Editing K2 (section)

===Use of supplemental oxygen===
For most of its climbing history, K2 was not usually climbed with supplemental oxygen. Small, lightweight teams were the norm.<ref name="him_alpine_style">{{cite book |last1=Fanshawe |first1=Andy |last2=Venables |first2=Stephen|title=Himalaya Alpine-Style |publisher= Hodder and Stoughton |date= 1995 |isbn=0-340-64931-3}}</ref><ref name="world_mountaineering">{{cite book |editor-last=Salkeld |editor-first=Audrey |title=World Mountaineering |publisher=Bulfinch Press|year= 1998 |isbn=0-8212-2502-2}}</ref> However, the 2004 season saw a great increase in the use of oxygen: 28 of 47 summiteers used oxygen in that year.<ref name="aaj_2005"/>

Acclimatisation is essential when climbing without oxygen to avoid some degree of [[altitude sickness]].<ref name=Acclimatisation/>
K2's summit is well above the altitude at which [[high-altitude pulmonary edema]] (HAPE) and [[high-altitude cerebral edema]] (HACE) can occur.<ref name=MedicalProblems/> In [[mountaineering]], when ascending above an altitude of {{convert|8000|m|ft}}, the climber enters what is known as the ''[[death zone]]''.<ref>{{cite web |last1=Woodward |first1=Aylin |title=What happens to your body in Mount Everest's 'death zone,' where 11 people have died in the past week |url=https://www.businessinsider.com/mount-everest-death-zone-what-happens-to-body-2019-5 |website=Business Insider |access-date=4 November 2022}}</ref>