Can bioimpedance spectroscopy be used to evaluate and capture changes in clinical status in patients with critical...

There is growing interest in critical care in the identification of biomarkers to indicate when patients' clinical condition progresses through the phases of critical illness. The aim of this study was to explore changes in novel bioimpedance spectroscopy (BIS) variables as potential biomarkers measured at intensive care unit admission through to hospital discharge and the relationship between these variables and clinical outcomes.

In a prospective observational substudy of the Intensive Nutrition Therapy Compared to Usual Care in Critically Ill Adults multicentre randomised controlled trial (July 2021-January 2023), BIS measurements were taken at trial day 1 and every 7 days thereafter until day 28 or hospital discharge, whichever occurred first. BIS variables included the 50-kHz phase angle (PhA), resistance (R)-infinity-to-R-zero ratio (R_inf:R₀), and characteristic frequency. Spearman rank correlations were used to evaluate relationships between BIS variables and clinical outcomes.

Of 22 critically ill adults screened, 14 were included (median [interquartile range] age: 56 [45-64] and 11 (79%) patients were male). Over the 28-day study period, the 50-kHz PhA increased (percentage change of 17 [-7 to 40] %). Conversely, R_inf:R₀ and characteristic frequency decreased over time (-2.45 [-7.19 to 4.27] % and -16.04 [-30.94 to 16.37] %, respectively). Baseline low 50-kHz PhA and a higher R_inf:R₀ were correlated with longer hospital length of stay (r = -0.702, p = 0.005 and r = 0.845, p < 0.001, respectively).

These findings highlight that bioimpedance variables change throughout the course of critical illness and recovery. These variables may indicate progression through critical illness and should be investigated further.