A tympanic thermometer, often called an ear thermometer, measures the infrared heat emitted from the eardrum (tympanic membrane). The eardrum shares the same blood supply as the hypothalamus, the body’s temperature-regulating center. This connection allows the device to quickly estimate the core body temperature. This method is popular due to its speed and non-invasive nature, making it a convenient choice for children and adults. The accuracy of a tympanic temperature reading relies entirely on achieving a clear and direct line of sight to the eardrum, making correct insertion technique paramount.
Proper Insertion Technique and Depth
The objective of insertion is to aim the infrared sensor directly at the tympanic membrane by straightening the naturally curved ear canal. For adults and children older than two or three, gently pull the outer ear (pinna) upward and backward. This motion aligns the ear canal with the probe, providing an unobstructed path for the infrared scan.
For infants and young children, the technique is adjusted by pulling the pinna straight back or slightly down and back. The thermometer probe should be inserted just far enough to create a seal that blocks out ambient air, but never forced. Depth is determined by achieving this snug fit and a clear visual path, not a specific measured distance.
Before insertion, place a clean, disposable probe cover over the tip to maintain hygiene and ensure accurate heat transfer. Hold the probe steady in the canal, maintaining the ear tug, until the thermometer signals the reading is complete, usually with an audible beep. Gently remove the device and discard the used probe cover.
Common Causes of Inaccurate Readings
Several factors can distort the temperature measurement, leading to readings that do not reflect the core body temperature. Excess ear wax, or cerumen, is a common culprit. A build-up can physically block the infrared sensor’s path to the eardrum, causing the thermometer to measure the cooler temperature of the cerumen or the ear canal wall, artificially lowering the final reading.
External environmental factors also influence the reading, so wait at least 15 to 30 minutes after certain activities before measuring. Lying on one ear, for example, can temporarily increase that ear canal’s temperature due to trapped heat, causing a falsely high result. Taking a reading immediately after being outside in extreme cold or heat can cause fluctuations due to rapid cooling or warming of the outer ear canal tissue.
Operator error includes not waiting for the device to stabilize between consecutive readings, especially when measuring both ears. Some individuals have naturally narrow or unusually curved ear canals, making it difficult to achieve a clear line of sight to the eardrum. The thermometer may then consistently scan the ear canal lining rather than the tympanic membrane, resulting in measurement inaccuracy.
When to Avoid Tympanic Thermometers
The use of a tympanic thermometer is inappropriate due to safety concerns or the likelihood of receiving a misleading result. Active ear conditions, such as an outer ear infection (otitis externa) or a middle ear infection (otitis media), make the site unreliable for temperature measurement. The presence of inflammation, discharge, or blood in the ear canal can interfere with the infrared technology and may cause discomfort or pain during insertion.
Contraindications
The tympanic method should also be avoided if the patient:
- Has recently undergone ear surgery.
- Has ear tubes (tympanostomy tubes) in place.
- Has any drainage present in the ear canal.
In these cases, the temperature reading will likely be compromised. If a condition affects only one ear, the uncompromised ear should be used, or an alternative temperature site should be chosen entirely.
Manufacturers advise against using ear thermometers on infants under three to six months of age because their ear canals are too small and curved to accurately reach the eardrum. For newborns and very young infants, a rectal temperature is typically recommended, as it is the most accurate reflection of core body temperature. Using the device when a contraindication is present may yield a false reading or risk injury to the delicate structures of the ear.