Endocrine Abstracts

Measurement of electrical impedance has been proposed as a way to determine whether a hyponatremic patient is hypovolemic or euvolemic. We compare the usefulness of the physical examination (PE) with bioimpedance for determination of volemia in an outpatient hyponatremia clinic.

Method: Descriptive prospective analysis. 11 patients attended at the hyponatremia clinic of a tertiary hospital were evaluated. Impedance was measured by a SECA, indicating the percent of weight corresponding to body water. Furthermore, by applying internal algorithms, SECA indicates whether total body water (TBW) and extracellular body water (EBW) are normal, increased, or reduced in a given patient, based on body composition, gender and age. Results were compared with ‘gold standard’ evaluation of volemia by inspection of the maximum height of the internal jugular vein pulse (PE). Patients were considered euvolemic if the pulse was 1–3 cm above the sternal angle when reclined, and hypovolemic if found below the sternal angle.

Results: 2/11(18%) women. Median age: 72 [IQR 14]. Four patients were hypovolemic by PE. In 3/4, TBW was found to be low by SECA. However, impedance found low EBW in only 1 patient. In fact, in 1 patient SECA analysis found ECW to be elevated. Based on PE, in 2 patients the tolvaptan dose was reduced, in another 2 fluid intake was increased. In all 4, clinical and analytical improvement ensued. In 3 patients who were euvolemic by PE, with serum sodium ≤ 135 mmol/l, SECA found TBW to be low, normal, or high, with corresponding ECBW low, high, and high respectively. Patients were told to reduce fluid intake. All had improved at follow-up. Four patients were eunatremic, and euvolemic by PE. SECA indicated low TBW in one, normal in 3. EBW was normal in 3, and upper limits in 1. Patient therapy was not modified. Patients were well at follow-up. SECA’s findings of TBW diverged from its observed EBW in 6/11 patients. SECA’s TBW report coincided with the PE in 7/11 cases, whereas SECA’s EBW report coincided with the PE in 6/11.

Conclusion: In a Hyponatremia clinic, physical examination of the internal jugular pulse, directly indicating volemia, provides a better tool for clinical decision-making than impedance measurement. Furthermore, given that water diffuses freely between body compartments, SECA’s discrepancy as regards total and extracellular body water is surprising. SECA impedance analysis appears to be of limited value in an outpatient setting for determination of volemia.