What a great topic Paulin. I would also suggest this review article:
Existential suffering in the palliative care setting: an integrated literature review_doi:10.1016/j.jpainsymman.2010.05.010
In addition, you may want to look at Karen Steinhauser's work. She has developed an instrument (the Qual-E) that measures quality of life at end of life. There is one item on the instrument, "Are you at peace?" that has held up independently for measuring spiritual suffering. (Arch Intern Med. 2006;166(1):101-105. doi:10.1001/archinte.166.1.101.)
I agree with all the suggestions mentioned above. You also might want to look at what happens to suffering when individuals who are close to death have what historically were called Deathbed Visions, now deathbed communications, since many of these experiences are auditory and kinesthetic as well as visual. I can send you a copy of this article about the research study I carried out on this topic.
Lawrence, M. & Repede, E. (2013) Incidence of death-bed communications and their impact on the dying experience. American Journal of Hospice and Palliative Medicine, 30 (7), 632-639.
My book, the link to Amazon is attached, is about all these experiences surrounding death. Individuals who have had a near-death experience (NDE) previous to being on palliative care or hospice, I have found, have much less suffering. One fellow I interviewed and videotaped actually said he couldn't wait to die because he knew it would be as wonderful as his experience during the NDE. We have always assumed everyone facing death is suffering but there are these exceptions.
Thank you for your valuable suggestion. could you pls mail me the article on
Lawrence, M. & Repede, E. (2013) Incidence of death-bed communications and their impact on the dying experience. American Journal of Hospice and Palliative Medicine, 30 (7), 632-639.
There is copious research confirming the value of palliative Care and other hospice services and many journals on this topic which you can explore in any good medical liibrary. They have focussed on pain relief, which is itself correlated with measures of 'distress'.