Spinal anaesthesia
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Spinal anaesthesia is a form of local, or more specifically regional, anaesthesia involving injection of a local anaesthetic into the cerebrospinal fluid (CSF), generally through a long fine needle.
There are hyperbaric, isobaric, hypobaric solutions of anesthetics to choose for the spinal anesthesia, usually the hyperbaric is chosen. Bupivacaine is the local anesthetic most commonly used, although lignocaine, ropivacaine, levobupivicaine and cinchocaine are also available. Regardless of the anesthetic agent used, the desired effect is to block the transmission of nerve signals to and from the affected area. Sensory signals from the site are blocked thereby eliminating pain, and motor signals to the area eliminate movement. In effect the result is total numbness of the area and paralysis. This allows medical procedures to be performed with little or no sensation whatsoever to the person undergoing the procedure, and provides a still patient or area for the surgeon to work on. Typically some sedation is provided to help the patient relax and pass the time during the procedure, however with a successful spinal anesthetic the surgery could be performed with the patient wide awake. Spinal anesthetics are limited to procedures involving most structures below the upper abdomen, as to administer a spinal anesthetic higher may affect the ability to breathe by paralyzing the intercostal respiratory muscles, and the diaphragm in extreme cases (high spinal), as well as the body's ability to control the heart rate.
Baricity refers to the density of a substance compared to the density of human cerebral spinal fluid. Baricity is used in anesthesia to determine the manner in which a particular drug will spread in the intrathecal space.
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