Hypoxemia During Surgery
Conditions
Brief summary
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
PROCEDUREPre-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.
PROCEDUREExamination 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.
PROCEDUREPre-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.
PROCEDUREExamination 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.
Sponsors
General Hospital of Ningxia Medical University
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
PREVENTION
Masking
SINGLE (Subject)
Masking description
Independent statisticians not involved in the study implementation generated random codes via computer and used sequentially numbered, opaque, sealed envelopes to conceal assignment assignments, which were opened immediately prior to intervention administration. Since postural intervention is an operational procedure, blinding could not be implemented for operators (anesthesiologists, endoscopists, or data collectors); subjects were informed of the standard positioning requirements. Data analysts remained completely blinded throughout the process, unaware of patient group assignments, thereby minimizing bias.
Eligibility
Sex/Gender
ALL
Age
18 Years to 75 Years
Healthy volunteers
No
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
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Incidence of hypoxemia | During procedure | Incidence of SpO₂ ≤ 90% for \>10 seconds during the examination. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Safe duration of pre-oxygenation | During procedure | 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). |
| Incidence of subclinical respiratory depression | During procedure | Defined as the proportion of participants experiencing SpO₂ between 90% and 95% (inclusive) at any time during the examination. |
| Requirement for jaw thrust | During procedure | Number of participants requiring manual jaw thrust to relieve airway obstruction during the examination. |
| Requirement for nasal cannula oxygen | During procedure | Number of participants requiring oxygen supplementation via nasal cannula during the examination. |
| Requirement for increased oxygen flow | During procedure | Number of participants requiring an increase in oxygen flow rate during the examination. |
| Requirement for mask ventilation | During procedure | Number of participants requiring bag-mask ventilation during the examination. |
| Requirement for endotracheal intubation | During procedure | Number of participants requiring endotracheal intubation during the examination. |
| Incidence of airway intervention | During procedure | Proportion of participants requiring any airway intervention (jaw thrust, nasal cannula, increased flow, mask ventilation, or intubation) |
| Severity of coughing | During procedure | Assessed using a 4-grade scale: Grade I (none), Grade II (single mild episode), Grade III (multiple episodes \<15s), Grade IV (continuous \>15s) |
| Length of stay in recovery room | Up to 30 minutes post-anesthesia care unit (PACU) admission | Time from arrival to discharge from the recovery room (maximum observation 30 minutes) |
| Endoscopist satisfaction score | During procedure | Assessed using a Numerical Rating Scale (NRS) ranging from 0 to 10, with higher scores indicating greater satisfaction. |
| Incidence of postoperative nausea, vomiting, headache, and dizziness | Up to 30 minutes post-anesthesia care unit (PACU) admission | Proportion of participants experiencing nausea, vomiting, headache, or dizziness after awakening in the recovery room. |
Countries
China
Contacts
CONTACTxiaoyong wei, Master's degree
STUDY_CHAIRXinli Ni, Doctoral
General Hospital of Ningxia Medical University
Outcome results
None listed