Testing for interactions between anaesthetic drugs

That response surface methodology (a technique that models the pharmacodynamic effect of two and three drug combinations) can define the interaction between sevoflurane and remifentanil for the duration of a general anaesthetic (approx 2 hrs). Remifentanil intravenously dose range 0.05 & 0.25%mcg/kg/min, and will be incremented. Sevoflurane dose range will be 0.25-1.25% mcg/kg/min. One drug will be randomly assigned as the start drug and ramped up to a preset randomly selected dose within the dose range (sevoflurane 0.25, 0.5, 0.75, 1.0 or 1.25%, remifentanil 0.05, 0.1, 0.15, 0.2 or 0.25%mcg/kg/min) then second drug will be introduced and ramped up until OASS score of 5 is attained. Doses will be incremented once 5 plasma half times have elapsed to allow equilibration at the effect site. This will approximately 5 mins for each increment. Increments will be ceased when patient is OASS 5 (unconscious and able to tolerate laryngoscopy) at which stage the patient will be intubated and preparations for surgery to be continued.