BACKGROUND Inefficiency of lung gas exchange during general anesthesia is reflected in alveolar (end-tidal) to arterial (end-tidal-arterial) partial pressure gradients for inhaled gases, resulting in an increase in alveolar deadspace. Ventilation-perfusion mismatch is the main contributor to this, but it is unclear what contribution arises from diffusion limitation in the gas phase down the respiratory tree (longitudinal stratification) or at the alveolar-capillary barrier, especially for gases of high molecular weight such as volatile anesthetics. METHODS The contribution of longitudinal stratification was examined by comparison of end-tidal-arterial partial pressure gradients for two inhaled gases with similar blood solubility but different molecular weights: desflurane and nitrous oxide, administered together at 2 to 3% and 10 to 15% inspired concentration (FiG), respectively, in 17 anesthetized ventilated patients undergoing cardiac surgery before cardiopulmonary bypass. Simultaneous measurements were done of tidal gas concentrations, of arterial and mixed venous blood partial pressures by headspace equilibration, and of gas uptake rate calculated using the direct Fick method using thermodilution cardiac output measurement. Adjustment for differences between the two gases in FiG and in lung uptake rate (VG) was made on mass balance principles. A 20% larger end-tidal-arterial partial pressure gradient relative to inspired concentration (PetG - PaG)/FiG for desflurane than for N2O was hypothesized as physiologically significant. RESULTS Mean (SD) measured (PetG - PaG)/FiG for desflurane was significantly smaller than that for N2O (0.86 [0.37] vs. 1.65 [0.58] mmHg; P < 0.0001), as was alveolar deadspace for desflurane. After adjustment for the different VG of the two gases, the adjusted (PetG - PaG)/FiG for desflurane remained less than the 20% threshold above that for N2O (1.62 [0.61] vs. 1.98 [0.69] mmHg; P = 0.028). CONCLUSIONS No evidence was found in measured end-tidal to arterial partial pressure gradients and alveolar deadspace to support a clinically significant additional diffusion limitation to lung uptake of desflurane relative to nitrous oxide. EDITOR’S PERSPECTIVE

中文翻译：

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气相扩散不会限制肺部挥发性麻醉剂的吸收率。

背景技术全身麻醉期间肺部气体交换的低效率反映在吸入气体的肺泡（潮气末）到动脉（潮气末-动脉）分压梯度中，导致肺泡死腔增加。通气-灌注不匹配是造成这种情况的主要原因，但尚不清楚呼吸树下方气相（纵向分层）或肺泡-毛细血管屏障的扩散受限会产生什么影响，尤其是对于高分子量气体，例如挥发性麻醉剂。方法 通过比较两种血液溶解度相似但分子量不同的吸入气体（地氟醚和一氧化二氮，分别以 2% 至 3% 和 10% 至 15% 的吸入浓度 (FiG) 对 17 名在体外循环前接受心脏手术的麻醉通气患者进行给药。同时测量潮气浓度、通过顶空平衡法测量的动脉和混合静脉血分压，以及使用热稀释心输出量测量的直接 Fick 方法计算的气体摄取率。根据质量平衡原则对 FiG 和肺摄取率 (VG) 中的两种气体之间的差异进行调整。与 N2O 相比，地氟醚的相对于吸入浓度 (PetG - PaG)/FiG 的潮气末动脉分压梯度比 N2O 大 20% 被假设为具有生理意义。结果 地氟醚的平均 (SD) 测量值 (PetG - PaG)/FiG 明显小于 N2O（0.86 [0.37] 对比 1.65 [0.58] mmHg；P < 0.0001），地氟醚的肺泡死腔也是如此。在对两种气体的不同 VG 进行调整后，地氟醚的调整后 (PetG - PaG)/FiG 仍低于 N2O 的 20% 阈值（1.62 [0.61] 对比 1.98 [0.69] mmHg；P = 0.028） . 结论 没有发现测量的潮气末至动脉分压梯度和肺泡死腔的证据支持地氟醚相对于一氧化二氮对肺摄取具有临床意义的额外扩散限制。编辑的观点 地氟醚的调整后 (PetG - PaG)/FiG 仍低于 N2O 的 20% 阈值（1.62 [0.61] 对比 1.98 [0.69] mmHg；P = 0.028）。结论 没有发现测量的潮气末至动脉分压梯度和肺泡死腔的证据支持地氟醚相对于一氧化二氮对肺摄取具有临床意义的额外扩散限制。编辑的观点 地氟醚的调整后 (PetG - PaG)/FiG 仍低于 N2O 的 20% 阈值（1.62 [0.61] 对比 1.98 [0.69] mmHg；P = 0.028）。结论 没有发现测量的潮气末至动脉分压梯度和肺泡死腔的证据支持地氟醚相对于一氧化二氮对肺摄取具有临床意义的额外扩散限制。编辑的观点