Training Transcript

Transcript for Immittance Training Part 1

– [Instructor] Immittance is one component of the hearing screening protocol used for Wyoming’s children. Otoscopic inspection of the ear and either the use of pure tone audiometry or otoacoustic emissions are also components of an age-appropriate hearing screening for infants, toddlers, and preschoolers. The immittance screening equipment currently available in Wyoming’s child development centers is appropriate for use with children nine months of age or older. Immittance screening is not part of the screening protocol currently used for children younger than nine months of age. So, why use immittance? Immittance screening provides information regarding the status of the middle ear portion of the auditory system. Immittance can provide information about the current status of middle ear function, if earwax or cerumen is occluding the ear canal, whether or not the eardrum is intact, and the current status of pressure equalization tubes should they be present. Immittance does not screen for hearing acuity. Even persons with profound bilateral sensorineural hearing loss can pass an immittance screening if their middle ear systems are functioning properly. Conditions in the middle ear can and do fluctuate or change day-to-day, week-to-week, and month-to-month. Immittance measures screen the status of the middle ear as it exists at the time of screening. Immittance screening results reflect these fluctuations and may be especially useful in determining when or if to make a referral to the child’s primary care physician. Let’s begin now by talking about and looking at how sound energy, for example, a parent’s voice, makes the journey from the time it is spoken to the time it is heard. In a normally functioning ear, sound energy from the environment is collected by the pinna, or outer ear. The sound energy then travels through the outer ear to the tympanic membrane, or eardrum. In turn, when the sound energy strikes the eardrum, it causes the eardrum to vibrate. The ossicular chain, which is connected to the eardrum, will then begin to vibrate as well. The three bones of the ossicular chain, the malleus, incus, and stapes, are the smallest bones in the human body. You may have heard them referred to as the hammer, anvil, and stirrup. These three bones are collectively known as the ossicles and are suspended by tiny ligaments and form a bridge across the air-filled space called the middle ear cavity. The ossicles convert the acoustic sound energy, your voice, into mechanical energy. The mechanical energy is passed on to the cochlea in the inner ear, where it becomes hydraulic energy. Microscopic hair cells in the cochlea convert the hydraulic energy into electrical energy in the form of nerve impulses. The nerve impulses then travel via the central auditory nervous pathway to the auditory cortex of the brain. Here, it becomes meaningful information for the listener. One way in which the hearing process we just described may be disrupted is if something prevents sound from being conducted through the ear canal, eardrum, or middle ear cavity. Let’s take a look at some of the ways in which the middle ear system may be affected as well as we would want it to. In order for the eardrum to vibrate freely and therefore efficiently pass on sound, the air pressure on either side of the eardrum needs to be as equal as possible. It is the job of the eustachian tube, which connects the middle ear to the back of the nasal pharynx, to allow air into the middle ear cavity and keep pressure on either side of the eardrum equal to one another. Typically, if the eustachian tube is functioning properly, the middle ear space will be filled with air pressure equal to that of the environment. For example, if you are on the top of a mountain, the pressure in your middle ear cavity should be the same as the pressure of the thinner mountain air. Similarly, if you find yourself in Death Valley, the pressure in the middle ear should be equal to that of the much denser air found at this low altitude. This all depends on a properly functioning eustachian tube. I want you to think about when you fly in an airplane. When you enter the aircraft, the pressure in your middle ear cavity is the pressure you brought aboard from the airport waiting area. After you are airborne, the cabin will have been pressurized and you may find yourself trying to pop your ears, or in other words, trying to equalize the pressure in your middle ear cavity to that of the now changed cabin pressure. This equalization of air pressure is accomplished via a healthy functioning eustachian tube. You may experience an uncomfortable flight if your eustachian tube is unable to equalize the air pressure in your middle ear space with that of the airplane cabin. Again, the eustachian tube’s function is responsible for the ventilation or delivery of air to the middle ear space. If the eustachian tube is doing its job well, the pressure in the middle ear space will be equal to the pressure of the environment around us. If the eustachian tube is not functioning well and therefore not ventilating the middle ear space, negative middle ear pressure may occur. Let’s take a look at how negative pressure forms in the middle ear. The middle ear space is lined with a mucosal lining similar to that found in your nose. This mucosal lining absorbs oxygen or air delivered to the middle ear cavity via the eustachian tube. If the middle ear mucosal lining absorbs or uses up the available oxygen and there’s no more being delivered due to a dysfunctional eustachian tube, then the negative middle ear pressure may develop. In other words, the pressure inside the middle