Comments a recent paper
about safety and success rate of intraneural injection for sciatic block.
In this recent study Ana Lopez and colleagues from Barcelona compared the injection of local anesthetic within the common connective tissue sheath (sub-sheath block) of the sciatic nerve just below the separation of the tibial and peroneal nerve with an injection close to the nerve outside the common sheath (peri-sheath) at the same level using an ultrasound-guided out-of-plane approach.
For the sub-sheath injection the needle was withdrawn when eliciting a motor response at 0.3mA or if a high opening pressure would was encountered, then they injected a rather large volume (30ml) of a 1:1 mixture of 1,5% Mepivacaine and 0,5% Levobupivacaine which resulted in a post-injection increase of the nerve area of at least 30%. For the peri-sheath block the group injected 15ml of the above mixture on both sides of the nerve to surround the sheath. Primary outcome was adequate surgical anesthesia at 30min. Secondary outcomes were block onset time and duration.
The study was terminated after the 36th of 100 planned patients due to an unexpectedly high failure rate of 33% in the peri-sheath group compared to 0% in the sub-sheath group. The block onset time was significantly faster in the sub-sheath group (9.1±7.4min vs 19.0±4.0min). No patient of either group reported symptoms suggestive of neurologic injury immediately after or within 4 weeks after surgery.
This very nice paper puts the spotlight on a interesting discussion that has started already in the early days of ultrasound guided regional anesthesia. After the clinical introduction of nerve stimulators in the early 1970s, millions of nerve blocks were performed with this very successful technique, pretending that a needle-nerve contact, as it was used with the paraesthesia technique for more than 50 years, or even an intraneural injection could no longer occur. After the introduction of ultrasound, several studies have proven this hypothesis to be wrong: Quite often no motor response is elicited despite clear visible contact of the needle to nerve. Moreover, the rate of nerve swellings after stimulation technique has been as high as 88% (1). Nevertheless even in those days persistent neurologic injuries were a rare complication with an incidence of 3-4/100'000.
This raises the question, whether the dogma of intraneural injection being potentially harmful and, therefore, to be avoided under any circumstance must be brought into question as we have already unknowingly administered injectionss whithin the nerve sheath for years...
Looking closely at the example of a sub-sheath injection described by Dr. Lopez et al. in their study, we notice that not only the tibial and peroneal part of the nerve are separated after injection, there seems to be some local anesthetic within the two nerves themselves. In another recent study by Techasuk et al. (2) ,the group deliberately injected anesthetic within the nerves at the supraclavicular level. They called this technique "intracluster injection", and likewise, the onset time was significantly shorter compared with the "pocket technique" without evidence of neurologic injury.
Eight years after the first report of unintended intraneural injection without neurologic deficit by Paul Bigeleisen (3), we should start considering intentionally injecting local anesthetic into the connective tissue as an alternative with a high success rate and a rapid onset time. Further studies are needed to support this hypothesis.
1- Intraneural injection during nerve stimulator-guided sciatic nerve block at the popliteal fossa. Sala Blanch X et al. Br J Anaesth 2009 Jun;102(6):855-61
2- A randomized comparison between double-injection and targeted intracluster-injection ultrasound-guided supraclavicular brachial plexus block. Techasuk W et al. Anesth Analg 2014 Jun;118(6):1363-9
3- Nerve puncture and apparent intraneural injection during ultrasound-guided axillary block does not invariably result in neurologic injury. Bigeleisen PESee comment in PubMed Commons belowAnesthesiology. 2006 Oct;105(4):779-83
Becoming an expert...
ROMAN ZÜERCHER MD
Alumnus of the University of Basel, Switzerland
2001-2014 Department of Anesthesiology, University Hospital Basel
2004 Board certification
2005-2014 Director Regional Anesthesia Program University Hospital Basel
2010/11/12/13/14/15 Faculty NWAC
2013/14 Faculty NYSORA
2013 Faculty NYSORA Outreach program
2012/13/14 Faculty AEA Clermont-Ferrand
Currently Senior Consultant and Director Regional Anesthesia Program Bethesda Hospital Basel, Switzerland.
Interview with the expert
1- Theoretically, you have to block axonal ion channels. How close to the nerve is close enough to “be happy with your needle”?
We should aim to safely bring the local anesthetic as close to its target as possible to achieve a high success rate and fast onset. I personally believe injections into the hyperechogenic connective tissue with a short bevel needle and low opening pressure to be a safe alternative for most blocks.
2- Sympathetic pain is a topic that worries you. When do you consider that it is more relevant and why?
Sympathetic pain plays an important role in ischemic pain as it occurs after long tourniquet time or compartment syndrome. It also has a role in the development of chronic pain after surgery. Its role in acute postoperative pain is probably underestimated, especially in trauma surgery. A case series published by John McDonnell (4) ,where he used stellate ganglion block for postoperative pain after shoulder trauma shows that sympathetic pain in the postoperative setting should come more into our focus in the future.
3- You are so friendly (and funny, too!) in your conferences and teachings and that is great to keep the audience attention. Give as other clues to succeed teaching, please.
Instead of seeing continuing education as a teacher-student interface, I see it more as an interaction between people with different expertise who are present to share their know-how. I always learn when I teach. Teaching should be fun…
4- Stellate ganglion blockade for analgesia following upper limb surgery. McDonnell JG et al. Anaesthesia. 2011 Jul;66(7):611-4
ROMAN ZÜERCHER MD
Senior Consultant and
Director Regional Anesthesia Program
Bethesda Hospital Basel, Switzerland.