Department of Critical Care Medicine, Critical Care Institute, Cleveland Clinic Abu Dhabi, Abu Dhabi, UAE.
Department of Anesthesiology and Critical Care Medicine, Centre Hospitalier du Dr. Schaffner de Lens, Lens, France.
PLoS One. 2018 Nov 8;13(11):e0206868. doi: 10.1371/journal.pone.0206868. eCollection 2018.
Central venous oxygen saturation (ScvO2) is often used to help to guide resuscitation of critically ill patients. The standard gold technique for ScvO2 measurement is the co-oximetry (Co-oximetry_ScvO2), which is usually incorporated in most recent blood gas analyzers. However, in some hospitals, those machines are not available and only calculated ScvO2 (Calc_ScvO2) is provided. Therefore, we aimed to investigate the agreement between Co-oximetry_ScvO2 and Calc_ScvO2 in a general population of critically ill patients and septic shock patients.
A total of 100 patients with a central venous catheter were included in the study. One hundred central venous blood samples were collected and analyzed using the same point-of-care blood gas analyzer, which provides both the calculated and measured ScvO2 values. Bland and Altman plot, intra-class correlation coefficient (ICC), and Cohen's Kappa coefficient were used to assess the agreement between Co-oximetry_ScvO2 and Calc_ScvO2. Multiple linear regression analysis was performed to investigate the independent explanatory variables of the difference between Co-oximetry_ScvO2 and Calc_ScvO2.
In all population, Bland and Altman's analysis showed poor agreement (+4.5 [-7.1, +16.1]%) between the two techniques. The ICC was 0.754 [(95% CI: 0.393-0.880), P< 0.001], and the Cohen's Kappa coefficient, after categorizing the two variables into two groups using a cutoff value of 70%, was 0.470 (P <0.001). In septic shock patients (49%), Bland and Altman's analysis also showed poor agreement (+5.6 [-6.7 to 17.8]%). The ICC was 0.720 [95% CI: 0.222-0.881], and the Cohen's Kappa coefficient was 0.501 (P <0.001). Four independent variables (PcvO2, Co-oximetry_ScvO2, venous pH, and Hb) were found to be associated with the difference between the measured and calculated ScvO2 (adjusted R2 = 0.8, P<0.001), with PcvO2 being the main independent explanatory variable because of its highest absolute standardized coefficient. The area under the receiver operator characteristic curves (AUC) of PcvO2 to predict Co-oximetry_ScvO2 ≥ 70% was 0.911 [95% CI: 0.837-0.959], in all patients, and 0.903 [95% CI: 0.784-0.969], in septic shock patients. The best cutoff value was ≥ 36 mmHg (sensitivity, 88%; specificity, 83%), in all patients, and ≥ 35 mmHg (sensitivity, 94%; specificity, 71%) in septic shock patients.
The discrepancy between the measured and calculated ScvO2 is clinically not acceptable. We do not recommend the use of calculated ScvO2 to guide resuscitation in critically ill patients. In situations where the Co-oximetry technique is not available, relying on PcvO2 to predict the measured ScvO2 value above or below 70% could be an option.
中心静脉血氧饱和度（ScvO2）常用于帮助指导危重症患者的复苏。测量 ScvO2 的标准金标准技术是比色法（Co-oximetry_ScvO2），它通常包含在大多数最新的血气分析仪中。然而，在一些医院，这些仪器不可用，只能提供计算的 ScvO2（Calc_ScvO2）。因此，我们旨在研究在一般危重症患者和感染性休克患者群体中 Co-oximetry_ScvO2 和 Calc_ScvO2 之间的一致性。
共有 100 名使用中心静脉导管的患者纳入研究。采集 100 份中心静脉血样，使用同一台即时血气分析仪进行分析，该分析仪同时提供计算和测量的 ScvO2 值。使用 Bland 和 Altman 图、组内相关系数（ICC）和 Cohen's Kappa 系数评估 Co-oximetry_ScvO2 和 Calc_ScvO2 之间的一致性。进行多元线性回归分析，以调查 Co-oximetry_ScvO2 和 Calc_ScvO2 之间差异的独立解释变量。
在所有人群中，Bland 和 Altman 的分析显示两种技术之间的一致性较差（+4.5[-7.1，+16.1]%）。ICC 为 0.754[95%CI：0.393-0.880)，P<0.001]，Cohen's Kappa 系数，在使用 70%的截断值将两个变量分为两组后，为 0.470(P<0.001)。在感染性休克患者（49%）中，Bland 和 Altman 的分析也显示出较差的一致性（+5.6[-6.7，+17.8]%）。ICC 为 0.720[95%CI：0.222-0.881]，Cohen's Kappa 系数为 0.501(P<0.001)。发现四个独立变量（PcvO2、Co-oximetry_ScvO2、静脉 pH 和 Hb）与测量和计算的 ScvO2 之间的差异相关（调整后的 R2=0.8，P<0.001），PcvO2 是主要的独立解释变量，因为它的绝对标准化系数最高。PcvO2 预测 Co-oximetry_ScvO2≥70%的受试者工作特征曲线下面积（AUC）在所有患者中为 0.911[95%CI：0.837-0.959]，在感染性休克患者中为 0.903[95%CI：0.784-0.969]。最佳截断值为≥36mmHg（敏感性，88%；特异性，83%），在所有患者中，≥35mmHg（敏感性，94%；特异性，71%）在感染性休克患者中。
测量和计算的 ScvO2 之间的差异在临床上是不可接受的。我们不建议使用计算的 ScvO2 来指导危重症患者的复苏。在无法使用 Co-oximetry 技术的情况下，依赖 PcvO2 来预测测量的 ScvO2 值高于或低于 70%可能是一种选择。
