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Effect of total intravenous vs volatile anesthetics on intraoperatively acquired electrically evoked compound action potential in children undergoing cochlear implant surgery: A randomized prospective study
Journal of Clinical Anesthesia 36 (2017) 80–83
Contents lists available at ScienceDirect
Journal of Clinical Anesthesia
Original contribution
Effect of total intravenous vs volatile anesthetics on intraoperatively acquired electrically evoked compound action potential in children undergoing cochlear implant surgery: A randomized prospective study Ala”a Alhowary, MD, Assistant Professor a,⁎, Khaled EL-Radaideh, FFA, Associate Professor a, Anas AL-Rusan, MBBS, Resident a, Diab Bani Hani, MD, Assistant Professor a, Wail Khraise, MD, Assistant Professor a, Ahmad AL Omari, FACS, Assistant Professor b, Firas Alzoubi, FRRC, Professor b a b
Department of Anesthesiology, Faculty of Medicine, Jordan University of Science and Technology, PO Box 953, Irbid 21110, Jordan Division of Otolaryngology, Department of Special Surgery, Faculty of Medicine, Jordan University of Science and Technology, PO Box 3030, Irbid 22110, Jordan
a r t i c l e
i n f o
Article history: Received 21 April 2016 Accepted 27 October 2016 Available online xxxx Keywords: Anesthesia Cochlear Evoked potentialsImplants General Implants Intravenous
a b s t r a c t Objective: The purpose of the present study was to compare the effects of inhalational anesthesia to those of total intravenous anesthesia on intraoperative electrically evoked compound action potential (e-ECAP) thresholds in children undergoing cochlear implantation. Study design: Randomized prospective study. Setting: Tertiary referral teaching hospital. Patients: Forty children aged 6 months to 17 years with bilateral severe-to-profound sensorineural hearing loss and undergoing cochlear implantation were enrolled in the study. Intervention: Patients were randomly assigned (1:1 ratio) into 2 groups to receive inhalational or total intravenous anesthesia. Measurements: The e-ECAP measurements were obtained with neural response telemetry software. Main results: All electrodes showed lower e-ECAP thresholds under propofol, and results were statistically significant for the apical electrodes (P b .05). There was no statistical difference in the impedances between the 2 groups. Propofol minimally affected the e-ECAP. In contrast, the impedance was not affected by anesthesia. Conclusion: Volatile anesthetics result in higher e-ECAP thresholds in children, suggesting that e-ECAP thresholds acquired during inhalational anesthesia overestimate auditory nerve stimulation levels, which may cause discomfort postoperatively and adversely affect the child's adaptation to the implant. We recommend the use of total intravenous anesthesia for the measurement of the e-ECAP thresholds during cochlear implant surgery. © 2016 Elsevier Inc. All rights reserved.
1. Introduction Successful cochlear implantation depends on appropriate postoperative programming of the speech processor, as the sound characteristics depend on this programming. Excitation of the auditory nerve with a progressive increase in energy intensity is essential to detect the hearing threshold (T level) as well as the maximum intensity allowed without discomfort (C level) through subjective psychophysical tasks [1,2]. ⁎ Corresponding author. Faculty of Medicine, Jordan University of Science and Technology, PO Box 953, Irbid 21110, Jordan. Tel.: +1 962 0 795770906; fax: +1 962 2 7200621. E-mail addresses: [email protected] (A.” Alhowary), [email protected] (K. EL-Radaideh), [email protected] (A. AL-Rusan), [email protected] (D.B. Hani), [email protected] (W. Khraise), [email protected] (A. AL Omari), fi[email protected] (F. Alzoubi).
http://dx.doi.org/10.1016/j.jclinane.2016.10.008 0952-8180/© 2016 Elsevier Inc. All rights reserved.
