A Cochrane review included 5 studies with a total of 453 subjects. Two were RCTs and three prospective controlled trials. All of the studies included only participants with advanced cancer.
One study found that sedation and myoclonus (involuntary contractions of muscles) were improved more in the intervention group (28 - hydration, 23 - placebo). Another study found that dehydration was significantly higher in the non-hydration group, but that some fluid retention symptoms (pleural effusion, peripheral oedema and ascites) were significantly higher in the hydration group (59 - hydration group, 167 - non -hydration group). The other three studies did not show significant differences in outcomes between the two groups.
Comment: The quality of evidence is downgraded by imprecise results (limited study size for each comparison) and study quality (several issues).