常温希釈体外循環における適正潅流量の検討:とくに酸素消費量の面より

19世紀から多数の研究者により報告された体外での臓器潅流の研究は,1937年Gibbon(1))の酸素付加装置による猫の潅流実験ののちに,さらに進展の度を早め,臨床的には,1951年Dennisら(2))が心房中隔欠損症の手術に試み,ついで1953年Gibbonが本症の手術に成功して以来,直視下心臓手術は人工心肺装置ならびに体外循環手技などの改良により広くおこなわれるようになった.一方,体外循環の副作用として,血清肝炎(3)),赤血球のsludgingやaggregation(4)),blood pooling(5)6))や同種血症候群(7)8))が問題となり,また装置充填に多量の新鮮血を要することも欠点であった.当時,生理学的研究では臓器潅流に電解質液を使用していたこと,Gollanら(9))が低体温下では赤血球の無い液体でも溶存酸素のみで組織は酸素を摂取しうることを示したことにより,血液希釈体外循環が考えられた.1951年PanicoとNeptune(10))が生理的食塩水で充填したのに始まり,Longら(4))の低分子量デキストラン,Gooleyら(11)),Zuhdiら(12)),De WallとLilleheiら(13))の5% 糖液,そしてNevilleら(14))の乳酸加リンゲル液の使用により希釈体外循環が主流となった.しかし,血液希釈にともなう問題も生じた.すなわち血液希釈によるヘモグロビン濃度の低下した血液は,酸素運搬能力も低下し,この低下を代償するために潅流量を増加しなければならないと考えられる.従来は全血体外循環時に設定された潅流量を希釈体外循環にも用いられてきたが,その可否を酸素消費量および血行動態の面より検討した.

Serial oxygen uptake determination were done in 39 patients and 24 mongrel dogs during 20% hemodilutional cardiopulmonary bypass at normothermia. In patients, the time of the bypass ranged from 37 to 161 minutes. In dogs, the bypass time was standardized at 120 minutes. In patients, average of the mean perfusion index was 2.03 l/M(2)/min in the group I (BSA≧1.2M(2),n=13), 2.47 l/M(2)/min in the group Ⅱ (0.8≦BSA<1.2M(2),n=6) and 2.72 l/M(2)/min in the group Ⅲ (BSA<0.8M(2),n=20). During total perfusion, the average of the mean arterial blood pressure was 75.7mmHg in group I, 53.6mmHg in group Ⅱ, and 44.1mmHg in group Ⅲ. The average of the mean oxygen saturation during perfusion were 60.5%, 64.2%, 56.7% and the average of the O(2) consumption were 72.5ml/M(2)/min, 94.7ml/M(2)/min and 112.6ml/M(2)/min respectively. O(2) consumption (during perfusion)/O(2) consumption (predicted) ranged 0.22 to 0.96 in all patients and 0.52, 0.62, 0.63 respectively. The average of the O(2) extraction rate during perfusion were 32.9% , 42.8% and 36.0% respectively. The average of hematocrit during perfusion was 24.4% in patients and 23.5% in dogs. In dogs, classified into 5 groups, group A perfused at rate 25ml/Kg/min had an average mean arterial blood pressure of 20.6mmHg, group B perfused at rate 50ml/Kg/min had 38.3mmHg, group C perfused at rate 75ml/Kg/min had 58.7mmHg, group D at rate 100ml/Kg/min had 67.7mmHg, group E at rate 125ml/Kg/min had 58.4mmHg. The average of the O(2) consumption were 1.66ml/Kg/min (group A), 2.87ml/Kg/min (group B), 4.10ml/Kg/min (group C), 3.62ml/Kg/min (group D), 5.91ml/Kg/min (group. E). 1) Mean arterial blood pressure varied directly with flow rate in dogs, but not in patients. During perfusion mean arterial blood pressure was maintained at a lower level and mean central venous pressure at a higher level than at pre-perfusion value. 2) There is a linear relationship between flow rate and oxygen consumption both in patients and dogs. Oxygen consumption during perfusion were considerably lower than normal oxygen consumption. 3) Venous oxygen saturation during perfusion was lower than pre-perfusion value. There is a linear relationship between flow rate and venous oxygen saturation in dogs, but not in patients. 4) In patients, relationship between perfusion index and O(2) consumption indicates that the perfusion index over than 2.7 l/M(2)/min will be desirable, and in dogs splanchnic pooling during perfusion suggested the flow rate 75-100ml/Kg/min will be desirable.