This task is challenging, particularly in infants and young children, because of limited communication capabilities and lack of auditory experience. There is a pressing need for objective methods that require minimal cooperation of the patient in the programming of the cochlear implant's speech processor and that do not rely solely on behavioral loudness judgments to determine the hearing dynamic range in small children. A range of different electrophysiological measures can be used for this purpose, namely, intraoperative electrode impedance measurement, electrically evoked stapedial reflex, and electrically evoked compound action potential (e-ECAP) [3,4]. At our center, we commonly use e-ECAP thresholds and electrode impedance measurement for guiding implant setting [5,6]. The e-ECAP thresholds are a measure of the activity of synchronous cochlear nerve fibers, which is elicited by electrical stimulation of the cochlear implant, and are determined using neural response telemetry
A.” Alhowary et al. / Journal of Clinical Anesthesia 36 (2017) 80–83
(NRT) software that can be used to objectively fit the sound processing system [7]. Impedance measurement is intended to ascertain the technical status of the implant's stimulator and electrodes [6,8]. The e-ECAP recordings can be made intraoperatively or postoperatively. When done intraoperatively, the child is still under general anesthesia. This allows the clinician to apply high stimulation levels, which results in a high success rate of recording e-ECAP responses [9]. In this situation, knowledge of the effects of anesthetics on these objective measures is important to optimize the outcome of pediatric cochlear implantation. An ideal anesthetic technique for cochlear implant surgery is one that has no effect on the evoked auditory responses that were measured. Several studies that have investigated the influence of anesthesia on electrically elicited stapedius reflex threshold measurements revealed that the total intravenous anesthesia (TIVA) gives more consistent responses than volatile anesthetics [4,7], but there are insufficient data in the literature concerning its effect on e-ECAP. It has been suggested that the depth of anesthesia can have a significant influence on the e-ECAP threshold and it is important to reduce the depth of anesthesia to achieve better results [6]. To the best of our knowledge, no studies have been performed to compare the effect of a volatile anesthetic with that of propofol anesthesia on intraoperative e-ECAP thresholds. The aim of this study was to compare the effects of inhalational anesthesia with those of TIVA on intraoperative e-ECAP and impedance measurements in children undergoing cochlear implant surgery at our center. 2. Methods After obtaining formal approval from our institutional ethics committee, we conducted a randomized, double-blind study involving 40 patients aged 6 months to 17 years with American Society of Anesthesiologists physical status I-II who were scheduled for elective cochlear implantation surgery under general anesthesia at a tertiary referral teaching hospital. All these patients had bilateral severe-to-profound sensorineural hearing loss. Children with compromised neural/cochlear anatomy were excluded. Implantations were performed consecutively between March 2013 and March 2014. For all patients, written informed consent for participation in the study was obtained from one of the parents or the legal guardian. The patients were randomly assigned (1:1 ratio) into 2 groups based on computer-generated random numbers that were kept in a sealed envelope. Immediately before the administration of anesthesia, the sealed envelope was opened to reveal the anesthetic regimen that has to be used for this patient.
81
(4-8 mg/kg per hour), and fentanyl infusion (0.3-0.6 μm/kg per hour) titrated according to hemodynamic responses. 2.2. Neural monitoring Cochlear implants had 22 active electrodes, with electrode 22 inserted toward the apical end of the cochlea and electrode 1 at the basal end. Electrode impedance was measured using stimulation modes MP1 + 2 (the ball electrode [MP1] and plate electrode [MP2]). 2.3. Determination of the auditory thresholds Auditory thresholds were determined after insertion of the intracochlear electrode array at least 90 minutes after induction of anesthesia. All electrodes (electrodes 1-22) were tested. Current level was measured in current units (CUs) as defined by the cochlear implant programming software. Each current level step is a 0.16-dB change in current. Electrical pulse trains of 500 milliseconds were delivered in a stepwise manner, first in increments of 10 CU and subsequently in decrements of 5 CU. The NRT was measured at the electrode located 2 electrode positions apical to the stimulating electrode on the intracochlear array. An exception was made for electrodes 21 and 22 for which the recording electrodes were 19 and 20, respectively. All the measurements were made automatically by Custom Sound software (version 4, Cochlear Ltd, Sydney, Australia). The lowest level of stimulation at which a wave could be detected by the software was defined as the threshold. Both the surgeon and audiologist were blinded to the anesthetic drug. The e-ECAP measurements were obtained with the NRT software and were judged by experts who assessed the success rate of the recordings and determined the threshold level for each patient to use the records as a reference for postoperative speech processor fitting. 2.4. Statistical analysis SPSS version 18 (SPSS IBM, New York, NY) and SAS 8.1 (SAS Institute Inc, Cary, NC) were used to perform the statistical analysis. Differences between intraoperatively measured values of impedance/ e-ECAP under TIVA and under inhalational anesthesia of the 22 channels were analyzed using the unpaired t test. Data were presented as mean ± SD, percentage, or absolute number. Patient noncategorical characteristics were analyzed using analysis of variance. χ2 Tests were used for comparisons of categorical demographic data. A generalized linear model for repeated measures was used to test for differences within and between groups. Bonferroni correction was applied for all comparisons. P values less than .05 were considered statistically significant.
2.1. Anesthetic management
3. Results
The patients were not premedicated. On arrival to the operating room, standard intraoperative monitors (pulse oximetry, noninvasive arterial blood pressure, and electrocardiogram) were applied and baseline values were recorded. General anesthesia was induced with 50% oxygen in nitrous oxide and 6% sevoflurane in the patients of the inhalational group (INHAL) or propofol (3 mg/kg) in the patients of the TIVA group. An intravenous line could be secured before the induction of anesthesia followed by fentanyl administration (2 μm/kg bodyweight). Neuromuscular blockade was achieved with 0.3 mg/kg rocuronium to facilitate tracheal intubation. In group INHAL, anesthesia was maintained with 50% oxygen in nitrous oxide and 2%-3% sevoflurane administered via a pediatric circle breathing circuit, and fentanyl infusion (1 μm/kg per hour) titrated according to hemodynamic responses. Ventilation was controlled to maintain normocapnia. In group TIVA, anesthesia was maintained with 50% oxygen in nitrous oxide, propofol infusion
All operations were performed by senior surgeon (FA). The patients were kept under general anesthesia, and the operation was performed using the minimally invasive lazy S–shaped incision and double-flap, transmastoid, posterior tympanotomy technique with round window insertion. All patients received Nucleus Freedom cochlear implant devices (Cochlear Ltd), which use NRT to elicit and record responses from the auditory system. All surgeries were completed uneventfully. Complete electrode insertion was ensured in all cases by impedance and NRT and confirmed on the next day by radiologic x-ray. Our study population consisted of 40 patients. Twenty patients were enrolled in each group. The mean age of the INHAL group was 7 years and 3 months (SD = ±4.36) and that of the TIVA group was 7 years and 9 months (SD = ±4.37), which was not statistically significant (P = .58). The male-to-female ratio was 10:10 in the INHAL group and 8:12 in the TIVA group. There was no statistical difference in the impedances between the 2 groups (Fig. 1). All electrodes had lower
82
A.” Alhowary et al. / Journal of Clinical Anesthesia 36 (2017) 80–83 Table 1 The mean NRT value for each electrode in the 2 groups with statistical significance.
