There are a growing number of medically complex children with implanted devices. Emergency physicians with a basic knowledge of these devices can troubleshoot and fix many of the issues that may arise. Recognition of malfunction of these devices can reduce morbidity and mortality among this special population. In this article, we review common issues that may arise in children with gastrostomy tubes, central nervous system shunts, cochlear implants, and vagal nerve stimulators.
Key points
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Medically complex children often have devices in place to improve their quality of life. These devices can malfunction and the emergency department practitioner should know basic troubleshooting.
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Gastrostomy tubes can become dislodged, obstructed, or infected.
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Ventriculoperitoneal shunts can become obstructed or infected, often with signs of increased intracranial pressure (obstruction) or fevers (infection) as presenting clues.
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Cochlear implants, used by some children with sensorineural hearing loss, can present with infectious complications in the setting of local surgical or ear related infections (otitis media, mastoiditis, rarely meningitis) requiring antibiotic therapy. Noninfectious complications are usually transient and include facial nerve palsy, vertigo, and tinnitus.
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Vagal nerve stimulators can be induced to fire by placing a strong magnet over the upper left chest to help break seizures, but this should be used only as an adjuvant to more definitive antiseizure medication therapy.
Video content accompanies this article at http://www.emed.theclinics.com .
Introduction
Medically complex children are frequently recipients of advanced technology to support or treat an underlying structural or physiologic problem, as well as improve their overall quality of life. This article reviews how to trouble shoot emergency problems that might arise related to these technological devices. This review specifically focuses on issues with feeding tubes, central nervous system (CNS) shunts, cochlear implants, and vagal nerve stimulators.
Gastrostomy tubes
Background
Common indications for using gastrostomy feeding tubes in children include neurologic impairment leading to swallowing dysfunction, chronic disease and resulting malnutrition, increased caloric needs, inability to take medications, and recurrent aspiration.
Types of devices
Feeding tubes vary both in anatomic positioning and method of placement. For enteral nutrition expected to be 4 to 6 weeks in duration, a simple nonsurgical nasogastric tube can be placed. For time periods lasting longer than 1 to 3 months, a gastrostomy tube or G-tube is indicated, where a direct connection is created from the stoma, through the anterior abdominal wall and to the patient’s stomach.
Gastrostomy tubes can be placed in several different ways, including endoscopically, surgically, and fluoroscopically. See Table 1 for common G-tubes used in children. Percutaneous endoscopic gastrostomy (PEG) tube are placed by pediatric gastroenterologists under general anesthesia or deep sedation. , G-tubes can then be converted to low-profile PEG buttons for convenience with the additional benefit of cosmetic appearance and reduced risk of dislodgement.
| Tube | Details |
|---|---|
| Pigtail G-tube |
|
| Gastrojejunostomy (GJ) tube |
|
| Balloon G-tube |
|
| Low-profile G-tubes (eg, secured by balloon, bulb, loop) |
|
| Mushroom-tip G-tube |
|
In patients with severe gastroesophageal reflux, G-tubes may also be combined with a gastric fundoplication surgery, in which the fundus of the stomach is wrapped around the distal esophagus to decrease the risk of aspiration.
A gastrojejunal (GJ) tube is used in patients who do not tolerate intragastric feedings due to severe reflux, intractable vomiting, or gastroparesis. With this device, the tube has a proximal port into the stomach for medication administration, and a more distal port in the jejunum for continuous feeds. GJ tubes are generally placed under fluoroscopic guidance by an interventional radiologist or via guidewire placement during gastroduodenoscopy by a gastroenterologist. ,
Complications
G-tube–related complications can be categorized as mechanical, infectious, gastrointestinal, pulmonary, and metabolic. Mechanical complications include tube clogging, migration, dislodgment, kinking, and obstruction. All can lead to patient discomfort and interruption of feeds. Tube dislodgment is the most common minor complication, occurring in nearly 65% of children within 5 years of initial tube placement. , , Clogging of the tube may be related to unexpected interactions that occur via enteral feeding tubes or the use of slowly degrading and coated medications. Local irritation at the exit site of the G-tube may also occur. Stoma-related complications include an enlarged stoma site due to a large wall incision, leakage of gastric fluid, granulation tissue, and fistula formation. , ,
Infectious complications occur 5% of the time, and can include cellulitis of the exit site, peritonitis, subcutaneous abscess formation, septicemia, and even septic shock. They commonly occur in the period immediately after PEG placement or after a “routine” PEG change.
