Causal relationships among factors associated with cancer-related fatigue.

PURPOSE: This study was conducted to develop and verify a comprehensive model, which illustrates the dynamic causal relationships between fatigue and its associated factors in cancer patients.
METHOD: The subjects were 110 in- or out-patients with various types of cancer being treated at a University Hospital, Incheon, South Korea. The comprehensive model consists of physical distress, sleep-related, physiologic, psychological distress, physical performance, and exercise factors.
RESULTS: Psychological distress had a significant direct effect on physical distress, and 81% of the variance in physical distress was explained by psychological distress. While psychological distress showed to have a significant total effect (the sum of direct effects of psychological distress and indirect effects through its relationship with physical distress) on fatigue, it was not found to have a significant direct effect on fatigue. Only exercise had a significant direct effect on fatigue and 70% of fatigue variance was explained by exercise alone. All remaining factors were not found to have significant direct effects on fatigue.
CONCLUSIONS: The hypothetical model was well suited to explain cancer-related fatigue. Our result indicates that psychological distress should be relieved in combination with a strategy to reduce physical distress in order to obtain better outcomes with respect to cancer-related fatigue. Only exercise had a significant direct effect on fatigue. In terms of the nursing implications, the proposed model can help oncology nurses better understand cancer-related fatigue and assess presence of correctable correlates. This model can be a future framework when developing intervention strategies for cancer-related fatigue.