Treatments & Therapies

Spinal anesthesia – treatment, effect and risks


When anesthetizing , 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 . Due to the 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 anaesthetized. Specific nerves or nerve branches are specifically 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. As a result, the conductivity to the brain is prevented, the impulses are not transported to it. A crucial factor is that the local anesthetic keeps the patient conscious. During the injection, the patient can feel whether the needle is placed correctly by means of a feeling of warmth.

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 cord canal, is punctured. The anesthetic can spread freely in the liquid in the limited area.

Function, effect & goals

Spinal anesthesia is widely used in two procedures: caesarean section and hip replacement surgery . Both are about making the affected area painless in a targeted manner without having to use general anesthesia . This type of local anesthetic is also used in numerous operations on 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 works very quickly. The patient often notices a noticeable effect already during the injection. Apart from that, depending on the chosen remedy, it takes different amounts of time before the full effect occurs. Spinal anesthesia has a long history. As early as the end of the 19th century, the doctor August Bier and his assistant carried out experiments on himself. Back then, the anesthetic of choice was cocaine, and it took a lot of effort and failure to get the anesthetic done as expected.

Today they have to be dosed and calculated in advance. Medicines 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 surgeries. Anesthetics with a longer duration of action and fewer side effects are now known. The dose of the drug, which is injected directly into the cerebrospinal fluid, is calculated precisely in order to keep the risk of possible side effects as low as possible. 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 through the nerves to the brain.

If there is too little, the signal transmission stops. The incipient blockage spreads from bottom to top, according to the nerve conduction. If it decreases later, this happens in reverse order. Because the anesthetic, like all things, follows gravity, in some cases it may be necessary to position the patient in a specific, sometimes unusual, manner in order to achieve the best possible result. Spread can also be controlled via the amount of medication. 

In addition, it should be noted that in severely overweight patients, increased pressure is exerted on the cerebrospinal fluid due to the body mass. Here it is important to dose the amount correspondingly lower. The area between the third and fourth lumbar vertebrae is usually chosen for the puncture. It’s the safest method. Theoretically, the needle could also be placed differently, since the spinal cord is only at the level of the first or secondlumbar vertebra ends.

Risks, side effects & dangers

The blockage of certain nerve fibers entails some reactions in the sympathetic nervous system . 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, resulting in a lack of blood volume.The body often counteracts this by constricting the vessels in the numbed areas. 

In addition to the drop in blood pressure, there are also risks for the heart itself. The heartbeat slows down and it pumps weaker. The patient’s vital signs must therefore be closely monitored during spinal anaesthesia. It is possible to counteract a drop in blood pressure by administering fluids during the procedure or by injecting a vasoconstrictive medication. As is always the case with interventions directly on the spinal cord, it can be injured with serious consequences for the patient.

A cranial nerve disorder cannot be ruled out either. The injury can cause bleeding into the surrounding tissue in the area of ​​the dura mater. A peridural hematoma develops, which usually regresses. Headaches are common . Spinal anesthesia must not be carried out if the immune system is under strain from an infection, if the 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 .

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.