**1. Introduction**

Dyspepsia is the most common gastrointestinal disorder in primary medical assistance. In the general population, 40% of people will suffer from dyspepsia during their lifetime [1]. The most frequent category of dyspepsia is functional dyspepsia (FD). Among categories of dyspepsia, FD accounts for roughly 50% of the cases and is defined as dyspeptic symptoms not explained by structural or organic upper gastrointestinal disease [2]. The categories associated with organic alterations of the upper gastrointestinal tract are: reflux disease with normal endoscopy (20%); reflux esophagitis (20%); peptic ulcer disease (10%); and more rarely, Barret's esophagus and malignancy [2].

Dyspeptic symptoms comprise a heterogeneous group of symptoms that have in common their location. The symptoms must be located in the epigastrium and can be included in two syndromes: postprandial distress syndrome (PDS) and epigastric discomfort syndrome (EDS). PDS comprises bothersome postprandial fullness and early satiation; EDS includes epigastric pain or burning. In practice, it is common for symptoms to overlap, and as a rule patients are defined as dyspeptic when suffering symptoms of both syndromes [3]. Heartburn is not considered a dyspeptic symptom, as established in the latest definition by the Rome III consensus in 2006 [4].

The current definition of FD according to the Rome III consensus is the presence of one or more symptoms, with onset at least six months beforehand, being present during the last three months, in the absence of structural disease of the upper gastrointestinal tract (in clinical practice, ruled out by endoscopy and testing for *Helicobacter pylori*). The Rome III consensus gives the definitions of each of the four dyspeptic symptoms (Table 1). Nonetheless, even judicious criteria like these are not totally accurate to diagnose FD. There are reports showing

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only modest performance of the Rome III criteria, reaching only 60.7% sensitivity and 68.7% specificity for diagnosis of FD [5].


**Table 1.** Definition of dyspeptic symptoms as proposed by the Rome III consensus

Why do I classify FD as underestimated among end-stage renal disease (ESRD) patients? In my view, dyspepsia really deserves special attention among ESRD patients on hemodialysis (HD) for many reasons:


Despite the above, from my observations dyspepsia is not routinely screened in dialysis units as is done for cardiovascular disease, osteodystrophy and nutritional status. There is also a lack of randomized, placebo-controlled studies about treatment of FD among HD patients, and a clear explanation of the physiopathological mechanisms regarding FD in ESRD is missing.

In my institution, Federal University of Ceará in Brazil, data have been collected since the 1980s on the relationships between volemic status and gastric motility, especially in animal models, but also among healthy subjects [18-23]. As an attending physician, I have under my care at the dialysis unit of Santa Casa de Sobral Hospital ESRD patients who form an ideal sample for studying FD, gastric dismotility and hypervolemia. Thus, currently I am trying to find clinical evidence of the link between the results coming from bench research about the relationships of volemia and gastric emptying with gastroparesis, hypervolemia and FD, which are highly prevalent among HD patients. Therefore, I propose in this chapter to organize bench and clinical data on gastric motility, volume expansion and FD in ESRD patients, to provide insight to help the daily approach to FD among HD patients.
