内頸静脈血からみた重症損傷脳の循環・代謝障害

REDUCED ARTERIO-JUGULAR VENOUS OXYGEN DIFFERENCE FOLLOWING SEVERE HEAD INJURY

はじめに

　生理的な状態においては，脳の大部分の還流静脈血は内頸静脈に流入している。したがって内頸静脈血のたとえば血液ガス濃度を測定することによって，脳循環，脳代謝の一指標とすることができる。もちろん全脳血流量を測定することも重要であるが，内頸静脈血と動脈血の性状を比較するだけでも，簡単にしかもかなり適確な情報が得られる点が注目される。内頸静脈穿刺は移動させられないような重篤な患者でも，ベッドサイドで容易におこなえる点が最大の長所である。

　われわれはすでに重症頭部外傷患者について内頸静脈血酸素分圧を測定し，いくつかの成績を報告してきた^1）2）。今回は更に研究をすすめ，深い昏睡状態にある頭部外傷患者や，いわゆる脳死と呼ばれている状態の患者について，同様の方法で検討し，いくつかの新しい知見を得たので報告する。ことに脳損傷の可逆性や脳死を判定する上での本法の意義や，重症脳損傷における脳循環について若干の考察を加えた。

Blood gas data of the internal jugular vein were analyzed in forty-two patients suffering from severe head injury. Blood samples were taken from the superior jugular venous bulb by percut-aneous puncture, and compared with arterial and mixed venous blood samples obtained simultane-ously. The results are as follows.

1) Narrowed arterial-jugular venous oxygen difference (Ca-jvO₂) was of common finding in all cases, and the value was paralleled to the extent of cerebral injury. Whole cases of brain death showed extreme narrowing of Ca-jvO₂ below 3 vol %.

2) PCO₂ and PH values of internal jugular venous blood showed similar values of arterial blood as the aggravation of symptoms.

3) In the brain death state, all of PO₂ values of jugular venous blood were higher than those of mixed venous blood. This finding, as well as narrowed Ca-jvO₂ of below 3 vol %, was quite characteristic in the state of brain death.

4) In semicomatose patients, there was a signi-ficant change of Ca-jvO₂ related to arterial PCO₂. But this CO₂ response was not observed in deeply comatose and brain death state.

5) There was no definite relationship between arteriojugular venous glucose difference and the severity of brain damage.

In the state of severe brain injury, especially in the state of brain death, there were evidences thatinternal jugular venous blood was contaminated with extracerebral venous blood to significant ex-tent. For interpretation of the data by arterio-venous method, therefore, it should be taken into consideration that the internal jugular venous blood could not always represent the mixed venous blood of the brain.