Fig. 1. The mean impedance measurements in both groups. INHAL = inhalational; TIVA = total intravenous anesthesia.
thresholds with TIVA (Fig. 2), with those for the basal electrodes showing statistical significance (14-22; P b .05) (Table 1). Radiologic testing was compatible with intraoperative testing of the position and depth of electrode insertion in all cases.
Electrode
Group INHAL (n = 20)
Group TIVA (n = 20)
P value
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
197.6 191.2 194.4 190.8 189.2 189.2 189.9 194.9 199.6 198.9 199.6 195.5 198.4 197.3 201.7 200.7 197.5 197.8 199.6 196.4 197.4 196.2
188 173.8 176.6 176.1 177.5 185.3 184.4 191.6 174.4 188.4 186.8 184.3 184.7 183.1 180.1 178.3 173.7 174.7 174.4 171.7 171.3 173.5
.335 .053 .029 .033 .081 .624 .455 .624 .001 .179 .071 .203 .122 .036 .006 .012 .019 .012 .007 .003 .004 .038
Data are presented as mean. INHAL = inhalational; TIVA = total intravenous anesthesia.
4. Discussion The process of cochlear implantation consists of surgical insertion of the device followed by setting of stimulation parameters for proper hearing [8]. Cochlear implant devices are able to measure e-ECAP from the auditory nerve. The system applies an electrical pulse on a given intracochlear electrode, and the evoked neural response is recorded at a neighboring electrode [6]. Each electrode directly stimulates the auditory nerve when the electrical current necessary to trigger a hearing sensation passes. The amount of electrical current necessary to trigger an auditory sensation is different for each individual and for each stimulation canal. Therefore, each user's speech processor must be individually adjusted together with each stimulation canal in a process that is called programming or mapping. In adults, power levels must be determined through psychophysical measures (behavioral method). With the progressive increase in energy intensity in each of the channels, the individual reports on the lowest intensity at which he and/or she detects the stimulus (electrical threshold) as well as the maximum intensity tolerated without discomfort. In small children, the procedure requires techniques that may be inconsistent and nonsystematic because of hearing inexperience or the child's age. Thus, sole use of the behavioral method to program the speech processor may extend the implant adaptation process because of the difficulty in establishing the right stimulation levels [2]. In small children, the e-ECAP thresholds determined using NRT while the child is anesthetized are generally necessary to assist in the initial setting of the device. Moreover, potential testing during surgery is advantageous because it can be used to verify implant and auditory
nerve integrity during surgery, confirming that the implant is functioning optimally [2,7]. The e-ECAP thresholds obtained from NRT are routinely used to program the cochlear implant, especially in children, with the aim of predicting the appropriate limits for implant stimulation setting, thus achieving an optimum dynamic range. This is very important for proper hearing and the successful use of cochlear implants [5,6,9]. Hence, it is important to evaluate the effect of anesthesia on intraoperatively acquired e-ECAP measurements. Numerous studies that have investigated the influence of anesthesia on electrically elicited stapedius reflex threshold measurement have revealed that TIVA gives more consistent responses than volatile anesthetics [4,8,10]. However, relatively few studies have directly explored the influence of anesthesia on objective measurements such as e-ECAP. Some researchers [4] studied the effect of anesthetics on intraoperative monitoring of cochlear implant function and reported that volatile anesthetics suppressed the stapedius reflex in a dosedependent manner, whereas e-ECAP was unaffected by the concentration of volatile anesthetic or propofol. However, they did not compare the effect of inhalational anesthesia and TIVA on e-ECAP thresholds. One previous study reported on the effect of TIVA on the intraoperative monitoring of cochlear implant function [8] and concluded that TIVA had no effect on determining auditory thresholds in relation to maximum comfort level values 3 months postimplantation. On the other hand, Stronks et al [11] reached the contrasting conclusion that isoflurane dose-dependently increases the threshold of auditory
Fig. 2. The mean NRT measurements in the 2 groups. INHAL = inhalational; TIVA = total intravenous anesthesia.
