Parameters of Bioelectrical Impedance Are Good Predictors of Nutrition Risk, Length of Stay, and Mortality in Critically Ill Patients: A Prospective Cohort Study

Background: Assessment of nutrition risk in the intensive care unit (ICU) is limited by characteristics of critically ill patients, and new methods have been investigated for their applicability and predictive validity. The aim of the present study was to evaluate the validity of bioelectrical impedance analysis (BIA) parameters as predictors of nutrition risk and clinical outcomes in critically ill patients.

Methods: This was a prospective cohort study of patients admitted to an ICU. The modified Nutrition Risk in the Critically Ill score was used for assessment of nutrition risk, and BIA was performed in the first 72 hours of admission. Phase angle (PA) measurements were obtained, and bioelectrical impedance vector analysis (BIVA) was used to classify patients by hydration status (BIVA >70%). Patients were followed until hospital discharge and evaluated for hospital mortality, ICU length of stay, length of hospitalization, and duration of mechanical ventilation.

Results: Eighty-nine patients were included (62.5 ± 14.1 years, 50.6% female). A PA <5.5^o showed an accuracy of 79% (95% CI 0.59-0.83) in identifying patients at high nutrition risk and was associated with nearly 2 times greater risk for an ICU length of stay longer than 5 days (relative risk = 2.18 [95% CI 1.39-3.40]). Hyperhydration was a significant predictor of mortality (hazard ratio = 2.24 [95% CI 1.07-4.68]). Higher resistance and reactance values, adjusted for height, were found in survivors compared with nonsurvivors.

Conclusion: The predictive validity of BIA was satisfactory for the assessment of nutrition risk, ICU length of stay, and mortality in critically ill patients.