Nitrous oxide for the treatment of complex regional pain syndrome: a randomized blinded trial

• Published in: Regional anesthesia and pain medicine Vol. 49; no. 8; p. 573
• Main Authors: Hale, Jason, Xu, Jijun, Wang, Dong, Rodriguez-Patarroyo, Fabio, Bakal, Omer, Kopac, Orkun, Yamak Altinpulluk, Ece, Onal, Ozkan, Brooker, Jack E, Cruz, Miguel, Maurtua, Marco, Agudelo-Jimenez, Ruben, Sessler, Daniel I, Turan, Alparslan
• Format: Journal Article
• Language: English
• Published: England BMJ Publishing Group LTD 01.08.2024
• Subjects: Adult; Aged; Anesthesia; Anesthetics, Inhalation - administration & dosage; Chronic pain; Complex Regional Pain Syndromes - diagnosis; Complex Regional Pain Syndromes - drug therapy; Double-Blind Method; Female; Gases; Humans; Ketamine; Male; Mental health; Middle Aged; Narcotics; Nitrous oxide; Nitrous Oxide - administration & dosage; Nitrous Oxide - adverse effects; Pain Measurement - methods; Patients; Questionnaires; Regional anesthesia; Spinal cord; Statistical significance; Treatment Outcome; United States > US; Pain Perception; Complex Regional Pain Syndromes; Pain Management
• ISSN: 1098-7339; 1532-8651
• DOI: 10.1136/rapm-2023-104537

Complex Regional Pain Syndrome (CRPS) is a debilitating neuropathic condition often refractory to conventional treatments. N-methyl-D-aspartate (NMDA) receptor antagonists have a well-established role in the development and modulation of chronic neuropathic pain. Nitrous oxide is widely used and generally safe anesthetic gas with NMDA receptor antagonist activity. We therefore tested the hypothesis that brief periods of nitrous oxide exposure reduce pain in patients with CRPS. Patients with a diagnosis of CRPS were randomized to either 2 hours of nitrous oxide exposure on three alternating days (Nitrous Oxide) versus a placebo air/oxygen mixture (Air-Oxygen). Our primary outcome was patient-reported pain scores at 1 week and 1 month. Secondary and exploratory outcomes were physical and mental health (PRMOIS-29 v2 survey), specific neuropathic pain symptoms (McGill short-form questionnaire), and opioid consumption. 44 patients participated in the study; 20 were randomized to Nitrous Oxide and 24 were assigned to Air-Oxygen. Pain scores did not differ significantly, with the estimated difference in means (Nitrous Oxide-Air-Oxygen) of -0.57 (95% CI: -1.42 to 0.28) points, p=0.19. There were also no differences detected in secondary outcomes, with the estimated difference in mean Z-scores for physical health (Nitrous Oxide-Air-Oxygen) of 0.13 (95% CI: -0.16 to 0.43), mental health 0.087 (95% CI: -0.31 to 0.48), and Patient Global Impression of Change score -0.7 (95% CI: -1.85 to 0.46). Compared with air/oxygen, 2 hours of nitrous oxide/oxygen exposure for three sessions did not provide meaningful therapeutic potential for patients with chronic CRPS. Our results do not support using nitrous oxide for the treatment of CRPS.