Spinal anesthesia

With anesthesia, it is always useful to numb as little as possible in order to minimize possible harm to the patient. The Spinal anesthesia does exactly that and is the method of choice for some procedures that require anesthesia of the lower back or pelvic area. Due to its proximity to the spinal cord, it must be carried out meticulously.

What is spinal anesthesia?

Spinal anesthesia is a local anesthetic in which certain sections of the lower spinal cord are anesthetized. Certain nerves or nerve branches are targeted in order to prevent pain during an operation in the lower extremities, the lower abdomen, the perineum and the pelvis.

It is a temporary disruption of the nerve pathways. This prevents conductivity to the brain, the impulses are not transported to it. A decisive factor is that the patient's consciousness is maintained through the local anesthetic. During the injection, the patient can feel warm, whether the needle is in the right place.

For additional safety, a small sample of liquor is drawn in before the anesthetic is injected. Another locally invasive anesthetic in this body segment is epidural anesthesia. The big difference is that with spinal anesthesia the dura mater, the hard meninges on the spinal canal, is pierced. The anesthetic can spread freely in the liquid in the limited area.

Function, effect & goals

Spinal anesthesia is used to a large extent in two operations: a caesarean section and a hip joint operation. Both are about making the affected area pain-free without having to use general anesthesia. In addition, this type of local anesthesia is used in numerous operations in the area of ​​the legs, abdomen and lower back.

In addition to the sensitivity, the motor skills of the affected area are also switched off. The local anesthetic works very quickly. Often the patient notices a noticeable effect during the injection. Apart from that, depending on the chosen remedy, it takes different lengths of time until the full effect occurs. Spinal anesthesia has a long history. At the end of the 19th century, the doctor August Bier carried out self-experiments with his assistant. Back then, the anesthetic of choice was still cocaine and it took some effort and failure to get the anesthetic as expected.

To dose them precisely today and calculate them in advance. The drugs have changed. For a long time, lidocaine was the drug of choice because its duration of one to one and a half hours was well suited for most operations. Anesthetics with a longer duration of action and fewer side effects are now known. The dose of the drug that is injected directly into the nerve water is precisely calculated in order to minimize the risk of possible side effects. The nerves are blocked by changing the flow of ions in the cells. Sodium ions can no longer pass through the cell membrane because the required channels are blocked. Sodium is necessary for the formation of action potentials, which deliver signals to the brain via the nerves.

If too little is available, the signal transmission stops. The onset of the blockage spreads from bottom to top according to the nerve conduction. If it decreases later, this is done in reverse order. Since the anesthetic, like all things, follows gravity, in some cases it may be necessary to position the patient in a certain, sometimes unusual, position in order to achieve the best possible result. Spread can also be controlled via the amount of drug.In addition, it should be ensured that in severely overweight patients, the body mass exerts increased pressure on the nerve water. Here it is important to dose the amount correspondingly lower. The intermediate area between the third and fourth lumbar vertebrae is usually chosen for the puncture. It is the safest method. Theoretically, the needle could be placed differently, since the spinal cord only ends at the level of the first or second lumbar vertebra.

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Risks, side effects & dangers

The blockage of certain nerve fibers causes some reactions in the sympathetic area. The pressure in the veins drops and with it the blood pressure. This is done by widening the corresponding vessels. The total return flow of blood to the heart is reduced, which results in a lack of blood volume.

The body often counteracts this by narrowing the blood vessels in the anesthetized areas. In addition to the pure drop in blood pressure, there are also risks for the heart itself. The heartbeat slows down and it pumps less. The patient's vital signs must therefore be closely observed during spinal anesthesia. It is possible to counteract a drop in blood pressure by giving fluids during the procedure or by injecting vasoconstricting medication. As always with surgery directly on the spinal cord, it can injure it with serious consequences for the patient.

A cranial nerve disorder cannot be ruled out either. The injury may result in bleeding into the surrounding tissue in the area of ​​the dura mater. A peridural hematoma develops, which usually regresses. Often there is a headache. Spinal anesthesia must not be performed if the immune system is stressed by an infection, if the blood volume is too low, if the central nervous system is affected, if there are coagulation disorders or if there is increased intracranial pressure.