AORN J O U R N A L AUGUST 1989, VOL. 50, NO 2

Multichannel Cochlear Implants HELP FOR THE PROFOUNDLY DEAF

Julia A. Yeager, RN; Dianne G. Joyce, LPN

amage to the inner ear, or cochlea, can occur from many factors (eg, elevated D body temperature, congenital defects, or

medications). These factors can damage nerve fibers in the cochlea. Some individuals, however, have some remaining fibers that, if electrically stimulated, can send sound signals to the brain. The cochlear implant provides that electrical stimulation and is an option for those who receive little or no benefit from a hearing aid.

Replacing a major sensory organ may seem like science fiction, but today the cochlear implant is a reality. The US Food and Drug Administration (FDA) approved the multichannel cochlear implant in October 1985. An investigational license for cochlear implants for children between the ages of two and 17 also has been approved.

The Equipment

he implant discussed in this article is a 22- channel device that is manufactured in T Australia. The multichannel capabilities of

the unit enable the wearer to hear a variety of pitches, in both low and high ranges. Each channel produces a different pitch sensation, which is important in distinguishing speech and everyday sounds.

The implant consists of two external compo- nents (ie, microphone/transmitter, speech processor) and two implanted components (ie, receiver/stimulator, electrode array/channels) (Fig 1).

The microphone/transmitter, which is placed behind the ear much like a hearing aid, serves

two purposes. The microphone initially receives sounds. The sounds are sent from the microphone to the speech processor through the thin cable that connects them. The speech processor is a compact, portable unit worn on a belt, shoulder strap, or in a pocket. The speech processor selects and digitally encodes the sounds that are most useful for understanding speech. The electronic codes are sent back to the transmitter through the thin cable.

Julia A . Yeager, RN, BSN, was a staff nurse at the Moses H. Cone Memorial Hospital, Greensboro, NC, when this article was written. She is a surgical assistant in private practice with Campbell, Stroud and Brown, DDS, PA, Greens- boro, NC. She received her associate degree in nursing from Northern Virginia Community College, Annandale, and her bachelor of science in nursing degree from the University of North Carolina, Charlotte.

Dianne G. Joyce, LPN, OR1: is an operating room technician at Greensboro (NC) Head and Neck Surgery Associates, PA. She completed her LPN education at Guilford Technical Communiry College, Jamestown, NC, and the operating room technology program at the Moses H. Cone Memorial Hospital, Greensboro, NC.

The authors acknowledge Eric M. Kraus, MD, The Ear Center of Greensboro, Kraus Otologic Associata, PA, and Sylvia J. Tate, RN, otohryn- gology primary nurse, the Moses H Cone Memorial Hospital Greensboro, NC for their assismce.

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Fig 1. Diagram showing the parts of the cochlear implant system. Sound enters the microphone/transmitter (Q) and is transmitted to the speech processor (b) where it is electronically coded. The coded signals are returned to the transmitting coil in the microphone/transmitter and passed on to the electrode array in the patient’s cochlea (c). The electrode array stimulates hearing nerve fibers in the ear, and the fibers send the messages to the brain (d). (Adapted from Nucleus 22 Channel Implant System Surgeon’s Manual wirh permksion from Cochlear Corp, Englewood, Colo)

The transmitting coil, a plastic-covered ring that is approximately 34 mm in diameter, sends the codes across the skin to the surgically implanted receiver/stimulator. The receiver is permanent and has no wires protruding through the skin. The receiver/stimulator contains a customdesigned integrated circuit that converts the codes to special electronic signals and sends them along the electrode array.

