Background and objectives Characteristics of a nerve block depend on the distribution of local anesthetic (LA) close to the nerve. The relationship between longitudinal distribution of LA and nerve block characteristics has not been investigated in vivo, but one in vitro study showed decrements in action potential amplitudes with increasing exposure length. We describe the influence of longitudinal neural exposure to LA on nerve block duration adjusted for other likely influential factors.
Methods We analyzed data from an ethical board approved prospective consecutive collected dataset of 180 healthy volunteers with a common peroneal nerve block (2.5–20 mL, 5–40 mg of ropivacaine). Data were retrieved from three independent randomized controlled trials. The longitudinal neural exposure to LA in millimeters was evaluated using ultrasound. Interventional covariates and demographics were retrieved. Nerve block duration, the dependent variable in the primary assessment, was defined as time of insensitivity to a cold stimulus and was evaluated blinded to all other covariates. Using a multiple linear mixed-effects model, we explored the association between neural exposure to LA and nerve block duration.
Results We found a significant positive association between longitudinal neural exposure to LA and block duration (p<0.01). A 10% increase in longitudinal exposure resulted in an 8.7 (2.5; 15) min increase in block duration. LA dose was associated to block duration (p<0.001) but LA volume had no impact (p=0.93).
Conclusions Longitudinal neural exposure to LA was significantly associated with nerve block duration. LA dose was the strongest determinant for block duration whereas LA volume had no influence.
- lower extremity
- upper extremity
- interventional pain management
- postoperative pain
- ultrasound in pain medicine
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Presented at This work was presented in part at the 36th Annual ESRA Congress, Lugano, Switzerland, September 2017.
Contributors MHM: Study conception and design, acquisition of data, statistical methodology, analysis and interpretation of data and drafting of the article. CBC: Acquisition of data, interpretation of data and critical revision of the article. CR: Study conception. LHL: Study design, statistical methodology, analysis and interpretation of data, critical revision of the article. KHWL: Study conception and design, interpretation of data, critical revision of the article.
Funding This work was funded by Innovation Fund Denmark and by Nordsjællands Hospital.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval This study was a retrospective analysis of experimental data from three independent RCTs in healthy volunteers, approved by The Danish Regional Scientific Ethics Committee (Capital Region, Denmark, ref. H-16000430, H-16000184 and H-17022555) and The Danish Medicines Agency (ref. 2016010332, 2016010130 and 2017073679).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement The data are de-identified participant data and can be retrieved from the corresponding author.