Dexter F, Hindman B J
Department of Anesthesia, University of Iowa, Iowa City, USA.
Undersea Hyperb Med. 1998 Spring;25(1):43-50.
Microscopic cerebral arterial air emboli (MCAAE) cause neurologic injury during cardiac surgery. We used a mathematical model of gas absorption to gain a preliminary assessment of what physical or physiologic parameters affect MCAAE absorption in the setting of cardiac surgery with its unique set of normal values. Simulated MCAAE of radii 50 and 200 microns have absorption times of 2 and 32 min, respectively. Predicted absorption times depend dramatically on PaN2. MCAAE are predicted to be absorbed twice as quickly at a PaN2 of 0 vs. 380 mmHg (FiO2 approximately equal to 0.50). Moderate hypothermia (27 degrees C) is predicted to cause only small decreases in absorption time. Changes in cerebral blood flow (for example, as affected by hemoglobin concentration, PaCO2, PaO2, collateral circulation, anesthetics, or cerebral metabolism) probably have only small effects on absorption time. Intravascular perfluorocarbons are predicted to cause small-to-moderate decreases in absorption time. In conclusion, there is probably only one important determinant of MCAAE absorption time during normothermic or moderately hypothermic CPB: arterial nitrogen partial pressure.
微小脑动脉空气栓塞（MCAAE）在心脏手术期间会导致神经损伤。我们使用气体吸收的数学模型，对在心脏手术这一具有独特正常数值集的环境中，哪些物理或生理参数会影响MCAAE的吸收进行了初步评估。模拟半径为50微米和200微米的MCAAE的吸收时间分别为2分钟和32分钟。预测的吸收时间极大地取决于动脉血氮分压（PaN2）。预计在PaN2为0时，MCAAE的吸收速度是PaN2为380 mmHg（吸入氧分数约等于0.50）时的两倍。预计中度低温（27摄氏度）只会使吸收时间略有缩短。脑血流量的变化（例如，受血红蛋白浓度、动脉血二氧化碳分压、动脉血氧分压、侧支循环、麻醉剂或脑代谢影响）可能对吸收时间只有微小影响。预计血管内全氟碳化合物会使吸收时间有小到中度的缩短。总之，在常温或中度低温体外循环期间，MCAAE吸收时间可能只有一个重要决定因素：动脉血氮分压。