ear space is negative or less than the pressure found in a person’s surrounding environment. This negative pressure in the middle ear space can cause the eardrum to become retracted or pulled inward, away from the eardrum’s natural and more neutral position. Imagine the air being sucked out of an empty plastic bottle. When the air pressure inside the bottle is reduced, it creates a vacuum inside the bottle and the sides are pulled inward by the negative pressure or vacuum inside. So, if negative middle ear pressure continues in the middle ear cavity for a period of time, fluid may be drawn from the mucosal lining of the middle ear, the same lining that absorbed the oxygen. When this fluid initially forms, it’s relatively pure. However, coughing or sneezing may allow bacteria to enter the middle ear space via the eustachian tube, causing the fluid to become infected as a result. This fluid in the middle ear cavity is referred to as effusion. As you will come to understand, it is important to identify excessive negative middle ear pressure since it may be a precursor to the development of middle ear effusion. While your screening procedures and results are an excellent tool to identify middle ear problems, ultimately, only the physician provides the diagnosis. Either condition, negative middle ear pressure, or middle ear effusion, may interfere with the movement of the eardrum and the conduction of sound through the middle ear system, resulting in a conductive hearing loss. Again, it is very important to understand that a child can have fluid in his or her middle ear space that may not be infected and therefore not require immediate medical management. But it is equally important to understand and to remember that the presence of middle ear fluid, whether infected or not, may cause conductive hearing loss and, as a result, affect a child’s ability to have access to the full spectrum of speech and language. Our job as screeners is to use admittance to identify children who may have middle ear problems and, when appropriate, refer them to their physician. For children with persistent and/or recurrent middle ear fluid, the primary care physician may deem it appropriate to refer the child to an otolaryngologist, or ear, nose, and throat doctor, for further evaluation and treatment. The ENT physician may recommend the insertion of pressure equalization tubes, or PE tubes, as they are commonly called. In the absence of a properly functioning eustachian tube, PE tubes allow for the equalization of the middle ear pressure to that of the environment. PE tubes can do the work for the eustachian tube until the eustachian tube is capable of functioning properly. Remember our example of the plastic bottle? What would you do if you wanted to eliminate the vacuum inside the bottle? By poking a hole in the bottle, it would allow air outside the bottle to enter the bottle, equalizing the air pressure and eliminating the vacuum, or negative pressure. A ventilation tube in the eardrum is designed to provide the same function. Another circumstance that may affect immittance screening results is if there is something occluding, or blocking, the flow of sound in the outer ear canal. When wax, or cerumen, is present in the ear canal wall-to-wall and edge-to-edge, sound may simply not be able to go through, under, or around it and reach the ear canal. This may cause a conductive hearing loss. However, a fully occluded ear canal due to wax is very uncommon. The presence of a perforation in the eardrum may also affect immittance screening results. Depending on the size and location, a perforation, or hole, in the eardrum may interfere with the eardrum’s ability to vibrate and conduct sound energy efficiently. It’s very important to note that a hole, or perforation, in the eardrum may also allow bacteria to enter the middle ear space. Therefore, a perforation of the eardrum is a concern because it can put a child at risk for both hearing and health issues. Therefore, once a perforation is suspected, a child should be referred to his or her primary care physician. Immittance screening is an objective measurement of the function of the middle ear system. No response is required from the child during immittance screening, and background noise will not interfere with obtaining valid results. Few directions to the child, if any, are needed. The child simply needs to sit, stand, or lie quietly in order for the immittance screening to be completed. You may want infants and toddlers to sit on a familiar lap while the hearing screening, including immittance, is completed. Having preschoolers stand close to you while you are seated is also a good option. It’s also recommended that when beginning an immittance screening, you don’t ask the child for his or her permission. Posing this question may lead to a lack of cooperation on the part of the child. Comments such as, “Can I put this in your ear?” or “This won’t hurt,” are usually the child’s cue that the screening may very well hurt, which it won’t. Simply and gently begin the screening process. If the child asks, “What does that do?” simply respond with something like, “This looks in your ear,” or “This checks your eardrum.” Taking advantage of diversions for younger children is also very helpful. For example, you could encourage them to watch the lights on the equipment or have them watch the tracing develop on the screen. This may very well keep them occupied while the screening is being completed. You could also try talking to the child while conducting an immittance screening. This may have a calming effect on that child. The effects of creating a relaxed testing environment will greatly assist you in obtaining reliable