Introduction
Anaesthesia is generally defined as a condition in which no pain can be felt. This state is needed, for example, in the context of operations. As a rule, the anaesthesia, i.e. the sensation or painlessness, is induced by an anaesthetist, a specially trained doctor.
Anaesthesia is distinguished between general and regional anesthesia. General anesthesia is also called general anesthesia and differs from regional anesthesia in that it causes a loss of consciousness in addition to the inhibition of pain sensation. Regional anesthesia, also called local anesthesia, is characterized instead by a loss of pain sensation while remaining conscious.
Depending on the type of intervention or operation, either general or regional anesthesia or both can be used to induce numbness and painlessness. Which method is chosen depends on the duration of the procedure and the severity of the intervention. The anaesthetist has the task of advising and informing the patient which procedure is possible and recommendable. The decision whether general or regional anesthesia should be performed prior to the procedure is therefore made jointly by the patient and the physician.
Procedure of regional anesthesia
Regional anesthesia is a local form of anesthesia, i.e. an inhibition of the pain sensation in a specific region of the body while maintaining consciousness. In order to achieve local anesthesia of a body region, the anesthetist injects a drug into the immediate vicinity of a nerve, which normally ensures that pain can be felt at the corresponding body region. The drug interrupts the transmission of information from the nerve to the brain and pain can no longer be felt at that location.
The drugs used in regional anesthesia are called local anesthetics. Important representatives of this group are lidocaine, ropivacaine and bupivacaine. The medications are applied through thin needles or special cannulas.
It is important that the puncture site is first thoroughly disinfected so that no pathogens can penetrate. Venous regional anesthesia is a procedure that is used especially in outpatient treatment. It is a procedure in which the local anesthetic is injected directly into the vein and from there is distributed in the tissue.
Since the local anaesthetic must not enter the systemic bloodstream under any circumstances, the blood supply is blocked. First, the arm or leg is elevated and tight bandages are used to force the blood out of the vessels. When the desired area is almost bloodless, a blood pressure cuff or tourniquet is attached to the upper edge of the arm or leg to prevent further blood flow.
The local anesthetic is now injected into the veins and takes full effect after about fifteen minutes. The duration of the procedure is limited to less than one hour, as the arm or leg must be supplied with oxygen-rich blood again afterwards. Venous regional anesthesia is considered a procedure with few complications.
A frequently reported side effect is the pain when the blood supply is cut off. In rare cases, the local anaesthetic enters the systemic bloodstream and can cause severe complications such as seizures, cardiac arrhythmia and respiratory paralysis. This happens especially when the blockage is not tight enough or is released too early.
Venous regional anesthesia should not be used in cases of known vascular diseases. The word peripheral means generally away from the trunk of the body. Peripheral regional anesthesia therefore includes all procedures that are applied to individual nerves or nerve plexus away from the spinal cord.
These include foot block, finger block, plexus anaesthesia and many other procedures. The word plexus anesthesia is derived from the Latin word plexus, the plexus of nerves. Plexus anesthesia involves an entire plexus of nerves which can be located beforehand using a nerve stimulator.
Such nerve plexuses are located on the arms, in the lumbar region and on the coccyx. The underlying system is always the same. The local anesthetic is injected near a supplying nerve and the signal transmission is interrupted at this point.This interruption may be in the immediate vicinity of the surgical area, as in the case of the Colonel’s finger block, or at a significant distance from this area, as in the case of plexus anesthesia for wrist surgery.
In the second variant, the surgical site is located at the wrist and the anesthesia is set at the level of the armpit or neck. Surface anaesthesia is a very common procedure. Here the anaesthetic drug, the local anaesthetic, is applied in the form of a spray on the skin (for example, to make it easier to place indwelling cannulas in the hospital) or on mucous membranes (for example, for painful inflammations in the mouth and neck area), thus anaesthetising the smallest superficial nerves.
Another form of regional anesthesia is infiltration anesthesia, which is used especially by dentists. Here, the local anesthetic is injected into the tissue, for example into the oral mucosa, with the help of a fine needle. The active ingredient then gradually mixes with the tissue and anaesthetizes the fine nerves inside.
The local anesthetic can be given as a single injection or through a catheter. The catheter allows for easy re-injection of medication if the procedure takes longer. Peripheral regional anesthesia is associated with fewer side effects than spinal and general anesthesia.
Regional anesthesia can be applied to the arm at different heights. The planned area is disinfected and the anatomical structures are visited. An ultrasound device can be used for support.
The cannula is inserted through the skin near the nerve and the local anesthetic is injected. Before injection, the syringe plunger is retracted a little and the doctor tests whether blood flows back. After about fifteen minutes the desired area should be numb and feel no more pain.
The hand block is a regional anaesthetic procedure in which all relevant nerves of the hand above the wrist are anaesthetised. The hand becomes completely numb, while some muscle functions are preserved. The responsible nerves are the radialis nerve, the ulnar nerve and the medianus nerve, therefore three single injections are necessary.
The hand block is used for small operations or for wound treatment of the hand and fingers. The effect of the hand block sets in after only a few minutes and lasts for about two hours. For anaesthesia procedures near the spinal cord, the local anaesthetic is injected near the spinal cord and takes effect directly at the nerve roots.
A distinction is made between epidural anaesthesia, also known as PDA, in which the drug is injected over the hard skin of the spinal cord, and spinal anaesthesia, in which the drug is injected directly into the liquor space. The two methods differ in the depth of penetration into the so-called spinal canal. The spinal cord is located in the spinal canal, where it is embedded in cerebrospinal fluid.
Above this spinal canal there is a layer of connective and fatty tissue, which is called the epidural space. In spinal anesthesia, the cannula penetrates to the spinal canal and the local anesthetic is injected there. Finally, in the spinal canal, the local anesthetic mixes with the nerve fluid, which anesthetizes the entire lower half of the body.
In epidural anesthesia, the needle only penetrates the epidural space. Here the local anesthetic mixes with the fatty tissue and thus mainly causes an anesthetic of the nerve roots at the level of the needle insertion point. A major advantage of epidural anesthesia is that a longer catheter can be used for postoperative pain relief.
Spinal anesthesia has a faster onset of action. The two methods can also be combined. Examples of operations under epidural anesthesia are gastrointestinal tract operations, hip implant changes and obstetrics.
In the latter case, the advantage is used that different types of nerves react differently to local anesthetics. The pain is already eliminated while the muscles are still working. Spinal anaesthesia is used, for example, in caesarean sections, pelvic operations and foot operations.
Depending on the duration of the operation, different local anaesthetics such as bupivacaine or mepivacaine are used. Saddle block is a special form of spinal anesthesia. Especially the sacral segments of the spinal canal are affected.A distinction is made between the real saddle block, also called breeches anaesthesia, and the extended saddle block, which also reaches lumbar segments.
The real saddle block is used in proctology, gynecology and obstetrics, as well as in urology, since the anus, perineal area, pelvic floor muscles and the external genitals are anaesthetised. Operations on abdominal organs are only permitted with the extended saddle block. It is a relatively safe procedure with similar side effects to normal spinal anaesthesia, but these side effects are usually mitigated.
The exact position where a local anaesthetic is to be injected is not always easy to find. With an ultrasound machine, the anaesthetist can assess exactly where the nerves and blood vessels are located. This increases the safety of regional anaesthetic procedures, as local anaesthetics rarely reach blood vessels and the nerves can be anaesthetised more easily. The ultrasound device is most frequently used for regional anesthesia in the groin region or at the arm plexus, since the location of the nerves is relatively deep in the tissue there and much other tissue can be in the way.