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The ED₉₅ of end-tidal sevoflurane concentration for the smooth exchange of the tracheal tube for a laryngeal mask airway is 2.97%

[La DE₉₅ de la concentration télé-expiratoire de sévoflurane nécessaire au remplacement sans à-coups du tube endotrachéal par un masque laryngé est de 2,97 %]

From the Department of Anesthesiology Critical Care Medicine Hokkaido University Graduate School of Medicine Sapporo Japan.

Address correspondence to: Dr. Koichi Takita, Department of Anesthesiology and Critical Care Medicine, Hokkaido University Graduate School of Medicine, Kita-15, Nishi-7, Kita-ku, Sapporo 060-8638, Japan. Phone: +81-11-706-7861; Fax: +81-11-706-7861; Email: ktakita{at}med.hokudai.ac.jp

Purpose: Exchanging the tracheal tube for the laryngeal mask airway (the TT/LMA exchange) while the patient is still anesthetized avoids coughing associated with tracheal extubation. This study was conducted to determine the end-tidal concentration of sevoflurane that prevented response to this exchange in 50% patients (MAC_TT/LMA).

Methods: We studied 21 adult male patients, ASA I, aged 21–54 yr. Anesthesia was induced with thiamylal and sevoflurane, and the trachea was intubated following vecuronium neuromuscular blockade. Anesthesia was maintained with sevoflurane and nitrous oxide in oxygen. After surgery, a predetermined end-tidal sevoflurane concentration was achieved and a steady state was maintained for at least 20 min. The concentration at which the TT/LMA exchange was attempted was determined by a modification of Dixon’s up-and-down method with 0.25% as the step size. At the time of the TT/LMA exchange, no residual nitrous oxide > 3% was detected, and the return to normal neuromuscular function was confirmed. When the TT/LMA exchange was accomplished without coughing, movement, or airway obstruction, it was considered a smooth exchange.

Results: Sevoflurane MAC_TT/LMA determined using the up-and-down method was 2.63% ± 0.14%. The 50% effective dose obtained using a probit analysis was similar [2.53% (95% confidence limits, 2.13–2.82%)].

Conclusion: Sevoflurane MAC_TT/LMA in adult male patients was 2.63% (1.54 MAC) and may be useful for the smooth exchange of the tracheal tube for the LMA in a clinical setting.