While not standard practice we were often asked by the ALS medics to transit “as low as possible”. Usually +-500 /1000 ft AGL kept everyone happy day VMC.
When transporting a scuba diver suffering from “The Bends” we stayed pretty darn low all the way to the nearest decompression chamber at VNE. These were very infrequent trips but procedure, location of chambers ( there were 3 in our area ), helipads etc. were well covered in crew training briefings whenever new crew came onboard.