Hardman J G, Bedforth N M
University Department of Anaesthesia, University Hospital, Nottingham, UK.
Br J Anaesth. 1999 Mar;82(3):346-9. doi: 10.1093/bja/82.3.346.
Estimation of venous admixture in patients with impaired gas exchange allows monitoring of disease progression, efficacy of interventions and assessment of the optimal inspired oxygen fraction. A pulmonary artery catheter allows accurate measurement, although the associated risks preclude its use solely for estimation of venous admixture. Non-invasive methods require assumed values for physiological variables. Many of the required data (e.g. haemoglobin concentration (Hb), base excess, inspired oxygen fraction, arterial oxygen (PaO2) and carbon dioxide (PaCO2) tensions, temperature) are available routinely in the intensive therapy unit. We have compared a typical iso-shunt-style estimation of venous admixture (assuming Hb, base excess, PaCO2 and temperature), and estimation using the Nottingham physiology simulator (NPS), with measured data. When the arteriovenous oxygen content difference (CaO2-CvO2) was assumed to be 50 ml litre-1, the 95% limits of agreement (LA95%) for venous admixture using the NPS were -3.9 +/- 8.5% and using an iso-shunt-style calculation, -6.4 +/- 10.6%. CaO2-CvO2 was 41.1 ml litre-1 in the patients studied, consistent with previous studies in the critically ill. When CaO2-CvO2 was assumed to be 40 ml litre-1, LA95% values were 0.5 +/- 8.2% and -2.1 +/- 10.1%, respectively.
对气体交换受损患者的静脉混合情况进行评估，有助于监测疾病进展、干预措施的疗效以及评估最佳吸入氧分数。肺动脉导管可实现精确测量，不过其相关风险使其无法仅用于静脉混合情况的评估。非侵入性方法需要假定生理变量的值。许多所需数据（如血红蛋白浓度（Hb）、碱剩余、吸入氧分数、动脉血氧（PaO2）和二氧化碳（PaCO2）分压、体温）在重症监护病房中可常规获取。我们将静脉混合情况的典型等分流式评估（假定Hb、碱剩余、PaCO2和体温）以及使用诺丁汉生理模拟器（NPS）的评估与实测数据进行了比较。当动静脉血氧含量差（CaO2 - CvO2）假定为50 ml/L时，使用NPS评估静脉混合情况的95%一致性界限（LA95%）为-3.9 ± 8.5%，使用等分流式计算时为-6.4 ± 10.6%。在所研究的患者中，CaO2 - CvO2为41.1 ml/L，与先前对危重症患者的研究结果一致。当CaO2 - CvO2假定为40 ml/L时，LA95%值分别为0.5 ± 8.2%和-2.1 ± 10.1%。
