Exploratory clinical trial to evaluate the efficacy and safety of carbon dioxide paste in healthy people

Scarring and pain are postoperative complications in patients after head and neck cancer treatment; however, there is no effective treatment. These complications are affected by local blood flow disorders, and it is well known that the transcutaneous application of carbon dioxide (CO(2)) improves local blood flow. Previously, we have shown that the transcutaneous application of carbon dioxide causes absorption of CO(2) and increase the oxygen (O(2)) pressure in the treated tissue; it is expected that the application of CO(2) may reduce scarring and pain caused by cancer treatment. We newly introduced the CO(2) paste as a new CO(2) application method, which does not need to use CO(2) gas directly. In this study, we aimed to apply of CO(2) paste to healthy people and to investigate its usefulness, safety and feasibility by analysing the increase in blood flow and frequency of adverse events. METHODS: We applied carbon dioxide paste to skin over the sternocleidomastoid and gastrocnemius muscles of eight healthy volunteers. The changes in blood flow before and after the CO(2) paste application using dynamic MRI, and changes in the vital signs were evaluated. RESULTS: In the neck area and middle layer of the lower leg, the signal intensity (SI) significantly increased 60 seconds after application. In the surface layer of the lower leg, the SI was significantly increased 60 and 300 seconds after paste application. Although mild heat was noted after the paste application, no obvious adverse events occurred. CONCLUSION: We demonstrated the increase in SI by dynamic MRI at the site of the carbon dioxide paste application, which indicates the paste application is effective in improving the blood flow.