To investigate the independent effects and interaction of pre-oxygenation position (left lateral vs left lateral with 30° head-up tilt) and examination position (left lateral vs left lateral with 30° head-up tilt) on hypoxemia during painless gastroscopy and colonoscopy using a 2×2 factorial design.
Aged 18 to 75 years, regardless of gender
Body mass index (BMI): 18.5 - 35 kg/m²
ASA physical status class I, II or III
Scheduled for painless gastroscopy, painless colonoscopy, or combined painless gastroenteroscopy
Severe cardiopulmonary diseases, including severe COPD, heart failure, severe arrhythmia and pulmonary hypertension
Difficult airway identified before anesthesia
Severe obstructive sleep apnea (OSA)
Spinal or thoracic deformity