Intrathecal and Epidural drug injections : Not only Bupivacaine or Lidocaine and Not only Anesthesia or Analgesia

The concept that a barrier exists between the blood and the brain was first formulated nearly a century ago. Colored dyes injected into the circulation of laboratory animals stained all tissues except the brain. However, when the same dyes were introduced into cerebral spinal fluid (CSF), the liquid that bathes, nourishes, and cushions the brain and spinal cord, brain cells were readily stained. Clearly, something was preventing these dyes from escaping from the blood vessels in the brain, although they readily leaked from the vessels throughout the rest of the body.