Because bronchoalveolar lavage, one of many procedures used here, is an invasive medical procedure that has no purpose other than to obtain information for diagnosis or scientific research. A small endescope is passed down the trachea, and part of the lung tissue irrigated with fluid, and the fluid (now containing cellular detritis) analysed. It is intensely uncomfortable if performed without sedataion and bronchoscopy is typically performed under heavy sedataion as a result. All of these facts carry risk -- risks which, under international law, the patient has to consent to.