Gilfix B M, Bique M, Magder S
Critical Care Division, Royal Victoria Hospital, Montreal, Quebec.
J Crit Care. 1993 Dec;8(4):187-97. doi: 10.1016/0883-9441(93)90001-2.
We evaluated the clinical application of a model of acid-base balance, which is based on quantitative physical chemical principles (Stewart model). This model postulates that acid-base balance is normally determined by the difference in concentration between strong cations and anions (strong ion difference [SID]), PCO2, and weak acids (primarily proteins). We measured electrolytes and blood gases in arterial blood samples from 21 patients in a medical or surgical intensive care unit or emergency room of a tertiary care hospital. The measured SID frequently differed from SID calculated from the measured blood components, which indicates that unmeasured cations or anions are present; these could not be accounted for by lactate, ketones, or other readily identifiable ions. We used an approach to acid-base analysis that is based on changes in base excess or deficit due to changes in: (1) free water as assessed by [Na+]; (2) in [Cl-]; (3) protein concentration; and (4) "other species" (ie, anion and cations other than [Na+], [K+], and [Cl-]). The contribution of "other species" was obtained from the difference between the SID measured and that predicted from Stewart's equation. It could also be calculated from the difference between the standard Siggaard-Anderson calculation of base excess and base excess attributable to free water, [Cl-], and proteins (ie, base-excess gap). Our results indicate that the SID gap, base excess gap, and anion gap reflect the presence of unmeasured ions, and both the anion-gap and base-excess gap provide readily available estimates of the SID gap. This provides a simple bedside approach for using the Stewart model to analyze the nonrespiratory component of clinical acid-base disorders and indicates that, in addition to unmeasured anions, unmeasured cations can be present.
我们评估了一种基于定量物理化学原理的酸碱平衡模型（Stewart模型）的临床应用。该模型假定酸碱平衡通常由强阳离子与阴离子之间的浓度差（强离子差 [SID]）、PCO₂ 和弱酸（主要是蛋白质）决定。我们在一家三级医院的内科或外科重症监护病房或急诊室，对21例患者的动脉血样本进行了电解质和血气测量。测得的SID常常与根据测得的血液成分计算出的SID不同，这表明存在未测量的阳离子或阴离子；乳酸、酮类或其他易于识别的离子无法解释这些差异。我们采用了一种酸碱分析方法，该方法基于因以下因素变化导致的碱剩余或碱缺失的变化：（1）通过 [Na⁺] 评估的游离水；（2）[Cl⁻]；（3）蛋白质浓度；以及（4）“其他物质”（即除 [Na⁺]、[K⁺] 和 [Cl⁻] 之外的阴离子和阳离子）。“其他物质”的贡献是通过测得的SID与根据Stewart方程预测的SID之间的差值获得的。它也可以从标准Siggaard-Anderson碱剩余计算值与归因于游离水、[Cl⁻] 和蛋白质的碱剩余（即碱剩余间隙）之间的差值计算得出。我们的结果表明，SID间隙、碱剩余间隙和阴离子间隙反映了未测量离子的存在，并且阴离子间隙和碱剩余间隙都能提供对SID间隙的现成估计。这为使用Stewart模型分析临床酸碱紊乱的非呼吸成分提供了一种简单的床边方法，并表明除了未测量的阴离子外，还可能存在未测量的阳离子。