immittance screening results. Before performing immittance screening, the screener must first visually inspect the external ear canal using an otoscope. If you see a foreign object or drainage from the ear during your cursory otoscopic inspection, do not proceed with the screening. Instead, make a medical referral to the child’s primary care physician. If, however, you see PE tubes, note their presence on the child’s screening paperwork and proceed with the immittance screening. The immittance screening results may provide valuable information about the current status of the tubes. Also, while inspecting the outer ear, you may wanna notice the size and direction of the ear canal. This information will help you determine the correct probe tip for that particular child. Probe tip fit, as you will quickly learn, is critical in obtaining accurate and reliable immittance screening results. When choosing the probe tip size, it is recommended you choose one that is slightly larger than the child’s ear canal opening. Generally, you will find the same size probe tip is appropriate for similar age groups. After the appropriately sized probe tip is selected, it is fitted over the metal or plastic stem of the immittance probe assembly. The tip should fit completely over the end of the stem. Next, gently pull the child’s ear up and back. This will help to straighten the ear canal and obtain an airtight seal by the probe tip. The probe tip is then firmly applied to the ear canal opening. The goal is to obtain an airtight seal. Getting and maintaining a good seal at the ear canal opening is one of the most important steps in obtaining accurate immittance screening results. Once a good seal has been obtained, the equipment will automatically begin the screening process. Depending upon the equipment being used, a flashing light or a steady green light on the probe assembly or display screen may appear. This indicates that the external ear canal is indeed sealed and that screening has successfully begun. Check the equipment for messages like air leak or block or testing. Such signals or messages will indicate the status of the seal. If you’re having difficulty obtaining or maintaining a good airtight seal, here are several helpful suggestions. Try removing the probe tip, take a look at the ear canal, re-examine its direction, and then reinsert the probe tip. Pulling the pin gently up and back to help straighten the ear canal may also help. You may also find that you just simply need to change the size of the probe tip. Sometimes the probe tip is being pushed against the ear canal wall, causing your immittance equipment to indicate a block signal. Troubleshooting this situation can be as simple as lightly and gently adjusting the angle at which the probe tip is inserted into the entrance of the ear canal. Now that we’ve discussed how immittance screening results are obtained, let’s move on to understanding what the results reflect. A cursory description of how immittance equipment operates is a good place to start. The immittance probe assembly has three openings or portals. One portal allows a limited amount of air pressure to be introduced into the sealed ear canal. As air pressure is delivered into the ear canal, an audible tone is emitted from a second opening. A small microphone located in the third portal measures the loudness of the sound reflected or bounced back from the eardrum as it moves in response to the pressure changes of air inside the sealed ear canal. What this three-step process is doing is measuring how easily an eardrum can move in response to pressure changes. In other words, as the eardrum is pushed gently inward and pulled outward by changing air pressure in the sealed ear canal, the immittance unit is measuring how well the eardrum is able to move. A typical eardrum should move easily in response to these pressure changes. In addition, your immittance equipment will also reflect if wax is completely occluding the ear canal, if there is a perforation of the eardrum, or if ventilation tubes are functioning properly. When the immittance screening is complete, your equipment will display the results in the form of a tympanogram, and if the option was selected, an indication of whether or not an acoustic reflex was present or absent. The information provided by these results will help determine if the child passes or fails the hearing screening. If the results suggest a fail, immediately repeat the immittance screening. Be sure that you secure and maintain a good ear canal seal. If you obtain a second fail result, you can, but do not need to, obtain a third screening result for verification purposes. If the first screening indicates a pass, then the screening does not need to be repeated. A tympanogram, like the one shown here, is a graphic representation, or picture, of how well an eardrum moves. There are three key components we consider when looking at a tympanogram. They are ear canal volume, tympanic membrane compliance, and middle ear pressure. Under some circumstances, we will also consider the absence or presence of the acoustic reflex. Understanding how each of these components, or measurements, is derived, is essential to your ability to understand immittance results. It’s also necessary for you to understand the relationship between these components. It’s important to let you know that individual manufacturers of immittance screening equipment do not always label these components in a uniform fashion. Therefore, it’s recommended that you familiarize yourself with individual screening equipment features and designations. Let’s take a look at how the specific values that determine a tympanogram are derived. After an airtight