Effect of anesthesia on transient evoked otoacoustic emissions in humans: a comparison between propofol and isoflurane

Gas Anesthesia Impairs Peripheral Auditory Sensitivity in Barn Owls (Tyto alba)

Auditory nerve single-unit recordings were obtained from two groups of young barn owls (age, between posthatching days 11 and 86) in terminal experiments under two different anesthetic regimes: ketamine (6-11 mg/kg) plus xylazine (∼2 mg/kg); or isoflurane (1-1.5%) in oxygen, delivered via artificial respiration. In a second series of minimally invasive experiments, auditory brainstem responses (ABRs) were recorded in the same four adult barn owls (Tyto alba; age, between 5 and 32 months) under three different anesthetic protocols: ketamine (10 mg/kg) plus xylazine (3 mg/kg), isoflurane (1-1.5%), and sevoflurane (2-3%) in carbogen. Finally, the ABR measurements on adult owls were repeated in terminal experiments including more invasive procedures such as artificial respiration and higher isoflurane dosage. The main finding was a significant deterioration of auditory sensitivity in barn owls under gas anesthesia, at the level of the auditory nerve (i.e., a very peripheral level of the auditory system). The effect was drastic in the young animals that experienced threshold elevations in auditory nerve single-unit responses of ≥20 dB. ABR thresholds assessed repeatedly in experiments on adult owls were also significantly higher under isoflurane and sevoflurane, on average by 7 and 15 dB, compared with ketamine/xylazine. This difference already occurred with minimal dosages and was reversibly enlarged with increased isoflurane concentration. Finally, there was evidence for confounding detrimental effects associated with artificial respiration over many hours, which suggested oxygen toxicity.

Comparison of anesthetic agents on otoacoustic emissions in children: propofol vs ketamine

BACKGROUND

Otoacoustic emission (OAE) tests are important evaluation tools for diagnosis of peripheral auditory pathology. Sedation or general anesthesia may be required for the performance of the OAE tests. The aim of this retrospective study was to compare the effects of anesthetic agents, propofol and ketamine, on OAEs in children.

METHODS

Fifty healthy children who underwent tonsillectomy and/or adenoidectomy under general anesthesia were included in this study. Three anesthesia induction protocols were defined for this study and the anesthesiologist applied his or her own choice. Transient evoked otoacoustic emissions (TEOAEs) and distortion-product otoacoustic emissions (DPOAEs) were automatically recorded in both ears of each patient prior to anesthetic (predrug) and following the loss of consciousness 5 min later (postdrug) by an audiologist blinded to the method of anesthesia. Acceptable TEOAEs were defined as signal noise ratio (S/N) of above 3 dB SPL (decibel sound pressure level) and DPOAEs of 6 dB SPL or above. Between-group and within-group comparisons and correlations were performed for statistical analysis.

RESULTS

Retrospective review of the anesthesia charts from 44 cases that completed the study showed that propofol, ketamine, and sevoflurane induction protocols were used in 21, 18, and 5 cases, respectively. Measurements of 36 ears in the propofol group and 34 ears in the ketamine group were included in the final analysis. Postdrug TEOAE and DPOAE amplitudes were significantly lower than predrug amplitudes except at 8 kHz in the ketamine group. There was no significant statistical difference in postdrug DPOAE measurements between propofol and ketamine groups but a significant difference was observed at 2 and 3 kHz of postdrug TEOAE measurements. TEOAE measurements were below 3 dB in 8 of 34 ears after ketamine and in 1 of 36 ears after propofol administration. There was a significant difference between the groups with respect to the incidence of successful measurements of TEOAEs. The DPOAE measurements were affected less by these drugs.

CONCLUSION

DPOAE measurements were reduced similarly by propofol and ketamine anesthesia. Lower false outcome ratio in TEOAE measurements made propofol a better option than ketamine.

