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

Official title

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

Overview

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.

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.

Interventions

• 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
• 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°, s
• 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°): Durin
• 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 pillo

Primary outcome measures

• Incidence of hypoxemia [Time frame: During procedure]

Secondary outcome measures (12)

• Safe duration of pre-oxygenation [Time frame: During procedure]
• Incidence of subclinical respiratory depression [Time frame: During procedure]
• Requirement for jaw thrust [Time frame: During procedure]
• Requirement for nasal cannula oxygen [Time frame: During procedure]
• Requirement for increased oxygen flow [Time frame: During procedure]
• Requirement for mask ventilation [Time frame: During procedure]
• Requirement for endotracheal intubation [Time frame: During procedure]
• Incidence of airway intervention [Time frame: During procedure]
• Severity of coughing [Time frame: During procedure]
• Length of stay in recovery room [Time frame: Up to 30 minutes post-anesthesia care unit (PACU) admission]
• Endoscopist satisfaction score [Time frame: During procedure]
• Incidence of postoperative nausea, vomiting, headache, and dizziness [Time frame: Up to 30 minutes post-anesthesia care unit (PACU) admission]

Eligibility criteria

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

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: No

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Single blind

Primary purpose

Prevention

Study locations

China · 1 center

• General hospital of Ningxia medical university — Yinchuan

Identifiers

NCT: NCT07673042 · dywe0003

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