Circulation 80,350 • Volume 21, No. 3 • Fall 2006   Issue PDF

Is an In-line Oxygen Monitor Still Necessary

Michael Nakata, MD; Stanley Weitzner, MD; Michael A. Olympio, MD; Robert Clark; Julian Goldman, MD; Dr. Siegfried Kästle; Dan Alt; Erv Moss, MD

I am medical director of a free-standing surgery center. One of our anesthesia machines has a non-functioning O2 sensor. We have an older Ohmeda Excel 110. Our biomedical person claims the sensor box would be impossible to replace. He said since we monitor O2 on our end-tidal/agent analyzer, this would satisfy O2 monitoring requirements. Is he correct, or do we need the inline O2 sensor?

Thank you,
Michael Nakata, MD


In Response:

The anesthesia machine standard of 1979, as well as the anesthesia workstation standards of 1988 and 2000 (I chaired the committees that wrote the latter 2) required an “in-line” O2 analyzer. It was our belief that the analyzer was the last line of defense against a machine-generated hypoxic mixture, and further, would alarm sooner than an expired gas monitor. I hope I have been of some help.

Stanley Weitzner, MD

Editors’ Note:

ASTM F-1161 was published in 1989, but has since been withdrawn and replaced by ASTM F-1850. The relevant requirements from ASTM F-1850-00 are as follows:

Clause 51.11.1 The ANESTHESIA WORKSTATION shall be provided with an oxygen monitor in compliance with Specification F 1462 for measurement of the O2 concentration in the inspiratory limb or the Y-piece, or the manufacturer(s) of the ANESTHESIA GAS SUPPLY DEVICE and ANESTHESIA BREATHING SYSTEM shall state in the accompanying documents that such a means is required. Automatic Enabling – Means shall be provided that the monitor and alarms mentioned in clauses 51.9.3 (breathing system pressure), and 51.11 (oxygen concentration) shall be in the enabled condition and functioning automatically whenever the anesthesia gas supply device is in use. . . .

Dr. Olympio

In Response:

The important aspect here is not where the O2 is measured or by what, but rather that the O2 measurement is activated when the anesthesia machine is turned on. There are numerous reports from history where stand-alone monitors for parameters were available on the machine, but the incident occurred nonetheless because the user had forgotten to turn the device on or had not realized that the alarms were disabled.
In our view the O2 measurement should be checked during the machine startup and should be automatically activated on power-up of the machine. It should also have the same battery support time as the gas machine.

Robert Clark
CareArea Director
Perioperative Care
Dräger Medical, Inc.
Telford, PA USA

In Response:

The role of the O2 analyzer is to assess the “machine”—not solely the patient. Both machine and patient monitoring could be accomplished with a side-stream gas analyzer positioned at the Y-piece, if it is always used. When a machine complies with the workstation standard, there are other requirements as well. For example, monitors must be activated when the machine is turned on. Therefore, it is tempting, but not necessarily possible, to create the equivalent of a workstation with a handful of eBay components.

To the best of my knowledge, conformance to a current equipment standard is not necessarily required for clinical use. In fact, it is almost impossible for equipment to continue to comply with constantly updated standards. Naturally, new equipment should comply. In this case, the old machine no longer complies with an old standard. The ASA’s statement on machine obsolescence may be relevant:

This issue probably resides within the scope of practice standards. Is the machine otherwise safe and fit for use? Will the O2/CO2 respiratory gas monitor always be used when the machine is used? If so, it should be OK.

Julian Goldman, MD
Massachusetts General Hospital
Departments of Anesthesia and Biomedical Engineering
President, Society for Technology in Anesthesia

In Response:

Before fast oxygen measurements became available as part of anesthesia gas analyzers, it was a safety requirement to monitor the O2 content in the inspiratory limb of the breathing circuit. This was a relatively slow measurement (response time of seconds, not milliseconds) accomplished with polarographic or fuel cells. They served to detect failures in the oxygen supply.

In my opinion, a modern gas analyzer measuring as close as possible to the patient’s lung, namely at the Y-piece of the circuit, does an even better job. It not only monitors the O2 content delivered to the patient but also captures the amount of oxygen coming out of the lungs. This gives more information about oxygen delivery and it even provides a sign of effective ventilation.

So, I think if the anesthesia machine is not compromised elsewhere, it should be safe to use the O2 information from the gas monitor. But of course, one must take care that the defective O2 sensor does not generate distractive alerts on the anesthesia machine, thus adding risk.

Kind regards,
Dr. Siegfried Kästle
Project Manager R&D
Patient Monitoring Division
Philips Medizin Systeme Böblingen GmbH
Hewlett-Packard-Strasse 2
71034 Böblingen, Germany
[email protected]

In Response:

I’d say that, no, a facility doesn’t have to maintain an anesthesia unit to adhere to F1850, since that standard applies to manufacturers of new devices. Once a device is in a facility’s inventory, that facility has an obligation to maintain and operate it in accordance with current standards of care, but that’s outside the scope of ASTM. ASA and AANA standards are better guidelines for the practitioner and clinical engineer.

In his original question, Dr. Nakata pointed out that his medical-gas monitor can measure O2 concentrations, and I’d say that’s sufficient to meet ASA/AANA requirements. When healthcare facilities assemble anesthesia systems (the anesthesia unit, gas monitoring, and physiologic monitoring) from separate components, there’s almost inevitably some overlap of monitoring function. Paying greater attention to a monitoring function on one component at the expense of the same feature on another component isn’t unreasonable.

What’s tricky is this: How does Dr. Nakata’s facility ensure that a) everyone knows that the anesthesia unit’s O2 monitor is unusable and b) the gas monitor is always present and in use? Whatever method he chooses, Dr. Nakata needs to make sure that the gas monitor (or other O2 monitor) is automatically enabled during each case and that no one ever thinks to rely on the anesthesia unit’s (now defunct) integrated O2-monitor. If he can’t guarantee this, the safer route is to replace the anesthesia unit entirely.

Additionally, I agree strongly with 2 points raised by other respondents. First, as more than one response pointed out, Dr. Nakata will need to ensure that the problem is truly limited to an inability to monitor and/or display oxygen concentrations and does not extend to other functions of the anesthesia machine. Second, as Rob Clark (Dräger Medical) pointed out, the new monitoring component should be supported by battery power at least as long as the anesthesia machine is supported (as should any important monitoring feature).

Best regards,
Dan Alt
Senior Project Engineer, Health Devices Group
Manager, Problem Reporting System
P: +1-610-825-6000 ext. 5445
F: +1-610-834-1275
[email protected]

In Response:

An in-line O2 sensor tells you what is coming out of the machine. In New Jersey, it is not replaced by any other peripheral sensor.

Erv Moss, MD

The information in this column is provided for safety-related educational purposes only, and does not constitute medical or legal advice. Individual or group responses are only commentary, provided for purposes of education or discussion, and are neither statements of advice nor the opinions of APSF. It is not the intention of APSF to provide specific medical or legal advice or to endorse any specific views or recommendations in response to the inquiries posted. In no event shall APSF be responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with the reliance on any such information.