Lisa,

This is a great question. We frequently see patients needing HBO on drugs that may be contraindicated in the HBO environment. Baude and Cooper did a good review of the commonly contraindicated chemotherapy drugs in the HBO environment (https://www.ncbi.nlm.nih.gov/books/NBK560873/). These drugs include. Bleomycin, Doxarubicin, Cis-Platnin. Additionaly, Gawdi and Cooper (https://www.ncbi.nlm.nih.gov/books/NBK557661/) list additional drugs should not be used in conjunction with HBO, Disulfram and Mafenide.  Amiodarone is also a questionable drug that is typically treated similarly to Bleomycin in the hyperbaric environment. As to your question, I could not find anything specific on Keytruda safety in the hyperbaric environment. There have been research trials using Carboplatin and HBO as well as other chemotherapy agents as a treatment for non-small cell lung cancer. For Cis-platin given WITH HBO, the main negative effect is with wound healing (fibroblast collagen production).  The reported half life of Carboplatin I found was 30 hours, so you may want to wait at least one week and maybe up to 2 weeks after the last dose of Carboplatin to begin HBO. Finally, for completeness, you may want to get input from the patients Heme/Onc Physician with respect to the Keytruda.