Effects of head posture on the oral, pharyngeal and laryngeal axis alignment in infants and young children by magnetic resonance imaging

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Objective anatomical studies supporting the different recommendations for laryngoscopy in infants and young children are scarce. The objective of this study was to measure by magnetic resonance imaging (MRI) the consequences of head extension on the oral, pharyngeal and laryngeal axes in infants and young children. Thirty patients (age: 33 +/- 28 months; weight 14 +/- 9 kg), under general inhalated anesthesia delivered via a laryngeal mask airway, were studied in two anatomic positions: head in the resting position and in simple extension. The following measurements were made on each scan: the face and the neck axes, the pharyngeal axis, the laryngeal axis, and the line of vision of glottis. The various angles between these axes were defined: delta angle between line of vision and laryngeal axis, and beta angle between pharyngeal axis and laryngeal axis. From an anatomical point of view, laryngoscopy and passage of a naso-tracheal tube would be facilitated if these angles are narrow. Placing the patient from the resting position into extension led to a narrowing of the angle delta but a widening of the angle beta. In infants and young children, under general anesthesia and with a laryngeal mask airway in place, just a slight head extension improves alignment of the line of vision of the glottis and the laryngeal axis (narrowing of angle delta) but worsened the alignment of the pharyngeal and laryngeal axes (widening of angle beta).