A.” Alhowary et al. / Journal of Clinical Anesthesia 36 (2017) 80–83
compound action potential. The same result was obtained indirectly by another study wherein e-ECAP thresholds were significantly lower (P b .001) when measured within 24 hours postoperatively than when measured intraoperatively [12]. It was suggested that neuronal sensitivity to electrical stimulation could be restored during this period, but the possible effect of anesthesia was not considered. More recently, a study reported that the depth of anesthesia can have a significant influence on the e-ECAP threshold and it is important to reduce it to achieve better results [6]. Moreover, when e-ECAP cannot be recorded by some electrodes during surgery, reduction of the depth of anesthesia may be helpful to obtain recordable results. Several studies have reported higher thresholds in the basal electrodes than in the apical electrodes [1,13-15]. Possible explanations of these findings could be that there are a smaller number of preserved vital neurons in the basal part of the cochlea, which is consistent with postmortem pathohistologic studies of the temporal bones [14]. Jeon et al [13] studied the relationship between e-ECAP thresholds and behavioral measures of perceptual dynamic range for the range of stimuli commonly used to program the speech processor. They reported a substantial amount of cross-electrode variance in the e-ECAP threshold data and observed that the e-ECAP thresholds can exceed C levels, particularly for the more basal electrodes in the array. Moreover, the cross-electrode variance in the e-ECAP threshold data did not correspond well with the cross-electrode variance in the loudness estimates. The best correlation was between e-ECAP thresholds and M levels for electrodes in the apical half of the electrode array. Based on their results, it also appears that if behavioral estimates of M level are unavailable, the best option may be to record e-ECAP thresholds for 1 or 2 apical electrodes and then use them to set M levels for a speech processor program. With regard to the effect of anesthesia on e-ECAP thresholds, our results showed lower thresholds with TIVA for all electrodes (Fig. 2), but statistical significance was observed only with the apical electrodes (14-22; P b .05) (Table 1). Thus, NRT under inhalational anesthesia will offer higher e-ECAP thresholds, particularly for the more apical electrodes. Our results also confirm that TIVA has a smaller effect on e-ECAP thresholds than volatile anesthetic. This results in higher e-ECAP thresholds in children under volatile anesthetic. If these levels are too high and eECAP measurements are used for fitting the speech processor, the stimulation will be uncomfortably loud, particularly on the apical electrodes, and thus will induce rejection of the cochlear implant. Hence, it is important to use total intravenous anesthetic for anesthesia in children undergoing cochlear implant surgery to achieve better results. 5. Conclusions The results obtained in this study showed that type of anesthesia could have a significant influence on e-ECAP threshold. Inhalational anesthesia can result in higher e-ECAP thresholds in children under anesthesia, particularly for apical electrodes. Total intravenous anesthetic has less effect on e-ECAP thresholds than volatile anesthetic; therefore, TIVA is recommended for children undergoing cochlear implant surgery to obtain more accurate intraoperative measurements. In addition, impedance measurement was not affected by any type of anesthesia.
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Disclosures All authors have no conflicts of interest or financial ties to disclose. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Acknowledgments Authors would like to thank all patients who accept to participate in this research and also all physicians and nursing staffs in the operating room, recovery room, and ear, nose and throat (ENT) wards at King Abdullah University Hospital.
References [1] Guedes MC, Brito Neto RV, Gomez MV, Sant'Anna SB, Peralta CG, Castilho AM, et al. Neural response telemetry measures in patients implanted with Nucleus 24. Rev Bras Otorrinolaringol 2005;71:660–7. [2] Guedes MC, Weber R, Goffi Gomez MVS, de Brito Neto RV, O Peralta CG, Bento RF. Influence of evoked compound action potential on speech perception in cochlear implant users. Rev Bras Otorrinolaringol 2007;73:439–45. [3] Oghalai JS, Tonini R, Rasmus J, Emery C, Manolidis S, Vrabec JT, et al. Intra-operative monitoring of cochlear function during cochlear implantation. Cochlear Implants Int 2009;10(1):1–18. [4] Crawford MW, White MC, Propst EJ, Zaarour C, Cushing S, Pehora C, et al. Dosedependent suppression of the electrically elicited stapedius reflex by general anesthetics in children undergoing cochlear implant surgery. Anesth Analg 2009;108: 1480–7. [5] Al Muhaimeed H, Al Anazy F, Hamed O, Shubair E. Correlation between NRT measurement level and behavioral levels in pediatric cochlear implant patients. Int J Pediatr Otorhinolaryngol 2010;74:356–60. [6] Eftekharian A, Amizadeh M, Mottaghi K, Safari F, Mahani MH, Ranjbar LA, et al. Effect of depth of general anesthesia on the threshold of electrically evoked compound action potential in cochlear implantation. Eur Arch Otorhinolaryngol 2015;272:2697–701. [7] Botros A, van Dijk B, Killian M. AutoNR: an automated system that measures ECAP thresholds with the Nucleus Freedom cochlear