The gastrointestinal tract comprises diverse functions. Despite recent developments in technology and science, there is no single and universal tool to monitor GI function in intensive care unit (ICU) patients. Clinical evaluation is complex and has a low sensitivity to diagnose pathological processes in the abdomen. We performed a MEDLINE and Pubmed search connecting abdominal assessment and critical care. Based on these findings we defined the following major categories of monitoring and diagnostic measures: clinical investigation; assessment of motility and digestive function; microbiome monitoring; perfusion monitoring; laboratory biomarkers and hormonal function; intra-abdominal pressure measurement; and imaging techniques. Only a few of these monitoring and assessment tools have found their way into clinical practice, as most of them have one or more significant objections preventing broad implementation in daily clinical practice. Further research should be directed to reaffirm and define the use of current techniques to ascertain their validity and usefulness to monitor gastrointestinal function in ICU patients.