Characters, including The Warden, that fall in combat receive a debilitating injury that lowers an attribute until treated. These injuries can stack. To remove a persistent injury, you must return to your party camp, have your Spirit Healer use Cleansing Aura, or use an injury kit. (For some reason, Cleansing Aura will not remove an injury on the Spirit Healer themself.)
As with poultices, each kit has a certain level of potency that determines how much damage it’s able to repair. Lesser injury kits heal a single injury and a small amount of health, for example.
Taking the wrong item from the chests in the quest Jammer's Stash will also give you an injury.