1 School of Medicine, Imperial College London.
2 Respiratory Medicine, Imperial College Healthcare NHS Trust.
Ann Am Thorac Soc. 2017 Jun;14(6):903-911. doi: 10.1513/AnnalsATS.201611-872OC.
Pa and Sa are commonly measured in respiratory practice, but arterial oxygen content (Ca) refers to the volume of oxygen delivered to the tissues per unit blood volume. Ca is calculated from Sa and the hemoglobin concentration in blood, recognizing that each gram of hemoglobin can transport approximately 1.34 ml of oxygen when fully saturated.
To prospectively evaluate serial changes in Ca in humans, incorporating and excluding dynamic changes to oxygenation and hemoglobin parameters that may occur during life.
A cohort of 497 consecutive patients at risk of both hypoxemia and anemia were recruited. The patients had radiologically proven pulmonary arteriovenous malformations (PAVMs), which result in hypoxemia due to right-to-left shunting, and concurrent hereditary hemorrhagic telangiectasia, which placed them at risk of iron deficiency anemia due to recurrent hemorrhagic iron losses. Presentation Sa (breathing room air, by pulse oximetry), hemoglobin, red cell and iron indices were measured, and Ca calculated as Sa × hemoglobin × 1.34 ml/g. Serial measurements were evaluated in 100 cases spanning up to 32.1 (median, 10.5) years.
Presentation Ca ranged from 7.6 to 27.5 (median, 17.6) ml/dl. Ca did not change appreciably across the Sa quartiles. In contrast, hemoglobin ranged from 5.9 to 21.8 g/dl (median, 14.1 g/dl), with a linear increase in Ca across hemoglobin quartiles. After PAVM embolization and an immediate increase in Sa, hemoglobin fell and Ca was unchanged 1.6-12 (median, 4) months later. When hemoglobin fell because of iron deficiency, there was no change in Sa. Similarly, when hemoglobin rose after iron treatment, there was no change in Sa, and the expected Ca increment was observed. These relationships were not evident during pregnancy when hemoglobin fell, and PAVMs usually deteriorated: in pregnancy Sa commonly increased, and serial Ca values (incorporating hemodilution/anemia) more accurately reflected deteriorating PAVM status. An apparent fall in Ca with age in females was attributable to the development of iron deficiency. There was an unexplained increase in Ca with age in follow-up of males after embolization.
Hemoglobin/Ca should be further incorporated into oxygenation considerations. More attention should be given to modest changes in hemoglobin that substantially modify Ca.
Pa 和 Sa 常用于呼吸实践中，但动脉血氧含量 (Ca) 是指单位血容量输送给组织的氧量。Ca 是根据 Sa 和血液中的血红蛋白浓度计算出来的，因为当血红蛋白完全饱和时，每克血红蛋白可以运输大约 1.34 毫升的氧气。
前瞻性评估人类 Ca 的连续变化，纳入并排除生命过程中可能发生的氧合和血红蛋白参数的动态变化。
招募了一组有发生低氧血症和贫血风险的 497 例连续患者。这些患者患有放射学证实的肺动静脉畸形 (PAVM)，由于右向左分流导致低氧血症，同时患有遗传性出血性毛细血管扩张症，由于反复出血性铁丢失，他们有缺铁性贫血的风险。测量了患者的 Sa（在呼吸室内空气时，通过脉搏血氧仪测量）、血红蛋白、红细胞和铁指数，并计算 Ca 为 Sa×血红蛋白×1.34 ml/g。对 100 例跨度长达 32.1 年（中位数 10.5 年）的连续测量值进行了评估。
患者的初始 Ca 范围为 7.6 至 27.5（中位数 17.6）ml/dl。Sa 的四分位数之间 Ca 没有明显变化。相比之下，血红蛋白范围为 5.9 至 21.8 g/dl（中位数 14.1 g/dl），随着血红蛋白四分位数的增加，Ca 呈线性增加。在 PAVM 栓塞和 Sa 立即增加后，血红蛋白下降，而 1.6-12 个月后 Ca 保持不变（中位数为 4 个月）。当血红蛋白因缺铁而下降时，Sa 没有变化。同样，当铁治疗后血红蛋白升高时，Sa 没有变化，并且观察到预期的 Ca 增加。这些关系在怀孕期间血红蛋白下降时并不明显，而 PAVM 通常会恶化：怀孕期间 Sa 通常增加，而连续的 Ca 值（包括血液稀释/贫血）更准确地反映了 PAVM 状态的恶化。女性中 Ca 随年龄的增长而下降归因于缺铁的发展。在栓塞后男性的随访中，Ca 随年龄的增长而增加，原因不明。
应进一步将血红蛋白/Ca 纳入氧合考虑因素。应更加关注血红蛋白的适度变化，因为这会显著改变 Ca。
