To the Editor:—
I read with interest the article by Motamed et al. 1in the February issue of ANESTHESIOLOGY, and agree with their finding that intravenously administered morphine-6-glucuronide (M-6-G) lacks an-algesic effect. However, I am troubled by their conclusion (reflected in the title) that preemptive M-6-G is not an effective analgesic. Their methods indicate that at the beginning of skin closure, patients received intravenous morphine sulfate, M-6-G, or saline. The use of the word “preemptive” in this regard is wrong because the analgesics were administered after the surgical incision and because they were not maintained postoperatively.
The goal of preemptive analgesia is to prevent the establishment of central sensitization, which then amplifies postoperative pain.2,3Postinjury analgesia usually has a reduced effect because central sensitization already has been established. Carr4cautions against the routine use of the word preemptive. He states that preemptive refers to measures that prevent sensitization of cells within the spinal cord dorsal horn and that preemptive anesthesia by definition must be accomplished before the onset of nociception. Central hypersensitivity may develop despite the use of analgesia before a noxious stimulus. This may happen if the analgesia is inadequate to prevent central sensitization or if the analgesia is only provided before the stimulus. Postinjury hypersensitivity develops secondary to inflammatory changes that occur as a result of an injury and can also lead to central sensitization.
In summary, preemptive analgesia must occur before the injury, must be adequate to prevent central sensitization, and must be maintained postoperatively to prevent the inflammatory changes associated with postinjury hypersensitivity.