Canadian Journal of Anaesthesia

, Volume 42, Issue 12, pp 1090–1095 | Cite as

The influence of changes in hand temperature on the indirectly evoked electromyogram of the first dorsal interosseous muscle

  • Aaron F. Kopman
  • Mona D. Justo
  • Moin U. Mallhi
  • Chinedu E. Abara
  • George G. Neuman
Reports of Investigation


The evoked EMG response commonly decreases in amplitude during the first few minutes of anaesthesia. The purpose of this study was to determine if a relationship exists between changes in hand temperature, which are known to occur with induction of anaesthesia, and drift in the EMG signal. The indirectly evoked response of the 1st dorsal interosseous muscle was measured using a Datex™ Relaxograph® in 15 patients undergoing elective surgery. The test arm was wrapped in towels in order to minimize heat loss. Core body temperature, hand temperature, and T1 were recorded at two minute intervals for the next 30 min. Patients then received a bolus of mivacurium 0.08 mg · kg−1 and additional doses were given as needed. Complete recovery was defined as a TOF ratio > 0.90. Regression analysis plotting Atemperature against Δ T1 was performed for each individual. The slope of the regression line for the relationship between Δ°C and δ T1 was then used to calculate a correction factor (CF) which might be used to “fine tune” the last measured T1. The initial hand temperature averaged 30.8 ± 1.4° C and this increased by 4.1 ± 1.2° C over the next 30 min. During this period T1 decreased by 24.8 ± 5.9% or-6.05%/° C. The final mean T1 value at the end of anaesthesia (uncorrected) was 70.6 ± 7% of control. The average corrected T1 value was 94.7 ± 8.5% (range, 83–111%). It is concluded that there was a correlation between Δ°C and ΔT1 during the first 30 min of anaesthesia (r2 = 0.77, P < 0.0001). However, in 5 of 15 individuals it was not possible to “temperature correct” the final T1 value to within ± 10% of control. Hence, while changes in muscle temperature probably play a major role in the T1 drift seen with the Datex monitor, other factors remain to be identified.

Key words

monitoring: neuromuscular junction, train-of-four, electromyography 


La réponse évoquée à l’EMG diminue ordinairement pendant les premières minutes de l’anesthésie. Le but de cette étude était de déterminer la relation possible entre les changements de température de la main qui surviennent à l’induction, et la dérive du signal de l’EMG. La réponse indirecte évoquée au 1er muscle interosseux dorsal a été mesurée avec un Relaxograph® Datex® chez 15 patients en chirurgie réglée. Le bras servant à l’expérience a été enveloppé dans des serviettes pour en atténuer la perte de chaleur. La température centrale, la température de la main et T1 ont été enregistrés aux deux minutes pendant 30 min. Les patients ont alors reçu un bolus de mivacurium 0,08 mg · kg−1 et des doses additionnelles administrées au besoin. La récupération complète a été définie comme un rapport de TOF > 90%. L’analyse de régression établissant la relation entre Δ température et ΔT1 a été effectuée pour chacun des sujets. La pente de régression pour la relation entre Δ°C et ΔT1 a été utilisée pour calculer un facteur de correction (FC) utilisable pour une mise au point finale du dernier T1 mesuré. La température initiale de la main était en moyenne de 30,8 ± 1,4° C. Elle augmentait de 4,1 ± 1,2° C pendant les 30 min suivantes. Pendant cette période, T1 diminuait de 28,4 ± 5,9% ou −6,05%/° C. La valeur finale moyenne de T1 à la fin de l’anesthésie (sans correction) était de 70,6 ± 7% du contrôle. La valeur moyenne corrigée de T1 était de 94,7 ± 8,5% (écart, 83–111%). En conclusion, il existe une corrélation entre Δ° C et AT1 au cours des 30 premières min d’anesthésie (r2 = 0,77, P < 0,0001). Toutefois, chez cinq des 15 sujets, il a été impossible d’appliquer la correction de température à la valeur finale de T1 à ±10% du contrôle. En conclusion, bien que les changements de température musculaire puissent jouer un rôle majeur dans la dérive de T1 observée avec le moniteur Datex, les autres facteurs en cause sont encore inconnus.


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Copyright information

© Canadian Anesthesiologists 1995

Authors and Affiliations

  • Aaron F. Kopman
    • 1
  • Mona D. Justo
    • 1
  • Moin U. Mallhi
    • 1
  • Chinedu E. Abara
    • 1
  • George G. Neuman
    • 1
  1. 1.Department of Anesthesiology (Room NR 408)St. Vincent’s Hospital and Medical Center of New YorkNew York City

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