腹腔内冷却による低体温麻酔下での循環停止に関する検討 Circulatory Arrest under Hypothermic Anesthesia Using Abdominal Cavity Cooling

本研究は, 腹腔内冷却による低体温麻酔法を用いた循環停止法の可能性を検討するために実施した.Isofluraneによる維持麻酔下で, crushed iceを腹腔内に入れ低体温麻酔を開始した.食道温30℃に達した時点で, 開胸後, 左心房-大動脈バイパス(左心バイパス)を作製し, バイパス循環を行いながら冷却効率の向上をはかった.食道温20-23℃の時点でYoung液をバイパスカテーテルを介して大動脈基部に注入し, 心臓を停止させた.約20分の循環停止の後, 左心バイパスを再循環させ蘇生を行った.拍動が安定したところで積極的に腹腔内を加温し, 30℃まで復温させ, 閉胸, 閉腹した.術後は保温マットにより38℃まで復温させた.冷却-循環停止-復温期間を通じて血行動態および血液ガスの分析を行った.18例中11例において覚醒と順調な術後経過が得られ, 覚醒が不可能であった7例では, 覚醒したものと比較して蘇生中のPaO_2が低値を示していた.一方, 血行動態の変化と冷却, 復温効率には有意な変化は認められなかった.以上のことから, 腹腔内冷却による低体温麻酔法を用いた循環停止法は, 循環停止中におけるアシドーシスの進行を遅延させることで円滑な蘇生および覚醒をはかることが可能であると考えられた.また, 冷却, 循環停止中においては心筋と同様に肺の保護が重要であることも示唆された.

The purpose of this study was to investigate the potential for circulatory arrest during surgery under systemic hypothermic anesthesia, using the abdominal cavity cooling method. Eighteen beagles, each weighing 10.5±2.3kg, were cooled by filling the abdominal cavity with crushed ice. Just after the esophageal temperature reached 30℃, the heart was exposed, and a left-heart bypass from the left atrium to the aortic root was created. At 20-23℃, the heart was arrested by infusing cooled Young's solution into the aortic root. After a period of cardiac arrest, resuscitation and rewarming were initiated simultaneously. Throughout these procedures, an electrocardiogram (ECG) and the arterial blood pressure (ABP)were monitored continuously. Hematocrit (Ht), total protein (TP), and arterial blood pH and gases were measured every 30min. The recoveries after surgery were divided into three types as follows, 1) recovery without any complications-11 dogs, 2) not extubated with spontaneous breathing-4 dogs, 3) no reappearance of heart beat-3 dogs. PaO_2 during resuscitation was significantly higher in dogs which recovered completely than in the rest of the dogs. These results suggest that hypothermia induced by the abdominal cavity cooling method could be useful for organ-protection during open-heart surgery, and that successful recovery may be attained through protection of the lung as well as the myocardium.