急性呼吸窘迫症候群(acute respiratory distress syndrome)是一種以急性發生、迅速惡化和嚴重低氧血症為特徵的臨床症候群。在急性呼吸窘迫症候群 的急性期，呼氣末正壓(positive end-expiratory pressure, PEEP)的設定非常重要。在臨床上，使用最佳肺部順應性(compliance)的來選擇呼氣末正壓是一種相當實用的方法，但有時會遇到在兩個不同呼氣末正壓之間皆存在肺部順應性。在本研究的第一部分，我們使用電阻抗影像 (electrical impedance tomography) 來量測肺部塌陷與過度擴張的百分比來評估合為較適當的設定。我們發現當出現兩個不同呼氣末正壓皆存在最佳肺部順應性時，設置較高的呼氣末正壓可能更有利於肺復張(lung recruitment)。但如果呼氣末正壓達到 15 cm H2O則應小心過高的肺部張力。除此之外，在急性呼吸窘迫症候群的恢復階段，患者通常會恢復自主呼吸並準備脫離機械通氣。然而，過大的自主呼吸力量可能會導致肺損傷，目前可以氣流擺動(pendelluft)作為替代指標。在臨床上有兩種監測氣流擺動的方法，包含氣流擺盪量(pendelluft volume)與氣流擺動幅度(pendelluft amplitude)，但尚未有研究進行兩者之間的比較。在本研究的第二部分中，我們比較了這兩種方法在氣流擺動估計中的差異，發現氣流擺動幅度是一種更敏感的方法，但在同一層內氣流擺動的比例較高時，可能會高估氣流擺動的程度。未來研究仍須著重於氣流擺動的陽性判定標準。

The acute respiratory distress syndrome (ARDS) is a clinical syndrome which characterized with acute onset, rapid-deteriorating, and severe hypoxemia. In the acute stage of ARDS, optimal ventilatory setting of positive end-expiratory pressure (PEEP) is important. The PEEP setting based on systemic compliance is a practical way, but sometimes there are similar compliance levels between two different PEEP level. In the first part of present study, we use electrical impedance tomography (EIT) to estimate percentage of lung collapse and hyperdistension. If there are similar compliances in two PEEP level, setting ventilator with higher one might be more beneficial in lung recruitment. However, it should be cautious with higher lung stress if the PEEP level reach 15 cm H2O. In contrast, in the recovery phase, patients with ARDS usually regain spontaneous breathing efforts and prepare to wean from mechanical ventilation. However, vigorous spontaneous breathing efforts might cause lung injury, with pendelluft as surrogate marker. Currently, there are two methods for pendelluft monitoring, but there is no study regarding their comparison. In second part of present study, we compared these two methods in pendelluft estimation, and revealed that the pendelluft amplitude is a more sensitive method, but may overestimate the degree of pendelluft due to higher proportion of intralayer pendelluft. The optimal cut-off criteria need further investigation.

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