Otological Dive Conditions

Georgina Heinzel-Kienberger/ Medical Student / Exeter University

Third year medical student, Georgina takes us through a review of the literature regarding the aetiology, diagnosis and management of the most common otological conditions; barotrauma and decompression sickness.

Over recent years, the number of people recorded to have taken part in scuba diving has decreased with an estimated 2,717,000 divers in the United States in 2019 showing a 4.63% decrease from 2018. ⁽¹⁾ However, according to a 2021 Sports and Fitness Industry Report, although the number of casual divers (one to seven dives per year) decreased by 6.7% from 2019 to 2020, the number of more serious divers (eight or more dives per year) increased by 1.3% among the American population. ⁽²⁾

Dive injuries occur primarily due to the effects of pressure when moving through the water. There is an extensive medical questionnaire which divers are required to fill in before in order to go some way to mitigating these injuries.

When done correctly with experienced guides, diving is usually not an unsafe activity. Nevertheless, incidents do occur, even with professionals. In a report by Divers Alert Network (DAN) between 2010 and 2013, 43.75% of injuries were head and neck related and of these, 72.53% were injuries to the ear. ⁽³⁾

Injuries relating to the ear such as barotrauma (injury due to pressure change) and decompression sickness (DCS) are more common dive issues.

This review discusses the aetiology, diagnosis, and management of common otological consequences of diving with a specific focus on inner ear decompression sickness (IEDCS), inner ear barotrauma (IEBt) and middle ear barotrauma (MEBt).

Incidence

Dive injury incidence is low. In a study by the DAN, who looked at 9,000 divers who did 135,000 dives, decompression illness occurred at a rate of 0.03%. ⁽⁴⁾ The study was conducted following safe and accepted dive procedures. When an injury occurs though, rapid diagnosis is beneficial. This can be a challenge due to the diverse range of symptoms and severity. Decompressing after a dive is important but one should also pay close attention to symptoms that may arise afterwards.

Figure 1 shows the anatomy of the middle and inner ear for reference.

Physics

Decompression Illness

Decompression illness is an umbrella term for two distinct aetiologies: decompression sickness and arterial gas embolus.

Decompression sickness is more relevant to otology and is largely impacted by Henry’s Law.

Henry’s Law states, ‘as the partial pressure of a gas above a liquid increases, that gas becomes proportionally likely to dissolve in that liquid’.

Due to the increased pressure that divers are under, the gas they inspire has a higher pressure. This can cause supersaturation of tissues meaning that they are at their capacity for the amount of inert gas they can hold. ⁽⁴⁾

Decompression sickness most commonly occurs when divers surface too quickly as the gas in tissues isn’t given enough time to be released slowly leading to supersaturation and bubble formation. These bubbles of evolved gas can cause a direct or indirect effect. The direct effect results in damage as the bubbles can occlude vessels, leading to ischaemia. The indirect effect is caused by an inflammatory response which activates the clotting cascade. Decompression sickness can occur at different levels of severity, but at worst can cause serious damage to the central nervous system and the cardiorespiratory system. ⁽⁵⁾ Arterial gas embolus can occur as a consequence of DCS. It is when the alveoli become over inflated and nitrogen bubbles enter the bloodstream and travel to the brain, for example, potentially blocking major vessels. This is usually less relevant to otology.

Barotrauma

Barotrauma, the damage to tissues caused by the direct effects of pressure, follows Boyle’s Law.

Boyle’s Law explains that, ‘as you descend deeper into water, the volume of a gas decreases but the pressure increases substantially’.

All enclosed spaces in the body such as the paranasal sinuses and the inner and middle ear can be affected by this increase in pressure. If this pressure build up is left, it can lead to pain, haemorrhage and perforation of anatomical structures.⁽⁵⁾

Divers are taught to equalise early and often as they descend, using the Valsalva manoeuvre, to avoid barotrauma.⁽⁶⁾ This manoeuvre equalises pressure across the tympanic membrane. When equalising, the air is forced through the eustachian tubes into your middle ear. This increases the volume of gas in your middle ear and decreases the pressure. This happens because as the diver ascends the trapped air expands by three to five times in volume, dependent on dive depth. ⁽⁷⁾

Middle Ear Barotrauma

Aetiology

The most common difficulties experienced by divers are middle ear barotrauma (MEBt) and eustachian tube dysfunction. ⁽⁸⁾ Eustachian tubes connect the middle ear space to the throat. This connection allows the pressure in the middle ear space and the external auditory canal to remain balanced or equalised. On the descent, pressure release is an active process. On the ascent, however, it happens passively. Disruption to the release of pressure can cause issues.

As divers descend, ambient pressure increases meaning that the volume of the gas in the middle ear decreases. This creates a vacuum. If equalisation cannot sufficiently compensate for this, MEBt occurs. The vacuum created causes blood flow to local vessels to increase in turn causing inflammation. ⁽⁸⁾ Blood vessels can then rupture and with the subsequent pressure increase, perforation of the tympanic membrane occurs.

Diagnosis

MEBt can present with difficulty equalising, discomfort and a stuffy sensation in the ear. ⁽⁹⁾ Diagnosis is difficult as often requires symptom reports from the patient which can be subjective. If suspected, an otoscopic examination is required to determine the grade of the injury.

There are three grading systems for MEBt: the Teed, the modified Teed and the O’Neill. The Teed Classification (1944) has been modified over the years but the current and most relevant is the O’Neill Classification. ⁽¹⁰⁾ The O’Neill consists of three grades as shown in Table 1.

