College of Veterinary Medicine

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Virtual Ventilator

  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.

  Virtual Ventilator

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

Last Edited: Aug 06, 2014 9:13 AM   

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