Annette M. Boyle
ROCKVILLE, MD — Morphine has met its match — and then some. After 200 years as the gold standard in battlefield analgesia, morphine is increasingly giving way to ketamine, a phencyclidine (PCP) derivative initially used in veterinary medicine.
Ketamine’s status has changed so rapidly that Army Col. Chester C. Buckenmaier III, MD, director, Defense and Veterans Center for Integrative Pain Management, has encountered some stiff resistance when using the drug. “I’ve twice had a nurse say, ‘You aren’t going to use that horse drug on my patient, are you?’”
|Army Col. Chester C. Buckenmaier III, MD, Director, Defense and Veterans Center for Integrative Pain Management, with a patient in Afghanistan in 2009.|
“That ‘horse drug’” is now one of the most effective tools available. Combat medics rate ketamine as more effective than morphine or fentanyl in providing rapid relief of severe pain, according to an ongoing survey conducted by the Naval Operational Medical Lessons Learned Center, Pensacola, FL.
Unlike morphine, ketamine does not cause hypotension or respiratory depression. It is “unique among anesthetics, because pharyngeal-laryngeal reflexes are maintained and cardiac function is stimulated rather than depressed,” said Air Force Lt. Col. John V. Gandy, MD, (ret.) in a Defense Health Board Decision Briefing.
In a March 8, 2012, memo to Jonathan Woodson, MD, assistant secretary of Defense (Health Affairs), the Defense Health Board (DHB) recommended adding ketamine to the Tactical Combat Casualty Care (TCCC) Guidelines as a battlefield analgesic. The memo noted that ketamine’s “clinical effects present within one minute of administration when given intravenously and within five minutes when given intramuscularly.”
“Four or five years ago, we would have had one or two patients on ketamine at Walter Reed; now about half are on ketamine on any given day. The use of ketamine in battlefield trauma has led the way to using it on wards — and even in civilian emergency departments,” Buckenmaier told U.S. Medicine.
Inhibits NMDA Receptors
Ketamine inhibits the action of the N-methyl d-aspartate (NMDA) receptors throughout the body and, at low doses, acts as a powerful analgesic and mild sedative and produces a sense of euphoria. At higher levels, it works as a dissociative anesthesia and provides moderate to deep sedation.
Ketamine also can cause hallucinations at higher doses, a problem seen particularly in its use in nonclinical settings as the street drug “angel dust” or “special K.” When used in surgical settings, especially for patients who have previously experienced hallucinations with ketamine, the International Committee of the Red Cross recommends using 10 mg of diazepam intravenously five minutes before and again at the conclusion of a procedure to minimize their incidence.
By blocking NMDA glutamate receptors, ketamine minimizes acute pain and decreases the wind-up pain caused by continual bombardment of the central nervous system. Wind-up amplifies incoming pain signals at the level of second-degree neurons in the spinal cord. Blocking these receptors also decreases tolerance to opioid medications.
“Inhibition of NMDA receptors in the acute phase is one of the few therapies that prevent development of chronic pain,” said Buckenmaier. Ketamine’s ability to reduce acute pain and short-circuit the development of chronic pain pathways makes it effective in any perioperative situation or trauma and can reduce post-operative and phantom-limb pain.