開心手術期間之心搏量的測量：食道超音波及肺動脈導管測量之比較

Cardiac Output Measurement during Cardiac Surgery: Esophageal Doppler Versus Pulmonary Artery Catheter

背景：以單次灌注輸液之血溫變化所得心搏量(BCO)，被視為心搏量的標準測量方法。此法需要配合肺動脈導管的置入。然而施行此一侵入性技術之利弊權衡，仍莫衷一是。再者，重複測量數值結果亦可見極大差異。往昔論文報告曾指出：持續監測血溫變化所得心搏量(CCO)，因其重複測量結果差異較小，被視為較精準的測量方式。經食道杜卜勒超音波監測器(ED-CO)能提供另一非侵入性心搏量持續測量的方法。本研究乃立意於，比較由超音波監測器及血溫變化測量所得之心搏量的異同。方法：二十四名接受開心手術的病人，隨機接受肺動脈導管置入以利BCO或CCO之測量，而此24名病患亦同時接受食道超音波的置入。第一組患者(n=12)於開刀全程（體外循環期間除外）當中，每15分鐘測量一次BCO，在同一時間亦紀錄ED-CO的測量值；而第二組患者(n = 12)亦於相同時間間隔，同時紀錄CCO及ED-CO的測量值。對所得數值之相似性，使用Bland-Altman分析法加以分析，而差異值定義為0.05。結果：測得心搏量的數值範圍各為2.1-9.4 l/min (BCO)，2.4-9.2 l/min (CCO)，以及2.3-8.9 l/min(ED-CO)。ED-CO及CCO所得數值有很好的相似性，其線性回歸係數r2為0.846，而變異係數及標準差為0.05 ± 0.49 l/min；相對地，BCO與ED-CO所測得數值相關性較小，回歸係數r2為0.406，而其變異係數及標準差為0.11 ± 0.12 l/min。尤有甚者，BCO的測量結果其重複性較差，而ED-CO及CCO兩者的測量值重複性較好。結論：對於血行動力變化的監測，經食道超音波監測器不失為一良好變通方法，且與CCO所得數值亦有良好之相似性。而由於其測量結果之明顯差異，BCO的正確性及精確度仍待存疑，故而不應視其為測量心搏出量的標準方法。

Background: Bolus thermodilution cardiac output (BCO) measurement has been considered as the 'gold standard' for cardiac output (CO) measurement. However, it requires placement of a pulmonary artery (PA) catheter, and questions have been raised regarding the risk/benefit ratio of this invasive technique. Furthermore, great variations between measurements have been reported. Continuous thermodilution CO (CCO) measurement is reported to be a better alternative, but it still requires the placement of a PA catheter. Esophageal echoDoppler ultrasonography (ED) provides non-invasive continuous measurement of CO (ED-CO). This study was thus designed to compare the agreement between ED-CO and both thermodilution techniques (BCO and CCO). Methods: Twenty-four patients undergoing primary coronary artery bypass graft surgery were randomized to have a PA catheter placed for measurement of either BCO or CCO. All patients also had an ED probe placed. In Group I patients (n = 12), BCO measurement was carried out every 15 minutes throughout the surgery except during cardiopulmonary bypass, with concurrent ED-CO reading recorded at the same time point. In Group II patients (n = 12), CCO and ED-CO measurements were recorded at the same designated points of time as in Group I. The agreement between methods (BCO vs. ED-CO or CCO vs. ED-CO) was assessed using Bland-Altman method. Results: The range of measured CO of each method was 2.1 to 9.4 l/min for BCO, 2.4 to 9.2 l/min for CCO and 2.3 to 8.9 l/min for ED-CO. ED-CO and CCO had excellent agreement with a linear regression coefficient (r2 value) of 0.846, and a bias (mean difference) and SD of bias of 0.05 ± 0.49 l/min. In contrast, the agreement between BCO and ED-CO was poorer; correlation was low (r2 value 0.406) and both the bias and SD of bias were high (0.11 ± 1.12 l/min). Furthermore, BCO measurements had poor reproducibility, whereas both ED-CO and CCO measurements had good reproducibility. Conclusions: Esophageal echo-Doppler ultrasonography is a satisfactory alternative for cardiac output measurement because it gives a value in good agreement with CCO measurement. With significant between-measurement variations, the accuracy and precision of BCO are uncertain, and it should not be considered as the 'gold standard'.