Horizon treks to the top of the world on a unique scientific expedition to Everest which could revolutionise the treatment of patients in intensive care.

In a special two-part documentary, cameras follow an extraordinary team of climbing doctors who risk their own lives in the most hostile environment on Earth in an attempt to rewrite our understanding of the human body.

The Caudwell Xtreme Everest Expedition is one of the largest ever to come to the Himalayas. Joining the 60 doctors and scientists are more than 200 volunteers who trek to Everest Base Camp to undergo a barrage of tests to see how different people adapt to a lack of oxygen at high altitude.