1. Improving Simulations in the Post Anesthesia Care Unit
Alyssa Z. Cherif 1
Advisors: Dr. Matt Weinger2,3, Ray Booker3, Bobby Gibbons3, Dr. Paul H. King1
1Department of Biomedical Engineering; 2Department of Anesthesiology; 3Simulations Technologies Program, Center for Experimental Learning and Assessment, Vanderbilt University School of Medicine
Problem Statement
Constraints and Parameters
Simulation Results
After undergoing a surgery involving anesthesia, the patient is sent to the Post Anesthesia Care Unit, or the PACU. Because general anesthesia affects the entire body, postoperative side effects tend to appear, the most common being pulmonary complications.
Balloon must be smaller than lung, so that it can fit inside
Balloon requires tubing to reach outside of lung, for external manipulation
With all parts assembled, prototype must remain airtight
Prototype should be easily repairable and replicable
Figure 5. Air was added to the saline bag, 10 cm3 at a time. As the volume of the saline bag increased, the pressure needed to inflate the lungs increased as well. This shows that the prototype effectively simulates an obstructive pulmonary disease.
Figure 1. SimMan on a bed in the PACU.
The PACU Simulation Center was
created to enable medical and nursing students to practice a variety of procedures on a simulated patient called SimMan. SimMan has several working bodily systems, including fully functioning lungs. His vital statistics can be externally controlled using a program called SimQuest. SimQuest can alter his statistics such as blood pressure and heart rate, and then display them on a monitor inside the Simulation Center. At the start of this project, there were only two options for lung size: fully functioning or completely collapsed.
To efficiently simulate all possible scenarios that could arise in the PACU, it is necessary to provide a range of pulmonary function. The overall goal for this project was to allow for a range in the available volume in SimMan’s lungs and to have it be externally controlled, thereby simulating an obstructive pulmonary disease; this was to be achieved in the most efficient and inexpensive manner possible.
Material Dimensions
Figure 5. Pressure needed vs. volume of the saline bag.
Object
Size
Lung Volume
1263ml
Bronchus length
11.4cm
Bronchus inner diameter
15.9mm
Bronchus outer diameter
19.1mm
Saline Bag Volume
1000ml
Saline Bag Width
12.1cm
Saline Bag Tubing diameter
6.35mm
Figure 6. Again, air was added to the saline bag, 10 cm3 at a time. During this trial VTE, the volume of air actually expired by the lungs, decreased as the saline bag volume increased, despite the constant 450ml tidal volume.
Figure 6. Volume of air expired vs. volume of the saline bag.
Ethical and Safety Issues
Benefits of Balloon Approach
As this project mainly pertains to a simulated patient, there are minimal ethical concerns; safety is of higher importance. The prototype indeed works well inside the chest cavity, without causing damage to the rest of SimMan’s functioning systems. Also, the prototype should not burst or cause any harm to those manipulating and working with SimMan.
Relatively simple idea
Externally controlled
Inexpensive to build
Easily repairable and reproducible
Meets all of the project requirements
Project Requirements
Lung must be airtight
Prototype must be able to withstand daily SimMan activities, such as CPR
Size of prototype must be the same size or smaller than the lung
Prototype must operate at a range of lung parameters
Prototype should be efficient and inexpensive, as well as easily repairable
Conclusions
All of the initial project requirements have been met by this prototype. The benefits of the design can be seen through regular use, including its simplicity in manufacturing, repair and operation. In addition, it was extremely inexpensive to build and it is a very safe device. This prototype effectively simulates an obstructive pulmonary disease, as shown by the increase in pressure needed to inflate the lungs, as well as by the decrease in air expired at a constant tidal volume.
Figure 4. SimMan with the prototype inside his chest cavity.
Building of Prototype
Materials used: lung, saline bag, tubing, washers, heat gun, glue
Saline bag inserted through a slit at the bottom of the lung
Exit hole made in the rear of the lung for saline bag tubing
Washers placed around tubing, both interior and exterior of the lung
Extra vinyl glued around tubing to ensure it would be airtight
Heat gun applied in an attempt to seal the lung; replaced by a vinyl glue due to time and potential burning
Once inside the chest cavity, new prototype attached
Tubing extended outside SimMan via a hole in his back; tubing connected to an air pump for external manipulation
Material
Cost
1000ml saline bag with tubing
$10.00
1.5 oz Vinyl Flexible Adhesive
$2.98
10 rubber washers (6.35mm inner diameter)
$1.27
Total Cost
$14.25
Future Directions
There are two improvements that could be made to this prototype to maximize its efficiency. The first is using a longer tubing without bulky appendages to attach to the saline bag. The second would be the development of a plastic washer to secure around the saline bag’s tubing. For increased simplicity in construction of the prototype, an efficient method of heat sealing would be ideal. A more distant goal is to integrate the volume of the saline bag into the SimQuest program.
Figure 2. One of SimMan’s unaltered lungs, fully deflated.
Potential Solutions
Mount a valve inside or around the bronchus
Problem: possible damage to valve due to CPR
Place a weight atop the lung, inside the chest cavity
Problem: possible injury to surrounding area
Insert a balloon of variable volume inside the lung
Balloon chosen: saline bag
Acknowledgements
Dr. Paul H. King, Department of Biomedical Engineering
Dr. Robert L. Galloway, Department of Biomedical Engineering
Advisors: Dr. Matt Weinger, Dr. Dan France, Ray Booker, Bobby Gibbons
Figure 3. Saline bag used in the lung.