4 Instruments and Implants The number of instruments should be limited but has to be sufficient for adaptation to the surgery when alternative surgical steps are needed. The instruments should always be arranged on the instrument table in the same order to facilitate easiest management by the scrub nurse. Fig. 4.1 The picture shown is of a table setup for regular mastoid surgery. Some instruments are not used in standard CI surgery. If a conversion to a more extended approach is needed (subtotal petrosectomy) this setup is still sufficient. Special CI instruments provided by the CI companies can be used in addition, to facilitate the placement of the implant. Preparation of pictures of each instrument table used may be helpful. A badly organized instrument table will frequently disturb the process of surgery and the surgeon’s concentration. We generally prefer straight instruments to angled ones, including the handpieces of drills, to ensure delicate manipulation. 1, folded gauze (large); 2, folded gauze (small); 3–6, metal cups with physiologic saline solution, antiseptic solution, and local anesthetic; 7, Silastic sheeting; 8, injectors; 9, skin retractor; 10, fascia pressure forceps; 11, forceps (uncinated); 12, nasal speculum; 13, rongeur; 14, self-retaining retractor; 15, needle holder; 16, scissors; 17, Vicryl (surgical thread); 18, handpieces for drills, straight and angled; 19, tungsten carbide and diamond burs; 20, cottonoid; 21, microforceps and microscissors; 22, spring scissors; 23, forceps (for incus); 24, scissors; 25, malleus nipper; 26, scissors; 27, forceps (fine tip); 28, nasal speculum; 29, scalpels; 30, Lempert periosteum elevator; 31, microdissectors; 32, curettes; 33, hooks and needle; 34, forceps with teeth; 35, suction tubes; 36, suction irrigators; 37, electrosurgical motor with hand drill. Fig. 4.2 Surgical kit for the Advanced Bionics HiRes 90K implant. 1, surgical silicone mock-up; 2, processor marking template; 3, device coil gauge model; 4, recess marking template; 5, recess template; 6, cochleostomy sizing gauge (for FDA markets); 7, insertion tool for the 1j electrode. Fig. 4.3 HIRES90K silicone surgical mock-up. Fig. 4.4 Behind the ear (BTE) processor template. Fig. 4.5 Receiver-stimulator template HIRES90K implant. Fig. 4.6 Recess marking template. Fig. 4.8 HiFocus 1j electrode insertion tool and tube. Fig. 4.9 HiFocus mid-scala insertion tool. Fig. 4.10 Helix cochleostomy sizing gauge. Fig. 4.11 Claw tool. Fig. 4.12 Electrode reloading tool. Fig. 4.13 From left to right: two implant templates; two contour electrode claws (gold and silver); two recess gauges (with and without electrode channel); one processor (BTE) template; one spacer for intraoperative testing (black). Not shown is an advanced off-stylet forceps. Fig. 4.14 Processor template. Fig. 4.15 Skin flap gauge. Fig. 4.16 MED-EL implant silicone template. Fig. 4.17 Diamond burs. The bur heads are shown in detail. The rounded bur (left) is 1.2 mm and the other (right) is 0.6 mm in diameter. Fig. 4.18 Angled microforceps for insertion. The right-sided version is shown. This type of forceps is also available angled to the other side. Fig. 4.19 Angled microforceps tip (angled tips right are shown here). Fig. 4.20 Surgical claw (detail). The Neurelec implants are fixed with screws. Their instruments are designed for this technique. See Fig. 4.21–Fig. 4.25. Fig. 4.21 Processor dummy. Fig. 4.22 Implant dummy. Fig. 4.23 Screwdriver. Fig. 4.24 Fixation screws. Fig. 4.25 Insertion fork. In general, antibiotics are not needed in tympanic and mastoid surgery. Of course many exceptions and preferences exist and CI surgery is one of the surgeries in which antibiotic coverage is preferred. There is no evidence-based protocol, but a number of considerations can help avoid infection, as described here. In the literature, the most common bacteria to cause a fulminant infection in combination with a cochlear implant are Pseudomonas aeruginosa and Staphylococcus aureus species.1,2 Device-related infections may be difficult to eradicate because these two species can develop biofilms on the implant. As these biofilms are more resistant to antibiotic treatment, they are involved in a higher rate of implant extrusion and the subsequent need to explant.3,4 The perioperative antibiotic regime should therefore cover at least these two species. An example of a peroperative intravenous regime is: In adults 24 hours, starting 45 minute prior to incision: • Clindamycin 600 mg 3 times a day for 1 day • Ceftazidime 2 g 3 times a day for 1 day In children 24 hours, starting 45 minute prior to incision: • Clindamycin 40 mg/kg/day in 3–4 doses (max. 1.8 g) • Ceftazidime 100–150 mg/kg/day in 3–4 doses (max. 6 g) Does the patient have a history of many ear infections? Is there a recent culture of the external ear canal? Is there a predominant anatomical/medical factor predisposing to development of ear infections, such as cleft palate or diabetes? Has there been any previous ear surgery? Is there a cholesteatoma, atelectasis, or radical cavity (see Chapters 12 and 14)? A preventive policy would be to culture the external ear canal in all CI candidates, and in case of a positive culture to treat the patient a week prior to the implantation using local eardrops according to the culture. As described in the section on complications in cochlear implantation (Chapter 7, Case 7.4), a patient with a history of Pseudomonas aeruginosa infections of the ear canal had a slowly