Abstract
IOM recording technology is founded on basic electrical principles including susceptibility to electrical interference, which in the operating room is predominantly due to electromagnetic coupling of noise sources with recording circuits. The underlying physics involved will be discussed in this chapter. Methods of improving physiologic signal acquisition and reducing electrical interference will be discussed.
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Electronic Supplementary Material
The following videos are provided as demonstrations of many of the principles discussed thus far.
The capacitance of skin
•Patient skin acts as an antenna for ambient electrical interference
•The location where electrical interference couples with the patient’s skin has an impact on how the interference is amplified. The skin of OR staff, for example the surgeon, can aid in coupling electrical interference to our patient
•Mechanical movements of our recording electrodes and leadwires can introduce motion artifact into our signals (AVI 201856 kb)
Capacitive and inductive coupling
•Electrical interference readily couples with our recording leadwires, whether inductively or capacitively coupled (AVI 166585 kb)
Importance of bundling leadwires
•Keeping leadwires close to each other decreases the amount of electrical interference amplified by increasing the extent to which the electrical interference is common to both leadwires
•Twisted or braided leadwires perform better than ribbon leadwires, which in turn perform better than loose leadwires (AVI 51689 kb)
Electrical interference fields of fluid warmer and surgical headlamp
•Both the fluid warmer and the surgical headlamp have directional electromagnetic fields
•Creating distance rotationally, horizontally, and vertically can selectively decrease the extent of coupling to our recording circuitry (AVI 238423 kb)
Electrical interference field of patient air warmer (AVI 95808 kb)
OR bed wall grounded and ungrounded demonstration
•Poor grounding of the OR table or other OR equipment can be a source of electromagnetic interference to our recording circuit
•Unplugging the OR table may decrease the amount of electromagnetic interference coupled to our recording circuit.
•It is possible that in the case where the ground of the OR table is helping to compensate for other noise sources, unplugging the OR table may increase the amount of electromagnetic interference
•The iso-ground is by definition isolated from the IOM equipment main ground. The condition of the ground of the IOM equipment is therefore usually not a source of interference. It is however a safety factor (AVI 191699 kb)
Importance of location of iso-ground placement on the patient
•The efficacy of the iso-ground electrode to decrease electromagnetic interference is highly dependent on placement location (AVI 160414 kb)
Dangers of electrode burns from coupled energy from the ESU
•The electromagnetic field emanating from the ESU cabling can couple with our recording electrode leadwires, resulting in electrode burns at the electrode patient attachment
•Contact between the patient’s skin and both ESU and IOM electrode cabling enhances the level of coupling occurring between the ESU cabling and IOM electrode cabling
•Like other electromagnetic fields, creating distance between the source (ESU cabling) and our recording leadwires decreases the amount of coupling (AVI 289000 kb)
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Netherton, B., Goldstein, A. (2017). IOM Instrumentation Layout and Electrical Interference. In: Koht, A., Sloan, T., Toleikis, J. (eds) Monitoring the Nervous System for Anesthesiologists and Other Health Care Professionals. Springer, Cham. https://doi.org/10.1007/978-3-319-46542-5_16
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DOI: https://doi.org/10.1007/978-3-319-46542-5_16
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