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Weight changes in critically ill patients evaluated by fluid balances and impedance measurements
A N Roos1, R G Westendorp, M Frölich
1Department of General Internal Medicine, University Hospital Leiden, The Netherlands.
Objective:
To study simple, rapid, and predictive methods to determine body weight changes in critically ill patients.
Design:
Prospective, consecutive sample.
Setting:
Medical intensive care unit of a university hospital.
Patients:
Thirty-one consecutive patients.
Interventions:
Calculated weight changes, using day-to-day and cumulative fluid balances corrected (in two ways) for insensible losses, were compared with the actual weight changes (mattress bascule). A tetrapolar impedance technique measuring resistance was evaluated for estimating weight changes.
Measurements And Main Results:
No reliable relationship was found between calculated weight changes using fluid balances corrected for insensible loss and the observed weight changes. An intraindividual relationship was found between actual weight changes and changes in resistance measured with the tetrapolar impedance technique in a group of 24 critically ill patients with large weight changes (11.1 +/- 6.7 kg). No such intraindividual relationship was found in seven patients with small weight changes (3.1 +/- 2.2 kg). In each patient, the slope coefficient of the change in weight and resistance relationship differed; this individual slope coefficient could be an indication for hydration.
Conclusions:
Calculated fluid balances are not predictive for actual weight changes in critically ill patients. Absolute weight measurements are indispensable. Changes in resistance correlated with weight changes in individual patients if weight changes were > 3 kg.