The purpose of this study is to quantify the tidal volume generated by the pressure release immediately following the application of pressure to the chest.

Airway management in the pediatric population differs from the adult population because of differences in their respiratory physiology and anatomy. For example the oxygen consumption is about three times higher in children as compared to adults; therefore, if there is a problem ventilating a child there is a higher impact on oxygen delivery and oxygen reserve. Current guidelines recommend that in respiratory emergencies where one "cannot ventilate and cannot intubate" that a cricothyroidectomy (insertion of a needle through the cricothyroid membrane in the neck) be performed. This procedure is very invasive and difficult to perform, especially in a small child. Since timing and simplicity are essential to successful airway management it is hypothesized that the investigators could utilize the physiological principles behind breathing to ventilate these children using the release of applied pressure to their chest. During, inspiration, the vertical and transverse dimensions of the thorax are increased, generating a negative pressure between the intrapleural space and the chest wall, allowing for air to be drawn into the lungs. As children have a very compliant rib cage one of the theoretical ways to improve lung inflation is to apply external pressure on the chest. The intrathoracic pressure increases above atmospheric pressure and air preferentially flows out of the lungs according to the pressure gradient. When the pressure is released and the chest recoils passively, a negative intrathoracic pressure is generated, which allows for air to flow into the lungs according to the pressure gradient created. If a sufficient tidal volume is generated by the release of pressure from the chest this could potentially become a simple, non-invasive, life-saving technique in children with difficult airways. By adapting the principles described above, it is possible that tidal volume and therefore, gas exchange can take place on release of the pressure applied to the chest.

Inclusion Criteria:

• All pediatric patients under the age of 18 years old.
• All patients requiring a general anesthetic with an endotracheal tube (whether the patient will be intubated with an endotracheal tube will be decided by the anesthesiologist responsible for the case)
• ASA (American Society of Anesthesiologists Physical Status Classification) I to III

Exclusion Criteria:

• Failure to obtain parental consent or patient assent when appropriate (in general children over 8 years old)
• ASA (American Society of Anesthesiologists Physical Status Classification) IV
• Patients with any cardiac pathology
• Patients with any respiratory pathology
• Patients with any form of chest deformity (examples being pectus excavatum, pectus carinatum, scoliosis)
• Patients who had previous cardiac/thoracic surgery

This is a prospective, cohort study with a sample size of approximately 100 pediatric patients. The population will be stratified equally into the following age groups: neonate (0-28 days or 44 post-conceptual weeks), infants (>1-12 months), toddlers (>12months-3 years), children (>3-8 years), pre-teen (>8-13 years) and adolescent (>13 years).