Through a multicenter, three-arm randomized controlled trial design, this study aimed to compare the effects of three positioning strategies-side-lying with elevated head position, supine with elevated head position, and standard side-lying position-on the incidence of hypoxemia during the recovery phase in patients undergoing painless gastroscopy and colonoscopy. The goal was to provide clinicians with a simple, non-invasive, and cost-effective optimization strategy.

Painless gastroscopy and colonoscopy have become the gold standard for screening and diagnosing gastrointestinal diseases due to their high patient comfort and excellent compliance rates, with their clinical application expanding annually. This procedure is performed under intravenous general anesthesia to achieve painlessness; however, anesthetic agents exert inhibitory effects on the patient's respiratory center. Additionally, the procedural manipulation causes irritation to the airways and gastrointestinal tract, leading to a high incidence of hypoxemia during the postoperative recovery phase-the most common respiratory adverse event associated with painless gastroscopy and colonoscopy. Mild cases may prolong patient recovery time, while severe cases can result in serious complications such as hypoxic brain injury or cardiac arrest, directly compromising patient safety and healthcare experience.

Positioning is a critical non-pharmacological intervention factor influencing perioperative respiratory function in patients undergoing painless gastroscopy and colonoscopy. Different positions alter thoracic compliance, airway patency, and diaphragmatic position, thereby affecting the patient's ventilation and oxygenation status. Currently, the standard lateral decubitus position is routinely used for painless gastroscopy and colonoscopy, and it has been demonstrated to reduce the incidence of hypoxemia. However, this position presents challenges such as difficulties in patient monitoring and localized pressure-related discomfort. In contrast, the supine head-up and lateral decubitus head-up positions, by elevating the head and adjusting the body angle, effectively mitigate tongue base prolapse and improve thoracic expansion, theoretically reducing the risk of hypoxemia. Nevertheless, there is currently a lack of multicenter, large-sample, prospective randomized controlled studies to compare the efficacy and safety of these three positions in preventing hypoxemia in recovery rooms for painless gastroscopy and colonoscopy patients. Consequently, there is no unified evidence-based guideline for selecting the optimal clinical positioning.

Based on this, this study focuses on three clinically common positions and employs a multicenter, three-arm, randomized controlled parallel design to systematically investigate the effects of lateral supine with head elevated, supine with head elevated, and standard lateral position on postoperative hypoxemia in patients undergoing painless gastroscopy and colonoscopy. The aim is to fill a research gap in this field and provide high-quality evidence-based medical data to optimize postoperative position management during recovery and reduce adverse respiratory events following painless gastrointestinal endoscopy.

Special Note：Prespecified subgroup analyses will be conducted based on age (<65 vs ≥65), sex, BMI, ASA class, smoking and alcohol use, Mallampati score, anesthetic agent (clobupol or propofol), type of endoscopy (gastroscopy, colonoscopy, or gastroenteroscopy), Ramsay sedation score (2-4), pre-procedure hypoxemia, prior pulmonary surgery, OSA, respiratory disease, and intra-procedural hypoxemia (SpO₂ ≤90% for >10 seconds). The influence of heterogeneity on the primary outcome will also be evaluated.

Inclusion Criteria:

1. Age ≥ 18 years.
2. Both sexes.
3. American Society of Anesthesiologists (ASA) physical status classification I-III.
4. Scheduled for combined painless esophagogastroduodenoscopy/colonoscopy or either of the two procedures.
5. Ability to understand the study protocol and provide written informed consent.
6. A broad set of inclusion criteria was adopted to enroll a patient population that better reflects routine clinical practice. The study aimed to enhance the generalizability of the findings by including patients with various comorbidities, such as preprocedural hypoxemia (room-air SpO₂ ≤ 90%), history of pulmonary surgery, obstructive sleep apnea (OSA), and other pulmonary conditions (including asthma, COPD, chronic bronchitis, emphysema, and pulmonary bullae).

Exclusion Criteria:

1. Severe cardiovascular or cerebrovascular diseases.
2. Pregnant patients.
3. History of hypersensitivity to ciprofol.

Withdrawal Criteria:

1. Endotracheal intubation required during the procedure.
2. Voluntary withdrawal requested by the patient or their legal representative.

An independent statistician not involved in the study implementation generated random codes via computer. The allocation was concealed using sequentially numbered, opaque, sealed envelopes that were opened immediately before intervention implementation. Due to the nature of the intervention (postural factors), blinding was not feasible; instead, outcome evaluators were blinded. Data collection and statistical analysis of outcome indicators were performed by healthcare professionals independent of the study operations to minimize bias.