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Ketamine ‘Resets’ System for Normal Pain Processing in Complex Syndrome Patients
Initial research on ketamine for CRPS focused on the inpatient setting.
“While we don’t really know all the reasons patients develop CRPS, data from Europe and Mexico show that using very high doses of ketamine in an intensive care (ICU) or post-anesthesia care unit (PACU) setting produces a dramatic reduction in CRPS,” noted Houston. “With a ‘ketamine coma,’ one-third of patients have full resolution of symptoms: They are cured. One-third experience dramatic, permanent reduction in pain. Others have temporary relief. There is a much higher response rate than with other treatment modalities.”
Hospitalized patients who are intubated and ventilated receive an average of 500 mg of ketamine per hour for five days. Prior research showed that three days was insufficient and that no additional benefit was seen after five days. Patients typically leave the hospital two days after terminating the infusion.
To monitor the neurocognitive effects of ketamine, patients undergo psychological assessments prior to treatment, immediately following treatment and six weeks later.
“Immediately following treatment, we note some vision changes, some hallucinations. But at the six-week mark, patients are actually better and more functional than at baseline. With the severe, chronic pain resolved, they can focus, function and respond better,” Houston said.
“We’ve had about two-dozen patients in ketamine comas in the ICU to treat pain. Some of them had neuropathic pain, and, when they went in for surgery, we used ketamine for sedation and kept them intubated,” he added.
Not everyone with CRPS, phantom-limb pain or other neuropathic pain is a candidate for ketamine treatment. Inducing a coma and ventilating a patient for five days is a high-risk procedure, Houston explained, and patients must have tried injections, nerve blocks, spinal-cord stimulation and other conventional treatments first. Typical candidates have disabling pain that has made them nonfunctional or created severe psychological distress.
“CRPS can make people suicidal. We want to help them before they get to the point of considering suicide or amputation for a limb involved in CRPS. Some patients think that removing a limb will eliminate the pain, but CPRS is a disorder of nerve processing, not of the limb, so amputation is ineffective. We want to provide a treatment that will work,” said Houston.
Proactive Use of Ketamine
The best approach to chronic pain is prevention, and ketamine may be able to help there, too. “We are using the treatment now for patients coming in from Afghanistan with multiple injuries. Using ketamine for sedation, we could prevent potential phantom-limb pain. There isn’t a lot of data yet, but it seems that using a higher dose of ketamine closer to the time of trauma may prevent some cases of neuropathic pain and phantom limb pain,” Houston recounted.
For now, the team at Walter Reed is focused on presenting the results of the international research and their own experience, as well as the protocol they’ve developed for use of ketamine in patients in military hospitals.
“Our goal is to identify more patients and get the information about this therapy out so more patients can find relief,” Houston said.
 Correll GE, Maleki J, Gracely EJ, Muir JJ, Harbut RE. Subanesthetic ketamine infusion therapy: A Retrospective Analysis of a Novel Therapeutic Approach to Complex Regional Pain Syndrome. Pain Medicine. 2004;3:263-275. http://www.thblack.com/links/RSD/PainMed2004_5_263_ketamine_infusion_therapy.pdf
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