DETERMINATION OF END-TIDAL SEVOFLURANE CONCENTRATION FOR TRACHEAL INTUBATION AND MINIMUM ALVEOLAR ANESTHETIC CONCENTRATION IN ADULTS

The purpose of this study was to determine both the concentration of s evoflurane required for tracheal intubation (MAC(EI)) and its minimum alveolar anesthetic concentration (MAC) in adults. The study group con sisted of 86 elective surgical patients, ASA physical status I or II, aged 16-59 yr. There was no premedication administered. For MAC(EI) de termination, after establishing and maintaining the predetermined end- tidal concentration for 20 min, tracheal intubation was attempted usin g a cuffed tracheal tube without muscle relaxant or other adjuvants. E ach concentration at which tracheal intubation was attempted was prede termined as follows: 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6 .5%, and 7.0%. For MAC determination, the patients examined were basic ally the same as those for MAC(EI) determination, except for those who received muscle relaxant or other adjuvants because they were ''not i ntubated smoothly.'' After establishing and maintaining the predetermi ned end-tidal concentration for 20 min, skin incision was attempted. E ach concentration at which skin incision was attempted was predetermin ed as follows: 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0%. The MAC(EI) of sevoflurane was 4.52% (95% confidence limits, 3.91%-5.21%), and the ED ,, for tracheal intubation was 8.07%. The MAC of sevoflurane was 1.58% (95% confidence limits, 1.14%-1.98%), and the AD(95) (anesthetic ED(9 5)) was 2.96%. The MAC(EI)/ MAC ratio was 2.86 (95% confidence limits, 2.63-3.43). Anesthesia induction followed by tracheal intubation can be accomplished in adults when sevoflurane is administered as a sole a nesthetic, but in excess of 8% end-tidal concentration.