Abstract
OBJECTIVE
To evaluate the relationship between changes in body bioelectrical impedance (BI) at 0.5, 50 and kHz and the changes in body weight, as an index of total body water changes, in acutely ill surgical patients during the rapid infusion of isotonic saline solution.
DESIGN
Prospective clinical study.
SETTING
Multidisciplinary surgical ICU in a university hospital.
PATIENTS
Twelve male patients treated for acute surgical illness (multiple trauma n = 5, major surgery n = 7).
SELECTION CRITERIA
stable cardiovascular parameters, normal cardiac function, signs of hypovolemia (CVP < or = 5 mmHg, urine output < 1 ml/kg x h).
INTERVENTIONS
After baseline measurements, a 60 min fluid challenge test was performed with normal saline solution, 0.25 ml/kg/min [corrected].
MEASUREMENTS AND RESULTS
Body weight (platform digital scale), total body impedance (four-surface electrode technique; measurements at 0.5, 50 and 100 kHz) and urine output. Fluid retention induced a progressive decrease in BI at 0.5, 50 and 100 kHz, but the changes were significant for BI 0.5 and BI 100 only, from 40 min after the beginning of the fluid therapy onwards. There was a significant negative correlation between changes in water retention and BI 0.5, with individual correlation coefficients ranging from -0.72 to 0.95 (p < 0.01-0.0001). The slopes of the regression lines indicated that for each kg of water change, there was a mean decrease in BI of 18 ohm, but a substantial inter-individual variability was noted.
CONCLUSION
BI measured at low frequency can represent a valuable index of acute changes in body water in a group of surgical patients but not in a given individual.
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