seal is obtained, your immittance equipment measures the space, or volume, beyond the probe tip. That amount is the ear canal volume, or point A on our example. The ear canal volume measurement provides information regarding the integrity of the eardrum. Is it intact? Do results suggest a possible perforation, or open PE tube? Ear canal volume also includes information about the status of the ear canal. Is it possibly blocked or occluded with cerumen? Be aware that ear canal size will vary depending upon the subject’s age and physical size. In other words, an infant’s ear canal volume will be smaller than the ear canal volume of an older child or adult. Also, a person’s right and left ear canal volumes are usually pretty similar to each other. If you observe a large difference between the ear canal volumes of a child’s ears, you should carefully evaluate your results. Just as your feet are usually the same size, so are your ear canals. A small ear canal volume, when the child’s age and physical size are taken into account, may be indicative of an occluded ear canal, or that the person’s ear canal volume probe tip is pushed against the ear canal wall. If the child has impacted wax, the immittance screening results will reflect a smaller ear canal volume number than what you would expect for the age and size of the child being screened. Large ear canal volumes, on the other hand, may be reflecting open or patent PE tubes, or it could also be indicating a perforation of the tympanic membrane. In the presence of a perforated tympanic membrane or patent PE tube, a large ear canal volume will be reflected because the screening equipment is measuring the volume of the ear canal plus the volume of the middle ear space. So remember, it is good practice to compare the ear canal volumes of the child’s right and left ears. Most of the time, we expect them to be similar. The next component of a tympanogram we will discuss is middle ear pressure. Middle ear pressure refers to the amount of air pressure in a person’s middle ear cavity in relation to the amount of air pressure in the room. Once an airtight seal is obtained and the ear canal volume has been measured, your immittance equipment will begin to look for the point at which the eardrum moves the best. The amount of air pressure in the ear canal will be changed from a positive amount of pressure to a negative amount of pressure via the probe assembly while it is held to the child’s ear. What the screening equipment is looking for is the pressure amount that was needed to equalize the air pressure on both sides of the eardrum. So remember, an eardrum moves best when the pressure is equal on both sides of it. Once the screening equipment determines the amount of middle ear air pressure, it’s displayed on your screen as a numerical value in decapascals. Again, your equipment will use a small amount of positive air pressure to gently push the eardrum inward. Then a small change to negative air pressure within the ear canal will slightly, but gently pull the eardrum back toward the ear canal. In a normal healthy ear, middle ear pressure is at or near zero decapascals. As the immittance screening unit increases and decreases this air pressure within the ear canal, the pressure amount at which the eardrum moved best is found. On this example, the middle ear pressure is reflected as point B. The third component we will discuss is tympanic membrane compliance. You may also sometimes see it referred to as peak compliance, static compliance, or just compliance. Tympanic membrane compliance refers to how much the eardrum moved while middle ear pressure was being determined. The eardrum mobility or compliance is determined by how the probe tone from the probe tip is reflected off the eardrum and back to the probe assembly. If the eardrum is flexible and compliant, the probe tone reflects less and the sound is passed on through the auditory system. But if the eardrum is stiff or non-compliant, it will easily reflect the probe tone back to the probe tip As the immittance screening unit increases and decreases air pressure in the ear canal, the equipment not only determines the point at which the eardrum moved best, the middle ear pressure, but also how compliant the eardrum was when it moved best. So on this example, the numerical difference between point A, which indicates where the ear canal volume measurement was taken, and point B, which indicates where the middle ear pressure amount was measured, shows the amount of tympanic membrane compliance. Notice that in this example, the compliance value is underlined in red. Finally, as the air pressure in the ear canal is lowered to point C, the tympanic membrane is once again returned to a default position. The appearance of normal tympanograms can vary greatly. For eardrums that are very compliant or mobile, the tympanogram will be tall or steep, like the one in this example. For eardrums that are less compliant, the tympanogram may appear more shallow, like this. The higher the tympanic membrane compliance, the more compliant or flexible the eardrum is. As you can see, the blue tympanogram would be considered more compliant or flexible than the red tympanogram, which appears more shallow. However, both fall within the range of normal. For eardrums that exhibit little or reduced compliance, they may appear flattened, with no definable peak. Or, they may appear more rolling, like this one. The absence of a definable peak on a tympanogram means that the eardrum is not as mobile as it is intended to be. Notice that in this example, the tympanogram appears to have no definable peak. This means that middle ear pressure could not be determined or found at the time