The electrode array is a set of 22 tiny electrode

bands that are arranged in a row around a piece of tapered, flexible silicone tubing. Each electrode has a wire that connects it to the receiver/ stimulator. The coded electronic signals are sent to specific electrodes in the array. Each electrode is programmed separately to deliver sounds that can vary in loudness and pitch. These electrodes then stimulate the appropriate hearing nerve fibers, which send the messages to the brain. The brain receives the signals and interprets them, giving

+ wall suction

video player and screen

I I ring stand f7 1-1

storage /

+ +

/

patient's Mayo stands

entrance

anesthesia

X X

uu sterile prep tray

case cart I

x-ray viewing lights

X bipolar

scalp1

-k -t r] im hemostatic

leg wraps clippers

electrocautery I 1 ' I I I 1 1

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1 I I I I L Fig 2. Diagram of the operating room layout for cochlear implant surgery for the left ear. The - symbol denotes electrical cables; the + symbol denotes suction lines.

the person the sensation of hearing.'

Patient Selection

andidates for a cochlear implant at the Moses H. Cone Memorial Hospital, C Greensboro, NC, must be profoundly deaf

in both ears, be unable to benefit from the most powerful hearing aids, have normal mental abilities, have x-ray evidence of an open cochlea,

and be able to tolerate general anesthesia. Children who are between the ages of two and 17 must meet these criteria, and they also must have hearing parents and currently be enrolled in a formal deaf- education program that includes as much spoken stimulation as possibie. Because the children's program is investigational at this time, the child must have as much opportunity as possible to listen and to learn through listening at home and at school. It is expected that initially the child

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will continue to use sign language, but as auditory skills improve, it is hoped that he or she will depend on listening combined with lipreading to communicate.

The initial assessment of the patient is done by the nurse who works at the surgeon’s office. He or she collects information regarding the date of the patient’s hearing loss, the patient’s communication techniques (eg, spoken word, sign language, lipreading), any benefits from hearing aids, current enrollment in deaf-education classes, and insurance information. The nurse gives the patient an information packet that contains brochures, a profile sheet, appointment times, and hotel reservations, if necessary.

The surgeon examines the patient and begins testing to determine if the patient meets all of the criteria. He or she uses many diagrams to explain the procedure to the patient. The patient must be fully informed to give consent to the surgical procedure. The surgeon can explain the procedure to younger patients with the use of a toy doll that wears a microphone headset and speech processor. The hair in the operative field is attached with Velcro’” and can be removed to show the incision site.

Preoperative Phase

he entire otology team should be ready before the patient enters the room. Even T though the patient cannot hear, he or she

can still feel a hurried commotion. The OR bed is placed in position for an ear,

nose, and throat procedure (ie, the head and foot of the bed are reversed) so that the surgeon has room to sit as close to the bed as possible (Fig 2). A small x-ray cassette is placed under a foam pad at the head of the bed. The microscope is balanced with the camera mount, camera, and video monitor. Three prep tables contain a Foley catheter, hair clippers and elastic leg wraps, and a sterile prep tray. (See “Equipment and Instruments for a Cochlear Implant.”) The scrub nurse sets up a sterile back table consisting of mastoid and middle-ear instruments, otology drills, and sterile drapes. Two Mayo trays, one for mastoid instruments

Equipment and Instruments for a Cochlear Implant

Equipment suction electrocautery console bipolar electrocautery console ear drill console microscope video player and screen hair clippers

Instruments stapedectomy set tympanoplasty/mastoid set otology drills cerebellar retractors hole puncher hemostatic scalpel electrocautery forceps and cords sizers insertion forks/claws dummy implant

and one for implant instruments, are used. The procedure requires two circulating nurses.

One circulating nurse dispenses a solution of 1% xylocaine and 1 : 100,OOO epinephrine, absorbable gelatin sponges, topical adrenaline, methylene blue, normal saline, and water to the scrub nurse. The second circulator meets the patient in the holding area. He or she does not leave the patient’s side until induction of anesthesia is complete.

The circulating nurse who meets the patient in the holding area carries large index cards with the names of the surgical team members and explanations of the activities taking place. These are indispensable tools when the faces of the surgical team are masked, and the patient only reads lips. When the patient is a child, an interpreter fluent in sign language is available in the holding area, in the OR until induction is complete, and in the postanesthesia care unit (PACU). The nurse tells the patient that he or she may wear eyeglasses preoperatively if he or she needs them to read the index cards.

