When undergoing anesthesia, it is always a good idea to use as little anesthesia as possible to minimize potential harm to the patient. Spinal anesthesia does just that and is the method of choice for some procedures that require anesthesia of the lower back or pelvic area. Because of its proximity to the spinal cord, it must be performed meticulously.
What is spinal anesthesia?
Spinal anesthesia is a local anesthetic in which specific sections of the lower spinal cord are anesthetized. Spinal anesthesia is a local anesthetic in which specific sections of the lower spinal cord are anesthetized. It involves targeting specific nerves or nerve branches to stop pain during a procedure in the lower extremities, lower abdomen, perineum and pelvis. It is a temporary interruption of nerve conduction pathways. As a result, conduction to the brain is cut off and impulses are not transmitted to it. A decisive factor is that the patient’s consciousness is preserved by the local anesthesia. During the injection, the patient can feel whether the needle has been placed correctly by means of a warm sensation. For additional safety, a small sample of cerebrospinal fluid is aspirated before the anesthetic is injected. Peridural anesthesia is another locally invasive anesthetic in this segment of the body. The major difference is that in spinal anesthesia, the dura mater, the hard meninges at the spinal canal, is punctured. The anesthetic is free to spread in the fluid in the confined area.
Function, effect, and goals
Spinal anesthesia is used extensively for two procedures: cesarean section and hip replacement surgery. In both, the goal is to specifically make the affected area pain-free without having to use general anesthesia. In addition, this type of local anesthesia is used for numerous surgeries involving the legs, abdomen and lower back. In addition to the ability to feel, the motor function of the affected area is also switched off. The local anesthetic acts very quickly. Often the patient notices a noticeable effect already during the injection. Apart from that, depending on the chosen agent, it takes different amounts of time for the full effect to take place. Spinal anesthesia has a long history. As early as the end of the 19th century, the physician August Bier and his assistant conducted self-experiments. At that time, the anesthetic of choice was still cocaine and it took some effort and failure until the anesthesia succeeded according to the ideas. Today they can be dosed precisely and calculated in advance. The drugs have changed. For a long time, lidocaine was the drug of choice because its duration of action of one to one and a half hours was well suited for most operations. Anesthetics with longer duration of action and fewer side effects are now known. The dose of the drug, which is injected directly into the nerve fluid, is precisely calculated to minimize the risk of possible side effects. The nerves are blocked by altering the ionic current in the cells. Sodium ions can no longer pass through the cell membrane because the necessary channels are blocked. Sodium is needed to form action potentials that deliver signals to the brain via the nerves. If too little is available, signal transmission stops. The onset of blockage spreads, corresponding to nerve conduction from bottom to top. If it subsides later, it does so in reverse order. Since the anesthetic, like all things, follows gravity, in some cases it may be necessary to position the patient in a particular, sometimes unusual, way to achieve the best possible result. Spread can also be controlled by the amount of medication. In addition, care must be taken to ensure that in severely overweight patients, the body mass exerts increased pressure on the nerve fluid. In this case, the dose should be reduced accordingly. The puncture is usually made in the area between the third and fourth lumbar vertebrae. It is the safest method. Theoretically, one could also place the needle differently, since the spinal cord ends only at the level of the first or second lumbar vertebra.
Risks, side effects, and dangers
Blocking certain nerve fibers entails some reactions in the sympathetic nervous system. The pressure in the veins drops and so does the blood pressure.This occurs due to a dilatation of the corresponding vessels. The total return flow of blood to the heart is reduced, resulting in a lack of blood volume. The body often counteracts this by constricting the 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 more weakly. During spinal anesthesia, therefore, the patient’s vital signs must be closely monitored. It is possible to counteract a drop in blood pressure by administering fluids during the procedure or injecting a vasoconstrictor drug. As always with interventions directly on the spinal cord, its injury can occur with serious consequences for the patient. Cranial nerve dysfunction also cannot be ruled out. As a result of the injury, it is possible that hemorrhage may occur into the surrounding tissue in the area of the dura mater. A peridural hematoma develops, which usually recedes. Headaches are common. Spinal anesthesia should not be performed if the immune system is burdened by infection, if blood volume is already too low, if there are diseases of the central nervous system, if there are coagulation disorders, or if there is increased intracranial pressure.
