Overview
Otic barotrauma (OBT) is traumatic injury of the middle ear and tympanic membrane resulting from a high-pressure differential existing between the middle ear and external environment. In common daily activities (e.g., driving to different elevations, air travel), individuals may experience slight changes in pressure of the middle ear, which results in mild, self-limiting otologic symptoms (e.g., slight aural discomfort). However, it is possible for these same activities to cause OBT, which is an increasingly encountered issue by otolaryngologists and otologists given the wide adoption of air travel; Over the past 50 years, the number of passengers has increased from 310 million to 3.7 billion annually, with approximately 1 million passengers flying at any given moment , and this number will likely continue to grow. Estimating the overall prevalence of OBT though varies considerably by types of activities that individuals participate in (e.g., scuba diving) and risk factors such as history of otitis media and head and neck cancers. To help address this clinical issue, this chapter will provide an overview of the pathophysiology, diagnosis, and medical and surgical management of OBT.
Eustachian tube and middle ear function
As described previously, the pathophysiology of OBT is related to an imbalance of pressures between the air-filled space of the middle ear and the external environment, which are separated by the tympanic membrane. Normally, the Eustachian tube, which connects the middle ear and the nasopharynx, will open briefly while yawning or swallowing to equalize middle ear pressure via the levator and tensor veli palatini muscles. Eustachian tube dysfunction (ETD), which reduces the ability for the Eustachian tube to open, may arise from several reasons such as increased mass near the Eustachian tube’s nasopharyngeal opening (e.g., tumor, enlarged adenoids) or swelling due to infections (e.g., acute otitis media). In addition, the middle ear mucosa and underlying vessels promote equalization of middle ear pressure via gas exchange. These intact physiologic processes are required to accommodate for ambient pressure changes that follow Boyle’s law, which states that as the volume of a gas increases, the pressure decreases proportionally, and vice versa. If the middle ear compartment’s pressure is not able to equalize properly, OBT can occur through a variety of mechanisms that are described below.
Pathophysiologic mechanisms
Air travel
Flying is the most common etiology of barotrauma , and can occur during both ascent and descent. As the aircraft ascends, the ambient cabin pressure gradually decreases, and the middle ear pressure must equilibrate through swallowing and passive Eustachian tube ventilation. If the middle ear gas volume remains elevated, the relatively positive pressure of this compartment will cause lateral movement of the tympanic membrane. During aircraft descent, the middle ear pressure conversely must reduce. Unlike ascent, the Eustachian tube cannot passively diffuse air from the middle ear, which may be related to the increase prevalence of OBT during descent. If compensations are not adequate, the tympanic membrane may bruise, bleed, or rupture, and the middle ear may produce fluid exudates.
Diving
OBT that occurs due to diving has a similar mechanism to flying, but pressure changes are of much greater magnitude, which rely on height and fluid density. Given water’s greater density than air and a diver’s relatively uncompensated state compared to a passenger in a dynamically-pressurized plane cabin, a minor change in water depth leads to a relatively greater increase in pressure where OBT has been observed to occur most often near the surface of the water. During descent, external pressure from the surrounding water moves the tympanic membrane medially and reduces middle ear space gas volume. Without performing a Valsalva maneuver, the pressure differential between the middle ear and external environment will continue to grow, leading to subsequent hemotympanum, middle ear edema, or tympanic membrane rupture. If the diver attempts to perform a Valsalva maneuver but the descent occurs too rapidly or has a blocked Eustachian tube, this may lead to inner ear barotrauma. Inner ear barotrauma may also occur during descent due to external water pressure pushing the tympanic membrane and stapes into the oval window. Within the labyrinth, perilymph and endolymph are not compressible, and the increased intracranial pressure may lead to rupture of the oval or round windows , and formation of a perilymphatic fistula. The presence of a perilymphatic fistula then allows for gases in the middle ear to enter in the inner ear, which may lead to permanent hearing loss. While ascending, OBT can also occur if middle ear gas does not pass through the Eustachian tube, leading to relatively a positive pressure gradient in the middle ear compartment.
