General information on defibrillator testing can be found in this 2009 article copied from the original MEDTEQ website.
One of the significant changes triggered by the IEC 60601-2-25 2011 edition is the inclusion of the defibrillator proof energy reduction test via the general standard (for patient monitors, this test already existed via IEC 60601-2-49). Previously, diagnostic ECGs tended to use fairly low impedance contact to the patient, which helps to improve performance aspects such as noise. The impact of the change is that all ECGs will require higher resistors in series with each lead, as detailed in the above article. The higher resistors should trigger retesting for general performance, at least for a spot check.
Experience from real tests has found that with the normal diagnostic filter (0.05Hz to 150Hz), the baseline can take over 10s to return, exceeding the limit in the standard. Although most systems have automated baseline reset (in effect, shorting the capacitor in an analogue high pass filter, or the digital equivalent), the transients that occur after the main defibrillator pulse can make this difficult for the system to know when the baseline is sufficiently stable to perform a reset. The high voltage capacitor used for the main defibrillator pulse is likely to have a memory effect causing significant and unpredictable baseline drift well after the main pulse. If a reset occurs during this time, the baseline can easily drift off the screen, and due to the long time constant of the 0.05Hz filter, can take 15-20s to recover.
The usual workaround is that most manufacturers declare in the operation manual that during defibrillation special filters should be used (e.g. 0.67Hz). The issue raises the question of why diagnostic ECGs need to have defibrillator protection, and if so, how this is handled in practice. If defibrillator protection is really necessary, sensible solutions may involve the system automatically detecting a major overload and switching to a different filter for a short period (e.g. for 30s). It is after all an emergency situation: expecting the operator to have read, understand and remember a line from the operation manual, and as well have the time and presence of mind to work through touch screen menu system to enable a different filter setting while at the same time performing defibrillation on the patient is a little bit of a stretch.
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