AANA Journal course: update for nurse anesthetists--improving the efficacy of subarachnoid and epidural blocks--Part B

In Part A of this two-part Journal course, issues of safety during subarachnoid and epidural blocks were examined (see the August 1997 issue of the AANA Journal). Part B deals with the effectiveness of spinal and epidural blocks. Although the overall failure rate for subarachnoid and epidural blocks is low, regional anesthesia is not always effective. Knowing the failure rates for various types of regional blocks and the factors that influence the rate of failure is useful for planning anesthetic care and choosing the most effective techniques. Combined spinal and epidural techniques offer the quick onset of a spinal with the continuous dosing and controllability of an epidural. The combined spinal and epidural technique is somewhat more complicated to perform especially in regard to test dosing. Opioids and vasoconstrictors enhance the density and duration of spinal and epidural blocks. In addition, opioids can be used to provide postoperative analgesia after the block has worn off. While opioid induced respiratory depression was a significant hazard during the initial development of spinal and epidural opioid techniques, refinements in dosing and monitoring of these patients have reduced the incidence of this complication to a low level. While alpha agonists, such as epinephrine, do prolong the duration of some types of blocks, they also introduce or exacerbate problems, such as urinary retention, itching, and even hypotension. Whatever technique is used, careful patient selection, allowing adequate time for the block to set up, and administering small doses of a systemic analgesic or sedative if needed may make the difference between the success or failure of a well-performed block.