Combining head-neck position and head-down tilt to prevent pulmonary aspiration of gastric contents during induction of anaesthesia: a volunteer and manikin study.

Context: Although a life-threatening complication, pulmonary aspiration of gastric contents caused by vomiting or regurgitation during induction of anaesthesia cannot be prevented. It may be prevented if the mouth is placed more inferiorly than the larynx and tracheal bifurcation by the use of head-down tilt and head-neck positioning.

Objective: We aimed to determine the head-down tilt required to prevent aspiration in the neutral, simple extension, sniffing and full cervical spine extension (Sellick) positions and to investigate the relationship between pulmonary aspiration and the vertical height of the mouth, larynx and tracheal bifurcation.

Design: Observational study.

Setting: Operating theatre at Nippon Steel Yawata Memorial Hospital.

Patients: Manikins with coloured fluid in the oesophagus and 30 adult volunteers.

Interventions: Use of head-down tilt between 0° and 50° in 5° increments in four head-neck positions (neutral, simple extension, sniffing and Sellick).

Main Outcome Measures: Aspiration of oesophageal contents (coloured fluid) from the oesophagus into the trachea and bronchi. Measurement of the mouth-arytenoid angle (manikin and volunteers) and the mouth-carina angle (manikin).

Results: The head-down tilts required to protect both the trachea and bronchi from aspiration were 45°, 35° and 10° in the neutral, simple extension and Sellick positions, respectively, which coincided with the mouth-arytenoid angle in those positions. The maximum tilt used in this study was not adequate to prevent aspiration in the sniffing position. The head-down tilt required to level the mouth with the tracheal bifurcation (mouth-carina angle) protected the bronchi from aspiration but not the trachea.

Conclusion: A head-down tilt equal to the mouth-arytenoid angle (levelling the mouth with the larynx) was necessary to completely prevent aspiration. This angle of tilt was within clinically relevant ranges only with the Sellick position.