Hyperbaric oxygen therapy
It is important to recognize that patients receiving hyperbaric oxygen therapy (HBOT) such as in settings to promote wound healing from burns and infections and improve flap circulation may experience OBT, which is one of the most common complications following HBOT. While receiving treatment in either a monoplace or a multiplace chamber, the supine positioning increases venous congestion and hinders the ability to increase pressure in the middle ear space. Given the middle ear’s relatively lower pressure compared with the ambient environment, medial movement of the tympanic membrane occurs with transudation of fluid in the middle ear space and OBT.
Blast injuries
Following an explosion, the creation of air pressure waves leads to a rapid increase in the ambient air pressure. In turn, the lack of time to equalize pressure between the middle and external ear results in OBT. , A more in-depth discussion is provided in Chapter 2, Chapter 5 .
Diagnosis
History
When evaluating a patient with suspected OBT, a history should be focused on understanding possible exposures to changes in ambient pressure through mechanisms such as those previously described. Patients with minor OBT may have mild symptoms including aural fullness and ear discomfort. It is important to note that ear pain is not a reliable indicator of OBT; in a study of repeated dives, 82% of dives were asymptomatic and did not report ear pain. For patients with more severe OBT, they may describe hearing loss due to transudative effusions in the middle ear space, hemotympanum, or tympanic membrane rupture. Often, patients with tympanic membrane rupture may report improvement of their pain and discomfort involving the affected ear. If patients describe may describe vestibular symptoms (e.g., vertigo, nausea) , or auditory symptoms (e.g., tinnitus, hyperacusis, and hearing loss), inner ear barotrauma may have occurred with possible development of a perilymphatic fistula.
Additional history should also be directed toward eliciting if the Eustachian tube’s ability to ventilate air may be compromised or if ETD is present. Specifically, history should be gathered for the presence of structures that impede the Eustachian tube’s ventilation function externally (e.g., adenoid hypertrophy or nasopharyngeal cancer ) or internally via polyps. Inflammation of the nasopharynx from several conditions such as gastroesophageal reflux disease, allergies, or viral infections may also decrease the ability for the Eustachian tube to open adequately.
Physical examination and evaluation
The physical examination for suspected OBT begins with examining the external auditory canal, which may reveal cerumen or exostoses that may prevent visualization of the tympanic membrane and be removed if possible. An otoscope should be used to examine the tympanic membrane for signs of hemotympanum, perforation, or effusions in the middle ear space. The Teed classification of middle ear barotrauma can be used to document the appearance of the tympanic membrane. While it may be challenging to obtain otoscopic examination prior to air travel or diving, the Teed classification can be used to monitor for the development of OBT following HOBT. There are six grades: 0 (normal tympanic membrane), 1 (erythema and retraction of the tympanic membrane), 2 (erythema of the entire tympanic membrane with slight hemorrhage), 3 (erythema of the entire tympanic membrane with gross hemorrhage), 4 (air–fluid level with gross blood), and 5 (tympanic membrane perforation) ( Fig. 13.1 ). , Periodic documentation with this classification system allows to track the resolution of OBT injury. Additionally, in severe cases of barotrauma, facial nerve weakness may be present, which is reversible.
If hearing loss is present, examination with a tuning fork and audiometric evaluation should be performed, which may reveal a conductive (e.g., hemotympanum, effusion) or sensorineural (e.g., inner ear barotrauma or perilymphatic fistula) hearing loss. If patients present with vestibular symptoms, patients should be examined for a positive Hennebert’s sign (positional nystagmus when the involved ear is moved into the dependent position) or gait instability.
