If they have refractory hypoxemia (low oxygen saturation that does not respond to oxygen delivered by face mask), the ve如果病人有难治性低氧血症(低氧饱和度，面罩供氧无效)，呼吸机就可以将高浓度的吸入氧输送到肺泡，并通过呼吸机输送的压力张开塌陷的肺泡。