Breathing apparatus includes a hood enclosing the patients head and having a gas inlet and outlet located on the hood in the region of the patients nose and mouth. Inlet tubing connects the gas inlet on the hood with an outlet of a gas supply unit outlet tubing connects the gas outlet on the hood with an inlet of the gas supply unit. A pump in the gas supply unit draws gas extracted from the outlet tubing through a scrubber to remove carbon dioxide from gas extracted from the enclosure. A mixer valve mixes gas from the scrubber with fresh gas from an oxygen and helium cylinder for supply back to the inlet tubing.
