It is not uncommon that a perfectly performed intrathecal injection of local anesthetic in an attempt to accomplish spinal anesthesia fails in a busy clinical practice. Despite the reliability of the technique, the possibility of failure can never be eliminated. Managing a patient with an ineffective or inadequate spinal anesthetic can be challenging, and prevention is better than cure.
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Possible mechanisms of failure include the inability to reach the subarachnoid space, errors in drug preparation or injection, the unsatisfactory spread of the injectate within the cerebrospinal fluid (CSF), ineffective drug action on neural tissue, and difficulties related to patient expectations and psychology rather than genuine block failure. [/box]