Many barriers are dependent upon the beliefs,  health and cognition of the individual patient being assessed for pain. Examples of these barriers: Is the patient non-verbal? Is the patient cognitively intact? What are the patient's pain beliefs (ie do they believe they should be pain free or do they accept some pain as a fact of life). Please see the article found in the link below:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3097898/

I may Add to Elizabeth`s comment that beliefs that we ourselves have as health care providers: how do perceive an elderly client, ad do we expect their pain to be normal happening for their age? it is the way we respond to their report of pain, what conditions the patients later on to stop reporting pain to US, plus how educated are we to use different scales of pain assessment to address the unique situation, one size does not fit all patients, especially those who have cognitive or expressive problems, but knowing their baseline behavior, and going with behavioral scales can be really helpful.below are two good articles

1. Chapman, S. (2010). Managing pain in the older person. Nursing Standard (Royal College Of Nursing (Great Britain): 1987), 25(11), 35-39.

2. Davis, M., & Srivastava, M. (2003). Demographics, assessment and management of pain in the elderly. Drugs & Aging, 20(1), 23-57 35p.

Pain assessment in an elderly characterised with some difficulties in that pain reaction and expression are culturally, ethnically and attitudinally influenced most especially in adult. If health caregivers are not confident and proactive enough it will be difficult to have accurate pain assessment.

pain assessment in older adult may be the cornerstone in management of pain and its consequences. in sum pain assessment is difficult especially if patient ventliated or have deterioration in conscous level ..pain assessment is what the patient said by his own words, what his feel looks like so it a subjective phenomena Assessment for critically ill may be not accurate sometime because it depent  on facial expression ,body movemet etc

another way of assessment may include vital signs especialy respiratry rate but also may be not sensitive because change in respiration may be dute to infection rather apin, so it very difficult to assure that the patient in pain ..it is a dilema even anestheologist cant have consensus about how to assess in comatosed pt

Cognitive impairment for sure, but also pain that is not adequately being managed which creates delirium. Certain pain meds, analgesic agents enhance the benzodiazepine effect with delirium. Often times this is then treated with hypnotics and sedatives, but not managing the pain which is at the root of the issue.

The Decision Assist site is an excellent resource for symptom management in this population. The link to the Pain page is http://www.caresearch.com.au/caresearch/tabid/3151/Default.aspx . As you will see, there are also links to many other symptoms as well, which you may find useful.

For barriers to pain management, try http://www.caresearch.com.au/caresearch/tabid/2393/Default.aspx

I would add, last but not least, the inadequacy (ignorance? distraction? haste? superficiality? prejudices?) of the clinicians who cure the elderlies, especially with cognitive deficits. Pain is a symptom, but in patients unable to report it, describe it and quantify it, must be deducted from  signs, which in our case, are sometimes difficult to interpret. Who is more in contact with the elderly, namely the patient care assistant who cleans, baths, feeds, makes bed, moves around the elderly, is in general who may notice behaviours that may suggest the presence of pain. However often is neither consulted nor involved in treatment decisions.

This, of course depends from country to country and from institution to institution, but I think that, at least in my country. constitutes the core of the problem.

I wish to add the older adults would not like to be regarded as people who are always complaining by the younger adults. They do not want to be disturbing their families and other health care team such as the nurses.

I would like to add to the list of barriers to pain assessment in older adults. The prior experience the elderly person has had with the health system can be a barrier. I work with clients who have mental health and or disability with chronic and complex health issues.  Often their literacy levels are poor let alone their communication skills. They have a poor insight into their health needs and are often fearful of the health professional. Regular contact building rapport with the client and engagement can develop and the assessment of pain by recognizing change in the clients presentation can open communication. 

Hi Violet, you have some great feedback already to your question, so not sure that what I add will necessary be of any extra use.  I agree with the previous comments - the barriers can be seen in relation to a number of factors, and as such can be categorised in terms of different characteristics.  I would suggest a simple way of approaching this might be to look at the barriers in terms of the concepts that make up nursing - nurse, patient, health, environment.  In this way you might consider the role of the nurse (or other healthcare professional) who is responsible for the assessment process - so this would include the personal factors, such as conscious or unconscious prejudice or assumption about elderly, expectations and anticipated behaviours; knowledge of the elderly in terms of physiology, pathophysiology and expected parameters of 'normal' response; familiarity with and use of different forms of pain assessment tool - eg those suitable for both verbal and non verbal patients, as well as those appropriate for cognitively impaired.  Focussing on the patient allows you to consider those barriers that originate from the individual recipient of care, such as interpretive problems where the patient may not understand or be able to contribute effectively to the assessment process (eg language issues, hearing or other physical impairment; intellectual disability etc); this also includes considering whether the patient feels safe to disclose complaints of pain - some may not wish to be a 'nuisance' or may fear that they will be 'punished' for asking for further assistance; it also includes cultural concerns where expressions of pain may differ between the culture of the patient and that of the nurse. By considering the definition of 'health' this raises issues of both the patient and health professionals understandings of what it is to be 'well' and also what constitutes 'pain' - while pain is certainly 'what the patient says it is', it is important to understand what factors contribute to the individuals understanding of pain - what previous experiences of pain, or of health care may be influencing their current interpretation.  Finally by looking at environment, it is possible to consider the external factors that can be a barrier to assessing pain - such as the business of the assessor - do they have the time to undertake a full assessment? do they have the necessary resources? the support of the workplace to ensure that this is a priority?

Just some thoughts, which I hope are helpful, and I am attaching some articles which may be of interest.