Vidiendal Olsen N, Christensen H, Klausen T, Fogh-Andersen N, Plum I, Kanstrup I L, Hansen J M
Department of Neuroanaesthesia, Copenhagen University Hospital, Denmark.
Anesthesiology. 1998 Dec;89(6):1389-400. doi: 10.1097/00000542-199812000-00016.
Using the renal clearance of lithium as an index of proximal tubular outflow, this study tested the hypothesis that acute hypocapnic hypoxemia decreases proximal tubular reabsorption to the same extent as hypocapnic normoxemia (hyperventilation) and that this response is blunted during normocapnic hypoxemia.
Eight persons were studied on five occasions: (1) during inhalation of 10% oxygen (hypocapnic hypoxemia), (2) during hyperventilation of room air leading to carbon dioxide values similar to those with hypocapnic hypoxemia, (3) during inhalation of 10% oxygen with the addition of carbon dioxide to produce normocapnia, (4) during normal breathing of room air through the same tight-fitting face mask as used on the other study days, and (5) during breathing of room air without the face mask.
Hypocapnic and normocapnic hypoxemia and hyperventilation increased cardiac output, respiratory minute volume, and effective renal plasma flow. Glomerular filtration rate remained unchanged on all study days. Calculated proximal tubular reabsorption decreased during hypocapnic hypoxemia and hyperventilation but remained unchanged with normocapnic hypoxemia. Sodium clearance increased slightly during hypocapnic and normocapnic hypoxemia, hyperventilation, and normocapnic normoxemia with but not without the face mask.
The results indicate that (1) respiratory alkalosis with or without hypoxemia decreases proximal tubular reabsorption and that this effect, but not renal vasodilation or natriuresis, can be abolished by adding carbon dioxide to the hypoxic gas; (2) the increases in the effective renal plasma flow were caused by increased ventilation rather than by changes in arterial oxygen and carbon dioxide levels; and (3) the natriuresis may be secondary to increased renal perfusion, but application of a face mask also may increase sodium excretion.
本研究以锂的肾脏清除率作为近端肾小管流出的指标，检验了以下假设：急性低碳酸性低氧血症与低碳酸性正常氧血症（过度通气）一样，会同等程度地降低近端肾小管重吸收，且在正常碳酸性低氧血症期间这种反应会减弱。
对8名受试者进行了5次研究：（1）吸入10%氧气期间（低碳酸性低氧血症）；（2）对室内空气进行过度通气，使二氧化碳值与低碳酸性低氧血症时相似；（3）吸入10%氧气并添加二氧化碳以产生正常碳酸血症期间；（4）通过与其他研究日使用的相同的密闭面罩进行室内空气正常呼吸期间；（5）不使用面罩进行室内空气呼吸期间。
低碳酸性和正常碳酸性低氧血症以及过度通气均增加了心输出量、呼吸分钟量和有效肾血浆流量。在所有研究日，肾小球滤过率均保持不变。计算得出的近端肾小管重吸收在低碳酸性低氧血症和过度通气期间降低，但在正常碳酸性低氧血症期间保持不变。在有面罩但无面罩时，低碳酸性和正常碳酸性低氧血症、过度通气以及正常碳酸性正常氧血症期间，钠清除率均略有增加。
结果表明：（1）伴有或不伴有低氧血症的呼吸性碱中毒会降低近端肾小管重吸收，并且通过向低氧气体中添加二氧化碳可消除这种作用，但不能消除肾血管舒张或利钠作用；（2）有效肾血浆流量的增加是由通气增加引起的，而非动脉氧和二氧化碳水平的变化；（3）利钠作用可能继发于肾灌注增加，但使用面罩也可能增加钠排泄。
