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〔背景〕患者の正確な血管内容量の推定はこれまで困難とされてきた.基礎代謝のおよそ99%が非脂肪組織で行われるにも拘わらず,心系数においては脂肪の影響は考慮されておらず,特に肥満患者においては適切でない値を推定している可能性がある.本研究ではCT画像を用いて脂肪の影響を除外し,血管内容量を推定する方法の有効性を評価するのが目的である.〔方法と結果〕CT画像より脂肪重量が得られ,体重より脂肪重量を引くことで非脂肪重量を算出した.血管内容量は人工心肺の記録から血液希釈法にて得た.非脂肪重量と血管内容量の相関関係を評価し,統計学的解析を行った.その結果,非脂肪重量と血管内容量には強い相関関係を認めた.〔結論〕CT画像により算出した非脂肪重量は血管内容量と良い相関を示した.今回の結果を考慮すると,肥満患者の血管内容量は低いと予想され,Swan-Ganz catheterにより得た肥満患者の心系数も過小評価している可能性がある., Background: It has been difficult to estimate a true patient's intravascular volume. Although about 99% of basic metabolic consumption is conducted in the non-fat tissues, the cardiac index itself does not include a fat effect and may predict inappropriate value in obese patients. This study evaluates the efficacy of the method excluding fat effect using computed tomography imaging to estimate the intra-vascular volume. Methods and results: Fat mass was obtained from the images of computed tomography and fat free mass was calculated by reducing the fat mass from the body weight. Intravascular volume was gained with a dilution method by the records of the cardiopulmonary bypass. Correlation between the fat free mass and the intravascular volume was assessed and statistic analysis was performed. There was a significant correlation between the fat free mass and the intra-vascular volume. Conclusion: Using computed tomography to calculate fat free mass, correlates well with the intravascular volume. Considering the result of this study, the Intra-vascular volume of obese patients would be low, thus the indicated Cardiac index value by Swan-Ganz catheter should be underestimated.