Toftegaard M, Rees S E, Andreassen S
Center for Model Based Medical Decision Support Systems, Aalborg University, Denmark.
Emerg Med J. 2009 Apr;26(4):268-72. doi: 10.1136/emj.2007.052571.
This paper evaluates a method in which arterial values of pH, carbon dioxide tension (Pco(2)) and oxygen tension (Po(2)) calculated from venous values and pulse oximetry are compared with simultaneously measured arterial values.
103 adult patients from three departments (pulmonary medicine, thoracic intensive care and multidisciplinary intensive care) were studied. The patients belonged to three groups: (1) 31 haemodynamically stable patients with a diagnosis of chronic obstructive lung disease (COLD); (2) 49 haemodynamically stable patients without COLD; and (3) 23 haemodynamically unstable patients without COLD. Arterial and venous (peripheral and, where possible, central and mixed) blood samples were taken simultaneously and anaerobically. Peripheral arterial oxygen saturation was measured with a pulse oximeter. The principle of the method is to simulate the transport of venous blood back through the tissues using the respiratory quotient (adding oxygen and removing carbon dioxide) until simulated arterial oxygenation matches that measured by pulse oximetry.
Calculated values of arterial pH and Pco(2) had very small bias and standard deviations regardless of the venous sampling site. In all cases these errors were within those considered acceptable for the performance of laboratory equipment, and well within the limits of error acceptable in clinical practice. In addition, the standard deviation (SD) of calculated values of pH and Pco(2) was similar to the variability between consecutive arterial samples. For peripheral oxygen saturation values < or =96%, the method can calculate Po(2) with an SD of 0.93, which may be useful in clinical practice. Calculations made from peripheral venous blood were significantly more accurate than those from central venous blood.
Arterial pH and Pco(2) can be calculated precisely from peripheral venous blood in a broad patient population. The method has potential for use as a screening tool in emergency medical departments and in medical and surgical wards to assess a patient's acid-base and oxygenation status prior to sampling arterial blood or to help in the decision to refer the patient to the ICU. In departments where arterial blood gas values are used to monitor patients (eg, pulmonary medicine), the method might reduce the number of arterial samples taken by replacing them with peripheral venous blood samples, thus reducing the need for painful arterial punctures.
本文评估一种方法，即将根据静脉血值和脉搏血氧饱和度计算得出的动脉血pH值、二氧化碳分压（Pco₂）和氧分压（Po₂）与同时测量的动脉血值进行比较。
对来自三个科室（肺病科、胸科重症监护室和多学科重症监护室）的103例成年患者进行了研究。这些患者分为三组：（1）31例血流动力学稳定且诊断为慢性阻塞性肺疾病（COLD）的患者；（2）49例血流动力学稳定且无COLD的患者；（3）23例血流动力学不稳定且无COLD的患者。同时采集动脉血和静脉血（外周血，尽可能采集中心静脉血和混合静脉血），并进行厌氧处理。使用脉搏血氧仪测量外周动脉血氧饱和度。该方法的原理是利用呼吸商（添加氧气和去除二氧化碳）模拟静脉血通过组织的回流运输，直到模拟的动脉氧合与脉搏血氧仪测量的结果相匹配。
无论静脉血采样部位如何，计算得出的动脉血pH值和Pco₂的偏差和标准差都非常小。在所有情况下，这些误差都在实验室设备性能可接受的范围内，并且远低于临床实践中可接受的误差限度。此外，pH值和Pco₂计算值的标准差（SD）与连续动脉血样本之间的变异性相似。对于外周血氧饱和度值≤96%的情况，该方法计算Po₂的标准差为0.93，这在临床实践中可能有用。从外周静脉血进行的计算比从中枢静脉血进行的计算明显更准确。
在广泛的患者群体中，可以从外周静脉血精确计算动脉血pH值和Pco₂。该方法有可能用作急诊科以及内科和外科病房的筛查工具，在采集动脉血之前评估患者的酸碱和氧合状态，或帮助决定是否将患者转诊至重症监护病房（ICU）。在使用动脉血气值监测患者的科室（如肺病科），该方法可能通过用外周静脉血样本替代动脉血样本，减少动脉血样本的采集数量，从而减少痛苦的动脉穿刺需求。
