The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

BACK PRESSURE BUILDUP IN MEDICAL GAS DELIVERY SYSTEMS

Steve T. Polston1, Holly W. Cummings2, Kendra L. Sikes3, In K. Kim4



Objective: We measured back pressures present in a gas delivery circuit for 100% oxygen and 70% helium:30% oxygen (70:30 heliox) at physiological temperature (37�C) using various sizes of nasal cannulae.

Design and Setting: A U-tube manometer was used to measure the back pressure in a Fisher-Paykel® MR850 gas delivery circuit that consisted of a gas source (either 100% oxygen or 70:30 heliox) flowing through a respiratory humidifier to various sizes of nasal cannulae. For each experiment, four trials were conducted.

Intervention: Experiments were conducted at 1 liter per minute (LPM) and 5 LPM of 100% oxygen and 1 LPM and 5 LPM of 70:30 heliox. Four trials were conducted: 1) A standard adult, pediatric, infant, and neonate nasal cannula was connected to the U-tube manometer. 2) A pediatric, infant, and neonate cannula with the nose piece removed was connected to the U-tube manometer. 3) A pediatric nasal cannula was connected to a pediatric, infant, and neonate nose piece, then connected to the U-tube manometer. 4) A pediatric, infant, and neonate ear tube was shortened to a length of 10 cm then connected to the U-tube manometer.

Results: Back pressures in the circuit were higher at 5 LPM flow rates than 1 LPM for both 100% oxygen and 70:30 heliox. At 5 LPM, back pressures were higher for 100% oxygen than for equivalent flow rates of 70:30 heliox. At 5 LPM, back pressures were higher for smaller nasal cannulae for the control, modified nose piece, and short ear tube trials. Decreases in back pressure were seen by using a pediatric nasal cannula and by shortening the length of the ear tubes.

Conclusion: Gas flow rates of 5 LPM produce back pressure in gas delivery circuits. Back pressure in gas delivery systems may be decreased by modifying the nasal cannulae and shortening ear tube length.