implant via machine intelligence. Artif Intell Med 2007;40:15–28. [8] Jana JJ, Vaid N, Shanbhag J. Effect of total intravenous anaesthesia on intraoperative monitoring of cochlear implant function in paediatric patients. Cochlear Implants Int 2013;14:169–73. [9] van Wermeskerken GK, van Olphen AF, van Zanten GA. A comparison of intra- versus post-operatively acquired electrically evoked compound action potentials. Int J Audiol 2006;45:589–94. [10] Bissinger U, Plinkert PK, Sesterhenn G, Grimm A, Lenz G. Influence of volatile and intravenous anesthetics on the threshold of the acoustically evoked stapedius reflex. Eur Arch Otorhinolaryngol 2000;257:349–54. [11] Stronks HC, Aarts MC, Klis SF. Effects of isoflurane on auditory evoked potentials in the cochlea and brainstem of guinea pigs. Hear Res 2010;260:20–9. [12] Chen JK, Chuang AY, Sprinzl GM, Tung TH, Li LP. Impedance and electrically evoked compound action potential (ECAP) drop within 24 hours after cochlear implantation. PLoS One 2013;26:e71929. [13] Jeon EK, Brown CJ, Etler CP, O'Brien S, Chiou L, Abbas PJ. Comparison of electrically evoked compound action potential thresholds and loudness estimates for the stimuli used to program the Advanced Bionics cochlear implant. J Am Acad Audiol 2010; 21:16–27. [14] Vlahovic S, Sindija B, Aras I, Gluncic M, Trotic R. Differences between electrically evoked compound action potential (ECAP) and behavioral measures in children with cochlear implants operated in the school age vs. operated in the first years of life. Int J Pediatr Otorhinolaryngol 2012;76:731–9. [15] Cafarelli Dees D, Dillier N, Lai WK, von Wallenberg E, van Dijk B, Akdas F, et al. Normative findings of electrically evoked compound action potential measurements using the neural response telemetry of the Nucleus CI24M cochlear implant system. Audiol Neurootol 2005;10:105–16.
Contents lists available at ScienceDirect
Journal of Clinical Anesthesia
Original contribution
Effect of total intravenous vs volatile anesthetics on intraoperatively acquired electrically evoked compound action potential in children undergoing cochlear implant surgery: A randomized prospective study Ala”a Alhowary, MD, Assistant Professor a,⁎, Khaled EL-Radaideh, FFA, Associate Professor a, Anas AL-Rusan, MBBS, Resident a, Diab Bani Hani, MD, Assistant Professor a, Wail Khraise, MD, Assistant Professor a, Ahmad AL Omari, FACS, Assistant Professor b, Firas Alzoubi, FRRC, Professor b a b
Department of Anesthesiology, Faculty of Medicine, Jordan University of Science and Technology, PO Box 953, Irbid 21110, Jordan Division of Otolaryngology, Department of Special Surgery, Faculty of Medicine, Jordan University of Science and Technology, PO Box 3030, Irbid 22110, Jordan
a r t i c l e
i n f o
Article history: Received 21 April 2016 Accepted 27 October 2016 Available online xxxx Keywords: Anesthesia Cochlear Evoked potentialsImplants General Implants Intravenous
a b s t r a c t Objective: The purpose of the present study was to compare the effects of inhalational anesthesia to those of total intravenous anesthesia on intraoperative electrically evoked compound action potential (e-ECAP) thresholds in children undergoing cochlear implantation. Study design: Randomized prospective study. Setting: Tertiary referral teaching hospital. Patients: Forty children aged 6 months to 17 years with bilateral severe-to-profound sensorineural hearing loss and undergoing cochlear implantation were enrolled in the study. Intervention: Patients were randomly assigned (1:1 ratio) into 2 groups to receive inhalational or total intravenous anesthesia. Measurements: The e-ECAP measurements were obtained with neural response telemetry software. Main results: All electrodes showed lower e-ECAP thresholds under propofol, and results were statistically significant for the apical electrodes (P b .05). There was no statistical difference in the impedances between the 2 groups. Propofol minimally affected the e-ECAP. In contrast, the impedance was not affected by anesthesia. Conclusion: Volatile anesthetics result in higher e-ECAP thresholds in children, suggesting that e-ECAP thresholds acquired during inhalational anesthesia overestimate auditory nerve stimulation levels, which may cause discomfort postoperatively and adversely affect the child's adaptation to the implant. We recommend the use of total intravenous anesthesia for the measurement of the e-ECAP thresholds during cochlear implant surgery. © 2016 Elsevier Inc. All rights reserved.
1. Introduction Successful cochlear implantation depends on appropriate postoperative programming of the speech processor, as the sound characteristics depend on this programming. Excitation of the auditory nerve with a progressive increase in energy intensity is essential to detect the hearing threshold (T level) as well as the maximum intensity allowed without discomfort (C level) through subjective psychophysical tasks [1,2]. ⁎ Corresponding author. Faculty of Medicine, Jordan University of Science and Technology, PO Box 953, Irbid 21110, Jordan. Tel.: +1 962 0 795770906; fax: +1 962 2 7200621. E-mail addresses: [email protected] (A.” Alhowary), [email protected] (K. EL-Radaideh), [email protected] (A. AL-Rusan), [email protected] (D.B. Hani), [email protected] (W. Khraise), [email protected] (A. AL Omari), fi[email protected] (F. Alzoubi).
http://dx.doi.org/10.1016/j.jclinane.2016.10.008 0952-8180/© 2016 Elsevier Inc. All rights reserved.