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A I-g bolus of cefazolin is given via the intravenous (IV) line. The patient is moved into the OR, and the nurse places warm blankets on the OR bed before the patient is transferred. The patient is placed on the OR bed in a supine position, and the nurse covers the patient with warm blankets and places a pillow under his or her knees for comfort. The nurse pads the arm on the operative side of the patient and then tucks it at the patient’s side. The opposite arm is secured on a padded arm board next to the anesthesia personnel. A sign is posted on the door to limit traffic and maintain quiet.

After the patient is anesthetized and intubated, the bed is rotated 90 degrees and centered in the middle of the room. The circulating nurses insert a Foley catheter and wrap the legs with elastic bandages while the surgeon shaves four inches of hair from behind the operative ear. The surgeon tapes the remaining hair out of the surgical area and marks the skin for placement of the internal receiver. To mark the placement site, the surgeon places the microphone head set behind the patient’s ear and marks the magnet position of the transmitter to ensure that the external ear will not press against it. The electrocautery and suction consoles are positioned near the patient’s feet.

To maintain hemostasis, the surgeon infiltrates the surgical area postauricularly with a solution of 1% xylocaine and 1:100,000 epinephrine using a 10-mL syringe and 25-gauge, 1 %-inch needle. The circulating nurse inserts a small sterile cotton ball in the ear canal to protect the tympanic membrane, and then he or she preps the operative ear with povidone-iodine paint. The nurse uses cotton-tipped applicators to clean the pinna and prep sponges to clean the surrounding area. The paint is blotted, and the prep is then repeated using rubbing alcohol.

The surgeon and scrub nurse drape the patient with four linen towels, a plastic U-drape posteriorly, a plastic rectangular drape that is placed on the side of the patient’s face so that his or her facial movements can be monitored, and disposable head/neck drapes. As the surgeon marks the operative site with methylene blue, the scrub nurse passes the suction, electrocautery, hemostatic scalpel, bipolar lines, and otology drills

from the area at the patient’s feet. The scrub nurse places a magnetic mat over the lines on the patient’s chest and places an instrument pouch at the patient’s head so it is within the surgeon’s reach.

Surgical Procedure

he surgeon makes an anteriorly based scalp flap incision in the postauricular area with T a # 15 hemostatic scalpel. The scrub nurse

uses two double skin hooks to assist the surgeon while he or she elevates the scalp flap. The surgeon exposes the temporoparietal bone with a periosteal elevator and places cerebellar retractors to hold the flap. The flap is then covered with saline- soaked sponges. The surgeon makes a cut with a small cutting burr along the methylene blue mark. He or she removes a fascia graft, and it is stored in saline and used to occlude the cochleostomy at the end of the procedure.

The surgeon identifies the antrum and tegmen mastoideum, the dome of the lateral semicircular canal, and the incus. He or she performs a limited mastoidectomy unless the patient has had previous surgery requiring a more extensive mastoidectomy.

The surgeon enlarges the facial recess (ie, the area between the posterior ear canal and the facial nerve) with small burrs and exposes the chorda tympani nerve and the middle ear. Drilling is necessary to reach the round window niche. The surgeon removes the lip of this niche with a small burr and identifies the round window membrane. He or she uses normal saline to irrigate the middle ear and then places a %-inch x ‘A-inch cottonoid in the facial recess.

The surgeon makes two depressions in the squamous temporal bone to house the receiver and its attached magnet. The surgeon positions a “dummy” receiver to measure the area and then uses medium to large cutting burrs to drill a deep anterior depression for the receiver and a posterior depression for the attached magnet. He or she drills a small trough from the anterior depression into the mastoid cavity, undercutting the posterior lip of the mastoid to receive the electrode array. The surgeon drills holes on both sides of the receiver depression to enable the implant to be secured to the bone with DacronTY ribbons, and

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Fig 3. The electrode array is directed into the cochlea until resistance is met. (Reprinted from Nucleus 22 Channel Implant System Surgeon's Manual, wifh permission from Ed Zilbem, illustrator, and Coch- lear Corp, Englewood, Colo)

the drill holes are checked for patency to avoid further drilling after the electrode array is placed in the cochlea by threading a suture through them.

