Monitoring of the fluid status of critically ill patients by bio-impedance vector analysis (BIVA): A before-and-after study

None listed

The monitoring of fluid status in critically ill patients is challenging. Fluid balance is often incorrect and does not take into account insensible fluid losses, which in febrile patients can add up to a litre or more/day. Weighing with beds equipped with electronic scales has been shown to be unreliable and inaccurate in ICU patients. Intravascular filling pressures are not reliably related to extravascular fluid accumulation. Oedema can only be detected once up to 4-5 litres of excess fluid have accumulated. These shortcomings in fluid assessment are particularly problematic in patients who stay in ICU for a longer period of time, where daily errors in assessment accrue to make estimates of fluid status particularly inaccurate. These technical problems are potentially clinically significance as fluid accumulation has been repeatedly identified as an independent risk factor for mortality in ICU patients. The development of novel bio-impedance vector analysis (BIVA) has recently been shown to provide a reliable, reproducible, robust, safe, and non-invasive assessment of hydration which can be performed at the bedside of critically ill patients by evaluating the bioelectrical impedance of the human body. This approach uses the administration of alternating (AC) microcurrents (microamperes) a low frequency (50kHz) with a standard four-electrode system. Such microcurrents are well below the sensation threshold for human beings. The resistance (R) and reactance (Xc) adjusted for height of the whole body provide information on the ability of the microcurrent to move from ankle electrodes and reach sensor wrist electrode. The relationship between resistance (dependent of body fluid volume) and reactance (dependent on the capacitance of membranes and tissue interfaces) allows the construction of a vector on an X-Y plot. This vector can be related to vectors obtained from >18,000 normal subjects which have been used to define reference values. These values identify states of low resistance and low reactance (fluid overload). Such individual vectors can then also be used to monitor changes in the fluid status of an individual. This approach has been applied to identify fluid overload in dialysis patients, cardiac failure patients, and, in pilot work, in critically ill patients. In this study, we propose to compare fluid management in mechanically ventilated patients expected to stay in ICU until the day after tomorrow treated with standard care during a period when clinicians are not informed of the bio-impedance measurement followed by a period in which they are informed of the measurement.

No related papers found yet.