10．チアノーゼ性心疾患の生理学—至適酸素飽和度はいくつか？

The physiology of cyanotic congenital heart disease

チアノーゼ性心疾患とは，先天性心疾患のなかでも，静脈血が動脈血に混合する右左シャントを有する疾患の総称である。小児期までの外科的治療によりほとんどの患者はチアノーゼのない血行動態となる。しかし，未治療の場合や単心室型循環でのFontan術未到達症例，Eisenmenger症候群などをはじめとして，チアノーゼを有したまま成人年齢に到達する患者も少なくない。

　チアノーゼ性心疾患は，解剖学的にも血行動態的にも非常に複雑多岐にわたり，各病態への理解が重要なのは言うまでもない。本稿では，チアノーゼ性心疾患の総論的な病態生理について解説し，各病態へ応用が利くようまとめる。

Cyanotic congenital heart disease （CCHD） is a highly diverse anatomical and hemodynamic entity. Basic physiology can be applied to improve the understanding of the complex hemodynamics. It is not easy to determine the optimal level of SaO² in patients with CCHD, but it is important to assess whether the oxygen supply is adequate to meet the oxygen demand of the tissues in each condition. Oxygen delivery （DO²） is mainly regulated by arterial oxygen saturation （SaO²）, hemoglobin concentration （Hb）, and cardiac output （CO）. In patients with decreased SaO², the Hb, and CO can act as compensatory mechanisms to preserve DO². In single ventricle physiology with parallel circulation, SaO² is determined by the pulmonary venous oxygen saturation （SpvO²）, systemic venous oxygen saturation （SsvO²）, and pulmonary to systemic blood flow ratio （Qp/Qs）. While an increase of Qp/Qs leads to an increase in SaO², it may also cause a decrease in DO² due to decreased systemic blood flow. SsvO² is an important indicator of DO². A decrease in SsvO² is critical, especially for these patients since it directly affects SaO², thereby further decreasing DO². Therefore, to maximize DO², it is necessary to balance Qp/Qs and prevent anemia and low cardiac output.