Management
Acute management
In the acute setting, if symptoms of OBT are recognized, individuals should attempt to reverse the underlying etiology causing the ambient pressure change. If OBT begins during HOBT, additional pressurization should not occur to provide time for pressures in the middle ear space to equilibrate. If symptoms persist or continue to worsen during HOBT, emergent intervention via myringotomy or tympanostomy tubes may be performed. To minimize the risk of injury to middle and inner ear structures, these procedures should be performed in the anterior inferior quadrant of the tympanic membrane. If individuals suspect OBT while diving, they should move in the opposite direction that caused symptoms to emerge (e.g., more shallow water after moving to a greater depth). In certain scenarios, however, individuals such as those operating aircrafts, it may not be appropriate to rapidly change altitudes.
If tympanic membrane rupture occurs, smaller defects will generally heal in several weeks, whereas larger defects and those that are not resolving will require surgical repair. Antibiotics are generally not needed unless if signs of infection develop. Ototoxic antibiotics such as gentamicin, neomycin sulfate, or tobramycin should not be used to prevent causing sensorineural hearing loss. At present, there is also no evidence to support the use of corticosteroids to promote tympanic membrane healing.
If inner ear barotrauma is suspected, patients should receive prompt conservative management to decrease intracranial pressure by remaining supine with head elevation for 1 week, use stool softeners, and avoid the Valsalva maneuver , while monitoring for resolution of audiovestibular symptoms. In most cases, these symptoms will improve in several days.
At present, there is no standardized approach to diagnose perilymphatic fistula. Historically, middle ear exploration was performed to directly visualize perilymph leakage, but the limited volume of perilymph in the inner ear is approximately equal to three drops of water, , and intermittent perilymphatic fluid flow raises the question if this diagnostic method is reliable. If surgical exploration is pursued, it may be difficult to discern if fluid in the middle ear may be present from middle ear mucosa or local anesthetic. Transudates in the middle ear space may also increase in volume due to heat from surgical instruments or manipulation of the middle ear mucosa. Recent studies suggest that improved resolution and availability of high-resolution computed tomography (HRCT) and magnetic resonance imaging (MRI) may adequately diagnose perilymphatic fistulas. , The presence of pneumolabyrinth or air in the inner ear or fluid in the round and oval windows on HRCT may suggest a perilymphatic fistula, which are repaired surgically. MRI may be used to visualize for the presence of congenital conditions such as Mondini dysplasia, which may raise suspicion for perilymphatic fistula as it increases the risk of formation; in these scenarios, the otolaryngologist may be more likely to pursue surgical management as the risk of meningitis is increased if left untreated. ,
Prevention
After addressing OBT in the acute setting, any predisposing factors for future development of OBT should be identified. Underlying causes of ETD that may prevent pressure equalization of the middle ear space should be addressed during the history and physical exam. If patients can anticipate when they will be in settings that may increase the risk of OBT, prophylactically using medications such as decongestants before diving or flying may improve ETD and reduce the probability of developing OBT. At present, however, limited evidence exists to support the use of decongestants to prevent OBT in children. For healthcare providers administering HBOT, evidence exists to support that a slow, linear increase in pressurization may decrease the risk of developing OBT.
Prophylactic myringotomy and/or tympanotomy tube placement can be used in select settings if patients experience recurrent OBT. In settings where the middle ear will remain dry, such as prior to HBOT and flying, these procedures do not significantly increase the risk of infection. However, this should not be performed to prevent OBT secondary to diving as this will increase the risk of otitis media.
Providing patient education plays an important role to prevent future OBT. Teaching patients how to perform techniques to promote pressure equilibrium between the external and middle ear can reduce the risk of developing OBT in settings with changes in ambient pressure such as the Valsalva maneuver (forced exhalation against a closed mouth and nose to open the Eustachian tube), Toynbee maneuver (swallowing air while pinching the nose to open the Eustachian tube), or yawning or swallowing. During HBOT sessions, using devices, such as the EarPopper, may help increase air pressure in a relatively negative middle ear space, , which uses a modified Politzer Maneuver (constant stream of air into the Eustachian tube), , to help improve middle ear ventilation. Additionally, if patients have an upper respiratory infection, which temporarily increases congestion and reduces Eustachian tube functioning, they may consider postponing activities that have increased risk for OBT until it resolves.
References
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