Variants | Local anesthetic

Variants

Surface anaesthesia is the lightest form of anaesthesia and acts on the fine, sensitive nerve endings of the skin. In the context of minor procedures and punctures, e.g. in the skin or oral cavity, ointments, gels, sprays or powders reduce the perception of pain.For example, the dentist can coat the oral mucosa with an anaesthetic gel in the course of the dental pain elimination process, so that the patient no longer feels the puncture of the syringe. Usually the effect of surface anaesthesia wears off after a short time, but it depends on the time of application and dosage.

The most common active substances include lidocaine, prilocaine, benzocaine or tetracaine. Spinal anaesthesia temporarily blocks the transmission of the spinal nerve roots. An anaesthetic is injected into the spinal space filled with cerebrospinal fluid (liquor), also known as the subarachnoid space.

In adults, the spinal cord usually ends at the border between the first and second lumbar vertebrae. In order to rule out injury in every case, the doctor therefore never injects the anesthetic higher than between the third and fourth lumbar vertebrae. Since spinal anaesthesia is nevertheless administered near the spinal cord, it is referred to as near spinal cord anaesthesia.

During the puncture, the patient usually assumes a sitting position and bends forward in a kind of ‘cat’s hump’. Within a few seconds, a blockage of the excitation line occurs, as the anesthetic is quickly distributed in the surrounding cerebral fluid. At the beginning, patients notice a tingling or ‘getting heavy’ of the legs, up to a rising feeling of warmth.

Depending on the type of anaesthetic, the type of posture and the height of the injection, the full effect of spinal anaesthesia sets in after 10-30 minutes. If a longer procedure is planned, a so-called permanent catheter can be placed in the spinal space. A fine microneedle allows the anaesthetics to reach the root of the spinal nerve continuously.

Spinal anaesthesia is particularly suitable for operations below the navel, such as operations on the knee joint or abdominal surgery. Theoretically, it is also possible to extend the anaesthesia to regions above the navel. However, such anesthesia requires special indications and may only be used after careful risk assessment.

In contrast to spinal anaesthesia, epidural anaesthesia involves the anaesthetic being injected into the epidural space, also known as the epidural space. It is located between the inner and outer layer of the hard meninges (dura mater). This method is very often used in obstetrics, for example during a caesarean section.

In this context, the term epidural or PDA is almost always used. In order to achieve the same effect, a significantly higher dosage of the anesthetic agent must be chosen compared to spinal anesthesia. In addition, the anesthesia sets in later.

However, epidural anesthesia has one major advantage: it can be used very specifically without undesirable side effects, such as blocking of motor nerve fibers. Furthermore, the catheters can remain in the epidural space beyond the intervention without any problems. This means that long-term pain therapy is possible even beyond the time of surgery.

Just like spinal anaesthesia, epidural anaesthesia is one of the so-called spinal cord near procedures. Local anesthesia can also be applied beyond the spinal column or spinal cord, and is then counted among the so-called spinal cord distant procedures. In the case of peripheral nerve blockage, anaesthetic is injected in the immediate vicinity of nerves, nerve plexuses or nerve trunks.

In order to achieve a safe anesthesia, the first step is to determine the exact course of the nerves under the skin. To do this, the physician can orientate himself, for example, on prominent bone points that are directly related to the nerve structure being investigated. Nowadays, technical means are increasingly used to locate the nerves.

Under ultrasound control, for example, the needle can be brought into an exact position and the distribution of the anesthetic can be observed. Another possibility is the stimulation of the motor nerve fibers by small electrical impulses. In this way, the nerve can be localized very precisely by muscle twitches of varying degrees of severity.

Overall, the risk of nerve injury in peripheral blockage is therefore extremely low. Peripheral local anesthesia is particularly suitable for operations in the arm and shoulder area. The brachial plexus is a large plexus of nerves and its fibers supply almost the entire arm as well as parts of the shoulder and chest.Since it runs well demarcated between the individual muscles, brachial plexus anesthesia can be performed at different points of the plexus: In contrast to the other local anesthetics, here the anesthetic is administered directly into the vein.

It is particularly suitable for shorter and less complicated procedures. The blood vessels are temporarily tied off so that the blood supply to the affected arm or leg is interrupted. A tightly applied blood pressure cuff ensures that the vessels remain bloodless even during the operation.

The anesthetic is then injected into the vein concerned and remains effective until the cuff is removed. Intravenous regional anesthesia is a particularly simple and safe method of anesthesia. However, many patients describe the prolonged congestion of the blood vessels as very unpleasant.

  • In the armpit/axillary: The simplest and most common of all plexus blockages. It is suitable for operations on elbow, forearm and hand.
  • Interscalenar: The anesthetic is injected between the two front scalene muscles (Mm. scaleni).

    This type of anaesthesia is preferred for operations on the collarbone and shoulder joint.

  • Supraclavicular: The injection is made above the first rib. This procedure is used less frequently for operations on the hand, forearm, upper arm and shoulder joint.
  • Infraclavicular: The injection is made below the collarbone. It is suitable for operations on the elbow, forearm and hand.
  • Of course, a peripheral nerve block can also be performed on the legs. However, the nerve plexuses cannot be localized so well there, which is why anaesthesia procedures close to the spinal cord are preferred for these procedures.