Deleterious cardiovascular effects should be anticipated and steps undertaken to minimize the degree of hypotension.Neuraxial blocks typically produce variable decreases in blood pressure that may be accompanied by a decrease in heart rate.Interruption of efferent autonomic transmission at the spinal nerve roots during neuraxial blocks produces sympathetic blockade.Differential blockade typically results in sympathetic blockade (judged by temperature sensitivity) that may be two segments or more cephalad than the sensory block (pain, light touch), which, in turn, is usually several segments more cephalad than the motor blockade.The principal site of action for neuraxial blockade is believed to be the nerve root. The mechanisms of spinal and epidural anesthesia remain speculative.Performing a lumbar (subarachnoid) spinal puncture below L1 in an adult (元 in a child) usually avoids potential needle trauma to the cord.Neuraxial blocks can be performed as a single injection or with a catheter to allow intermittent boluses or continuous infusions. Neuraxial anesthesia may also be used simultaneously with general anesthesia or afterward for postoperative analgesia. Neuraxial anesthesia greatly expands the anesthesiologists’ armamentarium, providing alternatives to general anesthesia when appropriate.
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