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Local anesthesia

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Local anesthesia is, in a strict sense, anesthesia of a small part of the body such as a tooth or an area of skin.

Regional anesthesia is aimed at anesthetizing a larger part of the body such as a leg or arm.

Conduction anesthesia is a comprehensive term which encompasses a great variety of local and regional anesthetic techniques. The term local anesthesia is sometimes used synonymously with conduction anesthesia.


Techniques

To achieve conduction anesthesia a local anesthetic drug is injected or applied to a body surface. The local anesthetic then diffuses into nerves where it inhibits the propagation of signals for pain, muscle contraction, regulation of blood circulation and other body functions. With relatively high drug doses and/or concentrations, all qualities of sensation as well as muscle control are usually inhibited. With lower doses and/or concentrations it is possible to inhibit pain sensation, to some degree, selectively, without affecting muscle power. This effect, termed differential block, is made use of in some techniques of pain therapy (e.g. "walking epidural" for labor pain).

Anesthesia persists as long as there is a sufficient concentration of local anesthetic at the nerve or nerves to be blocked. Depending on the drug and technique used, this time may vary from less than an hour to more than twelve hours. When a catheter is used for continuous infusion or repeated injection, local anesthesia can be extended for days or weeks. This is typically done for purposes of pain therapy.

Techniques of conduction anesthesia may be classified by the route of drug administration or by the region of the body involved.


Techniques of conduction anesthesia by route of administration

  • surface anesthesia - a local anesthetic spray, solution or cream is applied to the skin or a mucous membrane. The effect is of short duration and is limited to the area of contact.
  • infiltration anesthesia - a local anesthetic is injected into the tissue to be anesthetized.
  • field block - subcutaneous injection of a local anesthetic in an area bordering on the field to be anesthetized.
  • peripheral nerve blocks - a local anesthetic is injected in the vicinity of a peripheral nerve to anesthetize that nerve´s area of innervation.
  • plexus anesthesia - a local anesthetic is injected in the vicinity of a nerve plexus, often inside a tissue compartment that limits the diffusion of the drug away from the intended site of action. The anesthetic effect extends to the innervation areas of several or all nerves stemming from the plexus.
  • epidural anesthesia - a local anesthetic is injected into the epidural space where it acts primarily on the spinal nerve roots. Depending on the site of injection and the volume injected, the anesthetized area can vary from limited areas of the abdomen or chest to extended regions of the body.
  • spinal anesthesia - a local anesthetic is injected into the cerebrospinal fluid, usually in the lumbar spine (lower back), where it acts on spinal nerve roots and part of the spinal cord. The resulting anesthesia usually extends from the legs to the abdomen or chest.
  • intravenous regional anesthesia (Bier block) - blood circulation of a limb is interrupted using a tourniquet (a device similar to a blood pressure cuff), then a large volume of local anesthetic is injected into a peripheral vein. The drug fills the limb´s venous system and diffuses into tissues where peripheral nerves and nerve endings are anesthetized. The anesthetic effect is limited to the area that is excluded from blood circulation and resolves quickly once circulation is restored.
  • local anesthesia of body cavities (e.g. intrapleural anesthesia, intraarticular anesthesia)


Techniques of conduction anesthesia by region of the body

  • topical (e.g. surface anesthesia, infiltration anesthesia)
  • small peripheral nerves (e.g. Oberst block)
  • large peripheral nerves (e.g. femoral nerve block)
  • nerve plexus (e.g. brachial plexus block)
  • spinal cord and spinal nerve roots (spinal and epidural anesthesia)
  • peripheral nerves of a limb (intravenous regional anesthesia)
  • body cavities and joints (e.g. intrapleural anesthesia, intraarticular anesthesia)


Uses in surgery

Virtually every part of the body can be anesthetized using conduction anesthesia. However, only a limited number of techniques are in clinical use. Sometimes conduction anesthesia is combined with general anesthesia for the patient´s comfort and ease of surgery. Typical operations that can be done under conduction ansthesia are:

