Acoustic reflex as a predictor of middle ear effusion

The comparative efficacy of tympanometry and the acoustic reflex (threshold and supraliminal amplitude) in predicting the presence of fluid in the middle ear was studied just before myringotomy in 50 children (99 ears) prior to adenoidectomy. Impedance audiometry was carried out under a general anesthetic (ketamine and nitrous oxide) in 60%, and without anesthesia in 40% of the cases. The comparative efficacy of this test was assessed using objective criteria which were independent of the cut-off point between normal and abnormal groups. The prediction efficacy of acoustic reflex threshold and amplitude (Youden's index = 0.58) was superior to that of tympanometry peak amplitude and pressure (Youden's indexes = 0.29 and 0.36). The efficacy of the gradient was 0.41. Modifications due to anesthesia were not statistically significant for the whole group, but temporary abolition of the acoustic reflex at the start of anesthesia is probably related to the high percentage of false positives noted when the acoustic reflex is used alone in patients given a general anesthetic.