Michael Olympio, MD,
Alarm Requires Selection of Heart Rate Source
I am a CRNA with 13 years of experience. I never had a problem with a pulse oximeter until I encountered the Datex-Ohmeda Cardiocap 5. I was accustomed to a pulse oximeter alarming loudly anytime it was low or not on the patient. I have had 2 incidences in the last 2 years where the ECG beeped when the pulse oximeter was off, such that one might have thought the pulse oximeter reading was OK when not facing the monitor. While another patient was under monitored anesthesia care, the pulse oximeter initially was working, but ceased to work 3 minutes into the case. Once again the ECG beeped, but without the annoyingly loud alarm from the pulse oximeter; there was a single, short beep about every minute. The probe was not illuminated and had to be switched.
I think it is very dangerous to allow a monitor not to alarm if it is not working. I have worked with many monitors over the course of my career, and feel this is taking a step backward if the software cannot be adjusted. I appreciate any information. Thanks.
Kathleen Piotrowski, MSN, CRNA
Thank you for the opportunity to respond. I've reviewed this with our design center in Helsinki, Finland, and have observed the monitor's behavior in order to provide the most thorough response. First, I would like to provide you with my name and contact information and assure you that you are welcome to contact me directly at any time.
The Cardiocap/5 monitor is designed with a 3-tiered approach to alarm logic where advisory alarms are displayed in white with a single beep, serious alarms are in yellow and provide 3 beeps, and life-threatening alarms display in red and give 5 beeps.
In the situation you describe, I believe the monitor performed according to the specifications. The Cardiocap/5 monitor, by default, sources the heart rate automatically looking for ECG, Pleth, or Invasive Pressure for an available heart rate. When the heart rate is sourced from the ECG, you will hear the beat sound also sourced from the ECG, and the heart rate will be displayed in the same color as the ECG waveform and numeric. If the heart rate is sourced from the Pleth, the beat sound will be sourced from Pleth and will provide an audible tone different from the ECG tone. The heart rate will be displayed in the same color as the Pleth waveform and numeric.
If the current source becomes unavailable, for example the SpO2 probe falls off the patient's finger, the monitor will automatically search for another heart rate source (either ECG or invasive pressure). When the monitor switches to another source, ECG for example, the tone of the beat sound will change, the numeric on the display will change to match the color and value coming from the ECG, and a white advisory alarm will be displayed noting "SpO2 probe off" or "No SpO2 pulse," whichever is applicable. After several seconds, the white advisory alarm will escalate to a yellow serious alarm and provide 3 beeps. The yellow alarm remains active until it is either acknowledged, or the alarm event is corrected (i.e., probe returned to the patient's finger).
Based on the information we have available, I would speculate that the monitor is performing according to specifications. I would be more than happy to discuss this situation further and to engage our Field Service team to complete a more thorough investigation of the monitor to test the performance. Please feel free to contact me at the telephone or email address listed above.
This sounds like the identical mechanism on our Datex-Ohmeda S/5 monitoring system, and it has fooled some of our own clinicians as well. One option your response did not include is to select the heart rate source manually, instead of automatically. At least in the S/5, this would stop the tone, and cause the clinician to look upwards. Is that possible in the Cardiocap/5?
Michael A. Olympio, MD
You are correct—it should be the same mechanism as your S/5 monitor. The logic is almost identical throughout the Datex-Ohmeda family of monitors. You can set the heart rate source manually to Pleth, for example. This setting cannot be saved as a default, however. The loss of a pulse from Pleth will result in the loss of the beat sound and a yellow alarm.
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