Related, the ambulance system where I live has been running a clinical trail using a mobile ECMO unit (Extracorporeal membrane oxygenation) [1,2]. An invasive procedure that oxygenates and pumps blood. It's boosted survival rate for those who are not responding to CPR (15-20 minutes duration) from 3% to 28%. The general CPR survival rate is an exponential looking curve: starting around 20%, reducing to 10% at 10 minutes and 3% at 20 minutes [3].
[1] https://www.abc.net.au/news/2025-04-07/nsw-ambulance-ecmo-tr...
[2] https://www.nsw.gov.au/media-releases/mobile-cardiac-treatme...
[3] https://www.bmj.com/content/384/bmj-2023-076019
Edit: The numbers in [3] are optimistic, as they are for in-hospital CPR, not out-of-hospital CPR.