The Analysis and Design of a Pressure - Measuring Syringe Utilizing

Endotracheal tube insertion requires the measurement of very low pressure. Currently, there exists no reliable method or device that is integral with the inflation syringe for measuring this pressure. Thus, a device for quickly and easily reading the pressure was created within the syringe currently used to pressurize the tube. This device takes the form of elastomeric bellows. These bellows were analyzed to determine the optimum geometry for the pressures involved in the procedure. Although no closed-form model exists for this analysis, FEA was used to obtain accurate results. Using the optimized bellows, a complete for-manufacturing design was created. This design concept has received much acclaim from the medical community and has great promise in transforming many medical procedures which require such measurement. Thesis Supervisor: Alex Slocum Title: Professor of Mechanical Engineering and MacVicar Fellow Introduction Endotracheal tubes (ETTs) are continually used in medical situations. They provide a clear airway from the mouth to the trachea so that oxygen can be moved in and out of the lungs by medical staff or equipment. Doctors use ETTs during most procedures involving general anesthesia and throughout intensive care wards. Endotracheal tubes' necessity causes their widespread use throughout medicine. There are two major parts to the ETT (see figure 1). The first is the airway, a long plastic tube that, when the whole tube is inserted, runs from the trachea out the mouth and is the line used to move air in and out of the lungs. The second module is just as critical. For the whole tube to function correctly, there needs to exist a seal between the main tube and the trachea. This allows the lungs to be pressurized without loss past the tube. It also prevents material getting past the other way and keeps the lungs clear. This seal is accomplished with the ETT cuff. This balloon surrounds the main tube towards its end and is deflated during insertion. After the endotracheal tube is inserted past the throat, doctors use a second, smaller tube that runs along the main tube to pressurize the cuff. A syringe is typically used to pump air to the balloon. The pressure used to seal the tube to the trachea is critical. Too low and the cuff will not seal adequately. Too high and the capillaries in the trachea get overwhelmed, causing pain and, if left long enough in that state, necrosis. This range is also very small, ranging from 20 cm H20 to 30 cm H20 (2-3 kPa). To the P i respira±or