How does Spinal Anesthesia Work

The use of spinal anesthesia:

Spinal anesthesia is a widely used method in anesthetizing patients who undergo surgeries below the level of the abdomen and some times even higher. It has been found to be a safe alternative to general anesthesia in the elderly, patients suffering from airway diseases, elevated blood pressure as well as when the intubation techniques required in general anesthesia is not possible due to anatomical changes.

The principle behind the procedure:

When considering the principle behind this procedure, the most evident would be the use of ‘subarchnoid space’ which runs throughout the spine, covering the cord as a cushion. The nerve fibers which reach the vertebral column from various parts of the body will traverse this space in order to be linked up with the ascending fibers of the spinal cord. The most important characteristic of this space with regard to anesthesia would be, the presence of cerebrospinal fluid which provides access for an anesthetic agent to reach the nerve roots traversing the space.

As with any other fluid, a substance which is introduced to this space will move according to the density of the introduced agent when compared to the cerebrospinal fluid.

The technique:

In spinal anesthesia, the technique would be to instill such anesthetic agents into this space via a relatively long needle known as the ‘spinal needle’. The procedure will be performed on the theatre table under 100% aseptic conditions. Once the spinal needle reaches the ‘sub arachnoid space’ in the spinal cord at the level of lumber vertebrae, the anesthetic solution will be injected.

The anesthetic agents:

The anesthetic agents are made in such a way that there would be different densities for different anesthetic needs. Thus, the most often used anesthetic solution would be the ‘hyperbaric solution’ which is easy to control through adjusting the patients position. Apart from the ‘hyperbaric solutions’ there are other solutions which are either of the same density (Isobaric) or else low in density (Hypobaric).

The effect of the anesthetic agents:

These anesthetic agents, once in the space, would exert its effects on the nerve fibers which are carrying signals from the periphery. Most often, the sensory nerves or afferent pain fibers would be the once to get affected quickly as they do not possess a thick covering around the nerve. But, other types of nerves will also get affected with time. The duration of action in these anesthetic agents will be dependent on the dose given, any other substances which are added to give a long lasting action as well as the type of drug given for the anesthesia.

A person who has undergone spinal anesthesia would not feel the pain from waist below and they could tolerate any surgical procedure that takes part in that region with only the feeling of applying pressure.


It is most likely that a person undergoing spinal anesthesia would also be given a light sedation through a mask device and the recovery from the spinal anesthesia will take few hours.