Cricoid pressure (CP) confers Grade IIA evidence in preventing gastric insufflation during general anaesthesia. However, a retrospective review of computed tomography scans by Dotson et al. shows that 45% oesophagus is eccentric in the paediatric population aged 1 to 8 years old. In adults, the eccentric oesophagus is associated with reduced CP efficacy in occluding oesophagus. To date, no dynamic real-time study has been done to assess the incidence of the eccentric oesophagus in the paediatric population, the efficacy of CP in occluding eccentric oesophagus, and the effect of anaesthesia on oesophageal position.

Any patients aged 1 to 8 years old are eligible to participate This study will be conducted in the operation theatre of UMMC. The investigators plan to perform an ultrasound of the neck throughout the phases of anaesthetic induction and determine the oesophagus position and its compressibility with CP application.

In a survey presented by Society for Paediatric Anaesthesia in 2004, 68% of paediatric anaesthesiologists apply CP to prevent passive regurgitation of food into the pharynx. 33% of respondents use CP to prevent gastric insufflation during mask ventilation. Among the respondent, only 24% responded CP reliably occludes the oesophageal lumen.

The anatomically central oesophagus lies behind cricoid cartilage, by applying CP oesophageal lumen will be occluded. However, it remains debatable if eccentric oesophageal is compressible. Studies were conducted on the adult population. Efficacy of CP has been studied in adult patients by means of magnetic resonance imaging. It was shown that CP was ineffective in occluding the oesophageal lumen in adult patients with an eccentric oesophagus. In addition, the study raised the concern of CP application in itself might result in lateral displacement of the oesophagus. This is further supported by Lim et al.'s study which shows the ineffectiveness of CP in occluding eccentric oesophagus in adult patients.

Contrary to the aforementioned studies, Rice et al's demonstrated oesophagus was occludable regardless of the position. The author hypothesized that the hypopharynx and cricoid move as one anatomical unit and the oesophagus would be compressed following the application of CP.

Although the effectiveness of CP was extensively studied in the adult population, studies on the paediatric population remained scarce. A retrospective review of computed tomography scans by Dotson et al. shows that 45% oesophagus is eccentric in the paediatric population aged 1 to 8 years old. In our pilot study, the investigators found out that 90 per cent of the oesophagus in the paediatric population was successfully occluded following the application of CP regardless of its position.

Cricoid pressure is not without risk. CP was associated with oesophageal rupture. It has been known to disrupt the laryngoscopic view of the glottis and cause difficult intubation. Hence, it would be imperative to investigate whether CP is truly effective in occluding the oesophagus and preventing gastric aspiration in the paediatric population.

This would be a prospective observational study to study the real-time dynamic effect of oesophageal position and the effect of anaesthesia on oesophageal position. Most importantly, the investigators are hoping to investigate the effectiveness of CP in occluding oesophagus in the paediatric population.

Inclusion Criteria:

• ASA 1, 2
• Age 1-8 years old
• Scheduled for surgery under general anaesthesia requiring tracheal intubation

Exclusion Criteria:

• Presence of neck mass/ cervical spine pathology, prior neck surgery
• Pathology of the upper respiratory tract
• Anticipated difficult intubation / difficult mask ventilation
• Risk of pulmonary aspiration of gastric contents (eg. Gastroesophageal reflux disease, hiatus hernia, intestinal obstruction)
• Morbid obesity BMI ≥ 35 kg/m2 (above 85th centile) - overweight patients
• Inadequate fasting ( 6 hours solid food/ formula milk, 4 hours breast milk and 2 hours clear fluid) - definite indication for rapid sequence induction
• Uncontrolled cardiopulmonary disease
• Oesophageal conditions: achalasia, Zenker's diverticulum

ASA 1 and 2 children aged 1 to 8 years old undergoing general anaesthesia for elective surgery requires muscle paralysis and tracheal intubation. We rule out cases which need rapid sequence induction, high risk of aspiration and difficult airway.

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