This task is challenging, particularly in infants and young children, because of limited communication capabilities and lack of auditory experience. There is a pressing need for objective methods that require minimal cooperation of the patient in the programming of the cochlear implant's speech processor and that do not rely solely on behavioral loudness judgments to determine the hearing dynamic range in small children. A range of different electrophysiological measures can be used for this purpose, namely, intraoperative electrode impedance measurement, electrically evoked stapedial reflex, and electrically evoked compound action potential (e-ECAP) [3,4]. At our center, we commonly use e-ECAP thresholds and electrode impedance measurement for guiding implant setting [5,6]. The e-ECAP thresholds are a measure of the activity of synchronous cochlear nerve fibers, which is elicited by electrical stimulation of the cochlear implant, and are determined using neural response telemetry
A.” Alhowary et al. / Journal of Clinical Anesthesia 36 (2017) 80–83
(NRT) software that can be used to objectively fit the sound processing system [7]. Impedance measurement is intended to ascertain the technical status of the implant's stimulator and electrodes [6,8]. The e-ECAP recordings can be made intraoperatively or postoperatively. When done intraoperatively, the child is still under general anesthesia. This allows the clinician to apply high stimulation levels, which results in a high success rate of recording e-ECAP responses [9]. In this situation, knowledge of the effects of anesthetics on these objective measures is important to optimize the outcome of pediatric cochlear implantation. An ideal anesthetic technique for cochlear implant surgery is one that has no effect on the evoked auditory responses that were measured. Several studies that have investigated the influence of anesthesia on electrically elicited stapedius reflex threshold measurements revealed that the total intravenous anesthesia (TIVA) gives more consistent responses than volatile anesthetics [4,7], but there are insufficient data in the literature concerning its effect on e-ECAP. It has been suggested that the depth of anesthesia can have a significant influence on the e-ECAP threshold and it is important to reduce the depth of anesthesia to achieve better results [6]. To the best of our knowledge, no studies have been performed to compare the effect of a volatile anesthetic with that of propofol anesthesia on intraoperative e-ECAP thresholds. The aim of this study was to compare the effects of inhalational anesthesia with those of TIVA on intraoperative e-ECAP and impedance measurements in children undergoing cochlear implant surgery at our center. 2. Methods After obtaining formal approval from our institutional ethics committee, we conducted a randomized, double-blind study involving 40 patients aged 6 months to 17 years with American Society of Anesthesiologists physical status I-II who were scheduled for elective cochlear implantation surgery under general anesthesia at a tertiary referral teaching hospital. All these patients had bilateral severe-to-profound sensorineural hearing loss. Children with compromised neural/cochlear anatomy were excluded. Implantations were performed consecutively between March 2013 and March 2014. For all patients, written informed consent for participation in the study was obtained from one of the parents or the legal guardian. The patients were randomly assigned (1:1 ratio) into 2 groups based on computer-generated random numbers that were kept in a sealed envelope. Immediately before the administration of anesthesia, the sealed envelope was opened to reveal the anesthetic regimen that has to be used for this patient.
81
(4-8 mg/kg per hour), and fentanyl infusion (0.3-0.6 μm/kg per hour) titrated according to hemodynamic responses. 2.2. Neural monitoring Cochlear implants had 22 active electrodes, with electrode 22 inserted toward the apical end of the cochlea and electrode 1 at the basal end. Electrode impedance was measured using stimulation modes MP1 + 2 (the ball electrode [MP1] and plate electrode [MP2]). 2.3. Determination of the auditory thresholds Auditory thresholds were determined after insertion of the intracochlear electrode array at least 90 minutes after induction of anesthesia. All electrodes (electrodes 1-22) were tested. Current level was measured in current units (CUs) as defined by the cochlear implant programming software. Each current level step is a 0.16-dB change in current. Electrical pulse trains of 500 milliseconds were delivered in a stepwise manner, first in increments of 10 CU and subsequently in decrements of 5 CU. The NRT was measured at the electrode located 2 electrode positions apical to the stimulating electrode on the intracochlear array. An exception was made for electrodes 21 and 22 for which the recording electrodes were 19 and 20, respectively. All the measurements were made automatically by Custom Sound software (version 4, Cochlear Ltd, Sydney, Australia). The lowest level of stimulation at which a wave could be detected by the software was defined as the threshold. Both the surgeon and audiologist were blinded to the anesthetic drug. The e-ECAP measurements were obtained with the NRT software and were judged by experts who assessed the success rate of the recordings and determined the threshold level for each patient to use the records as a reference for postoperative speech processor fitting. 2.4. Statistical analysis SPSS version 18 (SPSS IBM, New York, NY) and SAS 8.1 (SAS Institute Inc, Cary, NC) were used to perform the statistical analysis. Differences between intraoperatively measured values of impedance/ e-ECAP under TIVA and under inhalational anesthesia of the 22 channels were analyzed using the unpaired t test. Data were presented as mean ± SD, percentage, or absolute number. Patient noncategorical characteristics were analyzed using analysis of variance. χ2 Tests were used for comparisons of categorical demographic data. A generalized linear model for repeated measures was used to test for differences within and between groups. Bonferroni correction was applied for all comparisons. P values less than .05 were considered statistically significant.