progressive intracochlear infection with Pseudomonas. This was probably due to iatrogenic bacterial transmission at implantation. From that case onward, we have included a preoperative culture and possible local antibiotics in the work-up of each CI patient. The duration of the procedure, presence of diabetes or systemic disease, an adequate (prophylactic) antibiotic regime, appropriate dosage (related to weight!) in a child, and proper sterilization of the implant tools are all of concern. The start of the antibiotic infusion must be at least 30 minutes before incision. The following should also be properly considered: hair shaving, which should be done just before incision; adequate cleaning and skin sterilization; changing of surgical gloves before insertion; use of clean tools for implant handling; reduction of the chances of hematoma development; and reduction of operation room door movements. A proper head bandage will reduce the chances of a hematoma. Postoperative antibiotics can be prolonged (therapeutic regime). Duration of stay of sutures, awareness of other health care professionals, and accessibility and continuation of specialized care (especially during evening hours and weekends) must all be considered. Hyaluronic acid (e.g., Healon; Abbott, Illinois, USA) is a viscous fluid that is often used in ophthalmologic surgery and is sold in a ready-to-use syringe with a fine needle. It can be used at insertion to decrease insertion forces and prevent bone dust and blood from entering the cochlea.5 Another preventive technique is to position a small Silastic sheet in the posterior tympanotomy to avoid debris, blood, or bone dust from attaching to the electrode at insertion. Forceful insertion should be avoided, and insertion should stop when the point of first resistance is reached. We have found that a viscous fluid combined with corticosteroids can be additionally helpful in hearing preservation. The use of corticosteroids in cochlear implantation is discussed extensively in Chapter 9 on electroacoustic stimulation. The idea of adding corticosteroids during implantation, or even prolonged use, has been considered since patients with residual hearing have been considered as CI candidates. Corticosteroids can be considered to avoid an immune reaction within the cochlea and consequent negative intracochlear effects. Systemic, local (middle ear/round window), and even intracochlear administration has been investigated.6,7 It appears that corticosteroid application improves the chances of residual hearing preservation. On the other hand, the overall immune reaction within a CI candidate can play a role,8 several dosing regimens are proposed,6,7 and several application routes are investigated, all of which make it difficult to give clear advice.9 Facial nerve monitoring is an additional security system, but not a substitute for knowledge on the anatomy of the facial nerve. We consider that too much reliance on the system may even carry risks, especially for beginners. If surgeon believes they are safe with the monitor, they may damage the nerve in one rough move before being warned. Especially in CI and auditory brainstem implant (ABI) surgery the facial nerve is always in the surgical field. Good knowledge of the system is required to be able to work with it as an extra tool during surgery and not get agitated by it. In malformations of the labyrinth there is often an associated abnormal course of the facial nerve.10 The surgeon should be prepared to skeletonize the facial nerve canal, and the use of the facial nerve monitor and stimulator can be very helpful in these cases. During surgery, the use of facial nerve monitoring and stimulation precludes the use of muscle relaxants. During intraoperative electrophysiologic tests, monitoring may show facial nerve stimulation by one or more electrodes, allowing the surgeon and/or the audiologist to try to solve the problem in the same stage. Extensive explanation of facial nerve monitoring is given in Section 4.2. Bipolar coagulation should be used around delicate middle ear and mastoid structures such as the facial nerve, the sigmoid sinus, and the middle or posterior fossa dura since the equipment allows precise coagulation with minimal risk of spreading current and heat to surrounding structures. Monopolar coagulation can cause facial nerve damage, rupture of the sigmoid sinus, or CSF leakage. To avoid any mistakes some surgeons use only bipolar coagulation during middle ear and mastoid surgery as bipolar coagulation is sufficient and the use of monopolar can easily be dispensed with. Once the implant is in place all coagulation should be avoided and preferably the coagulation device should be switched off to prevent artifacts in the neural response measurements. If coagulation is absolutely necessary then only bipolar coagulation with a low current should be used. The management of bleeding is described extensively in Section 4.2. At the time of the actual insertion, the audiologist has to be called into the operation room; few surgeons do the testing without an audiologist in the room.11 Every company has its own software for performing intraoperative measurement, and different names are given to these measurements depending with the particular software. However, overall, the intraoperative measurements are comparable between the different brands. Several types of measurements can be made; each is briefly explained below. The impact on the surgeon of these