Misinterpreting the Results of a Sternal Rub
By Joseph Mistovich
When assessing a patient who is not alert and does not respond to verbal stimuli, a painful stimulus may be applied to the body. The sternal rub is the most common stimulus practiced out in the field. However, it is possible to misinterpret the patient’s response to the stimuli depending on the duration the pressure is applied.
Response to the stimulus is used to make assumptions about the integrity of the brain and its function. If the patient responds to the pain with what is interpreted as purposeful movement, it is assumed that the brain received the impulse, was able to interpret it, and responded with some degree of a correct response.
If the patient does not respond, it is assumed the brain either did not receive the impulse or was unable to interpret the stimulus. If the brain is unable to interpret the painful stimulus and send out a correct response, one would think that its integrity is compromised and the patient is at grave risk for losing vital functions. Thus, a patient who does not respond to a painful stimulus would be thought to be critically ill or injured.
The most common painful stimulus applied to a patient in the prehospital setting is the sternal rub. The sternum is rubbed vigorously with the knuckles of a closed fist to create pain. This technique is often performed for only a few seconds while watching for a reaction from the patient. If there is no response within a few seconds of stimulation, one would assume that the patient is unresponsive and the brain’s integrity is compromised. If the patient reaches up and makes an attempt to remove the stimulus or actually grasps your hand, one would assume the patient has a higher level of brain function, which is an encouraging assessment finding.
It has been found anecdotally by nurses and physicians working on neurology floors that some patients require up to 30 seconds of continuous hard knuckle pressure on the sternum to elicit a response. So, how does this affect your interpretation of the painful stimulus in the patient assessment?
If only a few seconds of sternal pressure is applied, the patient may not respond. However, this lack of response may not be due to poor brain integrity, but from an improperly applied sternal rub. If no response is produced within a few seconds, you would typically note that the patient is unresponsive to a painful stimulus. This is a significant finding in the assessment and makes the patient a priority for transport. However, if the sternal rub is applied for the full 30 seconds, the same patient may actually respond with purposeful movement, which would change your interpretation of the assessment of the integrity of the brain. Thus, in some patients, it may not be poor brain integrity that is causing a lack of response, but an inadequate length of time the sternal rub is applied.
If you were to count off 30 seconds to yourself, even in a non-emergent situation, it is an awful long period of time to apply the sternal rub. However, if you don’t get a response for a sternal rub that hasn’t been applied for at least 30 seconds, you can’t say the patient is truly unresponsive. Keep in mind that the sternal rub only needs to be applied until a response is elicited.
Alternative methods to apply a painful stimulus to the core of the body can be used in place of the sternal rub. Two methods are a trapezius pinch and supraorbital pressure. With the use of the trapezius pinch or supraorbital pressure, there is no need to apply the stimulus for 30 seconds to be sure the interpretation of the results is accurate.
A trapezius pinch is applied by grasping at least two inches of the trapezius muscle at the base of the neck between your thumb and index and middle finger. While squeezing the muscle, twist it, which will cause significant pain. Watch the patient’s face for a grimace and the hands’ and arms’ response for any attempt to remove the stimulus.
Supraorbital pressure is applied by finding the ridge along the upper portion of the bony orbital structure. Carefully place the tip of your thumb in the midline along the bony ridge. Applying pressure straight upward will create severe pain and discomfort. Again, watch the face, hands and arms for any response.
It is important to note that the sternal rub, trapezius pinch, and supraorbital pressure are all applied to the core of the body. Applying a peripheral pain stimulus to the extremities may lead to misinterpretation of the test results due to reflexes. This will be further discussed in next month’s column.