Service de Réanimation Médicale et d'Assistance Respiratoire, Hôpital de la Croix Rousse, 103 Grande Rue de la Croix Rousse, 69004 Lyon, France.
Respir Care. 2010 Nov;55(11):1453-63.
The Stewart approach theorizes that plasma pH depends on P(aCO₂), the strong ion difference, and the plasma total concentration of non-volatile weak acids (A(tot)). The conventional approach measures standardized base excess, bicarbonate (HCO₃⁻), and the anion gap.
To describe acid-base disorders with the Stewart approach and the conventional approach in patients with chronic respiratory failure.
This was an observational prospective study in a medical intensive care unit and a pneumology ward of a university hospital. There were 128 patients included in the study, of which 14 had more than one admission, resulting in 145 admissions. These were allocated to 4 groups: stable respiratory condition and elevated HCO₃⁻ (Group 1, n = 23), stable respiratory condition and non-elevated HCO₃⁻ (Group 2, n = 41), unstable respiratory condition and elevated HCO₃⁻ (Group 3, n = 44), and unstable respiratory condition and non-elevated HCO₃⁻ (Group 4, n = 37). Elevated HCO₃⁻ was defined as ≥ 3 standard deviations higher than the mean value we found in 8 healthy volunteers. Measurements were taken on admission.
In groups 1, 2, 3, and 4, the respective mean ± SD values were: HCO₃⁻ 33 ± 3 mM, 26 ± 3 mM, 37 ± 4 mM, and 27 ± 3 mM (P < .001); strong ion difference 45 ± 3 mM, 38 ± 4 mM, 46 ± 4 mM, and 36 ± 4 mM (P < .001); and A(tot) 12 ± 1 mM, 12 ± 1 mM, 10 ± 1 mM, 10 ± 2 mM (P < .001). Non-respiratory disorders related to high strong ion difference were observed in 12% of patients with elevated HCO₃⁻, and in none of those with non-elevated HCO₃⁻ (P = .003). Non-respiratory disorders related to low strong ion difference were observed in 9% of patients with non-elevated HCO₃⁻, and in none of those with elevated HCO₃⁻ (P = .02). Hypoalbuminemia was common, especially in unstable patients (group 3, 66%; group 4, 65%). Normal standardized base excess (16%), HCO₃⁻ (28%), and anion gap (30%) values were common. The Stewart approach detected high effective strong ion difference in 13% of normal standardized base excess, and in 20% of normal anion gap corrected for albuminemia, and low effective strong ion difference in 22% of non-elevated HCO₃⁻.
In patients with chronic respiratory failure the acid-base pattern is complex, metabolic alkalosis is present in some patients with elevated HCO₃⁻, and metabolic acidosis is present in some with non-elevated HCO₃⁻. The diagnostic performance of the Stewart approach was better than that of the conventional approach, even when corrected anion gap was taken into account.
斯图尔特方法理论认为，血浆 pH 值取决于 P(aCO₂)、强离子差和血浆中非挥发性弱酸的总浓度(A(tot))。传统方法测量标准化基础过剩、碳酸氢盐(HCO₃⁻)和阴离子间隙。
用斯图尔特方法和传统方法描述慢性呼吸衰竭患者的酸碱失衡。
这是一项在大学医院的重症监护病房和呼吸科病房进行的观察性前瞻性研究。共有 128 名患者入组，其中 14 名患者有多次入院，共 145 次入院。这些患者被分为 4 组：呼吸状况稳定且 HCO₃⁻升高（第 1 组，n=23）、呼吸状况稳定且 HCO₃⁻正常（第 2 组，n=41）、呼吸状况不稳定且 HCO₃⁻升高（第 3 组，n=44）和呼吸状况不稳定且 HCO₃⁻正常（第 4 组，n=37）。HCO₃⁻升高定义为高于我们在 8 名健康志愿者中发现的平均值 3 个标准差。入院时进行测量。
在第 1、2、3 和 4 组中，相应的平均值±SD 值分别为：HCO₃⁻33±3mM、26±3mM、37±4mM 和 27±3mM（P<0.001）；强离子差 45±3mM、38±4mM、46±4mM 和 36±4mM（P<0.001）；和 A(tot)12±1mM、12±1mM、10±1mM、10±2mM（P<0.001）。在 HCO₃⁻升高的患者中观察到与高强离子差相关的非呼吸性疾病占 12%，而在 HCO₃⁻正常的患者中无此类疾病（P=0.003）。在 HCO₃⁻正常的患者中观察到与低强离子差相关的非呼吸性疾病占 9%，而在 HCO₃⁻升高的患者中无此类疾病（P=0.02）。低白蛋白血症很常见，尤其是在不稳定的患者中（第 3 组，66%；第 4 组，65%）。正常的标准化基础过剩（16%）、HCO₃⁻（28%）和阴离子间隙（30%）值很常见。斯图尔特方法在 13%的正常标准化基础过剩和 20%的白蛋白校正后的正常阴离子间隙中检测到高有效强离子差，在 22%的非升高 HCO₃⁻中检测到低有效强离子差。
在慢性呼吸衰竭患者中，酸碱平衡模式复杂，一些 HCO₃⁻升高的患者存在代谢性碱中毒，一些 HCO₃⁻正常的患者存在代谢性酸中毒。即使考虑白蛋白校正后的阴离子间隙，斯图尔特方法的诊断性能也优于传统方法。
