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Special Challenges with New Digital Anesthesia Machines

Toronto, Ontario

Anesthesia delivery systems have been in use in various forms for over 150 years, ever since general anesthesia was primitively administered using ether or chloroform soaked handkerchiefs covering the patient's face. Quickly, clinicians thought of a number of ways of improving anesthesia delivery beyond the use of "open drop" techniques, and this eventually lead to the concept of an anesthesia machine where anesthesia delivery could be monitored and controlled to help ensure continuing patient safety.

Continuing advances in computer technology in recent years have now lead to a number of interesting new anesthesia machines that have come to market. These machines all use embedded computer technology in one form or another. Also, all of these machines have a user interface that is different (indeed, sometimes very different) from the classic anesthesia machines extant prior to the days of widespread computerization.

At my hospital, the new Datex-Ohmeda (www.Datex-Ohmeda.com) ADU digital anesthesia machine has been in use for a good many months and has generally been quite well received by clinician users. However, the software-based design of the system has lead to some issues that were quite unexpected. We found, for instance, with one particular release of the embedded software, that if the unit was powered up with a desflurane anesthetic cassette in place, certain errors sometimes occurred, almost certainly as a result of an internal software design flaw. For a while, pending the software upgrade we received, every one of our ADU anesthetic machines had a note taped above the anesthetic canister slot that said "DO NOT CHECK WITH DESFLURANE".

Two other unanticipated problems that surfaced concern the computer-assisted anesthetic machine check that users are expected to carry out before starting a case. In some cases the machine refused to proceed when a small circuit leak was detected, such as when the CO₂ sampling line is present in the patient breathing circuit. Another potential problem is that after the machine checkout procedure is completed, the oxygen flow is set to zero, a fact that occasionally escapes the notice of some anesthesiologists until their patients promptly desaturate following the induction of anesthesia.

Another problem we have occasionally encountered with this unit is with the ventilator part of the anesthetic machine not turning on promptly if it had been previously turned off for a prolonged period (such as during cardiopulmonary bypass for heart surgery). We are unaware of the cause of this occasional problem.

A final problem appears to be the occasional corruption of capnogram data transmitted from the patient monitoring system to the colour display integral to the ADU. This problem is best illustrated by examining photographs I was able to take when I first noticed the bug and demonstrates the benefit to keeping a digital camera with one at all times. For details visit the web page I set up at http://canmed.net/ADUBug/.

Some digital anesthesia machines use "virtual" instead of "real" gas flowmeters. That is, instead of real glass flowmeters that can be seen and controlled, the unit uses simulated flowmeters on the video display. However, some clinicians are concerned that virtual flowmeters may not have the impact of real flowmeters in attracting the notice of the anesthesiologist. For example, as noted earlier, some anesthesiologists do not notice that the oxygen flow is set to zero at the end of the checkout procedure for the Datex-Ohmeda ADU machine, which uses a virtual flow meter arrangement.

The need for occasional software upgrades to deal with newly identified problems is another fact of life in the age of computer-based medical equipment. Purchasers of such equipment would be wise to ask for free software upgrades for the life of the product as part of the purchase agreement. Clinicians should also be aware that not all machines of the same type will always have the same software release, depending on how software upgrades are handled in various anesthesia departments.

In a recent discussion with Dr. Jeremy Sloan, a Toronto anesthesiologist advising the Canadian Standards Association on these matters, the possibility of a certification process to ensure appropriate competence with new anesthesia machines was explored. It would appear that the complexity and subtleties of these advanced machines may eventually mandate a formal training and certification process much like that required of pilots who require separate certification for each aircraft they wish to fly.

Notwithstanding the foregoing, digital anesthetic machines have much to offer to improve anesthesia care, provided that manufacturers make the effort to perform careful ergonomic evaluation of their designs and provided that they respond quickly with the necessary software upgrades as unanticipated problems are discovered.

This article has been cited by other articles:

				R. N. Merchant and D. J. Doyle Special challenges with new digital anesthesia machines Can J Anesth, November 1, 2001; 48(10): 1049 - 1049. [Full Text] [PDF]

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