First, the extremely injured were taken care of first. The less extreme cases were left to wait as the ones that needed it the most were treated.
Injuries were treated fast and quick, most of which where amputations of limbs which couldn't be saved. During the CW things that reduced pain didnt exist, so instead they gave some people chloroform which made them pass out during the "surgerie".
Once the wounded were treated, they were left to rest for a while, very few survivied, most people died of infection post operation. Some wounded died waiting or were left to die if surgeons couldn't do anything to help.