心脏瓣膜替换术后氧的供需关系变化

本文观察了４２例风湿性心脏病瓣膜替换术患者，术后早期氧耗（ＶＯ２Ｉ）的动态变化以及氧供（ＤＯ２Ｉ）、氧摄取率（Ｏ２ＥＲ）和心脏指数（ＣＩ）的变化对它的影响。麻醉诱导后经颈内静脉置入ＳｗａｎＧａｎｚ漂浮导管至肺动脉，用于血液动力学的监测。根据热稀释法原理测定心输出量；在测定前，同时抽取动脉及混合静脉血标本作血气分析。ＶＯ２Ｉ、ＤＯ２Ｉ、Ｏ２ＥＲ均根据Ｆｉｃｋ氏公式计算而得。结果显示：①瓣膜替换术后早期ＶＯ２Ｉ明显增加，机体处于高代谢状态；②其增加主要是通过Ｏ２ＥＲ的升高得以实现，与ＤＯ２Ｉ呈非依赖性关系；③术后２４小时后，ＣＩ明显增加，ＤＯ２Ｉ相应增加；而ＶＯ２Ｉ无显著增加，Ｏ２ＥＲ亦回落至正常范围并维持一平台，提示ＤＯ２Ｉ和ＶＯ２Ｉ在术后２４小时后已趋于平衡。本文还就ＶＯ２Ｉ升高的原因及Ｏ２ＥＲ增高的机制进行讨论。

THE CHANGES IN OXYGEN CONSUMPTION AND DELIVERY AFTER CARDIAC VALVE REPLACEMENT

The relative contribution of oxygen extraction ratio(O_2ER), oxygen delivery(DO_2I) and cardiac index(CI) to the increased cellular oxygen consumption(VO_2I) after cardiac valve replacement was studied prospectively in 42 patients of rheumatic heart disease. After induction of anaesthesia, a PA catheter(Swan-Ganz catheter, 7F. Arrow Company, CA) was inserted via an internal jugular vein to get the hemodynamic parameters.Immediately before cardiac output measurement, arterial and mixed venous blood samples were obtained for gas analysis. Cardiac output was determined by thermodilution technique. VO_2I, DO_2I and O_2ER were calculated from Fick's equations. The data indicated that the uneventful patients after cardiac valve surgery usually had a significant increase in VO_2I as well as O_2ER in the early postoperative period, and the increase of VO_2I was achieved mainly by the elevation of O_2ER. After 24 h ,VO_2I decreased gradually and O_2ER returned to normal, however, DO_2I still maintained a relatively higher level due to the increase of CI. It suggests that at the time of 24 h postoperatively,a relative balance between DO_2I and VO_2I has been established. Mechanism on the increase of VO_2I and O_2ER was also discussed.