P143
INVESTIGATION OF THE VALIDITY AND CLINICAL UTILITY OF BIOIMPEDANCE
MEASUREMENTS OF FLUID STATUS IN INTENSIVE CARE
David Keane1,2, Stuart Elliot3, Elizabeth Lindley1,2, Andrew Lewington1, Stuart Murdoch3
Departments of 1Renal Medicine, 2Medical Physics and 3Anaesthetics, Leeds Teaching Hospitals NHS Trust
INTRODUCTION: Patients admitted tointensive care units (ICU) frequentlyreceive large volumesof
intravenous fluid, particularly in the acute stages of their treatment.This fluid is intended to maintain blood
volume but will often leak into the tissues. Studies of critically ill patients appear to show a link between body
fluid gain and morbidity and mortality (Alsous et al, Chest, 2000). Treatment strategies designed to prevent or
reduce excessive fluid overload could improve survival. Fluid management is normally reliantupon fluid
balance charts (FBC) which attempt to documenttotal fluid intake and output.However, this method is prone
to inaccuraciesand canbe unreliable.Bioimpedance (BI) measurements provide a simple, non-invasive method
of assessing body fluid volumes and fluid status and have been shown to improve outcomeswhen used to
guide fluid management in patients with renal failure (Onofriescu et al, AJKD 2014). There is a lack of
published work around the use of the technology in ICU and this study aimedto determineif BI measurements
have the potential to provide an accurate and reliable indication of fluid status in ICU.
METHODS: Incident patients on the ICU of a large Teaching Hospital, who were identified within 24 hours
of admission and expected to be present on the unit for over 48 hours, were considered for inclusion.
Consentwas provided by either relatives or the patient dependent upon capacity.Daily BI measurements were
made using the Body Composition Monitor (BCM, Fresenius AG Bad Homburg)fromthe point of
identification, based on an estimated weight and a measured height.Clinical observations were also recorded
daily. BCM measurements were scored by an experienced user based on the acceptability of the raw data.
RESULTS:Consent was obtained from 30 of the 45 patients identified. Four patients died on the ICU during
the study. Acceptable measurements without
significant artefact were obtained in 91% (246/270) of
cases. The difference between BCM and FBC on the
first day of measurement ranged from negative 8 litres
up to positive 6 litres.The daily change in fluid balance
between BCM and FBC agreed in two thirds of cases
(139/206). Disagreement was no more likely to occur
in septic patients than non-septic patients. An example
of the relationship between BCM and FBC measures of
fluid status in one patient can be seen in fig. 1, showing
good agreement but a significant offset from day 1.
Figure 1: FBC and BCM measured hydration for one patient
Almost half of patients (10/23) left ICU with more than
3 litres of excess fluid.
DISCUSSION: Results suggest that BI measurements can be used reliably in this setting with appropriate
training and an understanding of measurement quality. Measurements may be most beneficial on ICU
admission where FBC assumes zero balance and afterinterventions, such as surgical procedures, where
input/output are not monitored.Objective measurements of fluid overload may allowfor greater
confidencewhen removing fluid once patients have stabilised than relying on FBC alone. The results showed
that patientsare frequently discharged from ICU with significant excess fluid, often to wards thatlackspecialist
support for fluid management.
CONCLUSION: BI measurements can provide useful information relating to fluid status that has the
potential to assist decision making in the ICU. Further research evaluating how BCM could be incorporated
into fluid management of the critically illis warranted.