Gastrointestinal complications include the development or worsening of gastroesophageal reflux disease, abdominal discomfort, bloating and cramping. Small bowel obstruction, adhesion formation, bowel perforation and hemorrhage, though much less common, have also been reported. Other uncommon complications include aspiration pneumonia, which should be considered in any patient who develops respiratory distress. Metabolic issues, such as refeeding syndrome, in those with chronic nutritional deficiencies and electrolyte imbalances are possible as well.
Emergency Department Management
On presentation for a mechanical G-tube concern, obtain a thorough history of the tube from the caretaker. Questions regarding the size of the tube (measured in French [Fr]), type of gastrostomy tube, date of tube placement, and timing of dislodgement (if pertinent) should be asked. Report of vomiting or feeding intolerance is important when assessing for gastrointestinal or metabolic complications.
Physical examination should include thorough inspection of the skin exit site for erythema, drainage, bleeding, granulation tissue, and fluctuance. Assess the size, type, and length of the tube at the level of the skin and the integrity of the anchoring (including the amount of water in the balloon if present). These factors may indicate whether or not there is migration of the tube, or breakage of the balloon. Abdominal distention, rigidity, tenderness, and loss of bowel sounds are important aspects concerning for obstruction or an acute abdomen. Fever, tachycardia, or hypotension may be present with G-tube site infection or peritonitis.
Tube replacement
The date of initial tube placement is important to note, as an immature versus mature tract is treated differently. Once the original gastrostomy tube is placed, the tract itself begins to mature in 1 to 2 weeks and is well-formed by approximately 4 to 6 weeks after placement. Consequently, bedside replacement of a tube dislodged within 4 weeks of initial placement should be avoided, as it could lead to tube migration, false tract formation, or peritoneal spillage through the immature track. Patients will need endoscopic or surgical replacement in these situations, and surgical consultation should be obtained.
In addition, the G-tube tract can start to close anywhere from 8 to 24 hours after dislodgement. If more than 24 hours have passed since tube displacement, a subspecialist consultation is often needed if replacement is not feasible. In the setting of GJ tube displacement, contact an interventional radiologist, as the tube must be replaced under fluoroscopy.
For mature tracts, emergency physicians can generally replace these tubes bedside. Replacement tubes can include a simple Foley catheter, a traditional, or button G-tube. It is important to have not only the same sized tube that was dislodged, but also a smaller size available should the stoma begin to close. Apply topical lidocaine to the stoma if you anticipate a tight stoma or several hours have elapsed since dislodgement. Next, check the size and prepare the tube to make sure the balloon works. Generously lube the tip of the replacement tube, then grasp the tube at distal end and use steady pressure while twisting it into the stoma. A helpful trick is to place the tip of the replacement catheter in ice-cold water for 10 to 15 seconds to make it firmer, which can aid in successful placement.
Inflate the balloon to designated volume. Pull back on the tube to ensure placement and secure the disc ( [CR] ). Once placed, check the pH of the secretions from the tube to confirm placement; this is often all that is necessary if the tract is mature.
If replacement was difficult, the tract is immature, or gastric sections cannot be obtained from a replacement tube, x-rays of the abdomen with 5 to 10 mL of contrast in the feeding tube can be obtained to confirm placement. If the outline of the stomach or jejunum is clearly visible on these films, then the tube is appropriately positioned.
There currently are no standardized guidelines for the indications warranting confirmatory studies. A newer diagnostic modality being studied is point-of-care ultrasound (POCUS). In 3 published case series to date, POCUS was deemed to be a successful tool in guiding and confirming pediatric G-tube replacement, with benefits including efficiency, noninvasive methodology, and minimization of radiation exposure from x-ray films.
Tube obstruction
In the setting of tube obstruction or clogging, try flushing the tube with warm water, the patient’s feeds, or a carbonated beverage using a 1-mL to 3-mL syringe. Pancreatic enzymes also can be trialed. If this remains unsuccessful, it may require tube replacement and gastrointestinal (GI), Interventional Radiology, or surgical consultation.
Stoma site issues
If there is leakage at the stoma site, skin protectants such as topical sucralfate or soft paraffin can be placed around the exit site to help create a physical barrier and promote healing. , Magnesium hydroxide, petroleum jelly, or zinc oxide may also be used.
