Direct sodium measurement prevents underestimation of hyponatremia in critically ill patients
Direct sodium measurement prevents underestimation of hyponatremia in critically ill patients
复制标题
直接钠测量可防止低估危重患者的低钠血症
作者：
W. Ancker;I. Haagen;P. H. Voort
亲爱的编辑：保持最佳的液体和电解质平衡是ICU专业人员的一项重要任务。假性低钠血症的临床意识是众所周知的，并被纳入指南[1]。然而，相反的情况，即假性高钠血症，目前被低估了，值得注意[2]。大多数化学分析仪在获得6到46倍的稀释后测量电解液浓度。对于电解质浓度的最终计算，假设体积的7%由脂肪和蛋白质组成，其余93%是发现电解质的水分部分。因此，在总蛋白/白蛋白浓度通常较低的危重患者中，使用间接方法时高估了钠浓度[3]。当使用血气分析仪直接测量钠时，这个问题就不存在了。在这项研究中，我们比较了直接和间接钠测量总蛋白和白蛋白浓度的差异。纳入的是连续的患者，他们同意他们的血液样本可以用于研究。对2336例患者的研究结果进行了回顾分析。钠、白蛋白和总蛋白浓度的间接测量是在Cobas系统上进行的(荷兰罗氏)。对于间接钠的测量，使用1：31稀释。钠的直接测量在血气分析仪(Radieter，荷兰)上进行。直接和间接钠测量在1小时的时间范围内进行。我们随意定义4 mmo1/L为临床相关差。在2,336例患者中，198例(8.5%)的间接钠测定值比直接测定法的测定值高4 mmol/L以上。间接法检测有80例(40%)出现假性高钠血症(14 5 mmol/L，2 1例)或假正常血症(135~145 mm ol/L，59例)，而直接测定者均为正常低钠血症。在407名患者中测量了总蛋白浓度，显示出与直接和间接钠测量之间的差异有很强的显著相关性(线性回归分析)(图1)。白蛋白浓度也有类似的结果(数据未显示)。在以前的论文中，假性高钠血症(或假性正常血钠血症)主要是在ICU科室的危重病人中描述的[2，3]。然而，在我们的研究中，21%的样本差值大于4 mmol/L来自ICU，其余79%来自急诊科(43%)和普通病房(36%)。这强调假性高钠血症不仅在ICU中发现，而且在普通医院人群中也存在。因此，当怀疑有假性高钠血症时，用血气分析仪测量电解质更可靠。然而，与化学分析仪相比，血气分析可能会遗漏分析前的误差，例如由于溶血导致的高钾或由于肝素过量而低估了带正电的电解质。危重病患者通常处于分解代谢状态，因此总蛋白浓度较低。对液体的严格监管
Dear Editor, Maintaining an optimal fluid and electrolyte balance is an important task for ICU professionals. Clinical awareness of pseudohyponatremia is commonly known and integrated into guidelines [1]. However, the opposite condition, i.e., pseudohypernatremia, is currently underestimated and warrants attention [2]. Most chemistry analyzers measure electrolyte concentration after obtaining a 6 to 46 times dilution. For the final calculation of the electrolyte concentration it is assumed that 7 % of the volume consists of fats and proteins, the remaining 93 % is the water fraction in which electrolytes are found. Therefore, in critically ill patients with often a low total protein/albumin concentration, sodium concentration is overestimated when using an indirect method [3]. When direct sodium measurement with blood gas analyzers is used this problem is not present. In this study we compare the difference between direct and indirect sodium measurement with the total protein and albumin concentration. Included were consecutive patients who agreed that their blood samples may be used for research. The results from 2,336 patients were reviewed in retrospect. Indirect measurement of sodium, albumin, and total protein concentration was performed on a Cobas System (Roche, the Netherlands). For the indirect sodium measurement a 1:31 dilution is used. Direct measurement of sodium was performed on a blood gas analyzer (Radiometer, the Netherlands). Direct and indirect sodium measurements were performed within a 1-h time frame. We arbitrarily defined 4 mmol/l as the clinically relevant difference. In 198 of 2,336 patients (8.5 %) indirect sodium results were more than 4 mmol/l higher than results obtained with the direct method. In 80/198 patients (40 %) this resulted in a pseudohypernatremia ([145 mmol/l, 21 patients) or pseudonormonatremia (135–145 mmol/l, 59 patients) based on the indirect method whereas direct measurement revealed a normoor hyponatremia respectively. In 407 patients the total protein concentration was measured, showing a strong significant correlation (linear regression analysis) with the difference between direct and indirect sodium measurement (Fig. 1). Similar results were found for the albumin concentration (data not shown). In previous papers pseudohypernatremia (or pseudonormonatremia) is mainly described in critically ill patients in ICU departments [2, 3]. However, in our research 21 % of samples in which a difference of more than 4 mmol/l was found derived form the ICU department, the remaining 79 % were from the emergency department (43 %) and the general wards (36 %). This emphasizes that pseudohypernatremia is not only found in ICUs, but also in the general hospital population. Thus, measurements of electrolytes with a blood gas analyzer is more reliable when a pseudohypernatremia is suspected. However, in contrast to chemistry analyzers, pre-analytic errors such as high potassium due to hemolysis or underestimation of positively charged electrolytes due to heparin excess can be missed with blood gas analysis [4]. In critical ill patients a catabolic state and consequently low total protein concentration are commonly found. Tight regulation of fluid