Supplementary Material for: Effect of Fluid Intake on Hydration Status and Skin Barrier Characteristics in Geriatric Patients: An Explorative Study

<b><i>Background/Aim:</i></b> Inadequate fluid intake is assumed to be a trigger of water-loss dehydration, which is a major health risk in aged and geriatric populations. Thus, there is a need to search for easy to use diagnostic tests to identify dehydration. Our overall aim was to investigate whether skin barrier parameters could be used for predicting fluid intake and/or hydration status in geriatric patients. <b><i>Methods:</i></b> An explorative observational comparative study was conducted in a geriatric hospital including patients aged 65 years and older. We measured 3-day fluid intake, skin barrier parameters, Overall Dry Skin Score, serum osmolality, cognitive and functional health, and medications. <b><i>Results:</i></b> Forty patients were included (mean age 78.45 years and 65% women) with a mean fluid intake of 1,747 mL/day. 20% of the patients were dehydrated and 22.5% had an impending dehydration according to serum osmolality. Multivariate analysis suggested that skin surface pH and epidermal hydration at the face were associated with fluid intake. Serum osmolality was associated with epidermal hydration at the leg and skin surface pH at the face. Fluid intake was not correlated with serum osmolality. Diuretics were associated with high serum osmolality. <b><i>Conclusions:</i></b> Approximately half of the patients were diagnosed as being dehydrated according to osmolality, which is the current reference standard. However, there was no association with fluid intake, questioning the clinical relevance of this measure. Results indicate that single skin barrier parameters are poor markers for fluid intake or osmolality. Epidermal hydration might play a role but most probably in combination with other tests.**背景与目的**：饮水不足被认为是失水性脱水（water-loss dehydration）的诱因，该病症在老年群体中属于重大健康风险。因此，亟需开发操作简便的诊断方法以识别脱水状态。本研究的总体目标为探究皮肤屏障参数（skin barrier parameters）能否用于预测老年患者的饮水量及/或水合状态。**研究方法**：本研究于一家老年病医院开展一项探索性观察对比研究，纳入年龄≥65岁的患者。研究人员记录了患者3天的饮水量、皮肤屏障参数、总体皮肤干燥评分（Overall Dry Skin Score）、血清渗透压（serum osmolality）、认知与功能健康状况以及用药情况。**研究结果**：本研究共纳入40例患者，平均年龄78.45岁，女性占比65%，日均饮水量为1747mL。依据血清渗透压检测结果，20%的患者存在脱水，22.5%的患者处于脱水前驱状态。多变量分析显示，面部皮肤表面pH值与表皮水合（epidermal hydration）水平与饮水量显著相关；血清渗透压则与腿部表皮水合水平及面部皮肤表面pH值相关。饮水量与血清渗透压无显著关联。利尿剂（diuretics）与高血清渗透压水平存在相关性。**研究结论**：以当前临床参考金标准血清渗透压为依据，约半数患者被诊断为脱水。然而该指标与饮水量并无关联，这对其临床应用价值提出了质疑。研究结果表明，单一皮肤屏障参数难以作为饮水量或血清渗透压的有效标志物。表皮水合水平或可发挥一定作用，但极有可能需要与其他检测手段联合应用方能发挥实际价值。