Spinal anesthesia is done by the injection of a local anesthetic solution into the low back into the subarachnoid space. Prior to beginning anesthesia, the anesthesiologist places monitors of blood pressure, electrocardiogram, pulse and oxygen saturation of the blood. The word subarachnoid translates to "below the arachnoid". The arachnoid is one of the layers of the meninges covering the nerves of the spinal column. In the subarachnoid space lies the cerebral spinal fluid (CSF) which surrounds the spinal cord and brain. In a spinal anesthetic, the subarachnoid space is located with a needle by the anesthesiologist, and the appropriate anesthetic medications are injected.

Local anesthetics, such as
lidocaine or bupivicaine (Marcaine), given into the subarachnoid space, bring on sensory and motor numbness. The anesthesiologist chooses the dose and type of drug depending on the patient’s age, size, height, medical condition, and the type of surgery.

Following the onset of numbness from spinal anesthesia, the patient may either stay awake for surgery, or more often intravenous sedation is given to achieve a light sleep. Sometimes light general anesthesia is given to supplement spinal anesthesia.
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