Bioimpedance-measured volume overload predicts longer duration of mechanical ventilation in intensive care unit patients.

Purpose: Bioelectrical impedance analysis (BIA) is a technology that provides a rapid, non-invasive measurement of volume in body compartments and may aid the physician in the assessment of volume status. We sought to investigate the effect of BIA-measured volume status on duration of mechanical ventilation, 28-day mortality, and acute kidney injury requiring renal replacement therapy in a population of medical/surgical patients admitted to the intensive care unit (ICU).

Methods: Prospective observational study of adult patients who required mechanical ventilation within 24 hr of admission to ICU. Bioelectrical impedance analysis measured extracellular water (ECW) and total body water (TBW) and these measurements were recorded on days 1, 3, 5, and 7.

Results: A total of 36 patients were enrolled. Mean (standard deviation) age was 61.8 (21.3) years and 31% of patients were female. The majority were admitted from the emergency department or operating room. The most common diagnosis was sepsis. At 28 days, eight patients (22%) had died. There was no association between ECW/TBW ratio at day 1 and 28-day mortality (odds ratio, 1.2; 95% confidence interval [CI], 0.6 to 2.3) after adjusting for age, sex, and Acute Physiology and Chronic Health Evaluation II score. The median [interquartile range] number of ventilator days was 5 [2.5-7.5]. On day 1, for each 1% increase in the ECW/TBW ratio, there was a 1.2-fold increase in ventilator days (95% CI, 1.003 to 1.4; P = 0.05). It is notable that 20% of eligible patients could not be enrolled because medical equipment interfered with correct electrode placement.

Conclusion: Bioimpedance-measured ECW/TBW on day 1 of admission to the ICU is associated with time on the ventilator. While this technology may be a useful adjunct to the clinical assessment of volume status, there are technical barriers to its routine use in a general ICU population.