of the screening as measured by the screening equipment. Your display may show NP, for no peak, or NA, for not applicable, when this circumstance occurs. When the middle ear pressure is in the negative value range, as shown here, it may be because of a poorly functioning eustachian tube. The significance of negative middle ear pressure is that it occurs both before and after the formation of fluid in the middle ear cavity. As negative middle ear pressure increases in the middle ear cavity, the eardrum is pulled inward, thereby reducing its compliance or its ability to move. In general, as negative middle ear pressure increases, eardrum mobility decreases. Again, values for both middle ear pressure and tympanic membrane compliance rely upon movement of the tympanic membrane. Without enough measurable movement, your equipment may be unable to provide numerical values. The last important component of immittance screening we will discuss is the acoustic or stapedial reflex. The stapedius muscle is the smallest muscle in the human body. It’s connected to the smallest bone in the human body, the stapes. In a normal functioning middle ear, if a loud sound is introduced, the stapedius muscle will contract, causing the ossicular chain to stiffen. This stiffening of the ossicular chain is detected as a slight contraction on the surface of the eardrum. This contraction causes a quick movement of the eardrum and is recorded by the immittance screening equipment as a present acoustic reflex. For tympanograms with very low tympanic membrane compliance, such as .1 milliliter or less, it’s necessary to use additional information to determine if the immittance results are a pass or a refer. In these situations, the absence or presence of the acoustic reflex is used to determine if the screening results are either a pass or a refer. Some healthy normal eardrums and middle ear systems just don’t move as well as others. Like the right ear on this example, the presence of an acoustic reflex will determine between a healthy eardrum with low compliance and an eardrum with low compliance that’s in need of a re-screen or referral to a primary care physician. Some pieces of immittance screening equipment will offer the acoustic reflex screening ability, but it will need to be turned on or activated before the function is available during screening. It’s important to understand that an acoustic reflex may or may not be present in a healthy middle ear, but only a healthy middle ear will produce a measurable acoustic reflex. An abnormal or unhealthy middle ear will not elicit an acoustic reflex. For screening to be considered a pass, the results must yield a middle ear pressure that falls between plus 100 and minus 250 decapascals. Values that fall outside of this range indicate a fail. If there’s no measurable middle ear pressure, as designated by an NA or NP on the equipment, it is also a fail. If the tympanic membrane compliance value is less than 0.2 milliliters, it is a fail. If the compliance is 0.1 milliliter and an acoustic reflex is present, it is considered a pass. Again, when the tympanic membrane compliance value is 0.1 milliliter, the presence of the acoustic reflex is your assurance that the middle ear system is working at a level to pass the immittance screening. Remember, an acoustic reflex may not be present in a healthy ear, but it will not be present in an abnormal or unhealthy ear. Only a healthy middle ear can produce an acoustic reflex. The use of the acoustic reflex in this instance is designed to reduce medical over-referrals from the screening program. The following ranges for ear canal volume should be used as a guide only. Remember, it’s the relationship between ear canal volume, tympanic membrane compliance, and middle ear pressure that allow you to determine a pass or refer result. All ear canal volume values will be relative to the size of the probe tip used, as well as the physical size of each individual child’s ear. Comparing measurements between ears and noting your otoscopic examination will also help. Again, middle ear pressure and compliance are dependent upon movement of the eardrum. For preschoolers, ear canal volume values are typically between 0.3 and 0.9 milliliters without tubes, and 1.2 and 5.5 milliliters if patent or open ventilation tubes are present. For elementary school students, ear canal volumes will generally fall between 1.1 and 2.1 milliliters. Any child who fails an immittance screening in one or both ears should be rescreened in four to six weeks. Often, middle ear problems will resolve on their own. Allowing four to six weeks between screenings is an appropriate time span for middle ear problems to resolve or improve. When a child is rescreened, do all portions of a screening, otoscopic inspection, pure tones or otoacoustic emissions, and immittance measures on both ears. Do not just screen the portion of the screening that was initially failed. Children failing the immittance portion of the hearing screening on two separate occasions, for example, the initial screening and then rescreening four to six weeks later, should be referred to their primary care physician. Children who fail otoacoustic emissions or pure tones while passing the immittance portion of the screening should be referred to an audiologist for an age-appropriate audiometric evaluation. Now that you’ve completed the screening, the instruction segment of the immittance tutorial series, please continue on to the training exercise portion in part six. There you will be presented with a variety of tympanograms. These additional examples will help you better familiarize yourself with tympanometry and test your knowledge of immittance results.