2.1. Anesthetic management
3. Results
The patients were not premedicated. On arrival to the operating room, standard intraoperative monitors (pulse oximetry, noninvasive arterial blood pressure, and electrocardiogram) were applied and baseline values were recorded. General anesthesia was induced with 50% oxygen in nitrous oxide and 6% sevoflurane in the patients of the inhalational group (INHAL) or propofol (3 mg/kg) in the patients of the TIVA group. An intravenous line could be secured before the induction of anesthesia followed by fentanyl administration (2 μm/kg bodyweight). Neuromuscular blockade was achieved with 0.3 mg/kg rocuronium to facilitate tracheal intubation. In group INHAL, anesthesia was maintained with 50% oxygen in nitrous oxide and 2%-3% sevoflurane administered via a pediatric circle breathing circuit, and fentanyl infusion (1 μm/kg per hour) titrated according to hemodynamic responses. Ventilation was controlled to maintain normocapnia. In group TIVA, anesthesia was maintained with 50% oxygen in nitrous oxide, propofol infusion
All operations were performed by senior surgeon (FA). The patients were kept under general anesthesia, and the operation was performed using the minimally invasive lazy S–shaped incision and double-flap, transmastoid, posterior tympanotomy technique with round window insertion. All patients received Nucleus Freedom cochlear implant devices (Cochlear Ltd), which use NRT to elicit and record responses from the auditory system. All surgeries were completed uneventfully. Complete electrode insertion was ensured in all cases by impedance and NRT and confirmed on the next day by radiologic x-ray. Our study population consisted of 40 patients. Twenty patients were enrolled in each group. The mean age of the INHAL group was 7 years and 3 months (SD = ±4.36) and that of the TIVA group was 7 years and 9 months (SD = ±4.37), which was not statistically significant (P = .58). The male-to-female ratio was 10:10 in the INHAL group and 8:12 in the TIVA group. There was no statistical difference in the impedances between the 2 groups (Fig. 1). All electrodes had lower
82
A.” Alhowary et al. / Journal of Clinical Anesthesia 36 (2017) 80–83 Table 1 The mean NRT value for each electrode in the 2 groups with statistical significance.
Fig. 1. The mean impedance measurements in both groups. INHAL = inhalational; TIVA = total intravenous anesthesia.
thresholds with TIVA (Fig. 2), with those for the basal electrodes showing statistical significance (14-22; P b .05) (Table 1). Radiologic testing was compatible with intraoperative testing of the position and depth of electrode insertion in all cases.
Electrode
Group INHAL (n = 20)
Group TIVA (n = 20)
P value
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
197.6 191.2 194.4 190.8 189.2 189.2 189.9 194.9 199.6 198.9 199.6 195.5 198.4 197.3 201.7 200.7 197.5 197.8 199.6 196.4 197.4 196.2
188 173.8 176.6 176.1 177.5 185.3 184.4 191.6 174.4 188.4 186.8 184.3 184.7 183.1 180.1 178.3 173.7 174.7 174.4 171.7 171.3 173.5
.335 .053 .029 .033 .081 .624 .455 .624 .001 .179 .071 .203 .122 .036 .006 .012 .019 .012 .007 .003 .004 .038
Data are presented as mean. INHAL = inhalational; TIVA = total intravenous anesthesia.
