there are lots of publications about this topic, but, to my knowledge, no new comprehensive RCT available at the moment. In our daily business we supplement calories and proteins quite often, though without real monitoring for it. We have ceased to perform the "nutrogramm" (lab parameters, too expensive, no evidence) on a routine base. We try to define some blood parameters as markers for our intervention, but haven't found the golden one(s) yet...
Anyway I can recommand this work, which summarizes very well the known evidence up to 2015.
The Role of Nutrition for Pressure Ulcer Management: National Pressure Ulcer Advisory Panel, European Pressure Ulcer Advisory Panel, and Pan Pacific Pressure Injury Alliance White Paper
Posthauer, Mary Ellen RDN, LD, CD, FAND; Banks, Merrilyn PhD; Dorner, Becky RDN, LD, FAND; Schols, Jos M. G. A. MD, PhD