measurements is debatable. Malfunctioning electrodes or a completely malfunctioning device (out-of-the-box) are very rare occurrences, as are misplacement or kinking. Although the audiologic measurements can support proper insertion, in case of doubt radiologic imaging is preferred.12 Fig. 4.26 Neural response measurements. Before closure of the wound the neural responses are measured. An audiologist can perform the measurements and stimulates the electrode at the different “channels.” The magnet coil (yellow arrow) is inserted in a sterile pouch, positioned on top of the implant magnet and at the other side connected to the computer (see insert). This is more important in children than in adults because, during the first fitting of young CI recipients, stimulation can be started just below the T levels (threshold levels) found in peroperative measurements. Impedance and stapedial reflex measurements are also (often) performed intraoperatively. Correct placement of the ground electrode(s) is often necessary to get proper impedance. Impedance measurement confirms the integrity of the electrodes on the electrode array in the cochlea and it provides information on individual electrode integrity, such as short or open circuits. High impedance can be due to a bubble of air in the cochlea, improper placement of the electrode (not in a “fluid-rich” environment), or improper placement of the ground electrode. The stapedial reflexes can be measured by suitable stimulation of CN VIII (afferent) followed by a visible contraction of the stape-dial muscle and tendon innervated via CN VII (efferent). This measurement can be done for the different electrodes. In some alternative surgical approaches a clear view of the tendon is impossible and therefore measurement of the ESRT is impossible. This measurement confirms the reaction of the auditory nerve. It is rapid, it is not degraded by motion artifacts, and it is unaffected by type or depth of anesthesia, making the neural measurements feasible in both the operating room and in the outpatient clinic. Absence of intraoperative neural responses is rare; however, when they are absent it does not indicate a lack of stimulation or a dysfunctional device.13 Spread of excitation measurements provide information regarding the selectivity of neural excitation fields around each electrode; when these overlap it may suggest presence of a tip fold-over.14 Although they are very rare, when using an alternative cochlear implantation technique (suprameatal technique) fold-overs can be more common and present in up to 5% of cases.15 See Fig. 4.26–Fig. 4.28. Fig. 4.27 Stapedial reflex measurement. With the electrode array inserted and the cochleostomy covered with periosteal pieces, impedance and stape-dial reflex measurements can be performed. The black arrow points at the stapedial tendon, which contracts when the cochlear nerve is well stimulated. Fig. 4.28 Neural response measurements. An example of the display of intraoperative neural response measurements from different electrodes. If the outcomes are satisfactory, the wound can be closed. (Note: Companies are listed in alphabetical order. The information is provided by the named companies and is liable to regional differences and changes over time, presented images of 2014.) Fig. 4.29 The Advanced Bionics HiRes 90K Advantage implant, shown with a 1j electrode. Fig. 4.30 The lateral wall HiFocus 1j electrode. Precurved electrode; number of electrodes, 16; length, 25 mm; diameter at base, 0.8 mm; diameter at tip, 0.4 mm. Fig. 4.31 The precurved HiFocus Helix electrode; stylet is removed. Lateral wall electrode; number of electrodes, 16; length, 24.5 mm; diameter at base, 1.1 mm; diameter at tip, 0.6 mm. Fig. 4.32 The HiFocus Mid-Scala electrode. Mid-scala electrode; number of electrodes, 16; length, 18.5 mm; diameter at base, 0.7 mm; diameter at tip, 0.5 mm. Fig. 4.33 Nucleus Cochlear CI422 implant. Fig. 4.34 Cochlear Nucleus CI422. Electrode enlargement; lateral wall electrode; number of electrodes, 22; length, 25 mm; diameter at base, 0.6 mm; diameter at tip, 0.3 mm. Fig. 4.36 Cochlear Contour Advance electrode with stylet. Precurved half-band electrode; number of electrodes, 22; length, 19 mm; diameter at base, 0.8 mm; diameter at tip, 0.5 mm. Fig. 4.37 Cochlear Contour Advance electrode after removal of stylet.
4.1 Cochlear Implantation: Instruments, Monitoring, and Implants
4.1.1 Instruments for Cochlear Implant (CI) Surgery
Operating Table Setup for Mastoid/CI Surgery (Fig. 4.1)
Special Instruments for CI Surgery Provided by the Supplying Companies
Advanced Bionics Instruments (Fig. 4.2–Fig. 4.12)
Cochlear Instruments (Fig. 4.13)
MED-EL Instruments (Fig. 4.14–Fig. 4.20)
Neurelec Instruments
4.1.2 Perioperative Medication in CI Surgery
Antibiotics and Infection Prevention
Bacterial Concerns
Outpatient Concerns
Preoperative Concerns
Perioperative Concerns
Postoperative Concerns
Hyaluronic Acid
Corticosteroids
4.1.3 Monitoring and Electrophysiologic Testing during CI Surgery
Facial Nerve Monitoring
Coagulation
Electrophysiologic Testing
Impedance Measurement
Electrically Evoked Stapedial Reflex Threshold (ESRT) Measurement
Neural Response/Electrically Evoked Compound Action Potential (ECAP) Measurement
Spread of Excitation (SOE)
4.1.4 Cochlear Implants and Electrodes Currently Available
Advanced Bionics Cochlear Implant (Fig. 4.29–Fig. 4.32)
Cochlear Nucleus Cochlear Implant (Fig. 4.33–Fig. 4.40)
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