|Year : 2013 | Volume
| Issue : 4 | Page : 225-229
The cochlear implantation surgery: A review of anesthetic considerations and implications
Sukhminder Jit Singh Bajwa1, Ashish Kulshrestha2
1 Department of Anaesthesiology and Intensive Care, Gian Sagar Medical College and Hospital, Ram Nagar, Banur, Punjab, India
2 Department of Anaesthesiology and Intensive Care, Government Medical College and Hospital, Sector-32, Chandigarh, India
|Date of Web Publication||7-Feb-2014|
Sukhminder Jit Singh Bajwa
Department of Anaesthesiology and Intensive Care, Gian Sagar Medical College and Hospital, Ram Nagar, Banur, Punjab
Source of Support: None, Conflict of Interest: None
The advancement in the technology of the cochlear implants has resulted in increasing trend of cochlear implantation in both the children and elderly population. The anesthesiologist is faced with the task of smoothly conducting the surgery without any interference in the stimulation techniques used. The preoperative evaluation is mainly focused on the presence of any congenital anomalies in these patients which may affect anesthetic technique. The reduction of anxiety of the patient as well as the parents of small children is an important aspect of the preoperative visit. Intraoperatively the anesthetic technique chosen should not interfere with the stimulation of the cochlear implant electrode assembly. The postoperative management is mainly focused at prevention of agitation and good analgesia. A close cooperation between the surgeon and the anesthesiologist is essential for a positive outcome in this surgery. The current review focuses on the important anesthesia aspects related to cochlear implant surgery.
Keywords: Anesthesia, cochlear implant, sensorineural deafness
|How to cite this article:|
Bajwa SS, Kulshrestha A. The cochlear implantation surgery: A review of anesthetic considerations and implications. Int J Health Allied Sci 2013;2:225-9
|How to cite this URL:|
Bajwa SS, Kulshrestha A. The cochlear implantation surgery: A review of anesthetic considerations and implications. Int J Health Allied Sci [serial online] 2013 [cited 2020 Mar 31];2:225-9. Available from: http://www.ijhas.in/text.asp?2013/2/4/225/126698
| Introduction|| |
A cochlear implant is an electronic device which is used to restore hearing in patients with bilateral severe sensorineural deafness in order to provide improved communication abilities. These electronic devices have an ability to transform speech and other sounds into electrical signals used to stimulate the existing fibers of auditory nerve in the inner ear. These are different from usual hearing aids in that these devices do not just amplify the sounds, but actually stimulate the auditory nerve. Cochlear implants are considered to be an important landmark development in otology.  Cochlear implants are very expensive electronic devices which need a careful surgical technique to place the internal compressor assembly within the mastoid antrum and connect the electrodes to the cochlear neurons. The surgical technique requires a team approach which includes use of such anesthetic technique so as to maintain a bloodless surgical field with stable intraoperative hemodynamics. As such role of the anesthesiologist is crucial during such expensive surgical procedures for a better outcome. Total intravenous anesthesia, locoregional anesthesia, newer induced hypotension techniques, and advent of newer drugs in anesthesia practice including newer sedative agents and many other techniques and drugs have allowed even complicated surgical procedures to be performed with a great ease. ,,
The most common candidates for cochlear implant surgery are children but adults and sometimes elderly people, with failure of hearing aids may be considered for this surgery.
| Preoperative Evaluation|| |
Selection of patient
Early detection of hearing impairment in childhood is essential for proper development of learning and listening skills and early implantation of cochlea leads to acquisition of these skills and thus also helps in mental and intellectual development of the child. It has been found that proper development of both the speech as well as vocabulary occurs if the child receives the cochlear implant before 2.5 years of age.  Surgical procedure itself needs the facial nerve to be identified and for which proper development of facial ridges is important which usually develops by 2 years of age.
After selecting the patients, further investigations required for surgery include objective assessment of hearing by steady state evoked potential, auditory brainstem evoked potential, and electrocochleography. Radiographs of skull and high resolution computed tomographic scan of the temporal bone are needed to visualize the basal turn of cochlea, its patency, and any abnormal ossification within it. It can also give useful information about degree of pneumatization of mastoid, any congenital abnormality in inner ear, and any fluid accumulation in middle ear. Magnetic resonance imaging (MRI) may be useful in identification of sequelae of labrynthitis with fibrous tissue filled cochlea where the placement of electrodes may be difficult.  The presence of acute or chronic suppurative otitis media with or without cholesteatoma was considered contraindication for cochlear implant surgery previously, but now with adequate control of the infection preoperatively and with the measures to prevent recurrence of the disease, it is no longer considered a contraindication.
The presence of mental retardation and any central nervous disease affecting the auditory pathway should be assessed preoperatively  and so is the presence of any congenital cataract which should be corrected preoperatively in order to achieve maximum help from the improved vision for postoperative hearing rehabilitation.
