Re: Beyond Opioids: Understanding Surgical Pain (October 2006, p. 60)
Is it possible to pre-empt pain?
I looked askance at Dr. Brennan's assertion that "you can't pre-empt pain." A recent meta-analysis of Level I studies failed to demonstrate pre-emptive analgesia with injection of local anesthesia before incision under general anesthesia. This paper wasn't able to consider the paradigm of dissociative anesthesia because there are no Level I studies. Under conditions of dissociative anesthesia, the injection of local anesthesia does not send noxious signals to the brain. In this manner, dissociative anesthesia is like a "mid-brain" spinal anesthetic for the 10 minutes to 20 minutes the effect of the 50 mg ketamine dose typically lasts. It is axiomatic that the brain cannot respond to signals it does not receive.
Pre-emptive analgesia does exist under specific, reproducible conditions. The dissociative effect is regularly observed when the NMDA receptors are saturated. The dissociative effect sets the stage for reproducible pre-emptive analgesia. There are a finite number of NMDA receptors in adults in the spinal cord and mid-brain. This number does not appear to vary with body weight in adults. A 50 mg IV ketamine bolus will effectively saturate the fixed number of NMDA receptors of 98 percent of adult patients. Completely blocking incoming noxious signals to the cortex using the dissociative effect (the so-called mid-brain spinal) is most likely responsible for the observed pre-emptive analgesia. Hypnosis (propofol to BIS <75) first, then dissociation (50 mg ketamine) eliminates the historically reported side effects of ketamine.
Barry L. Friedberg, MD
Cosmetic Surgery Anesthesia
Corona del Mar, CA
drfriedberg@doctorfriedberg.com
Barry L. Friedberg, MD
Cosmetic Surgery Anesthesia
Corona del Mar, Calif.
drfriedberg@doctorfriedberg.com
Dr. Friedberg (drfriedberg@doctorfriedberg.com) is the author of the upcoming textbook Anesthesia in Cosmetic Surgery, Minimally Invasive Anesthesia for Minimally Invasive Surgery.