Methods and Systems for Operating an Intraoperative Neurophysiological Monitoring System in Conjunction with Electrocautery Procedures

Abstract

Methods and systems for conditioning a signal indicative of electrosurgical unit activity are described. A hardware circuit acquires AC current from an electrosurgical unit on patient isolated circuitry and conditions the signal in either of two alternate processing methods. The processed signal is routed as input to an analog to digital converter circuit. A method for determining saturation on referential inputs and recovering inputs to an unsaturated state is also described.

1 . A circuit for use in a system for detecting noise causing interference on patient signals being monitored by an intraoperative neurophysiological monitoring (IONM) system, said noise having frequencies greater than 100 kHz and rate of occurrence greater than 30 kHz, the circuit comprising:
 a first filter configured to remove predefined low frequency signals to generate a filtered signal, wherein the low frequency signals comprise signals having a frequency less than 100 kHz;   a gain circuit configured to apply gain to the filtered signal and generate an amplified signal;   a rectifier circuit configured to rectify the amplified signal and generate a direct current voltage;   a delay circuit configured to attenuate the direct current voltage for contribution from periodic signals with frequencies greater than 100 kHz and rate of occurrence of less than or equal to 200 Hz; and   a second filter configured to remove said noise from the direct current voltage;   wherein the circuit is further configured to apply a threshold to the direct current voltage and determine activity of an electrosurgical unit in electrical communication with the patient.   
     
     
         2 . The circuit for use in a system for detecting noise causing interference on patient signals being monitored by an IONM system of  claim 1 , further comprising a transient voltage suppression diode configured to provide transient protection of circuit components with absolute voltage limit. 
     
     
         3 . The circuit for use in a system for detecting noise causing interference on patient signals being monitored by an IONM system of  claim 1 , wherein the delay circuit is configured to be charged by electrical signals having frequencies greater than 100 kHz and rate of occurrence of 30 kHz or more. 
     
     
         4 . A method for detecting noise causing interference on patient signals being monitored by an intraoperative neurophysiological monitoring (IONM), wherein the method is implemented using a non-isolated circuit that receives a signal from an isolated circuit, said non-isolated circuit comprising a microcontroller having an analog to digital converter, a diode, a first filter, a gain circuit, a rectifier circuit, a delay circuit, and a second filter, the method comprising:
 using the diode to protect the non-isolated circuit from electrical transients;   filtering the signal using the first filter to attenuate low frequencies in the signal and output a filtered signal, wherein the low frequency signals comprise signals having a frequency of 100 kHz or less;   amplifying the filtered signal by a predefined gain using the gain circuit and generating a gained signal;   rectifying the gained signal using the rectifier circuit and generating a rectified signal;   delaying the rectified signal with the delay circuit;   filtering said noise from the signal with the second filter, wherein said noise is characterized by frequencies greater than 100 kHz and rate of occurrence of greater than or equal to 30 kHz; and   inputting a signal resulting from the second filter into the analog to digital converter on the microcontroller.   
     
     
         5 . The method for detecting noise causing interference on patient signals being monitored by an IONM system of  claim 4 , wherein the delay circuit is configured to not be charged by signals having frequencies greater than 100 kHz and rate of occurrence of 200 Hz or less. 
     
     
         6 . The method for detecting a high frequency noise causing interference on patient signals being monitored by an IONM system of  claim 4 , wherein the delay circuit is configured to be charged by signals having frequencies greater than 100 kHz and rate of occurrence of 30 kHz or more. 
     
     
         7 . A method for detecting noise causing interference on patient signals being monitored by an intraoperative neurophysiological monitoring (IONM) system, said noise being attributed to an electrosurgical unit in electrical communication with a patient, the method comprising:
 capacitively coupling signals from an isolated circuit to a non-isolated circuit;   rectifying the coupled signals to generate rectified signals;   sampling the rectified signals using a processor for detecting a direct current value of the rectified signals; and   indicating detection of said noise if the detected direct current value exceeds a predefined threshold value.   
     
     
         8 . The method of  claim 7  wherein the signals are capacitively coupled by positioning a portion of the non-isolated circuit over the isolated circuit, and wherein said portion comprises a copper pad. 
     
     
         9 . The method of  claim 7  further comprising routing said coupled signals through a single pole high-pass filter. 
     
     
         10 . The method of  claim 7  further comprising routing said coupled signals through a multiple pole high-pass filter. 
     
     
         11 . The method of  claim 7  further comprising amplifying the coupled signals by a gain of 1 or more. 
     
     
         12 . The method of  claim 7  wherein the coupled signals are rectified using a rectifier circuit. 
     
     
         13 . The method of  claim 7  wherein the rectified signals are delayed by using a circuit comprising a capacitor and a resistor. 
     
     
         14 . The method of  claim 7  wherein the rectified signals from the isolated ground plane are routed through a low pass filter. 
     
     
         15 . The method of  claim 7  further comprising routing the rectified signals to an analog to digital converter using a microcontroller in the non-isolated circuit. 
     
     
         16 . The method of  claim 7  wherein detecting said noise comprises causing an alarm status to be set to a true state. 
     
     
         17 . The method of  claim 16  wherein the alarm status is set to the true state when the direct current value remains above the predefined threshold value for a predefined period of time. 
     
     
         18 . The method of  claim 7  further comprising setting an alarm status to a false state if the detected direct current value does not exceed the predefined threshold value. 
     
     
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