Majority of the patients coming for cochlear implant surgery are children with hearing impairment and hence communication with these children is very important to establish a good rapport preoperatively. The children and the parents should be counseled after detailed description of the surgical and anesthetic procedure. This also helps in allaying anxiety of both the child as well as the parents.
Preoperatively, it is essential to screen for the presence of various congenital syndromes leading to deaf-mutism as the systemic involvement in these syndromes may affect the anesthetic management. Also, the various types of dysplasia of temporal bone and cochlea associated with these syndromes may render the surgeons to change the surgical technique of cochlear implantation. The various congenital syndromes and their anesthetic implications are shown in [Table 1]. ,,,,,
|Table 1: Various congenital syndromes associated with deaf-mutism and anesthetic implications|
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A thorough preoperative examination is required to assess the presence of any congenital abnormalities, developmental milestones, cerebral palsy, any neuromotor deficits, and presence of any active upper respiratory infections.
Premedication with oral midazolam 0.5 mg/kg given about 20-30 min prior to anesthesia induction remains the preferred drug owing to its reasonable and reliable effect with no serious side-effects. It helps in reduction in separation and induction anxiety in children with a favorable pharmacokinetic profile and minimal effects on recovery profiles. 
Induction of anesthesia can occur in the standard manner in adults using thiopentone 3-5 mg/kg or propofol 2-3 mg/kg intravenously with the analgesia given by fentanyl 2 μg/kg intravenously. The induction in children without intravenous access can be achieved by inhalational induction by oxygen and sevoflurane. Tracheal intubation is achieved after neuromuscular blockade with vecuronium 0.1 mg/kg intravenously with appropriate sized endotracheal tube which is then firmly secured in place after confirming bilateral equal air entry. Attenuation of pressor response with preoperative dexmedetomidine in a dose of 1 μg/kg not only provides stable hemodynamics during induction and intraop period enabling a smoother control to provide a bloodless field during surgery, but also decreases the requirement of anesthetic drugs during periop period.  Anesthesia is usually maintained with oxygen, air, and isoflurane with intermittent doses of vecuronium. Alternatively, a total intravenous technique involving infusion of propofol can be used to maintain anesthesia. However, the choice of anesthetic technique and drugs is solely the priority of the attending anesthesiologist whether to use experience-based or evidence-based anesthesia based on scientific logical empiricism.  The standard monitoring should include five lead electrocardiogram, noninvasive blood pressure, pulse oximetry, capnography, and neuromuscular monitoring.
Regional anesthesia can be used by the block of great auricular nerve, but studies in tympanomastoid surgeries have not shown any benefit of such blocks on the reducing the incidence of postoperative pain.  The newer drugs and techniques have greater potential in providing adequate sedation during surgical procedure, but need larger studies so as to establish their overall efficacy and safety. ,
The surgical duration is usually 3 h with no significant blood loss and thus requirement of blood transfusion is minimal, however sometimes significant blood loss may occur from large non-collapsible mastoid emissary veins. Adequate blood volume is maintained by infusion of crystalloids compensating for fasting and blood losses and large amounts of fluids should be avoided as it can lead to bladder distension leading to postoperative agitation as catheterization is not done in the surgery.
An important step during the surgery is preservation of facial nerve which may be identified intraoperatively by electrical stimulation thus precluding the use of muscle relaxants. This should be used after the effect of the muscle relaxant used for intubation has weaned off as evidenced by the response on the train of four stimulation and during this process the anesthesia can be maintained by propofol infusion.
Cochlear implant being an electrical device, can easily be damaged by static electrical discharges from electrocautery so the use of electrocautery should be discouraged once the cochlear implant is inserted in place. However, proper hemostasis should be done before placement of cochlear implant. At the conclusion of surgery, the integrity of the implant is checked by brain stem auditory evoked responses and by electrically evoked stapedius reflexes. This is very essential for postoperative fitting of external speech processor which may be difficult in small children postoperatively.
The two main aspects of electrical stimulation are usually used, that is, the electrically elicited stapedius reflex threshold (ESRT) and electrically elicited compound action potential (ECAP).  ESRT mainly determine the maximum comfort level which is defined as the loudest sound tolerated without pain, while ECAP mainly determines the noise threshold, that is, lowest acoustic stimulus perceived as sound. Anesthesia can affect the ESRT leading to wrong estimate of the maximum comfort level which may produce pain during stimulation. In various studies it has been found that there is a strong correlation between the level of hypnosis and the mean stapedius reflex threshold value and it is thus postulated to reduce the concentration of inhalational agents with maintenance of normal carbon dioxide levels during such stimulations.  The use of electroencephalograph has been found to be useful in maintaining light but sufficient level of hypnosis. In a prospective study including children, it was found that the ESRT increased with increasing concentration of inhalational agent with minimal effect of propofol and nitrous oxide. The ECAP was not found to be affected by either the inhalational agents or the propofol. Thus, it can be concluded that the use of total intravenous anesthesia using propofol and opioid is beneficial in pediatric cochlear implant surgery. 
