Sympathetic Blockade: Treatment, Effects & Risks

Sympathetic nerve block refers to artificial interruptions of specific nerve branches of the autonomic sympathetic nervous system in specific regions of the body. The usually irreversible interruptions or transections of sympathetic nerves are achieved by endoscopic procedures by mechanical means or by local insertion of chemical substances into a vein that runs close to the nerve to be obliterated. The procedures are performed to treat chronic pain and to control abnormally increased sweating (hyperhidrosis).

What is sympathetic nerve blockade?

Sympathetic blockade is the term used to describe artificial interruptions of certain nerve branches of the autonomic sympathetic nervous system in specific areas of the body. The autonomic nervous system, also called the autonomic nervous system, unconsciously controls a variety of bodily functions, only a few of which can also be consciously influenced, such as breathing. The autonomic nervous system includes the sympathetic and parasympathetic nervous systems, which usually act antagonistically to each other. As a third component, the enteric nervous system (ENS), the visceral or intestinal nervous system, is also included in the autonomic nervous system. The activated sympathetic nervous system places the body under stress and controls bodily functions in such a way that brief muscular and energetic peak performance can be achieved for flight or attack. The parasympathetic nervous system usually acts as an antagonist to the sympathetic nervous system and represents recovery, growth and internal stabilization. The sympathetic system controls not only bodily functions, but also sensations that are consciously perceived such as pain and many others. Sympathetic blocks – contrary to what the term suggests – are usually not of natural origin, but are brought about deliberately by surgical intervention. Sympathetic nerve blocks are performed on specific branches of the sympathetic nervous system in order to literally eliminate obvious dysfunctions whose symptoms cannot be treated in any other way. Sympathetic blockade can be achieved either mechanically by endoscopic intervention or by an agent administered intravenously at the site in the immediate vicinity of which the sympathetic nerve branch passes. Most procedures are reversible unless the nerve has been completely severed.

Function, effect, and goals

The most important indications for performing sympathetic nerve block are primary hyperhidrosis, excessive and uncontrollable sweating of confined areas of the body, and certain chronic pain conditions. Sweating on the body is sympathetically controlled and normally serves to regulate body temperature. With increased perspiration on nearly the entire body surface, the cooling effect of evaporative cooling is utilized and is an effective means of cooling the body down during vigorous exercise and/or high outdoor temperatures. However, the secretion of sweat in certain regions of the body, such as in the armpits, on the forehead and in the intimate area, also serves to communicate, to communicate existing emotional feelings such as fear, aggression, anger or even sexual status. The odorants contained in sweat in these cases are largely absorbed unconsciously and processed directly in the brain stem. In this respect, it seems logical that sweating in the armpits or on the forehead can be the result of an increased stress level and does not have to be coupled with sweating on the entire body for cooling purposes. Some people experience pathologically increased sweating in the armpits and sometimes in other areas of the body, which is very unpleasant for those affected. The increased sweating is often coupled with a blushing in the face. If conservative therapies and symptom control with deodorants or powders are unsuccessful, the only effective therapy left is usually a blockade of the sympathetic nerves that cause excessive sweating in the body regions in question. In most cases, this involves sympathetic nerves in the chest area, when the head and hands are affected, and, with slight spotting, the armpits as well. Sympathetic nerves in the lumbar region must be blocked when the feet and intimate area are affected. Minimally invasive surgical procedures are usually used to block the sympathetic nerves.The blockage itself can be caused by scorching, severing or downright clamping by means of a titanium clip. Clamping by means of a titanium clip is usually reversible. The second field of application of sympathetic nerve blockade is the treatment of chronic pain, which must be diagnosed as being caused by sympathetic nerves. Often it is neuropathic pain as a “remnant” of a serious previous disease such as herpes zoster (shingles). As a therapy, sympathetic nerve blockade is used only when conservative therapies fail to provide lasting pain relief. The procedure usually chosen is blockage of the sympathetic nerve by chemical agents. The agents are injected into a vein that runs close to the nerve segment in question. The vein is tied off for about 20 minutes before and after the injection site during the procedure to prevent the agent from being transported further by the vein before it takes effect at the sympathetic nerve.

Risks, side effects, and hazards

Minimally invasive surgical procedures that aim to block specific nerve segments are very well developed, and the usual risks that apply to other minimally invasive procedures are not higher for sympathetic nerve blocks. However, the procedures require great care because there is a fundamental risk of injuring other nerves or vessels with sometimes serious consequences in individual cases. For example, in the case of a blockade of the sympathetic nervous system in the thoracic region (transthoracic sympathectomy), injury to the stellate ganglion can lead to a unilateral disturbance of facial expression with drooping eyelids (Horner syndrome). Similarly, there is a small risk of vocal cord paralysis. As an undesirable side effect, compensatory sweating occurs with every sympathetic nerve blockade for the treatment of hyperhidrosis, because the nerve blockade does not eliminate the cause of excessive sweating. In principle, surgical techniques that allow the nerve block to be reversed are preferable. In the case of chemical blockade of the sympathetic nervous system by local anesthetics, on the one hand there is the usual risk of injury to the vein or even arterial vessels and a small risk of infection. After reversal of the vein blockade, the anesthetic may cause allergic reactions if intolerance is present.