The surgeon copiously irrigates the surgical field with normal saline and ensures hemostasis with electrocautery or 3-0 chromic ties. The surgeon and the scrub nurse change their gloves, and the surgeon removes the implant from its sterile container.

It is very important to turn off and unhook the electrocautery machine. The entire unit must be moved away from the surgical field so it is not reconnected unknowingly because the titanium enclosure of the receiver acts as an electrical grounding device.* If electrocautery is used after placement of the receiver, only bi- polar electrocautery is recommended. It minimizes the possibility of passing current through the receiver.

The next part of the surgery requires complete silence because the inner ear is entered. Any disruption of cochlear tissue can result in the formation of fibrous tissue and new bone and may lead to sensorineural degeneration.)

The surgeon removes the saline-saturated cottonoid from the facial recess, and using small diamond burrs, creates a cochleostomy anterior/ inferior to the round window membrane. At this time, the scrub nurse threads the Dacron"" ribbons with nylon sutures so that the flat, wide ties can be threaded through the small drill holes. The surgeon directs the tip of the electrode array into the scala tympani using straight and angled claws and proceeds into the cochlea until resistance is met (Fig 3). The surgeon counts the number of support bands and electrodes that remain outside of the scala tympani to assess the number of electrodes in the cochlea. The electrodes that are

AUGUST 1989, VOL. 50. NO 2 A O R N J O U R N A L

Fig 4. The receiver is positioned in the bone and secured with 4-0 braided sutures. (Reprinted from Nucleus 22 Channel Implant System Surgeon’s Manual with permission from Ed Zilberts, illustrator, and Cochlear Corp, Englewood, Colo)

not located in the scala tympani are not used for stimulation and are inactivated during the initial programming of the device. The surgeon positions the receiver unit in the bone and secures it with 4-0 braided nylon sutures (Fig 4). A suture is placed over the electronics of the internal receiver, and another one is placed over the magnet. Three Dacron’” ribbons, which are packaged with the implant, are used to anchor the electrode array to the posterior lip of the mastoid cavity and in the trough.

After the receiver, magnet, and electrode array are secured into place, the surgeon begins to occlude the cochleostomy with the previously harvested pieces of temporalis fascia. The facial recess also is tilled with the facia. The surgeon places absorbable gelatin sponge disks that have been soaked in saline over the fascia in the facial

recess area, and he or she folds a large piece of gelatin sponge in half and places it within the mastoid to help anchor the electrode array.

An x-ray of the anterior/posterior transorbital view of the head is taken to verify the correct placement of the implant and to verify that there are no kinks, bends, or knots in the electrode array (Fig 5).

The mastoid cavity and subcutaneous tissues are carefully irrigated with a solution of 50,000 units of bacitracin in 500 mL normal saline. A closed drainage system is put in place and brought out through the inferior aspect of the incision. The scalp flap is closed with interrupted inverted 3-0 chromic sutures in the subcuticular deep layer and with staples in the skin layer. The surgeon then paints the wound with bacitracin ointment and covers it with a fluffed-gauze mastoid dressing.

Fig 5. An anterior/posterior transorbital x-ray of an implant. (X-ray courtesy of Cochlear Cop, Englewood Colo)

The elastic leg bandages and bladder catheter are removed. If a Foley catheter is not used, the patient may be straight catheterized depending on the length of surgery.

