Baseline force measurement
Baseline measurements of cricoid pressure force were obtained using a pharyngeal modelTM (Laerdal, Sentrum, Stavanger, Norway) attached to measuring scales (Salter Colorweigh Electronic Kitchen Scale, China) (Figure 1). The maximum recording value of the scales was 6.0kg. Participants were instructed to press down on the airway model and indicate to the study researcher (JW) when the intended force was reached and maintained. Participants were blinded as to the applied force and measurement to the nearest 100g was recorded by the study researcher (JW). Participants were blinded as to the applied force. Force measurements were recorded for all participants on “awake” and “anaesthetised” patients, with 3 attempts for each. Participants were required to remove their hand from the model between measurements of applied force.