VRDP07400 | Air conditioning units: oxygen concentrators, artificial respirators and similar apparatus
From HM Revenue & Customs · VAT Relief for Disabled People Manual
Oxygen concentrators, artificial respirators and similar apparatus are included within the zero rate under Note (4c) (see VRDP05100).
This is because these types of equipment work automatically and are specifically designed for the sole purpose of providing artificial ventilation for a patient, who is physically attached to the machine.