In these cases of leakage, avoid replacement of the tube with a larger bore size as it may result in further enlargement of the stoma site. Instead, appropriate balloon inflation and anchoring of the probe should be confirmed by pulling the tube back gently until the balloon is flush against the internal abdominal wall. , If there is still concern for an enlarged stoma, consider removal of the tube for a short period to promote constriction of the tract (with specialist consultation). A smaller lumen Foley catheter can then to be placed to prevent tract closure.
If granulation tissue is present and large, moist, or friable, it may be treated acutely with chemical cautery. The surrounding normal skin must be protected with a barrier cream to avoid burning. , For patients who may not tolerate silver nitrate, topical steroids is an off-label alternative, with triamcinolone 0.1% cream commonly used.
Infection
Uncomplicated exit site infections can be treated with antibiotics that cover typical skin flora. Treatment options for children with mild infections include topical mupirocin or bacitracin/polymyxin B, or oral courses of cephalexin or clindamycin. If the child has unstable vital signs, symptoms of a rapidly progressing infection, not tolerating oral intake, or other signs of peritonitis, admission for intravenous antibiotics is indicated.
Disposition
Dislodged and dysfunctional tubes are often replaced in the emergency department (ED). Once the dislodged tube is replaced, the patient can be discharged home to follow up with the service that placed the tube as an outpatient.
In cases of problematic G-tubes that the ED is unable to replace or troubleshoot, consultation with the institution-dependent service caring for the tube (GI, IR, surgery) should be done to determine whether an inpatient admission is necessary for definitive management. If the G-tube is unable to be replaced or the patient requires continuous feeds and requires a GJ tube, the patient require admission for intravenous (IV) hydration and close monitoring of electrolytes. In the event of major complications, including G-tube cellulitis that failed oral antibiotics, admission for further workup and IV antibiotics will be required.
Key Clinical Points
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Medically complex children may require gastrostomy tubes for long-term nutrition due to neurologic impairment, chronic disease, and malnutrition, increased caloric needs, inability to take medications, and recurrent aspiration.
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G-tube–related complications can generally be categorized as mechanical or infectious, with the most common being tube dislodgement and exit site infection.
Management by the ED provider requires a thorough history and physical examination surrounding the tube characteristics. Knowledge of the timing of the initial placement will dictate required consultants. If <4 weeks from initial tube placement, endoscopic or surgical replacement is required. If >4 to 6 weeks, the ED provider is generally able to replace these G-tubes at bedside.
Central nervous system shunts
Background
Indications
Congenital indications for shunt placement include neural tube defects, Arnold-Chiari malformation, Dandy-Walker syndrome, aqueductal stenosis, and arachnoid cysts. Acquired causes include brain tumors, infections such as meningitis, intraventricular hemorrhage particularly in premature infants, idiopathic intracranial hypertension, and traumatic brain injuries.
Ventricular shunt types
Hydrocephalus describes the buildup of cerebrospinal fluid (CSF) in the ventricular system. When there is excessive CSF production, obstruction in the normal outflow, or decrease in absorption of CSF into the blood stream, a ventricular shunt is used to divert the CSF from within the ventricles, cyst, or subdural spaces to an area outside the brain.
The ventricular shunt itself consists of a proximal catheter, a reservoir, a 1-way valve, and a distal catheter. The proximal catheter is most commonly placed in the right lateral ventricle and connected to a subcutaneously placed reservoir that helps with CSF sampling and intracranial pressure management. This reservoir connects to a distal catheter through a one-way pressure valve that prevents retrograde CSF flow and ascending infection.
Shunts differ primarily in the location of their distal catheters. Most often used is a ventriculoperitoneal (VP) shunt, in which the distal tip ends in the peritoneum. Other shunt types include ventriculoatrial, ventriculopleural, and ventriculocholecystic shunts, which drain into the atrium, pleura, or gall bladder, respectively.
The main differences between specific VP shunts are the type of valve used, and whether the valve is programmable. Fixed pressure valves are set at predetermined pressures to guide the amount of CSF drainage. They thus require neurosurgical revision if changes need to be made. Programmable shunts are newer and allow for the CSF flow to be adjusted with an external device, using a coded magnetic field to communicate to the intracranial device. More recently, antibiotic-impregnated shunt catheters have also been developed to decrease hardware infection-related complications.