Postoperative Care

he patient is extubated and then transported to the PACU. The PACU nurse connects T the patient’s closed drainage system to wall

suction so that fluid does not build at the implantation site and possibly move the electrode array. He or she monitors the patient’s vital signs every 15 minutes for the first hour. Because the patient cannot hear, the nurse must wipe any protective ointment from the patient’s eyes so he or she can see. Deaf patients may require more reassurance, and the continuous presence of the PACU nurse is helpful. The interpreter who accompanied the child into the OR should be

available to help if he or she becomes uncoop- erative or disoriented. Medications for nausea (droperidol) and pain (morphine sulphate) are administered as needed. The nurse continues to monitor the patient for bleeding. The nurse asks the patient to smile and squeeze his or her eyes together tightly to check for facial nerve deficits. The patient remains in the PACU between 60 and 90 minutes, and then the patient is moved to his or her room for a three to five day postoperative recovery period.

The surgeon removes the drain before the patient is discharged and instructs the patient to return to his or her ofice in 10 to 14 days for removal of the skin staples.

The patient begins the rehabilitative phase four to six weeks postoperatively. At this time, the microphone head set is magnetically coupled through the skin to the receiver. The audiologist then begins programming each of the electrodes

AUGUST 1989, VOL. 50, NO 2 AORN JOURNAL

within the scala tympani for a particular pitch and loudness according to the comfort levels of the individual. Some patients are able to discriminate between different environmental sounds within the first two to three months after the device is programmed.

The potential risks associated with this procedure include disturbance or damage to the facial nerve, stiffness or numbness around the ear, disturbance of taste or balance, or a noticeable change in tinnitus. The long-term effects of electrical stimulation on the cochlea and new bone formation are not known at this time.

At the completion of this procedure, the surgical team feels an exhilarating sense of accomplish-

ment. It is difficult for those of us who can hear to imagine the lonely world of the deaf. With a cochlear implant, the door is opened for them to be a part of the world, to feel safer, to do or have a better job, and to enjoy the sounds of the world around them.

Notes I . Nucleus 22 Channel Implant System (Englewood,

Colo: Cochlear Corp, 1986). 2. W Luxford, W F House, “House 3M cochlear

implant: Surgical considerations,” Annalr of Otology, Rhinoloay and Laryngoloay 96 no 128 supplement (January/February 1987) 13.

3. P Burgio, “Safety considerations of cochlear implantation,” Otolaryngologic Clinics of North America 19 (May 1986) 240.

Inexpensive Sunglasses May be Sufficient Recently, several sunglass manufacturers have developed expensive sunglasses that block at least 99% of ultraviolet (UV) rays. Unless exposure to UV radiation is excessive, standard glasses proba- bly are adequate for most people, according to the June 1989 issue of the Mayo Clinic HeaW Letter.

If a person’s eyes are sensitive to light, or if he or she overexposes them to the sun, tanning lamps, welding arcs, or lasers, UV radiation can injure the corneas. Within six to 12 hours of exposure, the corneas become inflamed, and it may feel as if the person has sand in his or her eyes. Also, it may be extremely painful to open the eyes in bright light. The corneas usually heal by themselves in a few days; however, extreme long-term UV exposure may lead to cataracts.

People may require the maximum-protection lenses if they spend long hours in the sun, partic- ularly in water or snow; work or spend time at high altitudes; or are outdoors in the summer between 10 AM and 2 PM. Other indicators include previous cataract surgery, phototherapy, and prescription medications (eg, oral contracep- tives or acne treatments that contain tetracycline) that increase sensitivity to UV radiation. Other- wise, less expensive general purpose sunglasses

that block some UV rays may be fine.

be determined by the darkness or tint of the lenses. Dark tints block brightness but do not necessarily block UV radiation. Very dark lenses that lack UV protection caw the pupils to dilate, allowing more UV rays to reach the eyes than not wearing sunglasses at all.

The UV-absorbing quality of sunglasses cannot

Information Available on Clinical Trials By calling a toll free number, the public can learn about new clinical trials involving experi- mental therapies for people with the acquired immune deficiency syndrome (AIDS), according to the May 5, 1989, issue of Medicine & Health. The public can get eligibility criteria, study loca- tions and durations, and contacts for each study. The National Institute of Allergy & Infectious Diseases is sponsoring the hot line. The number is (800) TRIALS-A or (800) 874-2572. Infor- mation can be given both in English and Spanish.