Complex sentence: By 21:00 they had enlarged the snow hole and, with the oxygen cylinders exhausted and fuel in their stove soon used up, they spent a cold night moving their limbs continuously and rubbing each other to keep any warmth in their bodies.
Split into simpler sentences: By 21:00 they had enlarged the snow hole and, with the oxygen cylinders exhausted and fuel in their stove soon used up. They needed to keep moving their limbs all night and rubbing each other to keep any warmth in their bodies.