The basics are that someone with minor UE investment into medical could begin CPR on someone who has been flatlined, extending the length of the death tunnel until they fully die and have to be cloned, with the extension being influenced by the practitioner's skill, with some (small) chance to resuscitate someone based on luck and skill(resuscitation negotiable).
The advantage of this would be to allow(as was discussed in XOOC and in the thread on cheaper resuscitation prices) for medics to come onto a scene, and still be part of that scene without risking that the flatlined will die while they RP.
It would also allow for more interesting group activity during a major incident. You can have a lower skilled medic performing CPR to keep one patient alive, while the doctor is resuscitating another patient, or have a solo attempt to keep a capture target alive in time for their medical backup to arrive. It also generally allows for a medic to show up at a scene, and remain part of the scene, rather than immediately moving away.
There is also potential(special thanks again to robotdogfighter for the idea!) to have doing CPR on a patient improve the chance of success to resuscitate, allowing for it to still be useful even in situations where the patient will need to eventually be dragged to a clinic to be resuscitated, or is already in a position to be resuscitated.
To top it all off, there's something inherently dramatic about CPR, those desperate moments where you just need to keep someone kicking until help comes, and I think that adds a lot to the theme and style of the game.