For expediency, general anesthesia is the most common form of anesthesia provided for elective cosmetic surgery. Local anesthesia is typically injected prior to the incision. Unfortunately, the pain of the local anesthesia is transmitted to the brain. This is why scientific (or Level) I studies have failed to document preemptive analgesia.
After providing a sleep level of propofol measured with a brain activity monitor, a dissociative dose of ketamine does block the transmission of the pain signals to the brain and does provide reproducible preemptive analgesia.
There are no Level I studies of dissociative technique. However, the object of those studies to assure reproducibility. As long as the BIS is below 75 prior to injection of ketamine, preemptive analgesia (without the historically reported negative side effects) occurs.
This is a major paradigm shift. It can provide increased safety for cosmetic surgery beyond that provided by general anesthesia.