The effects of hypotensive anaesthesia on otoacoustic emissions: a prospective, randomized, double-blind study with objective outcome measures

The aim of the present study was to compare pre- and post-operative otoacoustic emission examinations of patients who experienced surgery under hypotensive anaesthesia using distortion product otoacoustic emission (DPOAE) and transient evoked otoacoustic emission (TEOAE). Forty-one patients, admitted to our tertiary centre for nasal valve surgery, were prospectively and randomly assigned into two groups. Hypotensive group included 20 patients, while control group included 21 patients. All investigators and patients were blinded to anaesthesia assignment throughout the course of the study. DPOAEs and TEOAEs were performed before surgery and repeated after 15 days in both groups. In control group, DPOAE-DP1 levels per frequency increased significantly in the post-operative period when compared with the pre-operative values in all patients. However, DPOAE-DP1 levels decreased significantly in hypotensive group. Similarly, DPOAE-SNR levels per frequency decreased significantly in hypotensive group. In conclusion, we have observed that under the influence of hypotensive general anaesthesia, the amplitudes of OAEs are affected.

Influence of dose and duration of isoflurane anesthesia on the auditory brainstem response in the rat

OBJECTIVE

Isoflurane anesthesia can have significant effects on processing of sounds at the peripheral and central levels, manifesting in changes in auditory-evoked potentials. The current study tested whether duration of isoflurane anesthesia changes thresholds, amplitudes, and latencies of the auditory brainstem response (ABR).

DESIGN

The study tested ABRs in a rat animal model under isoflurane anesthesia. Study variables were duration of isoflurane anesthesia, stimulus frequency, stimulus level, and the dose of isoflurane. Rats were anesthetized with 1.5% or 2% isoflurane. ABRs were collected from 90 to 5 dB SPL at 5-40 kHz. Three full ABR series were collected over a 105-minute period. Thresholds were assigned, and ABR wave amplitudes and latencies were measured at each stimulus frequency and level.

STUDY SAMPLE

Ten Sprague-Dawley rats were tested in a repeated measures design.

RESULTS

Statistical analyses revealed no significant effects of dose or duration on threshold, but a series of significant interactions between test variables for the amplitude and latency measurements.

CONCLUSIONS

In the rat, dose and duration of isoflurane anesthesia induced inconsistent changes in latency and amplitude of the ABR. At 40 kHz, isoflurane dose had more powerful effects on latency and amplitude than occurred at other frequencies.

Clinical evaluation of cochlear hearing status in dogs using evoked otoacoustic emissions

OBJECTIVES

Evoked otoacoustic emission testing is the preferred test in human patients for sensorineural deafness screening in neonates and cochlear outer hair cell function monitoring in adults. This study evaluated evoked otoacoustic emission testing for cochlear function assessment in dogs within a clinical setting.

METHODS

Two populations of anaesthetised dogs were included. In group 1 the evoked otoacoustic emission response was compared to the brainstem auditory evoked response in 10 dogs having hearing assessment. Group 2 comprised 43 presumed normal dogs, in which the suitability of two types of evoked otoacoustic emissions, transient-evoked and distortion product otoacoustic emissions, were evaluated (brainstem auditory evoked response was not performed in this group).

RESULTS

Valid transient-evoked otoacoustic emission and distortion-product otoacoustic emission responses were successfully recorded within the clinical setting and correctly identified deaf and hearing ears. Within presumed healthy dogs, normal otoacoustic emission response was demonstrated in more than 80% of dogs using a single, short distortion-product otoacoustic emission run and in 78% of dogs with valid transient-evoked otoacoustic emission responses using a series of three repeated transient-evoked otoacoustic emission short runs.

CLINICAL SIGNIFICANCE

Transient-evoked otoacoustic emission and distortion-product otoacoustic emission testing provided a rapid, non-invasive frequency-specific assessment of cochlear function. Transient-evoked otoacoustic emission and distortion product otoacoustic emission testing is suitable as a screening procedure to detect loss of cochlear function in dogs, although further investigation is needed.

