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Failed Calibration of Anesthesia Machine Due to Look-Alike Oxygen Sensors

Dutoit, Andrea P. MD; Berger, Susanna R. DO; Shukry, Mohanad MD; Butt, Amir L. MBBS, MPH; de Armendi, Alberto J. MD

doi: 10.1097/ACC.0b013e31829c3c34
Case Reports: Case Report

Labels and medications with similar appearances have the potential to harm patients and cause delays in hospital services. We report a problem involving the Maxtec MAX-1 and MAX-11 oxygen sensors which are commonly used on anesthesia machines. These oxygen sensors have nearly identical labels which resulted in inadvertent interchanging of the sensors. The incident required the replacement of a MAX-11 sensor with a MAX-1 sensor to ensure proper functioning of the anesthesia machine. Identification of these cases can educate health care professionals of potential sources of labeling errors and safety issues and can also bring about Food and Drug Administration policy changes.

From the *Department of Anesthesiology, Oklahoma University Health Sciences Center, Oklahoma City, Oklahoma; Department of Anesthesiology, Virginia Commonwealth University, Richmond, Virginia; and Department of Anesthesiology, University of Nebraska Medical Center, Omaha, Nebraska.

Accepted for publication March 15, 2013.

Funding: No funding source.

The authors declare no conflicts of interest.

Address correspondence to Alberto J. de Armendi, MD, Department of Anesthesiology, Oklahoma University Health Sciences Center, 750 NE 13th St., OAC 200, Oklahoma City, OK 73104. Address e-mail to

Identical and ambiguous labeling of medications/medical devices continues to be a subject of debate. Despite policy changes in Food and Drug Administration labeling regulations, potential risks posed by look-alike labels and identical medical devices continue to surface.a The Food and Drug Administration policy focuses on label content without clear guidelines to distinguish between products made by the same manufacturer 21 C.F.R. § 801 (2012). In 2010, the Anesthesia Patient Safety Foundation published at the Medication Safety Conference that look-alike labels pose a potential threat to patients’ safety in hospitals.1

We report a look-alike label problem between the Maxtec MAX-1 and MAX-11 oxygen sensors (Maxtec Inc, Salt Lake City, UT) which are commonly used on anesthesia machines.b These oxygen sensors can be easily confused due to almost identical appearance and labeling (Fig. 1).

Figure 1

Figure 1

Consent and IRB approval were not required for this submission.

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During a routine preanesthesia machine check, the oxygen sensor was not able to be calibrated correctly. The anesthesiologist repeatedly inspected the anesthesia machine to make sure that all the replacement parts were properly installed and that the oxygen sensor and electrical components were properly connected. On inspection of the oxygen sensor, it was discovered that during the previous routine preventative maintenance check of the Dräger Fabius Tiro Anesthesia Workstation, a Maxtec MAX-11 oxygen sensor was incorrectly replaced with a Maxtec MAX-1 oxygen sensor. When the installed oxygen sensor (Maxtec MAX-1) was removed and replaced with the correct Maxtec MAX-11 oxygen sensor, the calibration of the oxygen sensor was successfully completed.

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These alkaline-based sensors are commonly used as replacement parts in anesthesia machines. The Maxtec MAX-1 oxygen sensor is designed as a replacement part for GE: Datex-Ohmeda, UK: 0237-2034-700 Excel Modulus, 4700 Oxicap, 5250 RGM, 5100, 5120, 5125, 5150 Handheld Monitor, and 7800 model machines. The Maxtec MAX-11 oxygen sensor is a dual cathode model designed as a replacement part for Dräger, Germany: Narkomed, Fabius GS, Fabius Series, Babylog, Evita Family, 6850645, 6803290, and Cato I 8000 model machines. Both of these sensors can easily be mistaken for the other due to identical appearance and labeling (Fig. 1). Both sensors are 2-cm tall with a diameter of 3 cm, encased in a translucent, white plastic housing, and have identical bases. These sensors have the same identification sticker, with only minor differences occurring within 2 small boxes including the model number, serial number, and the number of electrical rings.

This case emphasizes the importance of the preanesthetic machine check including recalibration of the oxygen sensor on a daily basis to ensure patient safety. In a survey of 169 anesthesia machines and monitors done in 45 hospitals, Kumar et al.2 described multiple malfunctions and maintenance issues that can be present in anesthesia equipment, the majority of which are preventable by completing a preanesthetic inspection of equipment. Awareness and identification of the causes of these problems are essential to ensure safe patient care. We believe that anesthesia providers should be aware of this identical oxygen sensor issue and suggest that Maxtec, the manufacturer, promptly address and rectify this problem.

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Although both the MAX-1 and MAX-11 sensors have similar form and fit functions, each was designed for use as a specific equipment sensor replacement. In the report by Dutoit et al. the MAX-11 sensor rather than the correct MAX-1 was inadvertently installed in the equipment. However, because the sensor did not meet the equipment specification and could not be calibrated it rendered the equipment “out of calibration” and not for use per hospital protocol. Although this matter is not a patient safety concern, it is an inconvenience for the industry as the equipment could not be used.

Maxtec, and many other sensor manufacturers, provide replacement sensors which are identified numerically as is standard industry practice. Replacement sensor manufacturers have designed these sensors to meet Original Equipment Manufacturer (OEM) sensor specifications with respect to millivolt output, response time, electrical connectors, etc., as established by the original equipment manufacturer. As a leader in the industry, Maxtec acknowledges the inconvenience that similar form function and similar labeling causes in the anesthetic space and in other applications where sensors are used. Maxtec appreciates the opportunity for improvement and will promptly implement further labeling for product differentiation.

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a “U.S. Inaction Lets Look-Alike Tubes Kill Patients,” The New York Times, August 21, 2010, sec. A1.
Cited Here...

b Anesthesia MAX Oxygen Sensors. Available at: Accessed February 25, 2013.
Cited Here...

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1. Eichhorn JH. APSF hosts medication safety conference. APSF Newsl. 2010;25:2–8
2. Kumar V, Hintze MS, Jacob AM. A random survey of anesthesia machines and ancillary monitors in 45 hospitals. Anesth Analg. 1988;67:644–9
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