Longitudinal changes in phase angle by bioimpedance in intensive care patients differ between survivors and...

Intensive care (ICU) patients suffer from metabolic stress, creating a catabolic state which might disturb nutritional status and body composition. Alterations in body fluid compartments by disease or massive volume resuscitation could invalidate bioimpedance hydrometry. Still bioimpedance might give other information.

52 ICU patients (35 male, 17 female, mean age 66 years), BMI 29,2 were assessed by bioimpedance spectroscopy. Phase angle (PhA) at 50 kHz was assessed.

On first assessment PhA was 3.7 ± 1.0°. In 26 patients reassessed after median 5 days PhA was not significantly changed, although R 50 kHz and Xc 50 kHz both increased (p = 0.047), indicating diminishing overhydration. Body weight and body cell mass decreased by 1.8 ± 5.7 and 2.8 ± 7.5 kg (p = 0.13). Fat free mass and extracellular water decreased 4.5 ± 8.9 kg (p = 0.032) and 1.5 ± 3.5 kg (p = 0.031), while CRP decreased 63 mg/l (p = 0.002). In 17 survivors PhA increased 0.62 ± 1.24° (NS), while in 9 non-survivors PhA decreased 0.24 ± 0.82° (p = 0.06), with 0.86° difference (p = 0.049) between groups.

Phase angle by bioimpedance is very low in ICU patients and positive changes in PhA seems to reflect more favorable outcome. Bioimpedance by Body Scout appears unsuitable for the assessment of fat free mass or overhydration in ICU patients.