  • eye surgery (surface anesthesia, retrobulbar block)
  • ENT operations, head and neck surgery, dental surgery (infiltration anesthesia, field blocks, peripheral nerve blocks, plexus anesthesia)
  • shoulder and arm surgery (plexus anesthesia, intravenous regional anesthesia)
  • heart and lung surgery (epidural anesthesia combined with general anesthesia)
  • abdominal surgery (epidural/spinal anesthesia, often combined with general anesthesia)
  • gynecological, obstetrical and urological operations (spinal/epidural anesthesia)
  • bone and joint surgery of the pelvis, hip and leg (spinal/epidural anesthesia, peripheral nerve blocks, intravenous regional anesthesia)
  • surgery of skin and peripheral blood vessels (topical anesthesia, field blocks, peripheral nerve blocks, spinal/epidural anesthesia)


Uses in acute pain

Acute pain may occur due to trauma, surgery, infection, disruption of blood circulation or many other conditions in which there is tissue injury. In a medical setting it is usually desirable to alleviate pain when its warning function is no longer needed. Besides improving patient comfort, pain therapy can also reduce harmful physiological consequences of untreated pain.

Acute pain can often be managed using analgesics. However, techniques of conduction anesthesia may be preferable because of superior pain control and fewer side effects. Low doses of local anesthetic drugs are often sufficient for pain control so that muscle weakness does not occur and patients may be mobilized.

Some typical uses of conduction anesthesia for acute pain are:

  • labor pain (epidural anesthesia)
  • postoperative pain (peripheral nerve blocks, epidural anesthesia)
  • trauma (peripheral nerve blocks, intravenous regional anesthesia, epidural anesthesia)


Uses in chronic pain

needs some more writing...


Miscellaneous uses

Topical anesthesia is often used for all kinds of punctures (e.g.ascites drainage, amniocentesis, access to blood vessels for angiography and many others). Some diagnostic procedures such as bronchoscopy (visualization of the lower airways) or cystoscopy (visualization of the inner surface of the bladder) are often performed under surface anesthesia.


History

The leaves of the coca plant Erythroxolon coca were traditionally used as a stimulant in Peru. It is believed that the local anesthetic effect of coca was also known and used for medical purposes. Cocaine was isolated in 1860 and first used as a local anesthetic in 1884. The search for a less toxic and less addictive substitute led to the development of the aminoester local anesthetic procaine in 1904. Since then, several synthetic local anesthetic drugs have been developed and put into clinical use, notably lidocaine in 1943, bupivacaine in 1957 and prilocaine in 1959.

Shortly after the first use of cocaine for topical anesthesia, blocks on peripheral nerves were described. Brachial plexus anesthesia by percutaneous injection through axillary and supraclavicular approaches was developed in the early 20th century. The search for the most effective and least traumatic approach for plexus anesthesia and peripheral nerve blocks continues to this day. In recent decades, continuous regional anesthesia using catheters and automatic pumps has evolved as a method of pain therapy.

Intravenous regional anesthesia was first described by August Bier in 1908. This technique is still in use and is remarkably safe when drugs of low systemic toxicity such as prilocaine are used.

Spinal anesthesia was first used in 1885 but not introduced into clinical practice until 1899, when August Bier subjected himself to a clinical experiment in which he observed the anesthetic effect, but also the typical side effect of postpunctural headache. Within few years, spinal anesthesia was widely used for surgical anesthesia and was accepted as a safe and effective technique. Although atraumatic (non-cutting-tip) cannulas and modern drugs are used today, the technique has otherwise changed very little over many decades.

Epidural anesthesia by a caudal approach had been known in the early 20th century, but a well-defined technique using lumbar injection was not developed until the 1930s. With the advent of thin flexible catheters, continuous infusion and repeated injections have become possible, making epidural anesthesia a highly successful technique to this day. Beside its many uses for surgery, epidural anesthesia is particularly popular in obstetrics for the treatment of labor pain.


DISCLAIMER

Please remember that Wikipedia is offered for informational use only. The information is in most cases not reviewed by professionals. You are advised to contact your doctor for health-related decisions.
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