體內水、鈉平衡失調常發生在住院病人尤其是重症、手術、創傷的病人身上，血鈉濃度異常只是反映血漿內的水份相對於血漿內的鈉過多或不足，並不能預測身體的鈉含量。本篇文章將介紹體液組成及分佈，水、鈉平衡的調節，評估及處置血容積失調及血鈉異常，進而利用腸道和靜脈營養治療的成份調整，幫助病人恢復正常的血容積及血鈉濃度。治療水、鈉平衡失調時需要緊密的監測血鈉濃度，避免因快速矯正低血鈉症或高血鈉症時，反而增加併發症的發生。

Abstract：Disorders of water and sodium imbalance occur frequently in the hospitalized patients, particularly those with critical illness, operation and trauma. Abnormal plasma sodium concentration only reflects a relative excess or deficit of plasma water in relation to plasma sodium but not total body sodium content. We review the composition and distribution of body fluid, regulation of water and sodium balance, and the evaluation and management of the disorder of blood volume and abnormal plasma sodium level. Modification of enteral and parenteral nutrition can be helpful to restore normal blood volume and plasma sodium concentration. Treatment of water and sodium imbalance requires close monitoring to avoid too rapid correction of hyponatremia or hypernatremia and thus to decrease the incidence of the complications.