Autoregulation of Human Inner Ear Blood Flow During Middle Ear Surgery with Propofol or Isoflurane Anesthesia During Controlled Hypotension

The effect of propofol infusion with topical epinephrine on cochlear blood flow and hearing: An experimental study

BACKGROUND AND OBJECTIVE

Propofol is the most commonly used intravenous (IV) anesthetic agent and is associated with hypotension upon induction of anesthesia. Intravenous propofol infusion has several properties that may be beneficial to patients undergoing middle ear surgery. Topical application of concentrated epinephrine is a valuable tool for achieving hemostasis in the middle ear and during mastoid surgery. The purpose of the present study was to determine the effects of propofol infusion with topical epinephrine on cochlear blood flow (CBF) and hearing in rats.

MATERIALS AND METHODS

Twenty one male Sprague-Dawley rats were divided into three groups. The rate of intravenous infusion of propofol was 4-6 ml/kg/hour. The first group (control group, n = 7) was given IV infusion of phosphate buffered saline (PBS) with topical application of PBS in the round window. In study group A (n = 7), the effect of topical phosphate buffered saline with IV infusion of propofol on CBF and hearing was evaluated. In study group B (n = 7), additional effects of topical epinephrine with IV infusion of propofol on CBF and hearing were evaluated. The laser Doppler blood flowmeter, CBF, and the mean arterial blood pressure (MAP) were measured and analyzed. Additionally, hearing test using auditory brainstem response (ABR) was performed in both groups.

RESULTS

In both groups, infusion of propofol induced a time-dependent decrease in MAP. Approximately 30 min after the start of the propofol infusion, the CBF started to decrease slowly. The decrease in CBF was significantly greater in the study group compared to the control group. The threshold was elevated in the study group relative to the control group.

CONCLUSION

During middle ear surgery, use of IV infusion of propofol with topical epinephrine cotton ball or cottonoid application is not recommended.

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.

Different effects of propofol and isoflurane on cochlear blood flow and hearing function in Guinea pigs

Objectives

To investigate the effects of isoflurane and propofol on mean arterial pressure (MAP), cochlear blood flow (CoBF), distortion-product otoacoustic emission (DPOAE), and the ultrastructure of outer hair cells (OHCs) in guinea pig cochleae.

Methods

Forty-eight male guinea pigs were randomly assigned to one of six treatment groups. Groups 1 to 3 were infused (i.v.) with a loading dose of propofol (5 mg/kg) for 5 min and three maintenance doses (10, 20, or 40 mg kg⁻¹·h⁻¹, respectively) for 115 min. Groups 4 to 6 were inhaled with isoflurane at concentrations of 1.15 vol%, 2.30 vol% or 3.45 vol% respectively for 120 min. CoBF and MAP were recorded prior to and at 5 min intervals during drug administration. DPOAE was measured before, immediately after, and 1 h after administration. Following the final DPOAE test, cochleae were examined using scanning electron microscopy.

Results

Propofol treatment reduced MAP in a dose-dependent manner. CoBF and DPOAE showed increases at propofol maintenance doses of 10 and 20 mg kg⁻¹·h⁻¹. Inhalation of isoflurane at concentrations of 2.30 vol% and 3.45 vol% reduced MAP and CoBF. DPOAE amplitude increased following inhalation of 1.15 vol% isoflurane, but decreased following inhalations of 2.30 vol% and 3.45 vol%. Cochlear structure was changed following inhalation of either 2.30 vol% or 3.45 vol% isoflurane.

Conclusions

Propofol could decrease MAP and increase both CoBF and DPOAE without affecting OHC structure. Inhalation of isoflurane at concentrations >2.30 vol% decreased CoBF and DPOAE, and produced injury to OHCs.

Gender differences in myogenic regulation along the vascular tree of the gerbil cochlea

Regulation of cochlear blood flow is critical for hearing due to its exquisite sensitivity to ischemia and oxidative stress. Many forms of hearing loss such as sensorineural hearing loss and presbyacusis may involve or be aggravated by blood flow disorders. Animal experiments and clinical outcomes further suggest that there is a gender preference in hearing loss, with males being more susceptible. Autoregulation of cochlear blood flow has been demonstrated in some animal models in vivo, suggesting that similar to the brain, blood vessels supplying the cochlea have the ability to control flow within normal limits, despite variations in systemic blood pressure. Here, we investigated myogenic regulation in the cochlear blood supply of the Mongolian gerbil, a widely used animal model in hearing research. The cochlear blood supply originates at the basilar artery, followed by the anterior inferior cerebellar artery, and inside the inner ear, by the spiral modiolar artery and the radiating arterioles that supply the capillary beds of the spiral ligament and stria vascularis. Arteries from male and female gerbils were isolated and pressurized using a concentric pipette system. Diameter changes in response to increasing luminal pressures were recorded by laser scanning microscopy. Our results show that cochlear vessels from male and female gerbils exhibit myogenic regulation but with important differences. Whereas in male gerbils, both spiral modiolar arteries and radiating arterioles exhibited pressure-dependent tone, in females, only radiating arterioles had this property. Male spiral modiolar arteries responded more to L-NNA than female spiral modiolar arteries, suggesting that NO-dependent mechanisms play a bigger role in the myogenic regulation of male than female gerbil cochlear vessels.

