A novel technique for safe intraoperative perilymph sampling in humans

To calibrate nylon epidural catheters against glass capillaries for obtaining reliable volume yields and present the development and implementation of a translatable human perilymph sampling methodology which minimally impacts cochlear function.

Two gauges of nylon epidural catheters were calibrated against glass capillary tubes to establish the minimum fluid column height to yield a desired sample volume. We also report development of a proposed surgical methodology for in vivo sampling, and implementation in a clinical cohort study of cochlear implant recipients. We assessed the impact of sampling on hearing in a subset of hearing preservation candidates.

Correlation equations for both 18G and 16G catheters yielding a desired sample volume ‘x’ with a fluid column height ‘y’. The equations for 18G and 16G catheters respectively are y = 6.538x + 1.0894 and 3.8008x + 0.6754. A sampling apparatus consisting of an epidural catheter passed through a house suction tip attached to a 1 mL syringe provides optimal ergonomics and manoeuvrability. Extracochlear ECochG amplitudes and thresholds are unaffected by collection of perilymph using this technique, as were 3-month hearing preservation outcomes.

These results describe a safe, accurate and transferrable alternative to using glass capillaries to sample directly from the human inner ear during surgery.