间接测热法和反向Fick氏法测定心脏手术病人术后氧耗量的比较

目的 采用反向Fick氏法和间接测热法测定心脏手术后病人的全身氧耗,并比较两种测量方法的相关性和准确性。方法8例心脏手术术后病人,分别在入ICU后2h和6h时同时采用反向Fick氏和间接测热法测定病人的全身氧耗量。结果 间接测热法和反向Fick法测得氧耗分别是(16±30)ml·min-1·m-2和(127±23)ml·min-1·m-2,前者的测定结果显著高于后者(P<0.01)。相关分析显示两者有较好的相关性(r=0.92,P<0.01)。采用Bland和Altman统计分析提示两种测定结果的平均偏离值为(35.5±13.4)ml·min-1·m-2,其95％的分布范围是(9～62)ml·min-1·m-2,提示两种测量结果间的一致性较差。结论 两种方法测定心脏病人术后全身氧耗的结果有明显差异,其中反向Fick氏法的测定结果误差大、准确性差,而间接测热法是较好的临床选择。

Comparison between methods for measuring oxygen con mption in patients after cardiac surgery: the reverse Fick method versus indirect calorimetry

Objective The purpose of this study was to compare the whole body oxygen consumption determined by reverse Pick method and indirect calorimetry in mechanically ventilated patients after cardiac surgery. Methods Eight NYHA II-III patients (2 male, 6 female ) aged 43-68 yr, undergoing aortic valve replacement, mitral valve replacement or coronary artery bypass grafting(CABG) under CPB. Swan-Ganz catheter was placed via right internal jugular vein. Anesthesia and operation were carried out uneventfully. The patients were placed in ICU after operation and mechanical ventilation was continued (IPPV, FiO2 40%-50% , PEEP 5 cm H2O) . PaCO2 was maintained at 35-45 mm Hg by adjustment of VT and RR. T was maintained at 37.0 1C+0.5C .Total body oxygen consumption was measured by the reverse Fick method and indirect calorimetry simultaneously at 2h and 6h after operation. Results The mean oxygen consumption (VO2 ) value determined by indirect calorimetry( 162 + 30 mlmin-1m-2) was significantly higher than that determined by reverse Fick method (127+23 ml min-1m-2)(P<0.01). Correlation analysis showed good correlation between the two measurements of VO2(r = 0.92, P<0.001). By using the Bland and Altman technique, the mean bias was (35.5 + 13.4) mlmin-1m-2 , the limits of agreement were 9-62 mlmin-1m-2 , indicating the poor agreement between the two methods. Conclusion The reverse Fick method is inaccurate and unreliable compared with indirect calorimetry when an estimation of VO2 is required in patients after cardiac surgery.