To the OP, I'm glad you appreciate the effort made by medical/nursing volunteers inflight. As Radgirl pointed out, there are obvious medico-legal issues surrounding 'good samaritan' acts outside of one's normal place of work and I've known colleagues who (during flights in US airspace) have deliberately not come forward for the fear of possible legal sequelae in case anything were to happen.
Thankfully I've only had to offer my services once, during an inter-European flight and the CC did actually produce pre-printed legal waiver forms for us to sign (LH). Does anyone know if this is common practice among other carriers?