Department of Respiratory and Critical Care Medicine, Otto Wagner Hospital, Sanatoriumstrasse 2, 1145 Vienna, Austria.
Intensive Care Med. 2013 Feb;39(2):302-8. doi: 10.1007/s00134-012-2691-0. Epub 2012 Oct 19.
Measuring or calculating plasma osmolality is of interest in critical care medicine. Moreover, the osmolal gap (i.e. the difference between the measured and calculated osmolality) helps in the differentiation of metabolic acidosis. A variety of formulas for calculating osmolality have been published, most of them relying on sodium, urea and glucose. A novel formula developed by Zander has recently been published, which also takes into account the effects of potassium, chloride, lactate and bicarbonate on osmolality. We evaluate the previously published formulas including the novel formula by comparing calculated and measured osmolality.
Arterial or venous blood samples from 41 outpatients and 195 acutely ill inpatients (total 236 subjects) were used to compare measured osmolality with calculated osmolality as obtained from 36 published formulas including the new formula. The performance of the formulas was statistically evaluated using the method of Bland and Altman.
Mean differences up to 35 mosmol/kg H(2)O were observed between measured and calculated osmolality using the previously published formulas. In contrast, the novel formula had a negligible mean difference of 0.5 mosmol/kg H(2)O. The novel formula also had the closest 95 % limits of agreement ranging from -6.5 to 7.5 mosmol/kg H(2)O.
Only 4 out of the 36 evaluated formulas gave mean differences between measured and calculated osmolality of less than 1 mosmol/kg H(2)O. Zander's novel formula showed excellent concordance with measured osmolality and facilitates a more precise diagnosis based on blood gas analysers. The new equation has the potential to replace separate measurements of osmolality in many cases.
在重症监护医学中，测量或计算血浆渗透压很有意义。此外，渗透压间隙（即测量渗透压与计算渗透压之间的差异）有助于区分代谢性酸中毒。已经发表了多种计算渗透压的公式，其中大多数依赖于钠、尿素和葡萄糖。最近发表了一种由赞德（Zander）开发的新公式，该公式还考虑了钾、氯、乳酸盐和碳酸氢盐对渗透压的影响。我们通过比较计算渗透压和测量渗透压来评估以前发表的公式，包括新公式。
使用来自 41 名门诊患者和 195 名急性住院患者（共 236 名受试者）的动脉或静脉血样，将测量渗透压与从 36 种已发表公式（包括新公式）中获得的计算渗透压进行比较。使用 Bland 和 Altman 方法对公式的性能进行了统计评估。
使用以前发表的公式，测量渗透压与计算渗透压之间的平均差异高达 35 mosmol/kg H2O。相比之下，新公式的平均差异可忽略不计，为 0.5 mosmol/kg H2O。新公式的 95%一致性界限也最接近，范围为-6.5 至 7.5 mosmol/kg H2O。
在评估的 36 种公式中，只有 4 种公式的测量渗透压与计算渗透压之间的平均差异小于 1 mosmol/kg H2O。赞德（Zander）的新公式与测量渗透压具有极好的一致性，并有助于基于血气分析仪进行更精确的诊断。在许多情况下，新公式有可能替代单独测量渗透压。
