Virtual Ventilator
Instruction within the Veterinary Curriculum in many disciplines has
traditionally relied upon the use of animal intensive laboratories to teach
the effects of a technique, procedure, or treatment on a living patient. Due
to concerns raised about live animal usage in teaching, many Veterinary
training programs have introduced static models or mannequins into their
curricula to facilitate teaching the mechanics of a task such as suturing a
wound. Such models, while valuable, provide little student feed back as to
how poorly the wound will heal if sutured improperly.
The practice of clinical anesthesia is in large part concerned with
feedback. The response of the patient to anesthetic drugs and techniques
dictates how the drugs and techniques will be applied to the individual
patient. A static model may suffice when teaching the technique of
endotracheal intubation, but clearly patient feedback is invaluable when
teaching how one should respond to severe hypotension or inadequate
ventilation. The Virtual Ventilator application attempts to combine the
simplicity of a static model with user feedback to provide the student a
realistic model/simulation of connecting patient to a mechanical ventilator.
Virtual Ventilator is a 32-bit application designed for a PC running either
Windows 95, 98, NT, or 2000. The Virtual Ventilator main screen is a
depiction of a ventilator bellows, several ventilator controls that are
manipulated using the mouse, and several digital/analog displays.
The student adjusts the ventilator settings using the controls while the displays and the position and movement of the bellows provide feed back as to the effects the chosen ventilator settings are having on the patient and on the ventilator itself. A split window permits viewing the patient's capnograph concurrently with the ventilator settings.
Beginning at the top left of the application, the first control is an LED
that turns green when the ventilator is powered up by clicking on the yellow
toggle switch just below. Proceeding to the right the ventilator bellows is
visible. When the power switch is turned on, the ventilator bellows will move
down to force volume into the patient’s lungs during inhalation, and will move
up as volume from the patient’s lungs enters the bellows during exhalation. The
current volume within the bellows is displayed at the bottom of the bellows
control while the currently selected maximum volume scale of the bellows is
displayed to the right of the bellows. To the right of the ventilator bellows is
a column of 3 control knobs labeled “Starting Volume, Inspiratory Time, and
Ventilator Rate. As the name implies, the starting volume knob controls the
starting position and therefore the starting volume of the bellows. By adjusting
this control it is possible to set the maximum volume of gas delivered to a
patient during inhalation. The knob below the starting volume knob labeled “Inspiratory
Time” controls the amount of time during the ventilatory cycle that is allotted
to inspiration. Below the Inspiratory Time knob is the Ventilator Rate knob
which is used to control the number of times per minute that the ventilator
cycles. At the top of the second column of controls is a knob labeled “Bellows
Flow”. This control allows you to vary the driving pressure with which the
bellows are moved downward, the higher the setting, the more rapid the rate of
bellows descent during inhalation. Below the flow control is the “I:E” ratio
control. This is a slider type of control with which you may select from one of
5 I:E ratios. The I:E ratio is the proportion of time within one complete
ventilatory cycle (one inhalation and one exhalation) devoted to inhalation
relative to the proportion of time devoted to exhalation. If the time for a
total ventilatory cycle is 4 seconds, an I:E ratio of 1:3 would allow 1 second
for inhalation and 3 seconds for exhalation. Just below the I:E ratio slider
control is a display of the patient’s actual respiratory rate. Often, the
patients actual RR will be equal to what is dialed in on the ventilator, but not
always. In the last column are 3 meters that display the patient’s end exhaled
CO2 (ETCO2), the airway pressure generated by the ventilator, and the tidal
volume that has been delivered by the ventilator. A split window permits viewing
the patient’s capnograph (exhaled CO2 graphed over time) concurrently with the
ventilator settings. Each vertical line on the capnograph represents 10 seconds,
thus the capnograph can display 30 seconds of exhaled CO2 data before resetting.
Many of the menu functions are also accessible using the tool bar buttons.
Clicking on the syringe tool bar button brings up the patient’s current arterial
blood gas status allowing the student to visualize the effects of changes in
ventilation parameters. The patient menu selection and tool bar button allow the
student to change the weight of the patient and to simulate mechanical
ventilation in patients having differing lung compliance. The student may choose
to ventilate a normal patient, one having restrictive lung disease, or one
having a thoracotomy. The ventilator properties menu selection and tool bar
button allow the student to change the size of the ventilator bellows to
accommodate patients of varying weight. These selections also permit the student
to configure the ventilator to have a fixed or variable I:E ratio and a dynamic
or static inspiratory time.
The simulation permits the student to make changes to the patient’s ventilation
parameters and observe the effect those changes have on the ventilator itself
and on the patient they are ventilating. Similar to static models and
mannequins, Virtual Ventilator affords the student the chance to practice
setting up the ventilator for a variety of patients having various degrees of
lung pathology. Unlike the static models, the simulation is able to give
immediate feedback to the student concerning the ventilatory parameters that
have been chosen. The breadth of different physiologic conditions that the
student may experience exceeds what may be achieved in a single live animal
laboratory experience.
The utility of the simulation as an aid to teaching the principles of mechanical
ventilation of anesthetized veterinary patients was evaluated using quantitative
and qualitative data obtained from veterinary students enrolled in an anesthesia
course. Students enrolled in the course were randomly assigned to either
participate in the Virtual Ventilator computer simulation prior to participating
in a live animal lab dealing with mechanical ventilation or to participate in
the live animal experience prior to participating in the computer simulation
lab. Quantitative data included results from a written test in which questions
about mechanical ventilation were asked. Additional quantitative data was
obtained by instructor evaluations of student’s abilities to operate mechanical
ventilators in the animal laboratory. Qualitative data was obtained from the
results of a survey administered to each enrolled student in which their
perceptions of the simulation and live animal laboratories were recorded.
Results of the study are reported in the paper “Evaluation of the Effectiveness
and Utility of a Mechanical Ventilation Simulation in a Veterinary Teaching
Program”. Briefly, quantitative data indicate that the students participating in
the Virtual Ventilator simulation prior to using the mechanical ventilators in a
live animal exercise, had higher written and performance-based scores compared
with students who had participated in the live animal laboratory exercise prior
to using the simulation. Qualitative data echoed that obtained by testing and
evaluation. Students practicing on the simulation prior to the live animal
laboratory both felt better prepared and thought they learned more in the live
animal lab compared with students who were scheduled to participate in the live
animal lab prior to the simulation. Survey results also indicated that the
simulation was well received and perceived to be a valuable method for providing
instruction within the anesthesia course.
Please direct inquiries concerning Virtual Ventilator to Dr. RD Keegan at
rdk@vetmed.wsu.edu.
Last Edited: Mar 06, 2007 2:15 PM