Complications
The term shunt failure is not well defined in the current literature. One widely accepted definition is any condition that leads to the inability to reach the goal of neurosurgery, resulting in shunt revision, replacement, removal of the valve, or even in patient death. Admissions for shunt complications are more common than for initial placements, accounting for nearly half of all admissions for hydrocephalus. Shunt failure within the first year of placement is known to occur in between 35% and 40% of cases with the most common reasons being shunt obstruction and infection. Most shunt revisions are thus done within the first year after initial VP shunt placement, particularly in infants during their first year of life. ,
In children, mechanical malfunction is the most frequent cause of CSF shunt failure, with estimated incidences as high as 50%. Common mechanical complications include shunt obstruction, disconnection, migration, and mechanical failure. Obstruction of CSF flow at any point along the length of the shunt results in increased intracranial pressure (ICP). Proximal shunt obstruction is more common than distal obstruction, and resulting symptoms are due to the ICP increase (headache, vomiting, irritability, and possibly cognitive changes), and if significant enough, the Cushing triad (hypertension, irregular breathing, bradycardia) and cranial nerve palsies (particularly CN VI) can be seen. Proximal catheter obstruction can occur due to brain debris, choroid plexus, blood, or tissue reaction. Rarely, obstruction at the valve itself can occur, and this is usually due to blood clot formation. Distal catheter obstructions are much less common, and can be a result of severe constipation leading to increased intra-abdominal pressure and impaired CSF drainage, or abdominal pseudocyst formation. Appropriate treatment of significant constipation can often relieve malfunction in these cases, allowing for avoidance of shunt exploration and revision.
A disconnected shunt can be a result of direct trauma or due to normal growth of pediatric patients. The more distal the connection is from the ventricle, the higher the likelihood of disconnection. Stress rupture of the shunt tubing usually takes place on the anterior neck or upper part of the chest wall and can be caused by repeated stretching and increased mobility. Patients describe a “popping” sensation with sudden movement, or there will be localized swelling at the exit site of the shunt on the scalp. Once the disconnection occurs, clinical symptoms of shunt failure and elevated ICP may follow.
In cases of distal tubing migration, the findings are related to the body compartment in which the migration has occurred. There are reports of the distal shunt tubing migrating through the bowel, stomach, liver and gallbladder, scrotal sac, bladder, and bronchi, as well as different areas of the heart. Perforation is the most severe form of this complication, and has been reported in almost every possible hollow viscus. Extrusion may also occur, with commonly reported sites being the anus, umbilicus, mouth, and vagina. ,
Mechanical valve failure is usually a result of malfunction in the different draining spaces. Examples being ventriculoperitoneal shunt failure in the setting of abdominal pseudocyst formation, ventriculopleural valve failure because of pleural fluid accumulation, and ventriculoatrial shunt failure due to pulmonary embolism or pulmonary hypertension.
Cerebral shunt infection is a feared yet frequent complication, with an overall infection rate of 11.7% within 24 months of uncomplicated initial shunt placement. Other data suggest that most (>90%) infections occur within 6 months of initial shunt placement or revision. Infections are thought to be due to colonization at the time of shunt placement. The common pathogens arise from the skin and enteric systems, and include Staphylococcus aureus and coagulase-negative Staphylococcus species such as Staphylococcus epidermidis , and gram-negative bacilli. Symptoms and signs of shunt infection may include fever, headache, nausea/vomiting, irritability, erythema or tenderness over the shunt site, and evidence of CSF leak or purulent drainage.
Another chronic complication may include slit ventricle syndrome, which refers to a group of varying pathophysiologic disorders unified by their finding of chronic headaches in shunted patients, with normal to small ventricles on imaging. These can be due to various etiologies, namely intracranial hypotension, shunt-related migraine, and increased ICP with or without a working shunt.
Emergency Department Management
History and physical
A high index of suspicion must thus be maintained by the provider evaluating a shunted patient with symptoms of increased ICP. History to gather includes the type of shunt the patient has, indication and timing of placement, the date of the last revision (if any), previous history of infections, and the patient’s presentation with past episodes of shunt malfunction.
