Predictive value of tetrapolar body impedance measurements for hydration status in critically ill patients.

OBJECTIVE

To design and evaluate a simple and rapid method to predict body hydration status in critically ill patients.

DESIGN

Prospective, consecutive sample.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

31 consecutive patients.

METHODS

All patients were classified daily for hydration status by the attending physician based on clinical impression, weight changes and laboratory measurements. The hydration status was scored as 'dehydrated', 'euvolemic' or 'edematous'. The total body impedance was measured daily by a tetrapolar impedance technique.

RESULTS

Resistances > 700 omega were found in dehydrated subjects and resistances of < 400 omega in edematous patients. Weight gain was observed in dehydrated and weight loss in edematous patients. A discriminant analysis was used to create a predictive model for hydration using the daily impedance and weight measurements. If a cutoff point of 60% for the predicted classification was used to categorize the patient's hydration as dehydrated, euvolemic and edematous, no false positive predictions were observed for the dehydrated or the edematous state.

CONCLUSION

Impedance measurements are in close agreement with the clinical impression of hydration of critically ill patients. Future investigations must elucidate the clinical importance.