Cause of Device-Related Incident
Device factors; External factors

Clinical Specialty or Hospital Department
Anesthesia; CCU / ICU / NICU; Clinical/Biomedical Engineering; Nursery; Nursing; OR / Surgery; Pulmonary / Respiratory Therapy

Device Factors
Design / labeling error; Device interaction

Document Type
User Experience Network (UEN) reports

External Factors
Environmental (temperature, humidity, light)

Mechanism of Injury or Death
Misdiagnosis; Monitoring failure

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
*Not stated

Oximeters, Pulse [17-148]

Ambient Light Interference with Pulse Oximeters

User Experience Network™ [Health Devices Sep-Oct 1987;16(9-10):346-7]


One brand of pulse oximeters when used with a disposable infant flex probe started displaying "Probe Off Patient" when under a hospital-constructed radiant warming unit. Covering the probes with a towel or blanket did not prevent the problem. As soon as the warmer was turned off, the oximeters returned to normal operation. The radiant warming unit included two 250 W infrared (IR) heat lamps and a household dimmer switch, which was used to control the power to the lamps and, thus, the radiated heat. We initially suspected high-frequency electrical interference from the dimmer switch as the source of the problem.


The hospital informed us of its problem, and we believe that the "Probe Off Patient" message was caused by saturation of the detector component of the probe by the intense light from the heat lamps. The operator's manual states that detector saturation will elicit this message. The small probes used in this instance are difficult to shield from ambient light. We are continuing to investigate probe designs that will help eliminate this kind of interference.


We previously reported on the effects of ambient light on the operation of pulse oximeters (see Health Devices 16:50-1, February 1987). In this case, we are reasonably certain that ambient IR radiation from the lamps was saturating the detector of the oximeter probe. Under our direction, the hospital performed certain tests that ruled out electromagnetic interference, either radiated or conducted, as the cause of the "Probe Off Patient" message. Bypassing the dimmer switch did not eliminate the problem, nor did replacing the heat lamps with 150 W white incandescent bulbs. Only multiple layers of dark cloth or boards of opaque material prevented the problem.

Oximeters are electro-optical systems that are subject to electrical, optical, and mechanical interference. Protection from interference can be accomplished in several ways (e.g., optical filtration, electrical filtration) and varies from one manufacturer to another. Hospitals that plan to purchase pulse oximeters should perform clinical trials on test units in the presence of the surgical lights, radiant warmers, and the general ambient light in their institution. Ideally, pulse oximeters should not be affected; but if they are, an error message should be displayed, as in this case. Erroneous pulse or O2-Hg saturations mimicking normal values should not be displayed, as discussed in our previous report.


Oximeters, Pulse [17-148]

Cause of Device-Related Incident

Device factors: Design/labeling error; Device interaction

External factor: Environmental

Mechanism of Injury or Death

Misdiagnosis; Monitoring failure


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