Effects of the depth of anesthesia on distortion product otoacoustic emissions

Abstract

To analyze the effects of the depth of anesthesia on inner ear function measured with distortion product otoacoustic emissions (DPOAEs) at 2f 1 - f 2. Thirty patients who underwent tonsillectomy under general anesthesia (GA) were included. Patients were assigned randomly to one of two groups: group 1 (n = 15) received propofol, group 2 (n = 15) sevoflurane as anesthetic agent. The sedation level was assessed by the bispectral index system. DPOAE measurements were performed before premedication (T 1), 5 min after premedication (T 2), 3 min after induction of general anesthesia (T 3) and every 10 min (T 4, T 5) thereafter until the end of surgery at about 23 min post-anesthetic induction, while sedation levels were obtained starting at the beginning until the end of anesthesia. After premedication, both blood oxygen saturation and heart rate decreased. Following induction of anesthesia systolic and diastolic blood pressure decreased, while, as expected, the level of sedation increased. Analyzing the propofol and sevoflurane group separately, both groups showed comparable overall courses of DPOAE levels at higher frequencies (2.8 kHz p = 0.310, 4 kHz p = 0.193, 6 kHz p = 0.269, 8 kHz p = 0.223) and no changes of DPOAE levels compared with baseline values were observed. At T5 the 1 kHz DPOAE level increased in the propofol group and slightly decreased in the sevoflurane group (p < 0.001). While the 1.4 kHz DPOAE level in the propofol group did not change over time the 1.4 kHz DPOAE level decreased in the sevoflurane group (baseline to T 4 p = 0.045; Baseline to T 5 p = 0.004). While overall there were different courses between these two groups in the 2 kHz DPOAE level, in the post hoc analysis only a tendency in the change from baseline to T 4 could be observed (p = 0.082). These results indicate that while the amplitudes of certain DPOAEs were influenced by GA, the depth of anesthesia had no effect on this measure of cochlear function in clinical routine. Therefore, DPOAE measurements in sedation and during GA are useful but the effect of anesthetic agents on DPOAE levels needs to be taken into account when analyzing the test.