A resuscitation unit, also referred to as a resuscitation tank, was an device which could be used to revive people who had been placed into suspended animation. The Fourth Doctor described it as resembling an oxygen cylinder.
Upon discovering that Sarah Jane Smith had been placed into suspended animation while aboard Nerva Beacon, the Fourth Doctor instructed Harry Sullivan to look for a resuscitation unit in order to revive her. It was while searching for this resuscitation unit that Harry found the corpse of a Wirrn inside one of the station's medical supply cupboards. The Doctor would later find that searching for a unit was unnecessary, as Nerva Beacon's resuscitation phase was already programmed into the station itself. (TV: The Ark in Space [+]Robert Holmes, Doctor Who season 12 (BBC1, 1975).)