Severe sleep apnea syndrome is usually defined as the occurrence of an average of more than 30 apneas per hour during 7 hours of sleep at night, with severe hypoxia and a minimum oxygen saturation of less than 65%. Due to prolonged breath-holding and hypoxemia, it brings great load and damage to the cardiovascular system, often combined with hypertension and other cardiovascular diseases, and the potential damage is real even without clear comorbidities. If preoperative non-invasive positive pressure ventilation is not performed to correct the hypoxemia, so that the cardiovascular damage can be relieved and restored to a certain degree and the central drive is enhanced, perioperative and intraoperative cardiovascular accidents are highly likely to occur. Therefore, patients with severe OSAHS require CPAP therapy preoperatively, usually for at least about two weeks.