How can a remote oximeter meet the standards of EMC?
Assuming the device is EMC compliant and legal (which isn't necessarily the case).
It is possible to design a rugged, 3-signal interface using current loops. That is, some proprietary protocol which uses current levels to modulate the digital protocol, rather than voltage levels. You can even do this with 2 signals if you also supply the device through the current loop signal.
Lots of high integrity systems use/used this before the CAN bus era. You'd preferably use a tiny MCU which translates the MAX IC SPI output to the current loop protocol. I suppose it could even be done without a MCU and just some manner of current driver, if the SPI baudrate is kept slow enough.