration for epidural anaesthesia, is defined as the concentration that minimises pain while preserving the sensation of the nerve roots. This distinct advantage allows the patient to provide feedback to the surgeon when the nerve roots are contacted.

Methods

We used a biased-coin design to determine the MTC, which was estimated by the 10% effective concentration (EC₁₀), ie, the concentration at which 10% of patients lost sensation in the nerve roots. The determinant for positive response was lack of sensory feedback upon contact with the nerve root, and the feedback from occurrence of sensations in the innervation area upon contact with the nerve root was defined as a negative response. Primary outcome was the response from contact nerve root. Secondary outcomes were the type and number of statements of negative response and each patient’s pain score during surgery.

Results

Fifty-four patients were included in this study. The EC₁₀ was 0.434% (95% CI: 0.410%, 0.440%) using isotonic regression in comparison with 0.431% (95% CI: 0.399%, 0.444%) using probit regression. Three type statements of negative response were reported including “tactile sensation”, radiculalgia, and numbness.

Conclusion

The MTC of ropivacaine used for epidural anaesthesia was 0.434% to avoid nerve injury in percutaneous endoscopic transforaminal lumbar discectomy.

Keywords:

• maximum tolerable concentration
• epidural anaesthesia
• transforaminal percutaneous endoscopic lumbar discectomy
• biased-coin design
• isotonic regression

Acknowledgments

Bingwei Hu and Xianhui Kang are co-first authors for this study. This research was approved by the Medical Ethics Committee of Tongde Hospital of Zhejiang Province (Zhe Tongde Expedited Review No. [2020]013) and is registered on the website of the Chinese Clinical Trial Registry (ChiCTR2000031593). We wish to thank the orthopaedist Leijun Yu for his first inspiring advice on the “tactile” feedback from nerve root contact. We would also like to express our gratitude to Nurse Qing Jiang for her excellent performance in the follow-up work.

Disclosure

The authors report no competing interests in this work.