Shunt failure may present in a myriad of ways: with a rapid or slow onset, and a variable rate of symptom progression. The common triad of symptoms in older children includes headaches, vomiting, and somnolence. Drowsiness, blurred vision or diplopia, neck or back pain, and new-onset or increase in seizures may also occur. Chronic manifestations of shunt malfunction may also be present including mild psychomotor slowing, decreased vision, unsteady gait and falls, decreased school performance, and mood changes. Credence should be given to the concerns of the caregiver, as with any child, as they are most perceptive of the child’s status.
The goal of the initial physical examination is to determine whether the patient is showing signs of worsening ICP, as this can quickly result in impending herniation. Begin with an assessment of the patient’s vital signs, noting any hypertension, irregular respirations, and bradycardia (Cushing triad). In all patients, note the general level of consciousness, pupil size, and reactivity, and for any signs of posturing. In infants, assess for irritability, vomiting, a bulging fontanelle, and increasing head circumference. Bradycardia and apneic spells also may be present in this age group. Palpate along the route of the shunt tube, assessing for any subcutaneous fluid connection or disconnection.
Diagnostic studies
Imaging
Clinicians rely heavily on imaging to evaluate for shunt-related complications. Noncontrast head computed tomography (CT) can be used to evaluate for ventriculomegaly, transependymal flow of CSF, and other signs of hydrocephalus, such as sulcal effacement and mass effect on the basal cisterns. It is important to compare old images, as change in ventricular size is most important. To minimize the radiation dose of CT scans, a fewer number of slices can be obtained by using “thick cuts” that still allow for evaluation of the ventricular size. CT of the chest and abdomen assists with evaluation of the distal end of the catheter, looking for pseudocysts, and CSF loculations.
Fast-brain MRI sequences are an alternate mode of imaging useful in evaluating the patient with a CNS shunt and can provide information about ventricular size, transependymal flow, subdural effusions, CSF over drainage, ventriculitis, and brain abscess formation. General advantages include lack of exposure to ionizing radiation, increased soft tissue and ventricular detail, and avoidance of sedation or anesthesia that is often needed when obtaining a routine pediatric brain MRI. , Be sure to note whether or not the valve is programmable, as they have different MRI safety precautions. Also be familiar with the settings of a programmable valve, as an inadvertent change could require reprogramming of the VP shunt.
A radiographic shunt series is another initial study that can be obtained, in which x-rays are obtained along the length of the shunt. This includes frontal and lateral radiographs of the head and neck, and frontal radiographs of the chest and abdomen. These plain films evaluate the shunt tubing for discontinuity, kinking, and catheter migration.
An upcoming area of research evaluates the utility of POCUS optic nerve sheath diameter (ONSD) testing as a screening tool for increased ICP and VPS failure in children. A high-frequency, high-resolution (5–14 MHz) linear array probe is used for evaluation, in which axial images are obtained via a transbulbar approach with the patient in a supine relaxed position. This method is thought to be less invasive and a quick diagnostic tool, although more data are needed to establish normal and optimal values of ONSD to validate its role as a screening modality. , Fast MRIs, if available, may be a practical and adequate study to replace CT examinations in the evaluation of a child with shunt-treated hydrocephalus.
Shunt taps
The risk of shunt infection is highest in the first 6 months after placement or revision. Tapping the shunt may thus be necessary to evaluate for shunt infection, determine the flow, and the pressure within the shunt system. Malfunction of the shunt without ventricular dilation can occur in ∼10% of pediatric patients who have had past infections, , so in some patients with a concerning history yet normal imaging studies, tapping the shunt can help clarify if there is shunt obstruction.
Whenever possible, it is preferable that the shunt tap is performed by a neurosurgery team. Use stringent sterile conditions, by preparing the scalp with povidone-iodine solution and accessing the reservoir with either a 23 or 25-gauge butterfly needle system attached to tubing. CSF collected can be sent for cell counts, protein, glucose, culture, and sensitivities.
Shunt malfunction is a concern if there is poor flow or increased opening pressure. To measure flow, check to see if CSF returns spontaneously. If not, gentle aspiration with a small syringe to encourage fluid leak can be attempted. If >1 mL of back pressure is needed, this is concerning for poor flow. Opening pressure can be assessed using a plastic manometer attached to the needle to fill a column of CSF, held vertically at a level above the patient’s ear while the patient is supine. Pressures above 25 cm H 2 O are considered elevated. In general, proximal shunt obstruction is the most common etiology for poor flow while elevated pressure with good flow usually indicates distal obstruction or valve issues. In the event of impending herniation, it is important the emergency clinician is capable of performing a shunt tap to acutely decrease ICP.
