Effect of Preoxygenation Position and Examination Position on Hypoxemia During Painless Gastrointestinal Endoscopy

Effect of Preoxygenation Position and Examination Position on Hypoxemia During Painless Gastrointestinal Endoscopy: A 2×2 Factorial Randomized Controlled Trial

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.

Study Overview

• Status: Not yet recruiting
• Conditions: Hypoxemia During Surgery
• Intervention / Treatment: Procedure: Pre-oxygenation Position （left lateral position）; Procedure: Examination Position（left lateral position ）; Procedure: Examination Position（left lateral head elevation in a 30-degree position）; Procedure: Pre-oxygenation Position（ left lateral head elevation in a 30-degree position）

Detailed Description

Painless gastroscopy and colonoscopy represent core minimally invasive techniques for colorectal cancer screening and the diagnosis and treatment of gastrointestinal diseases. By utilizing intravenous sedation to ensure a pain-free experience, these procedures are widely adopted in clinical practice. However, perioperative hypoxemia remains the most common and critical safety complication during sedation for endoscopy. It is primarily caused by anesthesia-induced respiratory depression, tongue base collapse, airway obstruction, diaphragmatic compression, and restricted thoracic movement, with significantly elevated risks observed in obese, elderly, snoring, and short-necked patients.

Hypoxemia may trigger bradycardia, arrhythmias, myocardial ischemia, and cerebral hypoxia. In severe cases, it can lead to apnea, laryngospasm, and forced termination of the procedure, making it a key indicator in endoscopic anesthesia quality control.

Pre-oxygenation is a fundamental measure to increase functional residual capacity (FRC) and prolong the safe apneic time prior to induction, thereby preventing hypoxemia. The examination position directly determines airway patency, mandibular relaxation, diaphragmatic position, and thoracic compliance throughout the procedure. Both are critical, controllable factors regulating perioperative oxygenation. Studies have confirmed that the left lateral position reduces the incidence of hypoxemia, while the left lateral position with 30° head elevation effectively relaxes the mandible, alleviates tongue base collapse, reduces abdominal organ pressure on the diaphragm, and improves ventilation and oxygenation by increasing FRC.

Current research largely focuses on either the pre-oxygenation position or the examination position in isolation, presenting notable limitations: first, the interaction between these two positions has not been evaluated, leaving the synergistic or antagonistic effects of combined interventions unclear; second, there is a lack of efficient validation using a factorial design, which is necessary to simultaneously analyze the main effects and interactions of both independent variables.

Addressing these clinical challenges and research gaps, this study employs a 2×2 factorial randomized controlled design. With pre-oxygenation position and examination position serving as the two intervention factors, the study aims to explore the individual and combined effects of both factors on perioperative hypoxemia. The objective is to identify the optimal positional combination, establish standardized and generalizable positioning protocols for painless endoscopy, accurately reduce the incidence of hypoxemia, enhance the precision of anesthesia management, and provide high-level evidence to guide clinical practice.

• Study Type: Interventional
• Enrollment (Estimated): 208
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: xiaoyong wei, Master's degree; Phone Number: 86-951-674-3252; Email: weixy9912@126.com

Study Locations

• China
  • Ningxia
    • Yinchuan, Ningxia, China, 750001
      • General Hospital of Ningxia Medical University
      • Contact: xiaoyong wei, Master's degree; Phone Number: 86-951-674-3252; Email: weixy9912@126.cm

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• 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
• Able to understand the study procedure and provide written informed consent

Exclusion Criteria:

• 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
• Preoperative baseline hypoxemia
• Known allergy to any anesthetic drugs used in this study
• Pregnant females
• Unable to cooperate with required intraoperative body position

