© 2006 World Institute of Pain, 1530-7085/06/$15.00 Pain Practice, Volume 6, Issue 1, 2006 34–38 Blackwell Publishing IncMalden, USAPPRPain Practice1530-70852006 World Institute of Pain? 2006 613438Original ArticleNeural Modulation by Blocks and InfusionsVARRASSI ET AL. Address correspondence and reprint requests to: Giustino Varrassi, MD, FIPP, Department of Anesthesiology, University of L’Aquila, Piazzale Salvatore Tommasi 1, 67100 L’Aquila, Italy. Tel: +39 0862433326; Fax: +39 0862433327; E-mail: giuvarr@tin.it. REVIEW ARTICLE Neural Modulation by Blocks and Infusions Giustino Varrassi, MD, FIPP*; Antonella Paladini, MD*; Franco Marinangeli, MD*; Gabor Racz, MD, FIPP † *Department of Anesthesiology and Pain Management, University of L’Aquila, L’Aquila, Italy; † Department of Anesthesiology, Texas Tech University Health Sciences Center, Lubbock, Texas, U.S.A.  Abstract: Neural blockade is widely used in clinical prac- tice to alleviate acute or chronic pain, including neuropathic pain. However, to date there is little controlled evidence to confirm the efficacy of nerve blocks in neuropathic pain. The most common indication for nerve blocks, especially sympa- thetic blockade, is complex regional pain syndrome, in which success rates of up to 38% have been achieved, depending on the type of the block used. Greater efficacy has been achieved by combining a nerve block with patient-controlled analge- sia. Sympathectomy is recommended for the treatment of neuropathic pain only after careful consideration of its use- fulness, effectiveness, and risk of adverse effects. Current evidence and clinical experience suggest that neural blockade could be a useful adjunct in the management of refractory neuropathic pain, but further well-controlled studies would be of great benefit to support this type of therapy.  Key Words: neural blockade, sympathetic block, neuropathic pain Neural blockade comprises a diverse group of proce- dures that are often used to treat pain in clinical prac- tice, including neuropathic pain. In general, these have been advocated to alleviate acute pain or an exacerba- tion of chronic pain, and to provide direct and localized therapeutic action, especially in patients in whom pain is accompanied by swelling and inflammation. Thera- peutic nerve blocks can help the patient maintain an ambulatory or outpatient treatment status, maintain participation in a physical therapy or rehabilitation pro- gram, decrease the need for analgesics and, in some cases, avoid or delay surgical intervention. MECHANISM OF ACTION The purpose of a nerve block is to interrupt transmission of the pain signal from sympathetic or somatic nerves, or both, to the brain. If the signal cannot reach the brain, then pain is not perceived by the patient. Normally, pain signals travel along nerve fibers to the brain in the form of action potentials; these potentials are propagated by transient depolarization of the nerve cells. The agents most often used to block nerves (eg, peripheral nerves, spinal roots, and autonomic ganglia) are local anesthetics (LAs) such as lidocaine and bupiv- acaine. These drugs block impulses by preventing gen- eration of the “sodium current,” the first step in initiating a nerve action potential. LAs bind to the sodium channel receptors and stabilize (deactivate) them. The sodium channels (which are vital for the generation and conduction of nerve impulses) are closed off, thus blocking the inward membrane-depolarizing surge of sodium ions. Sodium channel blockade pre- vents propagation of action potentials (Figure 1). Although the resting (fully polarized) potential of the blocked nerve is maintained, the LA renders the nerve