What is the minimum common mode rejection ratio for amplifiers used in evoked potential recording?

The minimum common mode rejection ratio (CMRR) for amplifiers used in evoked potential recording is crucial because it determines the amplifier's ability to filter out noise and interference, particularly from common noise sources, allowing clear measurement of the evoked potentials being studied. A CMRR of 10,000:1 indicates that for every 10,000 units of the signal strength from the desired evoked potential, the unwanted noise or interference that is common to both inputs of the differential amplifier is only 1 unit. This level of rejection is typically necessary to achieve high fidelity in the recording of small signals that are often obscured by larger common-mode noise, such as electrical interference from the operating room environment or from patient physiological signals. Achieving this level of performance ensures that the evoked potential signals, which can be quite small, are accurately captured without significant distortion from noise, making it a minimum standard for quality in intraoperative monitoring.