There are several well-established techniques for performing peripheral nerve blocks including paresthesia, nerve stimulation and local infiltration. Practitioners utilizing paresthesias for nerve localization claim a shorter time for block placement, faster onset of anesthesia, increased success rate, and decreased personnel requirements. Arguments against the use of this technique include increased discomfort for the patient and a possible increased risk of post-operative dysesthesias. Clinical and laboratory studies to date have not provided a concrete resolution to this debate. However, a brief review of the available literature may help practitioners draw their own conclusions.

A number of studies have been published comparing various techniques used to place peripheral nerve blocks. Taken together, these investigations have not shown that any one technique is superior to another for a particular block. Goldberg and colleagues found that for axillary blockade, transarterial, paresthesia, and nerve stimulator techniques all resulted in similar success rates (1). Correspondingly, McClain and colleagues investigated brachial plexus blockade with the interscalene approach, and found that utilizing paresthesias versus a nerve stimulator resulted in comparable success rates (2). Although both of these investigations reported success rates between 70 and 82%, there have been a multitude of studies reporting success rates well over 90% for all three of these approaches (3,4,5). This suggests that individual experience with a technique is the best predictor of success, and that one technique is not inherently more reliable than another.

Time needed to place a block and time until the onset of surgical anesthesia have also been sited as benefits of eliciting paresthesias over other techniques for regional blockade. While studies examining both paresthesias and non-paresthesia techniques report dramatically different times for block placement and anesthetic onset, there is no consensus that any one method consistently requires less time to perform or provides a faster onset of anesthesia. There is certainly no evidence to support the claim that using paresthesias consistently decreases either block placement or onset times. For example, Sia and colleagues studying axillary blockade reported a mean performance and onset time of 9 and 21 minutes, respectively, utilizing paresthesias to locate all four nerves, compared with 6 and 18 minutes, respectively, utilizing a nerve stimulator to perform the same task (6). Again, this suggests that individual experience with a technique is probably the best predictor of the time necessary for block placement and onset of surgical anesthesia, and that one technique is not inherently faster than another.

Non-paresthesia techniques have also been criticized for requiring an additional "pair of hands." However, tools such as the foot control unit for nerve stimulators as well as innovative techniques allow for single-operator block placement without relying on paresthesias (7,8). Furthermore, for procedures in which the non-dominant hand is not needed within the sterile field (e.g. posterior popliteal block), this non-sterile hand may be used to aspirate, inject, and adjust current amplitude.

Non-paresthesia techniques allow the practitioner to avoid potentially painful paresthesias during block placement (2). Moreover, post-operative short-term neuralgias appear to occur more frequently in patients who experienced a paresthesia—intentional or unintentional—during block placement. Plevak and colleagues retrospectively reviewed 716 patients who had axillary blocks placed with either a transarterial or paresthesia technique, and found a trend towards post-operative "persistent paresthesias" in the latter group (9). The incidence in the paresthesia group was 2.9% vs. 0.8% in the transarterial group (not statistically significant). Horlocker and colleagues retrospectively reviewed 607 patients who underwent 1614 axillary blocks and found that there was not a statistically significant difference in post-operative "neurologic complications" between the transarterial and paresthesia techniques (10). However, they did find that of patients for whom the necessary data was available, five of six patients with post-operative "neurologic complications" had experienced a paresthesia during placement of the block. Finally, Selander and colleagues prospectively studied 533 patients undergoing axillary block with paresthesia and needle-oscillation techniques in their classic article on this issue. They found that of 10 patients who experienced "post-anesthetic paresthe-sias," 9 had experienced paresthesias during placement of the block (11).

These studies do not demonstrate that using any one technique increases the risks for post-operative paresthesias. Rather, they suggest that if a patient experiences a paresthesia during block placement, then he or she is at a greater risk of post-operative dysesthesias. Because unintentional paresthesias are often experienced by up to 40% of patients receiving a block by a non-paresthesia technique, no prospective study to date has demonstrated an increased risk for post-operative dysesthesias of any one technique (12).

Eliciting paresthesias for nerve localization has not been shown to have any advantages over other techniques, can be less comfortable for patients, and may potentially increase the risk of post-operative dysesthesias. Until more convincing evidence of a "best" technique is available, we suggest careful attention to detail with any technique utilized.

References

1. Goldberg ME, Gregg C, Larijani GE, Norris MC, Marr AT, Seltzer JL: A comparison of three methods of axillary approach to brachial plexus blockade for upper extremity surgery. Anesthesiology 1987; 66: 814-6.

2. McClain DA, Finucane BT: Interscalene approach to the brachial plexus, Paresthesiae versus nerve stimulator. Reg Anesth 1987; 12: 80-3.

3. Urban MK, Urquhart B: Evaluation of brachial plexus anesthesia for upper extremity surgery. Reg Anesth 1994; 19: 175-82.

4. Fanelli G, Casati A, Garancini P, Torri G: Nerve stimulator and multiple injection technique for upper and lower limb blockade: failure rate, patient acceptance, and neurologic complications. Study Group on Regional Anesthesia. Anesth Analg 1999; 88: 847-52.

5. Cockings E, Moore PL, Lewis RC: Transarterial brachial plexus blockade using high doses of 1.5% mepivacaine. Reg Anesth 1987; 12: 159-64.

6. Sia S, Bartoli M, Lepri A, Marchini O, Ponsecchi P: Multiple-injection axillary brachial plexus block: A comparison of two methods of nerve localization-nerve stimulation versus paresthesia. Anesth Analg 2000; 91: 647-51.

7. Hadzic A, Vloka JD: Peripheral nerve stimulator for unassisted nerve blockade. Anesthesiology 1996; 84: 1528-9.

8. Wassef MR: A simplified maneuver for transarterial approach to axillary block for use by a single anesthesiologist—more explanation. Reg Anesth 1997; 22: 592-3.

9. Plevak DJ, Linstromberg JW, Danielson DR: Paresthesia vs non-paresthesia—the axillary block. Anesthesiology 1983; 59: A216.

10. Horlocker TT, Kufner RP, Bishop AT, Maxson PM, Schroeder DR: The risk of persistent paresthesia is not increased with repeated axillary block. Anesth Analg 1999; 88: 382-7.

11. Selander D, Edshage S, Wolff T: Paresthesiae or no paresthesiae? Nerve lesions after axillary blocks. Acta Anaesthesiol.Scand. 1979; 23: 27-33.

12. Selander D: Catheter technique in axillary plexus block. Presentation of a new method. Acta Anaesthesiol.Scand. 1977; 21: 324-9.