Effect of Tympanostomy Tube Placement on Intraoperative Auditory Brainstem Response.

BACKGROUND: Intraoperative auditory brainstem response (ioABR) testing under general anesthesia is commonly performed on children when sleep-deprived ABR and behavioral testing are not reliable or feasible. Several studies have reported potential confounding results when tube insertion is combined with ABR testing. PURPOSE: This article evaluates whether a temporary threshold shift (TTS) occurs following placement of tympanostomy tubes (TTs) in children who undergo ioABR testing. RESEARCH DESIGN: A case-control prospective study. Patients scheduled for combined TT and ioABR procedures were enrolled into this study. STUDY SAMPLE: Twenty children (38 ears), ranging in age from 6 months to 10.5 years, were enrolled. DATA COLLECTION AND ANALYSIS: ABR thresholds for tone bursts with center frequencies of 2 and 4 kHz were compared before and after tube insertion. The indication for surgery, comorbidities, and status of the middle ear were also recorded. A paired t-test was used to determine statistical significance. RESULTS: Data collection did not necessarily indicate suctioning and tube placement were causing a TTS; however, fluid present in the middle ear space prior to TT placement appeared to influence results. Although a paired t-test did not show statistically significant differences in ABR thresholds between groups of individuals with and without fluid and before and after tube placement, 50% of patients with mucoid fluid (two out of four patients) were noted to have 10 dB or greater worsening in ABR thresholds in two out of six ears. Twenty-nine percent of patients with serous fluid (two out of seven patients) were noted to have at least a 10 dB worsening in ABR threshold in 2 out of 10 ears. Further testing is needed to confirm these trends. CONCLUSION: This pilot study indicates that children with mucoid or serous fluid may experience worse ABR thresholds following TT insertion. ioABR testing immediately after TT tube placement and in the presence of middle ear fluid should be interpreted with caution. Additional studies with a larger sample size are needed to confirm these results.

Effects of Masker Envelope Fluctuations on the Temporal Effect.

Under certain conditions, detection thresholds in simultaneous masking improve when the onset of a short sinusoidal probe is delayed from the onset of a long masker. This improvement, known as the temporal effect, is largest for broadband maskers and is smaller or absent for narrowband maskers centered on the probe frequency. This study tests the hypothesis that small or absent temporal effects for narrowband maskers are due to the inherent temporal envelope fluctuations of Gaussian noise. Temporal effects were measured for narrowband noise maskers with fluctuating ("fluctuating maskers") and flattened ("flattened maskers") temporal envelopes as a function of masker level (Exp. I) and in the presence of fluctuating and flattened precursors (Exp. II). The temporal effect was absent for fluctuating narrowband maskers and as large as ~ 7 dB for flattened narrowband maskers. The AC-coupled power of the temporal envelopes of precursors and maskers accounted for 94 % of the variance in probe detection thresholds measured with fluctuating and flattened precursors and maskers. These results suggest that masker temporal envelope fluctuations contribute to the temporal effect and should be considered in future modeling efforts.