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.