微血管循環與重症醫學

Abstract

儘管早期目標導引治療與敗血症治療準則已推行多年，嚴重敗血症及敗血性休克的死亡率依然很高，降低嚴重敗血症及敗血性休克的死亡率是當前重症醫學努力的目標。隨著光學影像技術的進步，有學者觀察到敗血症病人有微血管循環異常的現象。敗血症的全身發炎反應會引起過度血管擴張造成低血壓，內皮細胞所大量分泌的發炎粘合分子、細胞激素和趨化素會增加微血管通透性而造成微血管滲漏與組織水腫。此外，內毒素會刺激內皮細胞表現組織因子來活化凝血作用，同時內毒素也會抑制內皮細胞相關的抗凝血機制和內因性纖維蛋白溶解，進而導致微血管血栓形成。上述過度血管擴張、微血管滲漏和微血管血栓都會造成微血管循環異常，導致組織與器官因灌流不足而損傷，嚴重時可造成多重器官功能失調症候群及死亡。本論文的首要目的是使用旁流暗視野影像顯微鏡測量嚴重敗血症及敗血性休克病人的舌下微血管循環，並藉此探討敗血症嚴重度與微血管循環異常程度的關係，更進一步本論文嘗試建立一個可觀察腸微血管循環的內毒素血症大鼠實驗模式，觀察不同劑量內毒素所造成的微血管循環異常，動物實驗中主要觀測微血管循環的儀器有以下兩種：(1) 全域雷射灌流影像儀可快速並連續定量微血管循環血流強度的變化；(2) 旁流暗視野影像顯微鏡可在預設時間點測量總微小血管(< 20 μm)密度、灌流微小血管密度、微血管血流指標、異質性指標。因為內毒素和類鐸接受器4 (Toll-like receptor 4, TLR4)的交互作用是革蘭氏陰性菌引發敗血症及微血管循環異常的主要機制，本論文假設使用TLR4的拮抗劑(eritoran tetrasodium [E5564])可抑制內毒素血症所引起的微血管循環異常，因此本論文的第二個目的是用內毒素血症大鼠實驗模式探討eritoran是否能改善腸微血管循環異常。在罹患敗血症時，因為發炎反應與凝血系統的交互作用會引發瀰漫性血管內凝血而阻塞微血管循環，各種抗凝血藥物也常被用來研究治療敗血症的效果，本論文的第三個目的是使用內毒素血症大鼠實驗模式來探討低分子量肝素(enoxaparin)是否能改善腸微血管循環異常。 敗血症的臨床試驗結果顯示28天存活組病人的總微小血管密度、灌流微小血管密度和微血管血流指標都較28天死亡組病人高。內毒素血症大鼠的實驗結果顯示接受高劑量內毒素(15 mg/kg)大鼠的腸微血管循環血流灌流強度下降最多。使用eritoran的內毒素血症大鼠在微血管循環血流強度、灌流微小血管密度、微血管血流指標和異質性指標等方面都較未使用eritoran的大鼠好，使用eritoran的內毒素血症大鼠之腫瘤壞死因子α、間白素–1β和D–雙合蛋白等血中濃度也較未使用eritoran的大鼠低，使用eritoran的內毒素血症大鼠之微血管血栓也較少。在enoxaparin的動物實驗中發現使用低分子量肝素(enoxaparin)的內毒素血症大鼠可藉由減少血栓的形成及維持較高的灌流微小血管密度來改善腸微血管循環。 手術壓力和疼痛所引發的發炎反應與交感神經活化可造成組織灌流不足，在此情況下丙酮酸會經無氧醣解作用產生乳酸，造成高乳酸血症；此外過度的發炎反應會增加有氧醣解作用，致使產生的丙酮酸量超過丙酮酸鹽脫氫酵素所能代謝的速度，過多的丙酮酸也會被轉成乳酸。因為組織灌流不足與過度發炎反應都與微血管循環有關，所以本論文的第四個目的是用外科術後重症病人的臨床試驗來探討術後24小時乳酸值 ≧ 3 mmol/L的病人與乳酸值 < 3 mmol/L的病人之泛手術期微血管循環相關參數是否不同。因為鎮靜藥物dexmedetomidine不但可抑制交感神經引起的過度微血管收縮，也可抑制發炎和凝血，本論文假設dexmedetomidine具有潛力可改善手術壓力與疼痛造成的微血管循環異常，所以本論文的第五個目的是建立一個大鼠實驗模式來探討dexmedetomidine是否可改善手術壓力與疼痛所造成的微血管循環異常。 外科術後重症病人的臨床試驗研究結果顯示手術後24小時血中乳酸值 < 3 mmol/L的病人之泛手術期總微小血管密度與灌流微小血管密度都較乳酸值 ≧ 3 mmol/L的病人高，其中手術前和術後第一小時的灌流微小血管密度跟術後24小時的乳酸值有統計顯著負相關，術後第一小時的總微小血管密度也與術後24小時的乳酸值有統計顯著負相關。在大鼠實驗模式中發現手術壓力與疼痛會造成腸黏膜與腸漿膜肌肉層微血管循環異常，使用dexmedetomidine除了可以改善手術壓力與疼痛造成的心跳變快、血壓升高，同時也可維持腸微血管循環血流強度及正常灌流微小血管密度。 微血管循環在未來醫學扮演的角色會日趨重要，需要更多研究去探討如何早期診斷及治療病人的微血管循環異常，並進一步評估維持良好微血管循環對降低多重器官損傷的臨床效益，希望能幫病人爭取更多時間接受多元模式醫療照護組合以提高存活率與生活品質。