4. Discussion The process of cochlear implantation consists of surgical insertion of the device followed by setting of stimulation parameters for proper hearing [8]. Cochlear implant devices are able to measure e-ECAP from the auditory nerve. The system applies an electrical pulse on a given intracochlear electrode, and the evoked neural response is recorded at a neighboring electrode [6]. Each electrode directly stimulates the auditory nerve when the electrical current necessary to trigger a hearing sensation passes. The amount of electrical current necessary to trigger an auditory sensation is different for each individual and for each stimulation canal. Therefore, each user's speech processor must be individually adjusted together with each stimulation canal in a process that is called programming or mapping. In adults, power levels must be determined through psychophysical measures (behavioral method). With the progressive increase in energy intensity in each of the channels, the individual reports on the lowest intensity at which he and/or she detects the stimulus (electrical threshold) as well as the maximum intensity tolerated without discomfort. In small children, the procedure requires techniques that may be inconsistent and nonsystematic because of hearing inexperience or the child's age. Thus, sole use of the behavioral method to program the speech processor may extend the implant adaptation process because of the difficulty in establishing the right stimulation levels [2]. In small children, the e-ECAP thresholds determined using NRT while the child is anesthetized are generally necessary to assist in the initial setting of the device. Moreover, potential testing during surgery is advantageous because it can be used to verify implant and auditory
nerve integrity during surgery, confirming that the implant is functioning optimally [2,7]. The e-ECAP thresholds obtained from NRT are routinely used to program the cochlear implant, especially in children, with the aim of predicting the appropriate limits for implant stimulation setting, thus achieving an optimum dynamic range. This is very important for proper hearing and the successful use of cochlear implants [5,6,9]. Hence, it is important to evaluate the effect of anesthesia on intraoperatively acquired e-ECAP measurements. Numerous studies that have investigated the influence of anesthesia on electrically elicited stapedius reflex threshold measurement have revealed that TIVA gives more consistent responses than volatile anesthetics [4,8,10]. However, relatively few studies have directly explored the influence of anesthesia on objective measurements such as e-ECAP. Some researchers [4] studied the effect of anesthetics on intraoperative monitoring of cochlear implant function and reported that volatile anesthetics suppressed the stapedius reflex in a dosedependent manner, whereas e-ECAP was unaffected by the concentration of volatile anesthetic or propofol. However, they did not compare the effect of inhalational anesthesia and TIVA on e-ECAP thresholds. One previous study reported on the effect of TIVA on the intraoperative monitoring of cochlear implant function [8] and concluded that TIVA had no effect on determining auditory thresholds in relation to maximum comfort level values 3 months postimplantation. On the other hand, Stronks et al [11] reached the contrasting conclusion that isoflurane dose-dependently increases the threshold of auditory
Fig. 2. The mean NRT measurements in the 2 groups. INHAL = inhalational; TIVA = total intravenous anesthesia.
A.” Alhowary et al. / Journal of Clinical Anesthesia 36 (2017) 80–83
compound action potential. The same result was obtained indirectly by another study wherein e-ECAP thresholds were significantly lower (P b .001) when measured within 24 hours postoperatively than when measured intraoperatively [12]. It was suggested that neuronal sensitivity to electrical stimulation could be restored during this period, but the possible effect of anesthesia was not considered. More recently, a study reported that the depth of anesthesia can have a significant influence on the e-ECAP threshold and it is important to reduce it to achieve better results [6]. Moreover, when e-ECAP cannot be recorded by some electrodes during surgery, reduction of the depth of anesthesia may be helpful to obtain recordable results. Several studies have reported higher thresholds in the basal electrodes than in the apical electrodes [1,13-15]. Possible explanations of these findings could be that there are a smaller number of preserved vital neurons in the basal part of the cochlea, which is consistent with postmortem pathohistologic studies of the temporal bones [14]. Jeon et al [13] studied the relationship between e-ECAP thresholds and behavioral measures of perceptual dynamic range for the range of stimuli commonly used to program the speech processor. They reported a substantial amount of cross-electrode variance in the e-ECAP threshold data and observed that the e-ECAP thresholds can exceed C levels, particularly for the more basal electrodes in the array. Moreover, the cross-electrode variance in the e-ECAP threshold data did not correspond well with the cross-electrode variance in the loudness estimates. The best correlation was between e-ECAP thresholds and M levels for electrodes in the apical half of the electrode array. Based on their results, it also appears that if behavioral estimates of M level are unavailable, the best option may be to record e-ECAP thresholds for 1 or 2 apical electrodes and then use them to set M levels for a speech processor program. With regard to the effect of anesthesia on e-ECAP thresholds, our results showed lower thresholds with TIVA for all electrodes (Fig. 2), but statistical significance was observed only with the apical electrodes (14-22; P b .05) (Table 1). Thus, NRT under inhalational anesthesia will offer higher e-ECAP thresholds, particularly for the more apical electrodes. Our results also confirm that TIVA has a smaller effect on e-ECAP thresholds than volatile anesthetic. This results in higher e-ECAP thresholds in children under volatile anesthetic. If these levels are too high and eECAP measurements are used for fitting the speech processor, the stimulation will be uncomfortably loud, particularly on the apical electrodes, and thus will induce rejection of the cochlear implant. Hence, it is important to use total intravenous anesthetic for anesthesia in children undergoing cochlear implant surgery to achieve better results. 5. Conclusions The results obtained in this study showed that type of anesthesia could have a significant influence on e-ECAP threshold. Inhalational anesthesia can result in higher e-ECAP thresholds in children under anesthesia, particularly for apical electrodes. Total intravenous anesthetic has less effect on e-ECAP thresholds than volatile anesthetic; therefore, TIVA is recommended for children undergoing cochlear implant surgery to obtain more accurate intraoperative measurements. In addition, impedance measurement was not affected by any type of anesthesia.
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Disclosures All authors have no conflicts of interest or financial ties to disclose. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Acknowledgments Authors would like to thank all patients who accept to participate in this research and also all physicians and nursing staffs in the operating room, recovery room, and ear, nose and throat (ENT) wards at King Abdullah University Hospital.
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