Co-administration of cisplatin and furosemide causes rapid and massive loss of cochlear hair cells in mice

The expanding arsenal of transgenic mice has created a powerful tool for investigating the biological mechanisms involved in ototoxicity. However, cisplatin ototoxicity is difficult to investigate in mice because of their small size and vulnerability to death by nephrotoxicity. To overcome this problem, we developed a strategy for promoting cisplatin-induced ototoxicity by coadministration of furosemide a loop diuretic. A dose-response study identified 200 mg/kg of furosemide as the optimal dose for disrupting the stria vascularis and opening the blood-ear barrier. Our analysis of stria pathology indicated that the optimal period for administering cisplatin was 1 h after furosemide treatment. Combined treatment with 0.5 mg/kg of cisplatin and 200 mg/kg furosemide resulted in only moderate loss of outer hair cells in the basal 20% of the cochlea, only mild threshold shifts and minimal loss of distortion product otoacoustic emission (DPOAE). In contrast, 1 mg/kg of cisplatin plus 200 mg/kg of furosemide resulted in a permanent 40-50 dB elevation of auditory brainstem response thresholds, almost complete elimination of DPOAE, and nearly total loss of outer hair cells. The widespread outer hair cell lesions that develop in mice treated with cisplatin plus furosemide could serve as extremely useful murine model for investigating techniques for regenerating outer hair cells, studying the mechanisms of cisplatin and furosemide ototoxicity and assessing the perceptual and electrophysiological consequences of outer hair cell loss on central auditory plasticity.

Hypotensive anaesthesia with remifentanil combined with desflurane or isoflurane in tympanoplasty or endoscopic sinus surgery: a randomised, controlled trial

Objective:

To compare the effect of remifentanil combined with desflurane or isoflurane on the quality of the operative field and surgical conditions, blood loss, and recovery during tympanoplasty or endoscopic sinus surgery.

Design:

Randomised, double-blinded clinical study.

Subjects:

Sixty-four patients were scheduled for elective tympanoplasty or endoscopic sinus surgery. The patients were randomly divided into two groups: desflurane or isoflurane. After anaesthesia induction, all patients received a continuous remifentanil infusion of 0.2–0.5 µg/kg/min until a mean arterial pressure of 65–75 mmHg was achieved. Heart rate and mean arterial pressure were recorded throughout anaesthesia. Blood loss was measured at the end of surgery. Achievement of a bloodless operative field was rated on a 100 mm visual analogue scale. Following completion of surgery, the time to extubation and to achievement of an Aldrete score of nine or more was recorded.

Results:

Sixty-three patients were evaluated. The total dose of remifentanil and the total blood loss were similar in both groups (p > 0.05). Time to extubation and to an Aldrete score of nine or more for the desflurane group was significantly less than for the isoflurane group (p < 0.05). No differences were found in the extent of achievement of a bloodless operative field, as assessed via visual analogue scale, comparing the study groups (p > 0.05).

Conclusion:

Although desflurane and isoflurane both enabled good surgical conditions (in terms of quality of operative field) and convenient induction of hypotension for tympanoplasty and endoscopic sinus surgery, the recovery characteristics of desflurane were better than those of isoflurane. Therefore, desflurane may be preferable to isoflurane in such circumstances.

Blood flow measurements in the ears of patients receiving cochlear implants

We measured cochlear blood flow in 12 patients who received cochlear implants, using a laser-Doppler probe with an outer diameter of 0.8 mm. The subjects had congenital deafness, idiopathic progressive sensorineural hearing loss, Waardenburg's syndrome, narrow internal auditory canal, or sudden deafness. Putting the probe tip to the site of drilling for cochlear implantation, we measured blood flow before, during, and after the cochlear bony wall was opened. The laser-Doppler output was confirmed even after the tip of the probe was inserted into the perilymphatic space in all cases. Our results revealed that blood flow was maintained in all cochleas, although there was a probability of reduction in blood flow volume. We conclude that laser-Doppler flowmetry is both relatively safe and useful for measuring blood flow in the ears during cochlear implantation procedures.

The influence of hypothermia on outer hair cells of the cochlea and its efferents

Transient evoked otoacoustic emissions (TEOAE) were recorded in 21 guinea-pigs undergoing hypothermia. The minimal average body temperature during cooling was 26 degrees C/24.9 degrees C measured orally or rectally, respectively. The animals were subsequently warmed to normal body temperature. A clear influence of body temperature on TEOAE could be documented. During cooling the amplitude and reproducibilities decreased, disappearing completely at a mean temperature below 28.5 degrees C (oral) and 27.3 degrees C (rectal). The emissions reappeared during rewarming at a mean temperature of 30.1 degrees C (oral) and 30.8 degrees C (rectal). Contralateral auditory stimulation (CAS) led to a decrease of the amplitudes of TEOAE during cooling down to a mean of 33 degrees C/32 degrees C (oral/rectal temperature). During rewarming, influences of the CAS could be recognized, again at an oral temperature above 35 degrees C. The changes to the TEOAE observed in these experiments suggest that hypothermia affects not only the outer hair cells (OHC) of the cochlea but also the efferent supply to the cochlea.