The subarachnoid space contains cerebrospinal fluid (CSF) that is contiguous with the intracranial CSF pathways and extends from the foramen magnum to the S2 spinal level in adults. Drugs injected into the CSF tend to have a rapid action due to direct contact on exposed nerve membranes of the spinal cord and nerve roots. Subarachnoid blocks (SAB) are used to treat various acute and chronic pain syndromes, for diagnostic purposes, and to treat muscular spasms associated with cerebral, motor, or spinal cord dysfunction. Potential complications of SAB with local anesthetics include Backache in up to 40% of patients, hypotension caused by sympathectomy, postdural puncture headache, nausea caused by unopposed vagal activity, and bradycardia from blockade of cardiac sympathetic fibers.