Local Anesthetics: Clinical Application as Spinal Anesthesia

Spinal anesthetics are given during surgeries of the lower abdomen and limbs to block sensory and motor neurons.

They are injected into the subarachnoid space of the lower lumbar region, where they come in contact with the surrounding cerebrospinal fluid or CSF.

Once in the CSF, local anesthetics or LAs are rapidly absorbed by the nerves causing a nerve blockade.

The level of blockade depends on the LA concentration. Usually, low concentrations of LAs are sufficient to block sensory neurons, while at high LA concentrations, motor neurons are also blocked.

The CSF also dilutes LAs while they diffuse away from the injection site.

The direction of diffusion depends on the density or baricity of the LA solution compared to the CSF. Due to gravity, hyperbaric solutions flow down in the CSF, while hypobaric solutions tend to rise. Isobaric solutions stay near the injection site, slowly diffusing in all directions.