May 5, 2009 Feature

Primary Prevention Pays Off

Detecting Small Hearing Threshold Shifts That Signal Hearing Loss

Small changes in a dynamic system often have dramatic long-term effects. This theory is often referred to as the "butterfly effect" and is an excellent description of how small acts—such as one-on-one counseling or increasing sensitivity of the case definition with respect to hearing threshold shift—have the potential for long-term impact on preventing noise-induced hearing loss in the workplace.

Medical experts and health care resource managers have long recognized occupational audiology as a major player in hearing loss prevention in industrial and military environments. Today's audiologist has a significant role to play in all three levels of prevention—primary, secondary, and tertiary (World Health Organization, 2006).

Primary preventive measures involve administrative and environmental controls that include the proper selection and use of hearing protection, noise-reducing equipment designs, continuing on-the-job education designed to modify behavior, and monitoring workers in designated risk environments. These measures are often taken for granted by employees because noise-induced hearing loss (NIHL) is often gradual, painless, and non-lethal—but can have a serious negative impact on an individual's quality of life.

When these primary prevention measures fail, secondary methods are engaged, including recognizing the early stages of NIHL and taking action to prevent its progression through intervention, follow-up screening, and clinical validation of results.

Primary and secondary preventive measures have proven successful in reducing the number of employees with hearing loss (McIlwain, Gates, & Ciliax, 2008). If they are unsuccessful, however, managing a negative long-term outcome moves to the tertiary tier—creating significant fiscal, logistic, and administrative expenditures for employers and taxpayers—that involves hearing aid fitting, aural rehabilitation, and additional administrative and environmental controls.

Challenges to hearing conservation efforts occur when small hearing threshold shifts—which can signal the early onset of NIHL—are overlooked. These small threshold shifts can result from improper hearing protection selection, lack of program compliance, or acoustical changes in the work environment, circumstances that warrant closer examination and detailed documentation. Because NIHL is irreversible, audiologists should aggressively assess early-warning physical manifestations of hearing loss. The audiologist's recommendations on when and how to react to threshold shifts often affect the remainder of an individual's life. The premium time for early intervention is when those small but permanent hearing changes caused by hazardous noise exposure are identified.

When a permanent threshold shift occurs (a 10 dB shift from the baseline audiogram in the four-frequency average of 2 KHz, 3 KHz, and 4 KHz in either ear), the employee's baseline audiogram is reset. However, audiologists can make the most of early intervention with increased sensitivity for engaging in secondary preventive measures.

The answer may be to use higher frequencies as an indicator for early intervention (but not for replacing permanent threshold shifts). Higher frequencies of hearing are more sensitive to hazardous noise exposure. For instance, employees with a small but permanent threshold shift (average positive 10 dB threshold shift at 4 KHz and 6 KHz or a positive threshold shift of 15 dB in either 4 KHz or 6 KHz, in either ear) should be informed that a slight change in hearing has occurred, be interviewed about possible causes, and given a more detailed explanation of the cause and further education about the long-term personal and professional consequences of hearing loss. A physical re-assessment of the workplace also may be in order.

A similar method of prevention has been used successfully by other professions for decades. For example, the American Heart Association defines a blood pressure level of 140/90 mm Hg or higher as hypertensive. A blood pressure between 120/80 mm Hg and 139/89 mm Hg is considered pre-hypertensive and a marker of increased risk of high blood pressure. At that level, health care providers strongly encourage patients to take steps to prevent high blood pressure by providing patient education and encouraging self-monitoring, even though the blood pressure is not yet abnormal.

Although hearing loss does not pose a threat to life, it poses an indirect hazard in many industrial or military work environments in which the ability to hear is necessary for safety and proper job performance. Small, permanent, high-frequency shifts should be viewed as an early indicator for more aggressive intervention strategies to prevent further NIHL.

A life without hearing is unjustifiable—quantitatively and qualitatively—when compared to the cost of prevention.

Scott D McIlwain, AuD, CCC-A, a major in the U.S. Army, is an adjunct assistant professor of epidemiology and biostatistics at the Texas A&M Health Science Center Graduate School of Rural Public Health, College Station. Contact him at scott@hearwell.org.

Bryan Sisk, RN, BSN, MPH, is a retired major in the U.S. Army. He is with Ambulatory Health Services, Central Texas Veterans Health Care System, and an adjunct faculty member at the Texas A&M Health Science Center Graduate School of Rural Public Health, College Station. Contact him at Bryan.sisk@va.gov.

cite as: McIlwain, S. D.  & Sisk, B. (2009, May 05). Primary Prevention Pays Off : Detecting Small Hearing Threshold Shifts That Signal Hearing Loss. The ASHA Leader.

References

McIlwain, D., Gates, K., & Ciliax, D. (2008). Heritage of the Army audiology and the road ahead: The Army hearing program. American Journal of Public Health, 98(12), 2167–2172. See figure 2 and the explanation on 2169.

World Health Organization (2006). Injury prevention and control: A guide to developing a multisectorial plan of action, surveillance and research. Cairo, Egypt: Author.



Three Levels of Prevention

Primary: Counter measures for factors that are present before an actual injury event

Secondary: Protective and monitoring measures for a possible injury event

Tertiary: Clinical management after an injury event

Information compiled from World Health Organization (2006). Injury prevention and control: A guide to developing a multisectorial plan of action, surveillance and research.Cairo, Egypt: Author.



  

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