Local Anaesthetic Resistance

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Dr Trescott tested 250 patients with a history of anaesthetic failure in their response to mepivicaine, lidocaine, and bupivicaine. 7.5% were found to respond only to mepivicaine, and an additional 3.8% only to lidocaine. The rest were responsive to all three anaesthetics or bupivicaine. She concluded that patients are questioned on any history of poor response to local anaesthetic infiltration (e.g. at the dentist), and are skin tested prior to any invasive procedure.[1]

Patients with Ehlers Danlos Syndrome may be more susceptible to local anaesthetic resistance, however the evidence for this association is limited to case series and a survey.[2]

There has been some genetic studies on this topic, and candidate genetic variants of voltage gated sodium channels have been identified.[3]

Questions Remain

The concept of local anaesthetic resistance is not widely supported or appreciated in New Zealand, or it is thought to be extremely rare. There are some factors that may explain failure apart from pure resistance that should be considered.

Local anaesthetics work the quickest on small nerve fibres. After blockade of these smaller fibres, the larger pressure sensing fibres will still be active. It may be that some patients are actually sensing pressure rather than pain, and due to the anxiety of having a procedure done are interpreting pressure as pain. In these patients it is anecdotally often helpful to give the anaesthetic a much longer time to work to enable blockade of these larger fibres.

References

  1. โ†‘ Trescot Local anesthetic "resistance". Pain physician 2003. 6:291-3. PMID: 16880874.
  2. โ†‘ Schubart et al. Resistance to local anesthesia in people with the Ehlers-Danlos Syndromes presenting for dental surgery. Journal of dental anesthesia and pain medicine 2019. 19:261-270. PMID: 31723666. DOI. Full Text.
  3. โ†‘ Clendenen et al. Whole-exome sequencing of a family with local anesthetic resistance. Minerva anestesiologica 2016. 82:1089-1097. PMID: 27243970.

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