van der Hoeven M A, Maertzdorf W J, Blanco C E
Department of Neonatology, Academic Hospital Maastricht, The Netherlands.
Crit Care Med. 1999 Sep;27(9):1885-92. doi: 10.1097/00003246-199909000-00029.
To examine the hypothesis that mixed venous oxygen saturation (SvO2) values, which reflect the residual oxygen after tissue oxygen extraction, would be similar during hypoxic and anemic hypoxia.
SvO2 values, oxygen delivery, arterial oxygen content, and fractional oxygen extraction were compared, and critical values were determined based on lactate, the lactate/pyruvate ratio, and oxygen consumption during hypoxic and anemic hypoxia.
Laboratory of physiology at a university hospital.
Two groups of eight piglets, 8 to 12 days old.
Piglets were anesthetized, tracheotomized, intubated, and ventilated. A thoracotomy was performed and a fiberoptic catheter was placed in the pulmonary artery to monitor SvO2. A transit time ultrasound flow probe was positioned around the ascending aorta to measure aorta flow. Progressive hypoxic hypoxia was induced by decreasing FI(O2) from baseline (0.30-0.75) to 0.21, 0.15, and 0.10. Progressive anemic hypoxia was induced by a repeated isovolemic exchange transfusion with 50 mL of pasteurized plasma.
Fifteen or 30 mins after each intervention, samples were taken from the carotid artery for blood gases, hemoglobin, lactate, and pyruvate and from the pulmonary artery for blood gases and hemoglobin. Hemodynamic, arterial oxygen saturation, and SvO2 measurements were made. The calculated oxygen delivery and oxygen consumption decreased in both hypoxic and anemic hypoxia. At the lowest oxygen delivery level of anemic hypoxia, the decrease in SvO2 was less than that in hypoxic hypoxia (-26% vs. -55%). The range of critical values for SvO2 calculated for each individual piglet below which lactate, the lactate/pyruvate ratio, and oxygen consumption rapidly changed from baseline value was significantly lower in hypoxic hypoxia (11% to 24%) than in anemic hypoxia (26% to 48%). Fractional oxygen extraction increased significantly but not with a change as high as in hypoxic hypoxia 0.31 (range, 0.20-0.41) vs. 0.49 (range, 0.41-0.54).
In comparison with hypoxic hypoxia, critical values of SvO2 are higher in anemic hypoxia, indicating that oxygen unloading from blood to tissues is impaired in anemic hypoxia. These characteristics in oxygen transport and capillary hemodynamics should be taken into consideration when SvO2 is used in clinical critical care.
检验这样一个假设，即反映组织氧摄取后残余氧的混合静脉血氧饱和度（SvO2）值在低氧性缺氧和贫血性缺氧期间会相似。
比较SvO2值、氧输送、动脉血氧含量和氧摄取分数，并根据低氧性缺氧和贫血性缺氧期间的乳酸、乳酸/丙酮酸比值及氧消耗确定临界值。
大学医院的生理实验室。
两组8只8至12日龄的仔猪。
仔猪接受麻醉、气管切开、插管并进行通气。实施开胸手术，将光纤导管置于肺动脉以监测SvO2。将渡越时间超声血流探头置于升主动脉周围以测量主动脉血流。通过将吸入氧分数（FI(O2)）从基线值（0.30 - 0.75）降至0.21、0.15和0.10诱导进行性低氧性缺氧。通过重复进行50 mL巴氏消毒血浆的等容性交换输血诱导进行性贫血性缺氧。
每次干预后15或30分钟，从颈动脉采集样本用于检测血气、血红蛋白、乳酸和丙酮酸，从肺动脉采集样本用于检测血气和血红蛋白。进行血流动力学、动脉血氧饱和度和SvO2测量。在低氧性缺氧和贫血性缺氧中，计算得出的氧输送和氧消耗均降低。在贫血性缺氧的最低氧输送水平时，SvO2的降低幅度小于低氧性缺氧（-26%对-55%）。为每只仔猪计算的SvO2临界值范围（低于该范围乳酸、乳酸/丙酮酸比值及氧消耗会迅速从基线值改变）在低氧性缺氧（11%至24%）中显著低于贫血性缺氧（26%至48%）。氧摄取分数显著增加，但增加幅度不如低氧性缺氧大（0.31（范围，0.20 - 0.41）对0.49（范围，0.41 - 0.54））。
与低氧性缺氧相比，贫血性缺氧中SvO2的临界值更高，表明贫血性缺氧时血液向组织的氧卸载受损。在临床重症监护中使用SvO2时，应考虑这些氧运输和毛细血管血流动力学特征。
