Hi,
You must use a safe insulation, rather than basic insulation. Transformer based technologies are basic insulation, and not recommended for mission critical applications like Medical.If you certify your design (e.g. acc to IEC-601) optocouplers are very good with their 5kV insulation.
I would recommend a widebody optocoupler, like HCNW series. What data rate do you carry on your dataline? There are different HCNW for different datarates. Some examples
HCNW2611 (10 MHz), HCNW136 (1MHz) from Avago....
Greetings!
Hakeen