The Inhaler is a "consumable" in I Am Alive. It replaces the lost Stamina after using Extreme Effort. It is a rare and powerful consumable and should be saved, for multiple Victims need one to survive and for the protagonist to get another Retry.
The second can be found at the top of the fire escape across the street from Henry's Apartment after the second aftershock. The third be found in the streets, in the area you first encounter the Dust storm, near the train next to a grappling hook point. The fourth can be found across the street from that train, with a pipe leading to it.