I read the article “Procaine Spinal Neurotoxicity” by Drs. Johnson and Swanson1with great interest. At the same time, I became curious about their use of 10% procaine for spinal anesthesia. The risks of intrathecal administration of highly concentrated procaine were outlined before, in both a clinical report describing 14 cases of cauda equina syndrome after durocaine (10% procaine with a vehicle of glycerin and ethanol) and an animal study suggesting that the induced cauda equina syndrome resulted not from drug additives but procaine itself.2,3 

In 1991, Rigler et al.  described four cases of cauda equina syndrome after spinal anesthesia using 5% lidocaine or 0.5% tetracaine.4Their report resulted in rediscovering and widely reporting the serious reality of the risks associated with the highly concentrated local anesthetics in use for spinal anesthesia. Although various mechanisms for local anesthetic neurotoxicity have been advocated, the mechanisms remain unclear. However, it is widely accepted that the use of highly concentrated local anesthetics is associated with a substantial risk for cauda equina syndrome.5Eisenach and Yaksh6also indicated the importance of this risk in an editorial, citing the dictum of Paracelsus that “there is no safe drug, only safe doses or concentrations.”

Why did the authors, who had previously raised concerns about the potential risks of procaine spinal anesthesia,7decide to use 10% procaine? I cannot find an acceptable justification in their report.

Tsuruta Orthopedic Clinic, Ushizu, Saga, Japan. 04923004@edu.cc.saga-u.ac.jp

Johnson ME, Swanson JW: Procaine spinal neurotoxicity Anesthesiology 2008; 109:349–51
Ferguson FR, Watkins KH: Paralysis of the bladder and associated neurological sequelae of spinal anaesthesia (cauda equina syndrome). Br J Surg 1938; 25:735–52
MacDonald AD, Watkins KH: An experimental investigation into the cause of paralysis following spinal anaesthesia. Br J Surg 1938; 25:879–83
Rigler ML, Drasner K, Krejcie TC, Yelich SJ, Scholnick FT, DeFontes J, Bohner D: Cauda equina syndrome after continuous spinal anesthesia. Anesth Analg 1991; 72:275–81
Strichartz GR, Berde CB: Local Anesthetic. Miller's Anesthesia. Vol. 1. 6th Edition. Edited by Miller RD. Philadelphia, Churchill Livingstone, 2005; pp 597–8Miller RD
Churchill Livingstone
Eisenach JC, Yaksh TL: Safety in numbers: How do we study toxicity of spinal analgesics? Anesthesiology 2002; 97:1047–9
Johnson ME: Neurotoxicity of spinal procaine – a caution. Reg Anesth Pain Med 2001; 26:288