The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

A MODEL FOR TEACHING HIGH-FLOW AND LOW- FLOW OXYGEN SYSTEMS

Doug Pursley M.Ed., RRT, Aaron Light, BSRT, RRT, Ozarks Technical Community College, Springfield, Missouri

Background: Respiratory care students sometimes have difficulty grasping fundamental concepts related to high-flow and low-flow oxygen systems. The key element that typically slows the education process in this area is helping students understand the important interrelationship between the patient's inspiratory flowrate and the total flowrate produced by an oxygen device. The purpose for developing this model was to create a mechanism which gives students real-time feedback of various respiratory parameters when ventilatory changes occur in a simulated patient or when changes are made to these types of oxygen systems.

Method:
We created our model by incorporating a Hans-Rudolph Series 1101 Breathing Simulator with an Armstrong Medical Adult Intubation Manikin. Using large bore tubing and appropriate adapters the manikin's trachea was connected to the breathing simulator's outlet so that as the simulator operates, air flows in and out through the manikin's mouth and nares or endotracheal tube. This essentially creates a "breathing patient" and allows tidal volume, respiratory rate, I:E ratio, and inspiratory flowrate to be independently monitored and controlled by making adjustments to the computerized simulator. By placing an oxygen analyzer in-line with the trachea, the additional observation of tracheal FIO2 can be made as flow and FIO2 are adjusted on the oxygen device or as the patient's minute ventilation or inspiratory flowrate is increased or decreased.

Results:
We found that our model gave students a supplementary tool to help them master the basic concepts of high-flow and low-flow oxygen systems. For example, a group of students performed three bench tests using our model. In the first test students set the model to simulate a normally breathing patient (VT 500 ml, f 12). After applying a non-rebreathing mask at 15 l/m, they observed that the tracheal FIO2 was 0.82. With the non-rebreathing mask still running at 15 l/m, they made the model hyperpneic and tachypneic (VT 900 ml, f 24) and observed that the tracheal FiO2 had dropped to 0.56. In the second test, the students set the model to simulate a tidal volume of 500 ml and respiratory rate of 15. After applying a nasal cannula to the model and setting the flowrate to 3 l/m, the tracheal FIO2 was observed to be 0.34. Next they increased the flowrate to 6 l/m and observed that the tracheal FIO2 had increased to 0.46. With the flowrate still set at 6 l/m, they then decreased the tidal volume to 250ml and observed that the tracheal FIO2 had increased to 0.71. Finally, in the third test, they set the model to simulate a hyperpneic and tachypneic patient (VT 900 ml, respiratory rate 24) breathing oxygen from a large volume nebulizer (LVN). The LVN was set to deliver an FIO2 of 0.50 while the oxygen flowrate was set for 15 l/m. The total flow of the LVN was calculated to be 40 l/m. The observed tracheal FIO2 in this situation was only 0.42 because the "patient's" inspiratory flowrate exceeded the total flowrate from the device. Increasing the set flowrate returned the tracheal FIO2 to 0.50.

Conclusions:
Our model helped students understand that a non-rebreathing mask does not always produce an FIO2 of 0.80 - 0.95, that under the right circumstances a nasal cannula can actually produce a moderately high FIO2, and that when a patient's inspiratory flowrate exceeds the total flowrate from a high-flow oxygen device, tracheal FIO2 (and presumably PaO2) is less than expected. The model also helps students recognize the effect of flowmeter adjustment on low-flow and high-flow oxygen systems as well as to help them realize the effect of varied breathing patterns on any type of oxygen delivery system.

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