An anesthesia trial can assign two drugs at fixed doses or titrate both to the same measured target. In the second design, the comparison concerns the strategies used to reach that target. A randomized trial comparing etomidate and propofol illustrates the distinction.
Sixty adults scheduled for modified radical mastectomy received the same midazolam and fentanyl premedication. The investigators titrated the assigned induction drug to an entropy value of 40 before giving vecuronium. Entropy is a processed measure derived from electrical activity that the researchers used as a target for hypnotic depth. They recorded blood pressure and heart rate around induction and for three minutes after intubation.
The investigators reported that more patients required rescue ephedrine in the propofol group. That result applies to the tested protocols, including the common premedication, target, population and observation period. The shared target does not make the doses interchangeable or establish the same cardiovascular response under different induction conditions.
Shah and colleagues, Journal of Anaesthesiology Clinical Pharmacology (2015). Journal article ยท Full text.