Predialytic hyponatremia is associated with poor outcome in hemodialysis patients. Hypotonic hyponatremia is the most frequently encountered disorder reflecting mixed disorders combining extracellular fluid overload and free water excess, resulting from the interplay of intermittency of dialysis and diet observance, and likely precipitated by an acute or subacute illness. In this context, hyponatremia requires to be detected and worked up to identify and cure the cause. In this clinical case report, we describe preliminary results of using an online biosensor on a dialysis machine that provides automated predialysis plasma sodium concentration derived from dialysate conductivity measurements. Based on this biosensor, within a 5 year time frame, 11 patients out of more than 130 maintenance hemodialysis patients and over 40,000 dialysis sessions were identified with episodes of predialysis hyponatremia (≤135 mmol/l). In all patients, hyponatremic episodes were indicative of a severe underlying illness associated with fluid overload leading to plasma hypotonicity. Automated online predialysis plasma sodium concentration measurement offers an innovative, reliable, and cost-free tool that permits to detect hyponatremia as marker of an underlying illness development in dialysis patients. The value of this tool in supporting clinical decision-making deserves further studies in a large dialysis population.
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