1

Introduction

During November 2008–October 2010, approximately 100,000 personnel of the military forces under the Royal Thai Army (RTA), took charge of peacekeeping operation in the Southernmost Provinces of Thailand. 565 of them sustained bomb blast injury and 99 personnel who had been affected by multiple injuries were transferred to Phramongkutklao Hospital.

The blast injury can be divided into 4 categories: 1) Primary blast injury; the direct result of the change in atmospheric pressure from the blast wave, usually occurs in air-containing organs, such as middle ear, lungs or gastrointestinal tract, 2) Secondary blast injury; occurs when metallic or sharp objects explode into several fragments and bounce off by the blast and cause blunt or penetrating injury, 3) Tertiary blast injury; occurs when the injured body is forcefully bounced off by the blast and hits other objects, or the injuries caused by structural collapse and fragmentation of buildings and vehicles, 4) Quaternary blast injury; the other injuries from the explosion, such as dust, smoke or chemical substance choking, burn wound from hot gas of the explosion .

Primary blast injury (PBI) has direct traumatic effects to the ear and auditory system. The symptoms of the PBI are as follows: 1) Tympanic membrane perforation, the injured personnel – whose location is close to the center of the blast, or in the confined area such as in the building – who were detected to have tympanic membrane perforation were more than half of the total number of the injured personnel. And if the distance from the blast increases, the number of the injured personnel who had Tympanic membrane perforation decreases . 2) Sensorineural Hearing Loss (SNHL) refers to a hearing loss as a result of temporary neurapraxia in the receptor organs of the inner ear, manifested by deafness, tinnitus, and vertigo. If dynamic overpressures are high enough, the ossicles of the middle ear can be dislocated. When the pressure is directly delivered through inner ear, it can damage the oval and round window. As a result, traumatic disruption of the oval or round window can cause permanent hearing loss .

In 2007, Tungsinmunkong reported the result of the terrorists’ bombings experience. The number of patient who experienced SNHL and tinnitus is approximately 66.67%. And the number of patient who experienced tympanic membrane perforations is 49.67%. Most of them were civilians who were attacked by the bomb blast in the open and semi-open space. There were 3 studies that reported on the otologic manifestations from the blast injury in the confined or closed space. The most common clinical presentations were SNHL, tinnitus, tympanic membrane perforations and vertigo.

The purposes of this study are to 1) determine the prevalence of SNHL and the otologic manifestations from primary blast injury among Military Personnel in Southernmost Thailand, and to 2) evaluate the impact of violence of explosive devices and distance from explosive devices on the prevalence of SNHL in various space conditions.

2

Materials and methods

The study design is an observational descriptive cross-sectional study. The population of this study is ninety-nine personnel who were affected by multiple injuries, transferred to Phramongkutklao Hospital during November 2008–October 2010 and treated at the veteran ward. Seventy-six injured personnel (without any history of trauma, otologic diseases or hearing impairment prior to perform the peace keeping operation) were included in our study.

The Military personnel who were affected from multiple injuries had an Ear Nose and Throat examination after they were stable from life-threatening conditions by the otolaryngologists, including audiogram by the audiologist with the Clinical Audiometer, Amplaid 460. The examinations were divided into Pure tone air-conduction audiometry: 8 frequencies; 250 Hz, 500 Hz, 1 kHz, 2 kHz, 3 kHz, 4 kHz, 6 kHz and 8 kHz. And Pure tone bone-conduction audiometry: 4 frequencies; 500 Hz, 1 kHz, 2 kHz and 4 kHz.

2

Materials and methods

The study design is an observational descriptive cross-sectional study. The population of this study is ninety-nine personnel who were affected by multiple injuries, transferred to Phramongkutklao Hospital during November 2008–October 2010 and treated at the veteran ward. Seventy-six injured personnel (without any history of trauma, otologic diseases or hearing impairment prior to perform the peace keeping operation) were included in our study.

The Military personnel who were affected from multiple injuries had an Ear Nose and Throat examination after they were stable from life-threatening conditions by the otolaryngologists, including audiogram by the audiologist with the Clinical Audiometer, Amplaid 460. The examinations were divided into Pure tone air-conduction audiometry: 8 frequencies; 250 Hz, 500 Hz, 1 kHz, 2 kHz, 3 kHz, 4 kHz, 6 kHz and 8 kHz. And Pure tone bone-conduction audiometry: 4 frequencies; 500 Hz, 1 kHz, 2 kHz and 4 kHz.