Volaemic assessment of the elderly hyponatraemic patient: reliability of clinical assessment and validation of bioelectrical impedance analysis.

BACKGROUND Hyponatraemia is the commonest electrolyte disturbance of hospital inpatients. Assessment of volaemic status is an important part of diagnosis and management. AIM To determine reliability of clinical assessment of volaemic state by assessing inter-observer variability of clinical measures of volaemic state. To assess validity of bioelectrical impedance analysis as a tool to measure total body water in elderly hyponatraemic patients. DESIGN Observational study conducted in a Department of Medicine for the Elderly. METHODS Hospital inpatients >65 years old (n=22) with serum sodium concentration <130 mmol/l were included. Two assessors determined volaemic state on two occasions 72 h apart. Level of agreement between observers was determined on each occasion. Total body water estimation was undertaken with bioelectrical impedance analysis and measurement of dilution of deuterium oxide. Correlation between these two measures was then analysed. RESULTS Cohen's κ for agreement between two observers for overall assessment of volaemic state was 0.59 (P<0.01). Values for agreement between individual clinical markers of volaemic state ranged between 0.16 and 0.45. Pearson correlation coefficient (r) for correlation between estimation of total body water undertaken by bioelectrical impedance analysis and by measurement of dilution of deuterium oxide was 0.69 (P<0.001). CONCLUSION There was moderate inter-observer agreement of overall clinical volaemic assessment of elderly hyponatraemic patients. Total body water estimation by bioelectrical impedance analysis correlates well with estimation by measurement of dilution of deuterium oxide, providing a potentially useful tool to improve the management of the elderly hyponatraemic patient.