Background: The objective of this study was to explore the underlying etiologies associated with the resolution and improvement of delirium in ill-hospitalized cancer patients. Methods: We conducted a secondary analysis of a multicenter, prospective, observational study to estimate the effectiveness of pharmacotherapy for delirium. Participants were cancer patients with delirium. We assessed the Delirium Rating Scale, Revised-98 (DRS-R98) severity scale score at baseline and three days after pharmacotherapy initiation. Delirium resolution was defined as a DRS-R98 severity scale score ≤9, and improvement was defined as ≥50% reduction at Day 3. Results: We enrolled 566 patients (491 patients had performance status of 3 or 4). The resolution and improvement rates in all patients were 22.6% and 19.3%, respectively. Univariate analysis determined that nonrespiratory infection (OR 2.18, 95% CI 1.38-3.45) was significantly associated with greater resolution, while dehydration (0.40, 0.19-0.87), organic damage to the central nervous system (CNS) (0.32, 0.43-0.72), hypoxia (0.25, 0.12-0.52), and hyponatremia (0.34, 0.12-0.97) were significantly associated with no resolution. Potential causes associated with delirium improvement were nonrespiratory infection (1.93, 1.19-3.13), organic damage to the CNS (0.40, 0.18-1.90), and hypoxia (0.32, 0.16-0.65). After multivariate analysis, dehydration (0.34, 0.15-0.76), organic damage to the CNS (0.25, 0.10-0.60), and hypoxia (0.29, 0.14-0.61) were significantly associated with no resolution. Conclusions: Delirium caused by nonrespiratory infection may be reversible, while delirium associated with dehydration, organic damage to the CNS, hypoxia, or hyponatremia seems to be irreversible in ill-hospitalized cancer patients.
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