Sudden coughing and bucking should be avoided at the end of surgery to prevent dislodgment of the electrode array of the implant and the neuromuscular blockade should be reversed and spontaneous respiratory efforts are allowed. The child can be extubated in deeper planes and kept in lateral recovery position to prevent sudden agitation. The child should be nursed in post-anesthesia care unit (PACU) in presence of the parents with proper care of postoperative analgesia.
The major postoperative concern in cochlear implant surgery is the prevention of postoperative nausea and vomiting (PONV) which is common in ear surgery. The various measures employed are adequate anxiolysis preoperatively, use of total intravenous anesthesia with propofol, avoidance of nitrous oxide, administration of antiemetics like ondansetron 0.1 mg/kg intravenously at the end of surgery, and the use of dexamethasone 0.15 mg/kg intravenously at the beginning of surgery. The use of dexamethasone has been found to augment the other antiemetics used and studies have suggested that the risk of infection after a single dose of dexamethasone is unclear. ,, Palonosetron has also proved to be an efficacious antiemetic drug which has got a long duration of action. 
Postoperative analgesia can be maintained with parent or nurse controlled boluses of opioids like fentanyl or morphine. However, intravenous or per rectal paracetamol has also been found to be effective in reducing doses of opioids and thus helps in prevention of opioid-related side effects. , The incidence of postoperative shivering can also be reduced to a large extent by use of perioperative dexmedetomidine.  The patient should be monitored in PACU till the consciousness is regained fully with minimal PONV.
The cochlear implant surgery is considered to be relatively safe and minimal or no anesthesia-related complications are reported. The complications are mainly surgical including minor complications like mild flap infection, change in taste, minor balance problems, and transient facial palsy. The major surgical complications include flap necrosis, device failure, device migration, cerebrospinal leak, meningitis, and persistent facial palsy. , Late postoperative complications requiring reimplantation can occur late and are less frequent and thus these patients should be followed for long-term.  Other less frequent complications include displaced magnet from the receiver pocket by magnetic toys and silicone allergy. 
Cochlear implantation in special population
Due to advancement in screening and diagnosing hearing problems, more number of young children often comes for early surgery for cochlear implantation. There is evidence suggesting that early bilateral cochlear implant surgery in children less than 12 months of age results in better auditory rehabilitation. A multidisciplinary approach involving pediatric anesthesiologist is essential for a positive outcome as studies in cochlear implant surgeries in infants have shown the age of the patient and experience and the skills of the anesthesiologist to be important risk factors. ,
Due to deterioration in the quality of life brought about by hearing impairment, many of the older population is now resorting towards more sophisticated cochlear implant devices. This is also due to noncompliance with the various hearing aids available. But the cochlear implant surgery is less commonly performed in elderly patients due to presence of coexisting systemic diseases which increase the anesthetic complications postoperatively. Recent evidence, however suggest that the incidence of such complications in elderly patients are minimal and can easily be managed. ,, Cochlear implantation with pericanal electrode technique and transcanal cochlear implantation can be performed under local anesthesia with monitored anesthesia care in high risk elderly patients.  However, special precautions have to be exercised in few selected patients who may either be taking alternative medicines or may have potential contagious diseases like hepatitis or acquired immunodeficiency syndrome (AIDS). ,
Anesthesia for incidental surgery in patients with cochlear implant
The major concern in an incidental surgery in patients with cochlear implant in situ is mainly the electrical interference caused by electrocautery and monopolar cautery should be avoided near head and neck areas in these patients. Even the bipolar cautery should be avoided directly over the extra cochlear electrodes to avoid damage. The use of electroconvulsive therapy in these patients should be avoided and so is the use of radiotherapy directly over the implant which can cause serious damage. MRI is also contraindicated in these patients and can lead to tissue damage and implant migration. However, if MRI is deemed to be necessary, the external magnet can be removed by a minor surgery, and thus MRI can be performed and the magnet can be replaced post procedure. 
| Conclusion|| |
In conclusion, the cochlear implantation surgery has gained popularity over the last decade and thus the attending anesthesiologist is faced with the responsibility of safely conducting the surgery. The anesthetic technique used may have implications on the method of stimulation of the electrodes of the cochlear implant intraoperatively. Moreover, most of these patients are children and it is the responsibility of anesthesiologist to prevent any agitation and smooth induction and emergence from anesthesia. A close cooperation between the anesthesiologist and surgeon is essential for a positive outcome.
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