The Virtual Anesthesia Machine

URL:∼eduweb/vam/, Publisher:  Sem Lampotang, Webmaster:  David Lizdas, Edwin B. Liem, Walter Dobbins

This original interactive computer simulation of an anesthesia machine stands alone as an award winner and is truly deserving of its “Best Scientific Exhibit” award at the 2001 annual meeting of the American Society of Anesthesiologists (ASA). Designed and developed by an integrated team of engineers and physicians at the University of Florida, it is a testimonial of our need to work with biomedical engineers. The visual and interactive nature of the program, coupled with slides, learning objectives, and tutorials, make complex learning fun and effective. In particular, this program is available for free, at any time. It can be used for teaching in real time, particularly with a large screen-projected image.

It took approximately 20 min to become oriented to the home page. Before downloading the required players, I started with the learning objectives and printed the two pages of questions. Reading through them, I believed that I would be quite competent if I could answer them after the tutorial. I then moved to the historical information pages to find out about the creators and viewed some photographs of their ASA exhibit. The 2000 ASA abstract was easily downloaded, but the link to the 2001 abstract failed. I noticed some differences in Netscape versus  Internet Explorer, with the latter being a bit more user friendly. I used a Windows NT, institutionally based Internet connection and had no other problems, except for a single crash (“script error”) while running the virtual machine through the Netscape-specific player. My computer froze, and I had to reboot.

The program itself is based on the Ohmeda Modulus II anesthesia machine (Datex-Ohmeda, Inc., Madison, WI), as indicated in the Preview, and this machine, of course, differs from other brands. However, the concepts are similar. I chose to start by playing with the interactive machine controls so as not to be biased by the tutorial. I had no problem “operating” the machine. The pause feature enables one to stop the action and to catch up with the flow of gas molecules, or to examine the functions of various components. I particularly enjoyed the demonstration of major principles, such as the high-pressure pipeline versus  cylinder supply of gas, and the interaction of the oxygen and nitrous systems. The pressure gauges were functional but not literal, and some should be modified for greater learning. For example, the cylinder pressure gauge could be designed to decrease slightly as the flush is activated, and the airway pressure gauge should go all the way to zero at the appropriate times. The sequence of alarms, nitrous oxide, and then oxygen cutoff as the oxygen pressure drops should be designed to occur more slowly and in sequence, to more robustly demonstrate the characteristic design of most anesthesia machines. The contribution (and danger) of fresh gas flow and oxygen flush to tidal volume was readily apparent. I would have enjoyed seeing this same effect with the ventilator activated at minimal set tidal volume; I could only lower the set volume to 500 ml. The visual depiction of inspiratory-to-expiratory ratio and inspiratory pause were nicely executed. I wish the patient and the breathing bag could be disconnected to show how absorbent is dehydrated by fresh gas flow—perhaps in a future version. The adjustable pressure limiting valve literally seemed to stick closed in manual ventilation mode, despite being set to the fully open position, and this caused the subtle but real inflation of the lung and unintentional positive end-expiratory pressure during scavenging of fresh gas. I do not think it is intentional because the tutorial specifically states otherwise. For that matter, I would like to see a dirty scavenger relief valve and its effect on the system. Another point to make is that the ventilator relief valve did not close when the ventilator was activated against a closed, manual ventilation selection valve, yet the bellows remained inflated. However, one is able to understand clearly the dynamic function of the ventilator relief valve and its mandatory cause of positive end-expiratory pressure as the bellows rises.

I must reiterate my fascination and extreme pleasure in using this program. It not only provides the novice with a clear understanding of machine function, but it also allows the trained observer to wonder about more robust features and interactions. I looked at their long “Revision History” and immediately knew that this enlightened group would continue to add to the accuracy of the virtual machine over time. I have already added this program to my repertoire of teaching materials and will be honored to reference such a talented group of researchers.