Isoflurane Dexmedetomidine

In 45 adult patients undergoing elective surgery, the 2-adrenoceptor agonist dexmedetomidine in a concentration of 0.7 ng/ml reduced the minimum alveolar concentration of sevoflurane required to suppress movement to skin incision by 17%, but a plasma concentration of 0.39 ng/ml had no effect (58). The larger reductions in isoflurane requirements found in earlier studies of dexmedetomidine were probably due to the use of potent opioids and intravenous induction as part of the anesthetic. 

Dexmedetomidine can reduce the dose requirements of thiopental, isoflurane, and other similar anaesthetics. 

A placebo-controlled study in women undergoing abdominal hysterectomy found that a dexmedetomidine infusion started 15 minutes before induction of anaesthesia caused a dose-dependent reduction in isoflurane MAC (by 35% and 47% with dexmedetomidine plasma levels maintained at 0.37 and 0.69 nanograms/mL, respectively). In another study, dexmedetomidine reduced the ED50 dose requirement ofisoflurane for anaesthesia (motor response) in 9 healthy subjects. Dexmedetomidine plasma levels of 0.35 and 0.75 nanograms/mL reduced the requirements for isoflurane by about 30% and 50%, respectively. Subjects who had received dexmedetomidine took longer to wake up. Dexmedetomidine has sedative, analgesic and anxiolytic effects and therefore, like other sedatives, may reduce the dose requirements of anaesthetics. However, it may also affect the distribution of thiopental and possibly other intravenous anaesthetics. 

Aantaa R, Jaakola M-L, Kallio A, Kanto J. Reduction of the minimum alveolar concentration of isoflurane by dexmedetomidine. Anes tesiology (1997) 86,1055-60. 

Khan ZP, Munday IT, Jones RIvL Thornton C, Ivfent TG, Amin D. Effects of dexmedetomidine on isoflurane requirements in healdiy volunteers. 1 Pharmacodynamic and pharmacokinetic interactions, Br JAnaesth (1999) 83, 372-80. 

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