During surgery, intraoperative monitoring is used to assess a patient’s hearing system by testing the nervous system. This is done by using evoked potentials to monitor the integrity of the auditory nerve. Auditory evoked potentials are electrical responses recorded from the auditory nerve and brain following the presentation of a stimulus. The purpose of intraoperative monitoring is for early detection of injury and allowing for immediate corrective measures. Audiologists work with physicians, anesthesiologists, nurses, and residents to ensure best outcomes for patients.
How Does Intraoperative Monitoring Work?
A trained audiologist attaches electrodes and insert phones to a patient in order to stimulate and record evoked potentials. Responses are received on a computer system from the electrodes. Interactive software carries out several tasks:
Activation of electrodes with appropriate timing
Processing and displaying the response signals as they are picked up by the recording electrodes
Responses are averaged over time and are compared to normative values
Challenges and Benefits of Intraoperative Monitoring
There are several challenges to intraoperative monitoring. The signals change according to various factors, including anesthesia, tissue temperature, surgical stage, and tissue stresses. There are also technical challenges to deal with. Those include electrical interferences generated by drills, suction devices, beds and operating microscopes.
Patients may benefit from intraoperative monitoring during surgical procedures where there is risk to the auditory system, such as removing a tumor. Intraoperative monitoring helps with early detection of audiologic injury, allowing for immediate corrective measures. Justification for intraoperative monitoring involves considering the cost effectiveness of intraoperative monitoring when compared to physical, emotional, and monetary costs resulting from an unforeseen neurological compromise of the auditory or facial nerve.
Sato S, Onozawa Y, Kumabe T, Okamoto H. [Intraoperative ABR Monitoring in Neurosurgery]. Masui. 2015 May;64(5):502-7. Japanese. PMID: 26422957.