Exertional Fatigue in Patients With CKD

Background: Fatigue is one of the most prevalent symptoms in chronic kidney disease (CKD). However, fatigue mechanisms are poorly understood due in part to nonspecific definitions. This study investigates exertional fatigue during simulated activities of daily living, focusing on oxygen delivery and utilization. Study Design: Explanatory matched-cohort study. Participants & Setting: 13 patients with CKD (stages 3b-4; mean age, 62 +/- 13 [SD] years) and 13 healthy controls, mean matched for age, height, body mass and composition, and physical activity level. Participants completed an incremental cycle ergometer test to simulate energy expenditure of typical activities of daily living. Factor: 4 exercise intensities: 1, 1.8, 2.4, and 3.1 metabolic equivalent tasks (METs). Outcomes: The primary outcome was exertional fatigue by rating of perceived exertion (RPE) on a 6-20 scale. Measurements: Other multidimensional measures of fatigue: UK Short Form Health Survey 36 (UK SF-36) Vitality and Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue) subscales. Physiologic measures of the oxygen transport and utilization chain (expired gas analysis, cardiac output, and arterial oxygen content) and blood lactate. Results: RPE was increased in patients compared with controls at 2.4 (10.5 [ie, light] +/- 2.7 vs 8.7 [very light] +/- 1.7 units) and 3.1 (12.5 [somewhat hard] +/- 2.6 vs 10.2 [light] +/- 1.7 units) METs (interaction P = 0.03), which was consistent with higher chronic fatigue in patients by both the UK SF-36 Vitality (P = 0.01) and FACIT-Fatigue (P = 0.004) subscales. Arterial oxygen content was decreased in patients (P = 0.001), but cardiac output and oxygen extraction ratio were unchanged, decreasing oxygen delivery (P = 0.04). Respiratory exchange ratio (P = 0.004) and blood lactate production (P = 0.002) were increased. Limitations: Those inherent to a matched-cohort study. Conclusions: Using a novel application of the outcome measure RPE, patients with non-dialysis-dependent CKD reported considerable exertional fatigue during simulated activities of daily living. Poor compensation for mild anemia contributed to this symptom. In addition to anemia, the entire oxygen transport chain needs to be targeted to treat fatigue in patients with CKD. Am J Kidney Dis. 60(6): 930-939. (C) 2012 by the National Kidney Foundation, Inc.