Brainstem Auditory Evoked Responses (BAERs)
Brainstem Auditory Evoked Responses (BAERs)
BAERs, also known as Brainstem Auditory Evoked Potentials (BAEPs) or Auditory Brainstem Responses (ABRs), are objective neurophysiologic assessments of auditory pathway function from the auditory nerve through the brainstem.
Key Points
- Non-invasive measurement of auditory pathway integrity
- Essential tool for newborn hearing screening
- Evaluates brainstem function and maturation
- Can be performed in sleeping or sedated patients
- Provides objective threshold estimation
Recording Parameters
- Stimulus Characteristics
- Click stimuli (100 microseconds duration)
- Tone burst for frequency-specific testing
- Rates typically 11-91 clicks per second
- Intensity range: 0-90 dB nHL
- Electrode Placement
- Active: mastoid or earlobe (A1, A2)
- Reference: vertex (Cz)
- Ground: forehead (Fpz)
- Recording Settings
- Bandpass filters: 100-3000 Hz
- Analysis time: 10-15 milliseconds
- Minimum 1000-2000 averages
- Two or more replications required
Testing Environment
- Sound-attenuated room
- Electromagnetic shielding
- Patient preferably sleeping or still
- Temperature maintenance (affects latencies)
Major Wave Components
- Wave I
- Generated by distal auditory nerve
- Latency: approximately 1.5 ms
- Key for peripheral hearing assessment
- Wave II
- Proximal auditory nerve/cochlear nucleus
- Latency: approximately 2.5 ms
- Often merged with Wave III
- Wave III
- Lower pons/cochlear nucleus
- Latency: approximately 3.5 ms
- Important for brainstem assessment
- Wave IV
- Upper pons/lateral lemniscus
- Often merged with Wave V
- Variable appearance
- Wave V
- Lower midbrain/inferior colliculus
- Latency: approximately 5.5 ms
- Most robust and reliable component
- Key for threshold determination
Primary Clinical Uses
- Hearing Assessment
- Newborn hearing screening
- Threshold estimation in infants
- Assessment of difficult-to-test patients
- Auditory neuropathy diagnosis
- Neurological Applications
- Brainstem lesion localization
- Demyelinating disease monitoring
- Coma prognostication
- Intraoperative monitoring
- Specific Conditions
- Acoustic neuromas
- Multiple sclerosis
- Brainstem stroke
- Neurodegenerative disorders
Age-Specific Considerations
- Neonates
- Modified stimulus parameters
- Adjusted normative values
- Consideration of maturational changes
- Higher intensity thresholds normal
- Infants
- Natural sleep preferred
- Frequency-specific assessment
- Multiple sessions may be needed
- Developmental tracking important
- Special Testing Situations
- NICU protocols
- Post-meningitis screening
- Syndromic hearing loss
- Risk factor monitoring
Normal Parameters
- Latency Measurements
- Absolute latencies for Waves I, III, V
- Interpeak latencies I-III, III-V, I-V
- Interaural latency differences
- Amplitude Analysis
- Absolute amplitudes of major waves
- Wave V/I amplitude ratio
- Interaural amplitude comparisons
Abnormal Patterns
- Peripheral Hearing Loss
- Delayed absolute latencies
- Normal interpeak latencies
- Preserved wave morphology
- Retrocochlear Pathology
- Prolonged interpeak latencies
- Abnormal wave morphology
- Interaural timing differences
- Brainstem Dysfunction
- Missing late waves
- Abnormal wave V/I ratio
- Inconsistent replication