Despite early goal-directed therapy and Surviving Sepsis Campaign have been developed for many years, the mortality of severe sepsis and septic shock is still high. Recent advances in imaging technology have enabled the observation of microcirculation, and several studies have demonstrated that derangements in microvascular flow play a role in sepsis-induced multiple organ dysfunction syndrome and death. The systemic inflammatory response syndrome may cause excess vasodilation and result in hypotension. The endothelial cells may secrete inflammatory adhesion molecules, cytokines, and chemokines, and these may increase microvascular permeability and result in capillary leakage and tissue edema. Moreover, endotoxin may activate the coagulatory function of endothelial cells and inhibit the anti-coagulation activity of endothelial cells and endogenous fibrinolysis, and it may result in microvascular thrombosis. Excess vasodilation, capillary leakage, and microvascular thrombosis can result in microcirculatory dysfunction, and it will lead to tissue hypoperfusion and finally to multiple organ dysfunction syndrome and death. The first aim of this thesis is to investigate the relation between severity of severe sepsis and septic shock and the severity of sublingual microcirculatory dysfunction in critically ill patients using a sidestream dark-field (SDF) video microscope. Furthermore, we also investigated the relation between severity of endotoxemia and the severity of intestinal microcirculatory dysfunction in a rat model. The following two devices were used to investigate the microcirculation in animal research: (1) full-field laser perfusion imager was used to continuously measure the change of microcirculatory blood flow intensity; and (2) SDF video microscope was used to investigate total small-vessel (< 20 μm) density (TSVD), perfused small-vessel density (PSVD), microvascular flow index (MFI), and heterogeneity index (HI). Because the interaction between lipopolysaccharide (LPS, from gram-negative bacteria) and Toll-like receptor 4 (TLR4) induces sepsis and subsequent microcirculatory dysfunction, this thesis hypothesized that antagonizing LPS-related signaling pathway by a TLR4 antagonist, eritoran tetrasodium (E5564), might reduce endotoxemia-related microcirculatory dysfunction. The second aim of this thesis is to investigate whether eritoran can improve intestinal microcirculation using the endotoxemic rat model. Moreover, interaction between inflammation and coagulation system may induce microvascular thrombosis during sepsis, and the third aim of this thesis is to investigate whether enoxaparin can improve intestinal microcirculation using the endotoxemic rat model. The results of clinical research of sepsis revealed that TSVD, PSVD, and MFI were higher in the 28-day survival group than in the 28-day non-survival group. The results of animal research of endotoxemia revealed that intestinal microcirculatory blood flow intensity were significantly lower in the high dose (15 mg/kg) LPS group than the other groups. Moreover, microcirculatory blood flow intensity, PSVD, MFI, and HI were better in the eritoran treatment group than the LPS group. Eritoran also reduced blood level of tumor necrosis factor α, interleukin-1β, and D-dimer and microthrombosis formation. This thesis also revealed that enoxaparin can restore intestinal microcirculation by reducing microthrombosis formation and maintaining higher PSVD. Surgical stress and pain may induce excess inflammation and activation of sympathetic nervous system and lead to tissue hypoperfusion. Both hypoperfusion-related anaerobic glycolysis and excess inflammation-related pyruvate overproduction can cause hyperlactemia. Because microcirculatory dysfunction may lead to tissue hypoperfusion and excess inflammation, the fourth aim of this thesis is to compare the perioperative microcirculation between critically ill surgical patients with blood lactate level ≧ 3 mmol/L and those with blood lactate level < 3 mmol/L at 24h after surgery. Because dexmedetomidine can induce sympatholytic vasodilation, inhibit inflammation, and produce hypocoagulation, it has the potential to improve surgical stress and pain-related microcirculatory dysfunction. The fifth aim of this thesis is to establish a rat model and investigate whether dexmedetomidine can improve intestinal microcirculatory dysfunction resulting from surgical stress and pain. The results of clinical research of critically ill surgical patients revealed that perioperative TSVD and PSVD were lower in patients with blood lactate level ≧ 3 mmol/L than in patients with blood lactate level < 3 mmol/L at 24h after surgery. There were significant correlations between postoperative 1h TSVD and PSVD and postoperative 24h blood lactate level. The results of animal research of surgical stress and pain revealed that the microcirculatory blood flow intensity and PSVD in intestinal mucosa and serosal-muscular layer decreased during surgical stress and pain. Moreover, it also revealed that dexmedetomidine can attenuate tachycardia and hypertension and restore the intestinal microcirculatory blood flow intensity and PSVD. Microcirculation will play a more important role in the future medicine. More researches are required to investigate how to early diagnose and treat microcirculatory dysfunction in patients, and further to evaluate the clinical benefit of maintain good microcirculation on reducing multiple organ injury. Wish gaining more time to conduct multimodal therapy for the patient can improve survival and quality of life.