IFCN recommended standards for brain-stem auditory evoked potentials. Report of an IFCN committee

Abstract

Electroencephalography and clinical Neurophysiology , 91 (1994) 12-17 © 1994 Elsevier Science Ireland Ltd. 0013-4694/94/$07.00 EEG 00007 IFCN recommended standards for brain-stem auditory evoked potentials. Report of an IFCN committee Marc R. Nuwer (Chairman) ( Los Angeles, CA, USA), Michael Aminoff (San Francisco, CA, USA), Douglas Goodin (San Francisco, CA, USA), Shigeaki Matsuoka ( Kitakyushu, Japan), Francois Maugui~re (Lyon, France), Arnold Starr ( Irvine, CA, USA) and Jean-Francois Vibert (Paris, France) (Received for publication: 14 February 1994) Introduction Brain-stem auditory and evoked potentials (BAEPs) have come into widespread use for assessment of the clinical state of the middle portion of the brain-stem and for assessment for hearing, particularly in the screening of infants at risk for hearing loss. They have found their way into routine hearing screening for infants. They have proven themselves as objective, re- producible, sensitive indicators of many types of brain- stem disturbances. The pathway tested by BAEPs include the acoustic conduction through the ear and the electrical transmis- sion from cochlea along th.e eighth nerve into lower pons, continuing rostrally through pons and up each lateral lemniscus into the midbrain. A series of 5 or more peaks are usually recorded from the ears and scalp vertex. The B A E P test can be easily recorded in most patients, including comatose or sedated patients in whom routine audiometry cannot be done. In fact, the best quality BAEP is often obtained with sleep or sedation. B A E P can be obtained in the presence of mild or moderate hearing impairment, but the main 5 peaks usually cannot be obtained in the presence of severe hearing impairment. Stimulation BAEPs are produced by a brief click stimulus. This is usually a square-wave electrical pulse 100/zsec Correspondence to: Marc R. Nuwer, M.D., Ph.D., Department of Clinical Neurophysiology, Reed Neurological Research Center, Uni- versity of California Los Angeles, 710 Westwood Plaza, Room 1194, Los Angeles, CA 90024 (USA). Fax: (310) 206-8461. SSDI 0013-4694(94)00045-M long. This brief pulse can move the earphone di- a p h r a g m either toward or away from the patient's ear. E a r p h o n e movement toward the ear is called an acous- tic condensation phase stimulus, whereas earphone movement away from the patient's ear is a rarefac- tion stimulus. Occasionally the two types of phase are concatenated, which is referred to as an alternating phase stimulus. The latter can be useful in reducing stimulus artifact seen with very loud stimulus intensi- ties. In clinical neurophysiology the rarefaction phase is usually chosen. Clicks are usually presented 10-70 t i m e s / s e e . At fast rates, data can be collected more quickly, but the peaks are more poorly defined. As a result, slower or intermediate rates are often chosen. The rates 11 and 3 1 / s e e are most commonly chosen. Rates are usually not exact factors divisible into 50 or 60 Hz, because such rates would predispose to line noise. Stimuli are often delivered at about 70 dB intensity. There are several different decibel scales in common clinical use. It is important to understand the differ- ence between these intensity scales. (1) Hearing level (dB NHL, dB HL, dB nHL): this scale refers to the n u m b e r of decibels of intensity c o m p a r e d to the threshold of hearing in a group of average normal subjects. Z e r o on this scale is defined as the threshold at which an average normal subject can just perceive the stimulus 50% of the time. (2) Sensory level (dB SL): this is the scale on which zero is defined as the point at which the individual patient can barely appreciate the stimulus. This may be very different from 0 dB HL. Patients with hearing loss may have their personal 0 dB SL found at very high intensities such as 70 dB NHL. (3) The physical definition (dB peSPL, peak equiva- lent sound pressure level): physical m e a s u r e m e n t of sound pressure levels use as the 0 dB reference level a