Shunt flow studies
A shunt flow study or the “shuntogram” consists of assessing the flow the CSF along the tube after injection of a small amount of radiopaque contrast into the reservoir. This is usually done when imaging and shunt tapping are inconclusive. For a study to be normal, the entire shunt system must be visualized and the radionuclide agent must evenly fill the peritoneal cavity. ,
Mechanical complications
Shunt obstruction, disconnection, and migration are treated with neurosurgical revision of the shunt, either the single segment for distal or valve obstructions or a total shunt revision for proximal shunt obstructions. If there are concerns for acutely worsening ICP while awaiting neurosurgical evaluation, shunt tapping for CSF removal can be a lifesaving maneuver. Otherwise, acute ICP decreasing measures, as studied in other populations, primarily should be instituted to decrease risk of impending herniation (raising the head of the bed to 30°, mannitol, acetazolamide, hypertonic saline, and the maintenance of normal systolic blood pressure).
Shunt infections
The highest treatment success rate for management of CSF shunt infections is reported with shunt removal, external ventricular drain placement, and treatment with intravenous antibiotics only. Some institutions will also administer intraventricular antibiotics to directly penetrate the CSF, shorten treatment course, and promote higher long-term cure rates. ,
In cases of abdominal pseudocyst, the new shunt should be placed in a different site such as the atrium or pleural cavity.
The choice of antibiotic therapy is guided by susceptibility patterns of the infecting organism, degree of antibiotic penetrance into the CSF, previous patient infections, and local practice patterns. The initial regimen should cover a broad spectrum of microbial flora and gram-positive organisms.
Disposition
It is imperative that neurosurgical consultation is obtained early in the evaluation and management of these children. Patients with suspected shunt obstructions, broken shunts, or migrated shunts must be admitted for revision or transferred to a center that is able to perform the revision.
Infected shunts will likely require shunt removal and intravenous antibiotics, as determined by the neurosurgical service. Patients with a suspected shunt malfunction may be discharged if all studies and clinical appearance are normal, after discussion with the subspecialist to ensure close follow-up. Given the high risk of complications, it also reasonable to admit patients who have normal imaging and flow studies to allow for observation and possible delayed revision.
Clinical Key Points
- 1.
Ventricular shunts are the mainstay of treatment for hydrocephalus due to both acquired and inherited causes. The location of the distal catheter varies but is most commonly located in the peritoneum.
- 2.
Shunt-related complications account for nearly half of all admissions for hydrocephalus, with mechanical obstruction being the most frequent cause of CSF shunt failure. Infection is also common, usually occurring within 6 months of shunt placement, and caused by skin flora.
- 3.
Shunt failure is a neurosurgical emergency; thus, clinicians rely on imaging to evaluate for complications. If these studies are inconclusive, after consultation with neurosurgery, tapping the shunt and obtaining a shunt flow study may be necessary.
- 4.
Most mechanical shunt complications will need revision or surgical correction. Infected shunts require shunt removal, and IV antibiotics.
Cochlear implants
Background
Cochlear implants (CIs) are surgically implantable devices that have revolutionized care of the child with sensorineural hearing loss too severe to be helped by hearing aids. CIs have been approved for use in children older than 12 months of age since 2000, and in March 2020 this age was lowered to 9 months.
What is a cochlear implant and how does it work?
A cochlear implant is an electronic device that can provide sound to a person who is profoundly deaf from a sensorineural cause. CIs bypass the bony structures of the ear directly stimulating the auditory nerve. They do not help hearing in patients with conductive hearing loss. The device ( Fig. 1 ) consists of an external portion that lies on the skin posterior to the pinna, and a part that is surgically placed under the skin. The device has the following parts: (1) a microphone, (2) a speech processor (which arranges sounds picked up by the microphone), (3) a transmitter with a receiver/stimulator (which receives signals from the speech processor and converts them into electric impulses), and (4) an electrode array running through the cochlear organ. These electrodes collect the electrical impulses from the stimulator and send them to different regions of the auditory nerve, allowing the patient to hear sounds.
