Department of Anesthesiology and Perioperative Medicine, University of Pittsburgh Medical Center, Pittsburgh, Pennsylania; Oscillogy LLC, Pittsburgh, Pennsylvania.
the Hedenstierna Laboratory, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden; the Department of Anesthesiology and Intensive Care Medicine, Otto von Guericke University, Magdeburg, Germany.
Anesthesiology. 2021 Dec 1;135(6):1042-1054. doi: 10.1097/ALN.0000000000004008.
Kinetics of the uptake of inhaled anesthetics have been well studied, but the kinetics of elimination might be of more practical importance. The objective of the authors' study was to assess the effect of the overall ventilation/perfusion ratio (VA/Q), for normal lungs, on elimination kinetics of desflurane and sevoflurane.
The authors developed a mathematical model of inhaled anesthetic elimination that explicitly relates the terminal washout time constant to the global lung VA/Q ratio. Assumptions and results of the model were tested with experimental data from a recent study, where desflurane and sevoflurane elimination were observed for three different VA/Q conditions: normal, low, and high.
The mathematical model predicts that the global VA/Q ratio, for normal lungs, modifies the time constant for tissue anesthetic washout throughout the entire elimination. For all three VA/Q conditions, the ratio of arterial to mixed venous anesthetic partial pressure Part/Pmv reached a constant value after 5 min of elimination, as predicted by the retention equation. The time constant corrected for incomplete lung clearance was a better predictor of late-stage kinetics than the intrinsic tissue time constant.
In addition to the well-known role of the lungs in the early phases of inhaled anesthetic washout, the lungs play a long-overlooked role in modulating the kinetics of tissue washout during the later stages of inhaled anesthetic elimination. The VA/Q ratio influences the kinetics of desflurane and sevoflurane elimination throughout the entire elimination, with more pronounced slowing of tissue washout at lower VA/Q ratios.
吸入麻醉药的摄取动力学已得到充分研究，但消除动力学可能更具实际意义。作者的研究目的是评估正常肺的总体通气/灌注比（VA/Q）对七氟醚和地氟醚消除动力学的影响。
作者开发了一个吸入麻醉药消除的数学模型，该模型明确将末端冲洗时间常数与肺部整体 VA/Q 比值联系起来。该模型的假设和结果通过最近的一项研究中的实验数据进行了测试，在该研究中，观察到了三种不同的 VA/Q 条件下七氟醚和地氟醚的消除：正常、低和高。
数学模型预测，正常肺的整体 VA/Q 比值会改变整个消除过程中组织麻醉剂冲洗的时间常数。对于所有三种 VA/Q 条件，动脉到混合静脉麻醉剂分压比 Part/Pmv 在消除 5 分钟后达到了一个恒定值，正如保留方程所预测的那样。经过不完全肺清除校正的时间常数比内在组织时间常数更能预测晚期动力学。
除了肺在吸入麻醉剂早期洗脱阶段的作用外，肺在调节吸入麻醉剂洗脱后期组织洗脱动力学方面也起着长期被忽视的作用。VA/Q 比值影响整个消除过程中七氟醚和地氟醚的消除动力学，VA/Q 比值越低，组织洗脱的减缓越明显。