A comparison of the effects of isoflurane and ketamine anesthesia on auditory brainstem response (ABR) thresholds in rats

The auditory brainstem response (ABR) is an acoustically evoked potential commonly used to determine hearing sensitivity in laboratory animals. Both isoflurane and ketamine/xylazine anesthesia are commonly used to immobilize animals during ABR procedures. Hearing threshold determination is often the primary interest. Although a number of studies have examined the effect of different anesthetics on evoked potential waveforms and growth functions, none have directly compared their effect on ABR hearing threshold estimates. The present study used a within-subject comparison and typical threshold criteria, to examine the effect of isoflurane and ketamine/xylazine on ABR thresholds for clicks and pure-tone stimuli extending from 8 to 32 kHz. At comparable physiological doses, hearing thresholds obtained with isoflurane (1.7% in O(2)) were on average elevated across a broad frequency range by greater than 27 dB compared to ketamine/xylazine (ketamine HCl, 50mg/kg; xylazine, 9 mg/kg). This highly significant threshold effect (F(1,6) = 158.3403, p = 3.51 × 10(-22)) demonstrates a substantial difference between general anesthetics on auditory brainstem sensitivity. Potential mechanisms and implications for ABR threshold determination under anesthesia are discussed.

Effect of isoflurane on the hearing in mice

Background and Objectives

The aim of this study was to investigate the relationship between inhalation anesthetics and hearing in mice.

Materials and Methods

As inhalation anesthetics, isoflurane was used. Auditory brainstem response and distortion product otoacoustic emission were used as measurement of hearing. Mice were divided into 2 groups. 'Isoflurane group' consisted of mice that were anesthetized with an inspired concentration of 2.0 vol% isoflurane with 2 L/min of oxygen (n=10). 'Control group' consisted of mice that were anesthetized with ketamine and xylazine (n=10).

Results

Auditory brainstem response thresholds in mice anesthetized with ketamine and xylazine was not different from those in mice anesthetized with isoflurane. Threshold of DPOAE was higher in mice with isolurane than with ketamine and xylazine. Changes of efferent control may be induced by isoflurane and consequently change the threshold of DPOAE in mice.

Conclusions

These results infer that, there was a change of central nervous system induced by inhalation anesthetics, this change also can be applied to the strategies for prevention of hearing loss.

Bilateral dorsal cochlear nucleus lesions prevent acoustic-trauma induced tinnitus in an animal model

Animal experiments suggest that chronic tinnitus (“ringing in the ears”) may result from processes that overcompensate for lost afferent input. Abnormally elevated spontaneous neural activity has been found in the dorsal cochlear nucleus (DCN) of animals with psychophysical evidence of tinnitus. However, it has also been reported that DCN ablation fails to reduce established tinnitus. Since other auditory areas have been implicated in tinnitus, the role of the DCN is unresolved. The apparently conflicting electrophysiological and lesion data can be reconciled if the DCN serves as a necessary trigger zone rather than a chronic generator of tinnitus. The present experiment used lesion procedures identical to those that failed to decrease pre-existing tinnitus. The exception was that lesions were done prior to tinnitus induction. Young adult rats were trained and tested using a psychophysical procedure shown to detect tinnitus. Tinnitus was induced by a single unilateral high-level noise exposure. Consistent with the trigger hypothesis, bilateral dorsal DCN lesions made before high-level noise exposure prevented the development of tinnitus. A protective effect stemming from disruption of the afferent pathway could not explain the outcome because unilateral lesions ipsilateral to the noise exposure did not prevent tinnitus and unilateral lesions contralateral to the noise exposure actually exacerbated the tinnitus. The DCN trigger mechanism may involve plastic circuits that, through loss of inhibition, or upregulation of excitation, increase spontaneous neural output to rostral areas such as the inferior colliculus. The increased drive could produce persistent pathological changes in the rostral areas, such as high-frequency bursting and decreased interspike variance, that comprise the chronic tinnitus signal.

