Changed to an invitro study using a mechanical lung rather than human subjects.

Prior to surgery the anesthesia team will be putting a breathing tube into the patient's windpipe and attaching it to a mechanical ventilator (breathing machine). This is to provide oxygen and anesthetic gas, and to help the child breathe while they're asleep. The ventilator also controls the amount of air that moves in and out of the lungs with each breath. This is called tidal volume and that amount is programmed into the machine by the anesthesia team. All of this is standard of care.

As part of the study the investigators will put a small flow sensor between the patient's breathing tube and the tubing from the ventilator. This will measure the amount of air that is moving in and out of the breathing tube. The study team will record the tidal volume that is set on the ventilator and compare it to the airflow measured by the ventilator and the airflow measured by the sensor and see if there is a difference.

Inclusion Criteria:

• children aged 0-18 years having surgery at Nationwide Children's Hospital, in whom a cuffed ETT and mechanical ventilation will be used

Exclusion Criteria:

• children with preexisting airway anomalies or respiratory compromise will be excluded from the study.

Children requiring intraoperative mechanical ventilation.