Table 1 – The O’Neill Classification (8)

Management

Most cases of MEBt are transient and may only require rest, a course of steroids or antibiotics. Grades 0-1 are mostly treated conservatively. In more severe cases, such as tympanic membrane perforations surgery might be considered. Diving should not be considered until injury and symptoms are fully resolved and in the case of perforation, the tear is fully closed. ⁽¹¹⁾

Inner Ear Barotrauma (IEBt) and Inner Ear Decompression Sickness  (IEDCS)

Aetiology

As the external pressure increases during descent, the tympanic membrane is pushed inwards. This increases the pressure in the cochlea. When the pressure differential rises above 90mmHg the ET tubes are no longer functional meaning the equalising of pressure can no longer take place. ⁽¹²⁾ IEBt can be termed implosive or explosive. The perilymphatic duct connects the cochlea to the subdural space in the superior cranial fossa. Subsequent failed Valsalva manoeuvres can therefore increase the intracranial pressure and the pressure in the cochlea. An increase in perilymphatic fluid pressure causes an explosive rupture whereas a decrease leads to an implosive rupture. Implosive rupture especially can have many subsequent effects such as tearing the internal cochlear membrane or basilar membrane.

A study by Nachum et. al. revealed that of divers diagnosed with IEDCS, 48% of them were suffering from other decompression illness symptoms. ⁽¹³⁾ Although not fully understood, IEDCS is believed to occur due to the formation of a bubble of compressed gas in the endolymphatic and perilymphatic spaces due to the supersaturation of local tissues. ⁽¹⁴⁾ A correlation between persistent foramen ovale (PFO) (a right-to-left shunt) and IEDCS has been seen suggesting that gas bubbles can enter the arterial circulation from the venous circulation rather than being exhaled from the lungs. This can cause ischaemic events due to gas emboli. In a study by Mitchell et. al., in cases where IEDCS was detected, 77% were also found to have a large right-to-left shunt. ⁽¹⁵⁾

Diagnosis

IEBt can present with problems with balance and coordination as well as tinnitus, sensorineural hearing loss and vertigo. ⁽¹⁶⁾ Surgery may be required if the symptoms do not improve over an observational period, usually of about ten days. Some injuries relating to IEBt have been seen to spontaneously resolve over several days, although instances of this are thought to be underreported due to less severe symptom presentation. ⁽¹⁷⁾

The overlap in symptoms between IEBt and IEDCS leads to misdiagnosis. Divers are often divided into risk groups considering various factors:

• Previous dive incidents
• Use of decompression stops with a controlled ascent
• The time of onset of symptoms after the dive
• Diving with mixed gas

The presence of these factors makes a diagnosis of IEDCS more likely. There is a criterion known as HOOYAH, as seen in Table 2, which is used to understand the aetiology of a presenting patient and differentiate between the diagnoses of IECDS and IEBt.⁽¹⁹⁾

Table 2 – HOOYAH criteria used to differentiate between IEBCS and IEBt ⁽¹⁹⁾

Important differences which aid in distinguishing between Inner Ear Decompression Sickness (IEDCS) and Inner Ear Barotrauma (IEB) are as follows:

Management

The importance of differentiating between the two becomes apparent when looking at their treatment methods. ⁽⁸⁾ The gold standard treatment for IECDS is urgent recompression using hypobaric oxygen treatment.

This works by increasing the pressure of the environment and consequently decreasing the size of the gas bubble (usually nitrogen) allowing more oxygen to be delivered to tissues and aiding dissolved gas offloading. ⁽¹⁴⁾ Until this can be administered, 100% oxygen must be given. ⁽²⁰⁾ Steroids to reduce inflammation can be given as an adjunctive treatment option. 

The incidence of PFO is higher in a patient with IECDS compared with the general population. This is a good indication for screening using Doppler sonography. However, a diagnosis of PFO would not necessarily restrict further diving as it is possible for people with PFO to dive following the ‘low bubble diving’ guidance. ⁽²¹⁾

For acute IEBt, bed rest and avoidance of actions that induce pressure transmission are advised. Suggested treatment for IEBt is usually a course of steroids at a high dose, for example, 250mg prednisolone for three days, followed by a steroid taper course. ⁽²²⁾ In circumstances where the patient’s hearing continues to deteriorate, further investigation is required, often by surgery. This is also the case if there is thought to be a perilymphatic fistula. For any patient experiencing IEBt, a high-resolution CT scan of the temporal bone is required to rule out further complications. ⁽²³⁾

After treatment patients are to be counselled on the further risks of diving and really that they should try to avoid it all together. However, a paper by Parell et. al, suggested that this advice might be ‘unnecessarily restrictive’. ⁽²⁴⁾ This study looked at twenty-one patients who, after receiving counselling, still decided to continue diving despite their IEBt diagnosis. They were taught effective middle ear equalisation techniques. After yearly follow-ups no further damage was seen in the inner ear of any of these patients posing a potential challenge to the conventional teaching advice on this. 

Conclusion

Diving carries a relatively high incidence of otological consequences. It is not only important that clinicians and instructors are aware of these but also divers themselves. More research into how we can improve patient management and what can be done to decrease the incidence of these pathologies needs to be conducted and published. It is also critical that these findings are presented to divers in a clear and timely fashion.

Patients should be appropriately counselled on prevention such as correct equalisation techniques and the importance of following guidance. The effects of diving irresponsibly can be devastating. Even in situations where otological injury is not severe, it can cause panic and the cascade of much more dangerous consequences.

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