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Prevention
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Group A1B1 (traditional conventional group); Pre-oxygenated left lateral position + examination in left lateral position	Procedure: Pre-oxygenation Position （left lateral position）; An angle measuring device is placed beside the head of the examination bed to enable precise adjustment of the head position. Pre-oxygenation phase: Administer pure oxygen via a standardized mask with tight fit, at a flow rate of 6 L/min; instruct the patient to take deep breaths while receiving continuous oxygen for 3 minutes, maintaining the same body position throughout. If the position is altered during this phase, discontinue the procedure. Left lateral pre-oxygenation: The patient assumes a left lateral position on a horizontal bed surface with the head elevated at 0°, supported by pillows to maintain a neutral spine position and avoid excessive neck extension or flexion.; Other Names: left lateral position; Procedure: Examination Position（left lateral position ）; Examination Phase: From the initiation of anesthesia and endoscope insertion until completion of the procedure, the patient's position and head-of-bed angle must remain fixed throughout; any adjustments are prohibited during this phase. If the position is altered midway through the examination, the patient will be excluded from the study. Left lateral position examination: The patient assumes a 90-degree left lateral position on a horizontal bed surface with the head of the bed elevated to 0°, supported by pillows to maintain a neutral spinal alignment, avoiding excessive neck extension or flexion.; Other Names: Left lateral position
Experimental: Group A1B2 (improved examination group); Left lateral position with pre-oxygenation + left head elevated 30° during examination	Procedure: Pre-oxygenation Position （left lateral position）; An angle measuring device is placed beside the head of the examination bed to enable precise adjustment of the head position. Pre-oxygenation phase: Administer pure oxygen via a standardized mask with tight fit, at a flow rate of 6 L/min; instruct the patient to take deep breaths while receiving continuous oxygen for 3 minutes, maintaining the same body position throughout. If the position is altered during this phase, discontinue the procedure. Left lateral pre-oxygenation: The patient assumes a left lateral position on a horizontal bed surface with the head elevated at 0°, supported by pillows to maintain a neutral spine position and avoid excessive neck extension or flexion.; Other Names: left lateral position; Procedure: Examination Position（left lateral head elevation in a 30-degree position）; Examination Phase: From the initiation of anesthesia and endoscope insertion until completion of the procedure, the patient's position and head-of-bed angle must remain fixed throughout; any adjustments are prohibited during this phase. If the position is altered midway through the examination, the patient will be excluded from the study. Left lateral decubitus examination: The patient assumes a left lateral position on a horizontal bed surface with the head elevated at 30°, supported by a pillow to maintain a neutral spinal alignment, avoiding excessive neck extension or flexion.; Other Names: left lateral head elevation in a 30-degree position
Experimental: Group A2B1 (pre-oxygenation improvement group); Left-sided head position at 30°, pre-oxygenated air administration + examination in left lateral decubitus position	Procedure: Examination Position（left lateral position ）; Examination Phase: From the initiation of anesthesia and endoscope insertion until completion of the procedure, the patient's position and head-of-bed angle must remain fixed throughout; any adjustments are prohibited during this phase. If the position is altered midway through the examination, the patient will be excluded from the study. Left lateral position examination: The patient assumes a 90-degree left lateral position on a horizontal bed surface with the head of the bed elevated to 0°, supported by pillows to maintain a neutral spinal alignment, avoiding excessive neck extension or flexion.; Other Names: Left lateral position; Procedure: Pre-oxygenation Position（ left lateral head elevation in a 30-degree position）; An angle measuring device is placed beside the head of the examination bed to allow precise adjustment of the head position. Pre-oxygenation phase: The patient receives pure oxygen via a standardized mask with tight fit, at a flow rate of 6 L/min; they are instructed to take deep breaths while receiving continuous oxygen for 3 minutes, maintaining the same body position throughout. If the position is altered during this phase, the procedure is discontinued. Left-sided head elevation (30°): During pre-oxygenation, the patient lies in a left lateral position on a horizontal bed surface with the head elevated by 30°, supported by pillows to maintain a neutral spinal alignment and prevent excessive neck extension or flexion.; Other Names: left lateral head elevation in a 30-degree position
Experimental: Group A2B2 (double-position improvement group); Left-sided head height at 30 weeks: pre-oxygenated condition + left-sided head height at 30 weeks examination	Procedure: Examination Position（left lateral head elevation in a 30-degree position）; Examination Phase: From the initiation of anesthesia and endoscope insertion until completion of the procedure, the patient's position and head-of-bed angle must remain fixed throughout; any adjustments are prohibited during this phase. If the position is altered midway through the examination, the patient will be excluded from the study. Left lateral decubitus examination: The patient assumes a left lateral position on a horizontal bed surface with the head elevated at 30°, supported by a pillow to maintain a neutral spinal alignment, avoiding excessive neck extension or flexion.; Other Names: left lateral head elevation in a 30-degree position; Procedure: Pre-oxygenation Position（ left lateral head elevation in a 30-degree position）; An angle measuring device is placed beside the head of the examination bed to allow precise adjustment of the head position. Pre-oxygenation phase: The patient receives pure oxygen via a standardized mask with tight fit, at a flow rate of 6 L/min; they are instructed to take deep breaths while receiving continuous oxygen for 3 minutes, maintaining the same body position throughout. If the position is altered during this phase, the procedure is discontinued. Left-sided head elevation (30°): During pre-oxygenation, the patient lies in a left lateral position on a horizontal bed surface with the head elevated by 30°, supported by pillows to maintain a neutral spinal alignment and prevent excessive neck extension or flexion.; Other Names: left lateral head elevation in a 30-degree position

