Objective: Advanced complex regional pain syndrome (CRPS) often involves generalized spreading from the primary site of injury. A recent previous study reported significant improvement in pain and function after a 5-day anesthetic “coma” dose of ketamine. (1) The results of that study depended on self-reporting of pain and function. This study aimed to assess: 1) Assess the dose of ketamine required on a daily basis to prevent adverse hallucinations. 2) Study the outcome of the 5-day infusion using pain thresholds as an objective measurement of pain.
Methods: After IRB approval and patient consent, 23 patients with intractable, generalized CRPS were included in the study. Research subjects failed all other treatments. Baseline measurements of pain were made using force gauges calibrated to a maximum force of 5 kg. (Algometer, Wagner Instruments, USA) Pain threshold measurements were made at primary site where the initial symptoms of CRPS took place and a secondary site (usually another extremity) where the CRPS had spread. Research subjects were admitted to the ICU, intubated and observed for hallucinations throughout the 5-day ketamine infusion.
1) None of the subjects awoke or experienced hallucinations during the 5-day infusion.
2) An increase in the dose of ketamine was required in order to maintain adequate anesthesia. (Figure 1, P<0.05).
3) There was a more rapid improvement in pain relief at the primary site compared to the secondary site at 1 month and the pain thresholds improved at both sites over the 3-month period. (See Figure 2, P<0.05).
4) No major or life-threatening complications were observed.
Conclusions: As reported previously, the ketamine coma procedure is an effective method for treating intractable, generalized CRPS. The results of this study provide a dosage guideline for maintaining an adequate depth of anesthesia to avoid hallucinations during the infusion period and point to pain thresholds as an objective and quantitative method for assessing clinical outcome in patients with CRPS.
(1) Ralph-Thomas Kiefer et al. Pain Medicine 2008;9: 1173 - 1201.