I assume when you refer to 'serial link' you mean that you are using Rpi UART interface to communicate with the STM32.
I can see the convenience of using UART but as a very cautionary advice, hospital environments are electrically quite harsh in terms of EM noise. A serial line even a short one can absolutely suffer from interference.
You already made it relatively fail-safe with the heartbeat/watchdog but please consider upgrading your design to use comms with a differential signal, anything like CAN or even RS-485 in that Rpi/STM32 link would be a significant improvement.
I can see the convenience of using UART but as a very cautionary advice, hospital environments are electrically quite harsh in terms of EM noise. A serial line even a short one can absolutely suffer from interference.
You already made it relatively fail-safe with the heartbeat/watchdog but please consider upgrading your design to use comms with a differential signal, anything like CAN or even RS-485 in that Rpi/STM32 link would be a significant improvement.