This proof of concept study shows that HR monitoring may identify situations that entail acute pain or discomfort in the daily lives of non-communicating persons with ID. Examples of such situations were passive extension of a spastic arm or transportation in a patient lift. Previous studies have found that caregivers that only use observation of behavior to identify pain, may fail to identify painful conditions in non-communicating persons with ID.17,27,28 HR monitoring may improve this situation.
Increased HR may be caused by both adverse and pleasant stimuli.29–33 This was illustrated in the present study by participants whose HR increased in response to situations that were likely to be painful and by participants whose HR increased during activities they probably enjoyed. Therefore, a HR increase has to be interpreted in light of its context. Such interpretation is indispensable and at the same time a potential source of error. Erroneous interpretation was illustrated in the present study by the participant who displayed increased HR when mounted in an apparatus used to helping her stand upright: her HR increase was interpreted by caregivers as reflecting joy until it was found that the apparatus was wrongly adjusted and probably caused discomfort or pain.
At present there is no gold standard for identifying pain in non-communicating persons with ID. In an experimental study in which non-communicating persons with ID received pressure-induced pain, Benromano et al. found facial expression, monitored by a video camera and analyzed retrospectively, to be a more reliable indicator of pain than HR.19 In the present study, however, only some of the participants had intelligible facial expression. Further, the use of video monitoring would have been difficult in our study, which took place in the daily lives of the participants in their communal residences or day care centers. At present, therefore, we believe that HR monitoring is a promising mode of identifying at least some acutely painful or distressing situations that non-communicating persons with ID experience.
In the present study we used increased HR as an indicator of acute pain or distress.29–31 Data are scarce on HR during prolonged or chronic pain, but some clinical studies suggest that prolonged pain is not accompanied by increased HR.34,35 These findings point to the need to find parameters other than HR to identify long lasting pain in non-communicating persons with ID.
Limitations
In the present study we used a definition of increased HR (HR that persisted > 5 seconds at 1 SD above the daily mean) that allowed for individual and day-to-day variations. This definition is arbitrary, however, and we may have failed to detect some cases of increased HR due to the definition being too strict. Further, although we found that HR increased in situations that could be expected to be stressful, we do not know our rates of false positive or false negative results. In some participants, HR did not increase consistently in situations that were interpreted as being stressful. This finding may reflect the occurrence of false negative results due to our definition of increased HR.
Autonomic responses to distress are modified by predictability: unpredicted distress causes stronger autonomic responses.36 We assume that non-communicating persons with ID are prone to experiencing distress as unpredictable because of their limited understanding of the necessity for painful procedures, such as physiotherapy for spasticity or pinpricks for blood glucose monitoring. We further assume that their reduced ability to avoid distress or to notify their caregivers about it makes stressful situations even more distressing than would be expected in the general population. Therefore, it is possible in the present study that the increases in HR that we detected in presumed distressing situations reflected some combination of pain and the fear that the pain provoked. We are at present not able to distinguish between the two.
HR is expected to increase in response to postural changes or muscle work, which could interfere with the interpretation of increased HR as a sign of distress. In the present study, however, such factors were probably not an important source of error, because HR monitoring predominantly took place when participants were seated or lying down, and because the occurrence of postural changes and muscle work was included in the contextual interpretation of HR variations. For instance, the increase in HR that was seen in several participants in transportation situations occurred at the mere sight of a patient lift, indicating an anticipatory reaction rather than a response to postural change.
We did not monitor HR after the introduction of changes to care practice, although doing so could have shed light on the validity of HR monitoring as a means of identifying acute pain or distress. Moreover, it could have shed light on whether the changes in care practice reduced distress or not. Therefore, studies with longer term HR monitoring are needed.