A modified train-of-four ratio to assess recovery from depolarizing neuromuscular blockade after succinylcholine, a prospective observational study

J Clin Monit Comput. 2021 Oct;35(5):1133-1138. doi: 10.1007/s10877-020-00560-5. Epub 2020 Jul 20.


Succinylcholine is still used in clinical practice. Its duration is highly variable and neuromuscular monitoring is recommended to assess its recovery. Unfortunately, depolarizing neuromuscular block cannot be evaluated by train-of-four (TOF) as no fade occurs. Only single twitch (ST) allows to monitor depolarizing block. The TOFScan monitor proposes a modified TOF ratio (T4/Tref) not referring to fade within a TOF series. We hypothesized that the T4/Tref allows to assess recovery from succinylcholine. This observational study aims to compare recovery from depolarizing block simultaneously assessed with T4/Tref and ST. After Ethics Committee approval and written informed consent 45 patients receiving a single dose of succinylcholine were included. ST recovery, measured with TOF-Watch SX, and T4/Tref recovery, measured by TOFScan, were assessed simultaneously. Difference between measurements was compared using Mann-Whitney U test and overall concordance with the intraclass correlation coefficient (ICC). The ICC was 0.85 [95% CI 0.82-0.87]. The first T4/Tref ratio ≥ 90% was 97% [95% CI 93-101%] the corresponding ST value was 91% [95% CI 87-97%]. The first T4/Tref ratio ≥ 100% was 103% [95% CI 102-107%], the corresponding ST value was 104% [95% CI 100-106%]; median [95% confidence interval of the median]. Time to recovery to 90% and 100% of baseline did not differ between ST or T4/Tref. It was10.0 [8.0-13.0] min vs 10.0 [8.0-12.0] min, P = 0.307 and 10.0 [9.0-15.0] min vs 10.0 [8.0-15.0] min, P = 0.546; respectively; median [IQR]. Agreement between both parameters was excellent. The T4/Tref can be used accurately to measure recovery from depolarizing neuromuscular block.

Keywords: Depolarizing neuromuscular blockade; Neuromuscular blocking agents; Single twitch monitoring; Succinylcholine; Train of four.

Publication types

  • Observational Study

MeSH terms

  • Anesthetics*
  • Humans
  • Monitoring, Physiologic
  • Neuromuscular Blockade*
  • Neuromuscular Monitoring
  • Succinylcholine


  • Anesthetics
  • Succinylcholine