Balasubramanyan N, Havens P L, Hoffman G M
Department of Pediatrics, Children's Hospital of Wisconsin and Medical College of Wisconsin, Milwaukee, USA.
Crit Care Med. 1999 Aug;27(8):1577-81. doi: 10.1097/00003246-199908000-00030.
This study was undertaken to compare three methods for the identification of unmeasured anions in pediatric patients with critical illness. We compared the base excess (BE) and anion gap (AG) methods with the less commonly used Fencl-Stewart strong ion method of calculating BE caused by unmeasured anions (BEua). We measured the relationship of unmeasured anions identified by the three methods to serum lactate concentrations and to mortality.
Retrospective cohort study.
Tertiary care pediatric intensive care unit in an academic pediatric hospital.
The study population included 255 patients in the pediatric intensive care unit who had simultaneous measurements of arterial blood gases, electrolytes, and albumin during the period of July 1995 to December 1996. Sixty-six of the 255 patients had a simultaneous measurement of serum lactate.
The BEua was calculated using the Fencl-Stewart method. The AG was defined as (sodium plus potassium) - (chloride plus total carbon dioxide). BE was calculated from the standard bicarbonate, which is derived from the Henderson-Hasselbalch equation and reported on the blood gas analysis. A BE or BEua value of < or =-5 mEq/L or an AG > or =17 mEq/L was defined as a clinically significant presence of unmeasured anions. A lactate level of > or =45 mg/dL was defined as being abnormally elevated for this study. The presence of unmeasured anions identified by significantly abnormal BEua was poorly identified by BE or AG. Of the 255 patients included in the study, 67 (26%) had a different interpretation of acid base balance when the Fencl method was used compared with when BE and AG were used. Plasma lactate concentration correlated better with BEua (r2 = .55; p = .0001) than with AG (r2 = .41; p = .0005) or BE (r2 = .27; p = .025). Mortality was more strongly related to BEua < or =-5 mEq/L (relative risk of death = 10.25; p = .002) than to lactate > or =45 mg/dL (relative risk of death = 2.35; p = .04). In logistic regression analysis, mortality was more strongly associated with BEua (area under the receiver operating characteristic curve = 0.79; p = .0002) than lactate (receiver operating characteristic curve area = 0.63; p = .05), BE (receiver operating characteristic curve area = 0.53; p = .32), or AG (receiver operating characteristic curve area = 0.64; p = .08) in this patient sample.
Critically ill patients with normal BE and normal AG frequently have elevated unmeasured anions detectable by BEua. The Fencl-Stewart method is better than BE and similar to AG in identifying patients with high lactate levels. Elevated unmeasured anions identified by the Fencl-Stewart method were more strongly associated with mortality than with BE, AG, or lactate in this patient sample.
本研究旨在比较三种识别危重症儿科患者中未测定阴离子的方法。我们将碱剩余（BE）和阴离子间隙（AG）法与较少使用的Fencl-Stewart强离子法计算未测定阴离子引起的碱剩余（BEua）进行了比较。我们测定了三种方法识别的未测定阴离子与血清乳酸浓度及死亡率之间的关系。
回顾性队列研究。
一所学术性儿科医院的三级护理儿科重症监护病房。
研究人群包括1995年7月至1996年12月期间在儿科重症监护病房同时进行动脉血气、电解质和白蛋白测定的255例患者。255例患者中有66例同时测定了血清乳酸。
使用Fencl-Stewart法计算BEua。AG定义为（钠+钾）-（氯+总二氧化碳）。BE由标准碳酸氢盐计算得出，标准碳酸氢盐由亨德森-哈塞尔巴尔赫方程推导得出，并在血气分析中报告。BE或BEua值≤ -5 mEq/L或AG≥17 mEq/L被定义为临床上存在显著的未测定阴离子。乳酸水平≥45 mg/dL在本研究中被定义为异常升高。BEua显著异常所识别的未测定阴离子的存在，通过BE或AG识别不佳。在纳入研究的255例患者中，与使用BE和AG时相比，如果使用Fencl法，有67例（26%）对酸碱平衡有不同的解读。血浆乳酸浓度与BEua的相关性更好（r2 = 0.55；p = 0.0001），优于与AG（r2 = 0.41；p = 0.0005）或BE（r2 = 0.27；p = 0.025）的相关性。死亡率与BEua≤ -5 mEq/L的相关性更强（死亡相对风险 = 10.25；p = 0.002），高于与乳酸≥45 mg/dL的相关性（死亡相对风险 = 2.35；p = 0.04）。在逻辑回归分析中，在该患者样本中，死亡率与BEua的相关性更强（受试者工作特征曲线下面积 = 0.79；p = 0.0002），高于与乳酸（受试者工作特征曲线面积 = 0.63；p = 0.05）、BE（受试者工作特征曲线面积 = 0.53；p = 0.32）或AG（受试者工作特征曲线面积 = 0.64；p = 0.08）的相关性。
BE和AG正常的危重症患者经常存在可通过BEua检测到的升高的未测定阴离子。在识别高乳酸水平患者方面，Fencl-Stewart法优于BE且与AG相似。在该患者样本中，Fencl-Stewart法识别出的升高的未测定阴离子与死亡率的相关性比与BE、AG或乳酸的相关性更强。
