The severity and frequency of respiratory events is increased in the supine body posture compared with the lateral position in emergency, difficult airway patients. The mechanism responsible is not clear but may relate to the effect of position on upper airway shape and size. 3D finite element model of upper airway filling based on MRI image reconstruction can effectively reflect the anatomy of the upper airway. This study compared the effect of body position on upper airway shape and size in individuals with lateral position among sedated subjects.

Anesthesiologists may encounter situations in which a accidental loss of airway patency occurs in patients in a lateral patient position during surgery. Intubation is required in the lateral position in cases of oropharyngeal bleeding to reduce the risk of aspiration, or in airway management in some patients with limited posture. The severity and frequency of respiratory events is increased in the supine body posture compared with the lateral position in emergency, difficult airway patients. The mechanism responsible is not clear but may relate to the effect of position on upper airway shape and size secondary to gravitational effects. Lateral positioning decreases upper airway obstruction in sleeping individuals, children breathing spontaneously, and adults during general anesthesia. The mechanical upper airway properties may become the dominant factor governing upper airway collapsibility during sedation due to the significant depression of consciousness and the impairment of neural mechanisms controlling compensatory neuromuscular responses. Anesthesiologists and surgeons who are responsible for airway management during procedures under sedation and the perioperative period should be well versed with the physiological and pathophysiological mechanisms affecting upper airway patency. 3D finite element model of upper airway filling based on MRI image reconstruction can effectively reflect the anatomy of the upper airway.

The primary aim of this study was to determine the changes in upper airway shape and size that occur when sedated, spontaneously breathing adults are placed in the lateral position. These findings may provide new guidance for the evaluation and prediction of difficult airway during clinical anesthesia.

Inclusion Criteria:

1. Subjects aged over than 18 years and less than 100 years
2. The American Society of Anesthesiologists (ASA) score was grade I to II
3. There was no serious cardiopulmonary disease

Exclusion Criteria:

1. Unable to maintain oxygenation before or during the examination and requiring intervention
2. Those with preoperative arrhythmia requiring intervention
3. Thosewith severe hematological diseases, severe metabolic diseases, severe liver and kidney organ insufficiency
4. Those do not consent to participate in the study

Healthy subjects aged over 18 years old, ASA 1~II without serious cardiopulmonary disease, scheduled for magnetic resonance imaging scan in the supine position and followed lateral position at a tertiary hospital from January 2024 to February 2024 were enrolled in this study.