A paradigm approach toward predicting barotrauma

The approach

The occurrence of otitic barotrauma in an otherwise healthy individual has been attributed to eustachian tube (ET) dysfunction.^[1-5] Hence, an approach to predict ET dysfunction would essentially support the prediction of barotrauma. Literature review revealed a recent consensus on ET dysfunction^[10] which classifies ET dysfunction into three subtypes, namely, dilatory ET dysfunction, patulous ET dysfunction, and baro-challenge-induced ET dysfunction [Figure 1].

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Figure 1:

Eustachian tube dysfunction subtypes with signs and symptoms.

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Dilatory ET dysfunction is often preceded by an upper respiratory tract infection, or sometimes by an exacerbation of allergic rhinitis, which presumably causes inflammation in the ET orifice or lumen, leading to its dysfunction. Patulous ET dysfunction presents with symptoms of aural fullness and autophony and is thought to be caused by an abnormally patent ET.^[10] On the other hand, baro-challenge-induced ET dysfunction is defined as the presence of aural discomfort, popping, or pain, which only arises in case of ambient pressure changes, without abnormalities on otoscopy or tympanometry,^[10] which is typical for occurrences explained above. In literature, this type of ET dysfunction has been described as a cause of barotrauma not only during scuba diving or on descent from altitude but also under conditions of less marked ambient pressure fluctuation.

A paradigm approach towards predicting barotrauma

Several tests exist to test for pressure regulation function of ET.^[11,12] Simple, non-invasive tests include Valsalva, Politzer, and Toynbee tests and ET catheterization, however, have been described to have poor sensitivity and specificity in diagnosis of ET dysfunction.^[11,12] ET function in individuals with intact tympanic membranes may be determined by manometry, tympanometry, or sonotubometry, which also have been shown to have poor predicting probability of an ET dysfunction during baro-challenge. This makes the diagnosis or detection of baro-challenge-induced ET dysfunction challenging with present routine tests.

Tailor et al. reviewed 16 studies involving seven different types of ET function tests.^[13] The tests in the included studies were required to measure ET function in patients reporting baro-induced ear symptoms or barotrauma. In their review, they found that the Bluestone’s nine-step test was the most commonly used outcome measure, with overall test sensitivity and specificity ranges of 37–100% and 57–100%, respectively. Tympanometry test sensitivity was consistently poor (0–50%) though specificity was higher (52–97%). Although they recommended that no single test could diagnose baro-induced ET dysfunction which could used in clinical practice, they suggested that a combination of the nine-step test with other objective tests or patient-reported measures as most promising in the diagnosis of baro-induced ET dysfunction.

The nine-step test was used by Hussein and Abousetta^[14] to predict ear barotrauma in aviators and found the test provides a reliable prediction of barotrauma with 89% sensitivity and 100% specificity. Uzun et al.^[9] studied use of nine-step test in prediction of middle ear barotrauma in scuba divers and found the test to be the most efficient with highest predictive values (positive predictive value 83% and negative predictive value of 95%), whereas the Valsalva and Toynbee tests were unreliable in predicting barotrauma (PPV of the Valsalva and Toynbee tests was 0% and 25%, respectively). In a systematic review of tests for ET function conducted by Smith and Tysome^[11] and Doyle et al.,^[12] it has been observed that the nine-step test and the 7-item ET dysfunction questionnaire (ETDQ-7) have highest sensitivity and specificity in detection of ET dysfunction. The summary of nine-step test is presented in Table 1 and schematic representation of Bluestone’s nine-step test is presented in Figure 2.

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Figure 2:

Schematic representation of Bluestone’s nine-step test.

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In 2012, McCoul et al. published a questionnaire for the evaluation of ET dysfunction named ETDQ-7 [Table 2].^[15] The questionnaire was validated with high sensitivity and specificity of >95%. Although the questionnaire was primarily used to discriminate between patients with obstructive type of ET dysfunction and controls, Van Roeyen et al.^[16] demonstrated that ETDQ-7 provides excellent discrimination between patients with baro-challenge-induced ET dysfunction and healthy controls. Therefore, ETDQ-7 can be useful in the diagnostic process of baro-challenge-induced ET dysfunction.

Recommendation

At present, the aircrew and paratroopers are screened for ET dysfunction by otoscopy and tympanometry before exposure to decompression runs. Literature review has shown that Bluestone’s nine-step test and the ETDQ- 7 questionnaire to have high negative predictive value (>95% specificity). Hence, the nine-step test and ETDQ-7 questionnaire are recommended as additional screening tests to screen for baro-challenge-induced ET dysfunction. The tests may be included for the evaluation of aircrew reporting for review after the resolution of otitic barotrauma or after ENT procedures before exposure to baro-challenge in the decompression chamber. With its high negative predictive value, the ETDQ-7 questionnaire, which can be easily administered, may also be used in the field by the authorized medical attendant for assessing presence of any possible baro-challenge-induced eustachian dysfunction in aircrew whenever required.