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Incidence of hypoxemia	Incidence of SpO₂ ≤ 90% for >10 seconds during the examination.	During procedure

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Safe duration of pre-oxygenation	Time from cessation of oxygen administration (start of anesthesia induction) to first SpO₂ <92% for ≥3 seconds. If no desaturation occurs, the value equals the duration from oxygen cessation to end of procedure (right-censored).	During procedure
Incidence of subclinical respiratory depression	Defined as the proportion of participants experiencing SpO₂ between 90% and 95% (inclusive) at any time during the examination.	During procedure
Requirement for jaw thrust	Number of participants requiring manual jaw thrust to relieve airway obstruction during the examination.	During procedure
Requirement for nasal cannula oxygen	Number of participants requiring oxygen supplementation via nasal cannula during the examination.	During procedure
Requirement for increased oxygen flow	Number of participants requiring an increase in oxygen flow rate during the examination.	During procedure
Requirement for mask ventilation	Number of participants requiring bag-mask ventilation during the examination.	During procedure
Requirement for endotracheal intubation	Number of participants requiring endotracheal intubation during the examination.	During procedure
Incidence of airway intervention	Proportion of participants requiring any airway intervention (jaw thrust, nasal cannula, increased flow, mask ventilation, or intubation)	During procedure
Severity of coughing	Assessed using a 4-grade scale: Grade I (none), Grade II (single mild episode), Grade III (multiple episodes <15s), Grade IV (continuous >15s)	During procedure
Length of stay in recovery room	Time from arrival to discharge from the recovery room (maximum observation 30 minutes)	Up to 30 minutes post-anesthesia care unit (PACU) admission
Endoscopist satisfaction score	Assessed using a Numerical Rating Scale (NRS) ranging from 0 to 10, with higher scores indicating greater satisfaction.	During procedure
Incidence of postoperative nausea, vomiting, headache, and dizziness	Proportion of participants experiencing nausea, vomiting, headache, or dizziness after awakening in the recovery room.	Up to 30 minutes post-anesthesia care unit (PACU) admission

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Safety outcome endpoints：heart rate	Recorded at T0 (before pre-oxygenation), T1 (before induction), T2 (scope insertion), and T3 (scope removal).	Baseline and during procedure
Safety outcome endpoints：blood pressure	Recorded at T0 (before pre-oxygenation), T1 (before induction), T2 (scope insertion), and T3 (scope removal)	Baseline and during procedure
Safety outcome endpoints：peripheral oxygen saturation (SpO₂)	Recorded at T0 (before pre-oxygenation), T1 (before induction), T2 (scope insertion), and T3 (scope removal).	Baseline and during procedure
Safety outcome endpoints：Incidence of hemodynamic instability in recovery	Occurrence of tachycardia (>100 bpm), bradycardia (<50 bpm), or hypotension (systolic blood pressure <80 mmHg) during the recovery period.	Up to 30 minutes post-anesthesia care unit (PACU) admission

Collaborators and Investigators

• Sponsor: General Hospital of Ningxia Medical University
• Investigators: Study Chair: Xinli Ni, Doctoral, General Hospital of Ningxia Medical University

Study record dates

Study Major Dates

• Study Start (Estimated): June 23, 2026
• Primary Completion (Estimated): July 31, 2026
• Study Completion (Estimated): August 31, 2026

Study Registration Dates

• First Submitted: June 15, 2026
• First Submitted That Met QC Criteria: June 24, 2026
• First Posted (Actual): June 29, 2026

Study Record Updates

• Last Update Posted (Actual): June 29, 2026
• Last Update Submitted That Met QC Criteria: June 24, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Other Study ID Numbers: dywe0003

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No