![]() ![]() Although historical comparisons are problematic, it is interesting that the frequency of early and late PONS (4/10,000) is nearly identical to the frequency of nerve injury reported a decade earlier from the French surveillance study, in which nearly all patients underwent PNS-directed block. 20 In the Australasian Regional Anaesthesia Collaboration study of over 7,000 nerve blocks, 21 the incidence of transient (up to 60 days follow-up) PONS was not statistically different between those patients who underwent regional anesthesia using either PNS or UGRA localization techniques. 19 A study that compared PNS to UGRA for interscalene block found no difference in PONS at 4- to 6-week follow-up (7% vs. A study that compared paresthesia-seeking and PNS techniques for interscalene block found no difference in the incidence of paresthesia (9.3% vs. 14 (Modified with permission from Anesthesiology.)Īlthough studies regarding PONS as a function of nerve localization technique are limited, several suggest that there is no difference in the incidence of significant injury. ![]() Figure created using human supraclavicular nerve block sonograms as reported by Bigeleisen et al. If the needle is intraneural, the nerve can be observed to swell during injection of local anesthetic. The needle can be seen to indent the nerve (B) or actually penetrate the nerve (C). Ultrasound guidance can reveal needle-to-nerve proximity in several different ways. Therefore, neither PNS nor UGRA is entirely sensitive or a specific tool for determining needle-to-nerve contact in a manner that predictably recognizes or prevents peripheral nerve injury.įIGURE 17-2. However, nerve swelling has not been correlated with actual nerve injury, 18 suggesting that ultrasound may more accurately depict needle-to-nerve contact as compared with PNS, but that the relationship of needle contact to actual injury remains unknown. For ultrasound-guided localization techniques, studies show that needle tips can be observed to touch and indent nerves 14 or herald subepineurial placement by observing nerve swelling upon injection of local anesthetic 14 – 18 (Fig. ![]() 14 Animal studies confirm this absence of consistency between electrical current and actual needle position, 15 suggesting that PNS is a fallible descriptor of needle-to-nerve relationship (Fig. This chapter defines permanent nerve injury as a neural deficit that remains 1 year after block placement, a definition that is generally agreed upon by neurologists. ![]()
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