Auditory evoked responses under total spinal anesthesia in rats

Area of Science:

• Neuroscience
• Anesthesiology
• Auditory System Physiology

Background:

• Understanding the impact of total spinal anesthesia on the auditory pathway is crucial for patient monitoring.
• The auditory brain stem response (ABR) is a sensitive indicator of neural function in the auditory pathway.

Purpose of the Study:

• To investigate the effects of total spinal anesthesia on the auditory pathway from the cochlea to the brain stem.
• To assess the reversibility of anesthetic effects on auditory evoked potentials.
• To determine if cochlear function is compromised under total spinal anesthesia.

Main Methods:

• Simultaneous recording of auditory brain stem response (ABR), compound action potential of the cochlear nerve (CAP), and cochlear microphonics (CM) in rats.
• Induction of total spinal anesthesia using continuous infusion of 2% lidocaine hydrochloride into the cerebrospinal fluid.
• Monitoring of electrophysiological responses during and after anesthetic infusion.

Main Results:

• Auditory brain stem response (ABR) completely disappeared within 1.5 to 4 minutes of anesthetic infusion.
• ABR reappeared sequentially starting from wave I after cessation of anesthesia, indicating reversibility.
• Compound action potential (CAP) latency changes mirrored ABR wave I; cochlear microphonics (CM) amplitude reduced but did not disappear.

Conclusions:

• The disappearance of ABR under total spinal anesthesia is attributed to anesthetic effects on the acoustic nerve and brain stem, not cochlear dysfunction.
• Auditory brain stem response monitoring can provide valuable information on brain stem neural activity levels during total spinal anesthesia.
• The auditory pathway's function can be preserved during anesthesia, with ABR serving as a key indicator of neural integrity.