From the Anaesthesia, Perioperative and Pain Medicine Program, Centre for Integrated Critical Care, University of Melbourne, Melbourne, Australia (P.J.P.) the Department of Anaesthesia, Austin Health, Victoria, Australia (P.J.P.) the Institute for Breathing and Sleep, Victoria, Australia (P.J.P.) the Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium (J.H.) the Department of Anesthesiology, Onze-Lieve-Vrouw (OLV) Hospital, Aalst, Belgium (J.H.) the Department of Clinical Pharmacy, Catharina Hospital, Eindhoven, The Netherlands (R.J.E.G.) the Discipline of Anaesthesiology, Royal Brisbane and Women's Hospital, The University of Queensland, Brisbane, Australia (A.V.Z.) the Department of Anesthesiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois (A.D.W.).
Anesthesiology. 2020 Sep;133(3):534-547. doi: 10.1097/ALN.0000000000003445.
According to the "three-compartment" model of ventilation-perfusion ((Equation is included in full-text article.)) inequality, increased (Equation is included in full-text article.)scatter in the lung under general anesthesia is reflected in increased alveolar deadspace fraction (VDA/VA) customarily measured using end-tidal to arterial (A-a) partial pressure gradients for carbon dioxide. A-a gradients for anesthetic agents such as isoflurane are also significant but have been shown to be inconsistent with those for carbon dioxide under the three-compartment theory. The authors hypothesized that three-compartment VDA/VA calculated using partial pressures of four inhalational agents (VDA/VAG) is different from that calculated using carbon dioxide (VDA/VACO2) measurements, but similar to predictions from multicompartment models of physiologically realistic "log-normal" (Equation is included in full-text article.)distributions.
In an observational study, inspired, end-tidal, arterial, and mixed venous partial pressures of halothane, isoflurane, sevoflurane, or desflurane were measured simultaneously with carbon dioxide in 52 cardiac surgery patients at two centers. VDA/VA was calculated from three-compartment model theory and compared for all gases. Ideal alveolar (PAG) and end-capillary partial pressure (Pc'G) of each agent, theoretically identical, were also calculated from end-tidal and arterial partial pressures adjusted for deadspace and venous admixture.
Calculated VDA/VAG was larger (mean ± SD) for halothane (0.47 ± 0.08), isoflurane (0.55 ± 0.09), sevoflurane (0.61 ± 0.10), and desflurane (0.65 ± 0.07) than VDA/VACO2 (0.23 ± 0.07 overall), increasing with lower blood solubility (slope [Cis], -0.096 [-0.133 to -0.059], P < 0.001). There was a significant difference between calculated ideal PAG and Pc'G median [interquartile range], PAG 5.1 [3.7, 8.9] versus Pc'G 4.0[2.5, 6.2], P = 0.011, for all agents combined. The slope of the relationship to solubility was predicted by the log-normal lung model, but with a lower magnitude relative to calculated VDA/VAG.
Alveolar deadspace for anesthetic agents is much larger than for carbon dioxide and related to blood solubility. Unlike the three-compartment model, multicompartment (Equation is included in full-text article.)scatter models explain this from physiologically realistic gas uptake distributions, but suggest a residual factor other than solubility, potentially diffusion limitation, contributes to deadspace.
根据通气-灌注（（方程式包含在全文中。））不均匀的“三腔”模型，全身麻醉下肺内（方程式包含在全文中。）散射增加反映在肺泡死腔分数（VDA/VA）增加，通常使用呼气末至动脉（A-a）二氧化碳分压梯度来测量。麻醉剂如异氟醚的 A-a 梯度也很显著，但已证明与三腔理论下的二氧化碳不一致。作者假设，使用四种吸入性药物（VDA/VAG）的部分压力计算的三腔 VDA/VA（VDA/VAG）与使用二氧化碳（VDA/VACO2）测量值不同，但与生理现实“对数正态”（方程式包含在全文中。）分布的多腔模型预测相似。
在一项观察性研究中，在两个中心同时测量了 52 例心脏手术患者的吸入麻醉剂（氟烷、异氟醚、七氟醚或地氟醚）的吸入末、动脉、混合静脉和二氧化碳分压。从三腔模型理论计算 VDA/VA，并比较所有气体。每个药物的理想肺泡（PAG）和毛细血管端部分压（Pc'G）也根据死腔和静脉混合进行调整，从呼气末和动脉分压计算。
氟烷（0.47±0.08）、异氟醚（0.55±0.09）、七氟醚（0.61±0.10）和地氟醚（0.65±0.07）的计算 VDA/VAG 均大于异氟醚（0.23±0.07），VDA/VACO2 （总体），并且随着血液溶解度的降低而增加（斜率[Cis]，-0.096[-0.133 至-0.059]，P<0.001）。所有药物的计算理想 PAG 和 Pc'G 中位数[四分位间距]之间存在显著差异，PAG 5.1[3.7，8.9]与 Pc'G 4.0[2.5，6.2]，P=0.011。所有药物的斜率与溶解度相关，与计算的 VDA/VAG 相比，对数正态肺模型的预测值较低。
麻醉剂的肺泡死腔比二氧化碳大得多，与血液溶解度有关。与三腔模型不同，多腔（方程式包含在全文中。）散射模型从生理现实的气体摄取分布解释了这一点，但表明除了溶解度之外，还有其他残留因素，可能是扩散限制，导致死腔。