Effects of isoflurane on auditory evoked potentials in the cochlea and brainstem of guinea pigs

Electrophysiological recordings of the auditory system are commonly performed in deeply anesthetized animals. This study evaluated the effects of various concentrations of the volatile anesthetic isoflurane (1-3%) on the compound action potential (CAP), cochlear microphonic (CM) and auditory brainstem response (ABR). Recordings were initiated in the awake, lightly restrained animal. Anesthesia was induced with a single dose of Hypnorm (fentanyl and fluanisone). After tracheostomy increasing isoflurane concentrations were applied in N(2)O/O(2) via controlled ventilation. Data were compared to recordings in the awake animal using repeated measures ANOVA and Dunnett's post hoc test. On average, isoflurane dose-dependently suppressed the amplitude and increased the latency of the CAP. CM amplitude was suppressed. These effects were most profound at high frequencies and were typically significant at isoflurane concentrations of 2.5% and 3%. Amplitude and latency of the second negative peak of the CAP (N(2)) were affected to a greater extent compared to the first peak (N(1)). On average, isoflurane dose-dependently reduced the amplitude and increased the latency of the ABR. These effects were typically significant at an isoflurane concentration of 2%. Effects on peak IV and V were more pronounced compared to the early peaks I and III.

Evaluation of anesthesia effects in a rat animal model using otoacoustic emission protocols

Anesthesia effects on otoacoustic emission (OAE) recordings were evaluated in a group of 72 Sprague-Dawley rats (mean weight 225+/-20 gr). Two anesthesia dosages (high and normal) and two anesthetic protocols (ketamine-xylazine, ketamine-xylazine-atropine) were tested. Transient evoked OAE (TEOAE) and distortion product OAE (DPOAE) responses were recorded in 10 min intervals, for a total period of 60 min. Analyses of the data with repeated measure models indicated the following: (1) The animals receiving a high dose of anesthesia (cumulative dose 66.6 mg of ketamine and 13.2 mg of xylazine/kg of body weight) presented significant alterations of the TEOAE response level and the signal to noise ratio at 3.0 kHz; (2) the animals receiving a normal dose of ketamine-xylazine anesthesia (cumulative dose 50 mg of ketamine and 10 mg of xylazine/kg of body weight) presented TEOAE and DPOAE responses invariant in terms of time; (3) significant differences were observed in the DPOAE responses from animals anesthetized with ketamine-xylazine and ketamine-xylazine-atropine. The data support the hypothesis that the ketamine anesthesia OAE suppressing mechanism is related to middle-ear mechanics.

Autoregulation of human inner ear blood flow during middle ear surgery with propofol or isoflurane anesthesia during controlled hypotension

We used controlled hypotension to obtain a bloodless cavity during middle ear surgery under an optical microscope. No previous study has assessed the effect of controlled hypotension on inner ear blood flow (IEF) autoregulation in humans receiving propofol or isoflurane anesthesia. In the present study, the IEF autoregulation was determined using laser Doppler flowmetry in combination with transient evoked otoacoustic emissions (TEOAEs) during controlled hypotension with sodium nitroprusside in 20 patients randomly anesthetized with propofol or isoflurane. A coefficient of IEF autoregulation (Ga) was determined during controlled hypotension, with a Ga value ranging between 0 (no autoregulation) and 1 (perfect autoregulation). During controlled hypotension with propofol, IEF remained stable (1%+/-6%; P > 0.05) but decreased by 25%+/-8% with isoflurane (P < 0.05). The Ga was higher during propofol anesthesia (0.62+/-0.03) than during isoflurane anesthesia (0.22+/-0.03; P < 0.0001). Under propofol anesthesia, there were individual relationships between TEOAE amplitude and change in IEF in four patients. Such a correlation was not observed under isoflurane anesthesia. These results suggest that human IEF is autoregulated in response to decreased systemic pressure. Furthermore, isoflurane has a greater propensity to decrease cochlear autoregulation and function than propofol.

IMPLICATIONS

The present study shows that inner ear blood flow is autoregulated under propofol, but not isoflurane, anesthesia during controlled hypotension in humans during middle ear surgery. Further studies are needed to explore the postoperative auditory functional consequences of the choice of the anesthetic drug used in middle ear surgery.