In patients ventilated with tidal volume (Vt) < 8 mL/kg, pulse pressure variation (PPV) and, likely, the variation of distensibility of the inferior vena cava diameter (IVCDV) are unable to detect preload responsiveness. In this condition, passive leg raising (PLR) could be used, but it requires a measurement of cardiac output. The tidal volume (Vt) challenge (PPV changes induced by a 1-min increase in Vt from 6 to 8 mL/kg) is another alternative, but it requires an arterial line. We tested whether, in case of Vt = 6 mL/kg, the effects of PLR could be assessed through changes in PPV (ΔPPVPLR) or in IVCDV (ΔIVCDVPLR) rather than changes in cardiac output, and whether the effects of the Vt challenge could be assessed by changes in IVCDV (ΔIVCDVVt) rather than changes in PPV (ΔPPVVt). In 30 critically ill patients without spontaneous breathing and cardiac arrhythmias, ventilated with Vt = 6 mL/kg, we measured cardiac index (CI) (PiCCO2), IVCDV and PPV before/during a PLR test and before/during a Vt challenge. A PLR-induced increase in CI ≥ 10% defined preload responsiveness. At baseline, IVCDV was not different between preload responders (n = 15) and non-responders. Compared to non-responders, PPV and IVCDV decreased more during PLR (by − 38 ± 16% and − 26 ± 28%, respectively) and increased more during the Vt challenge (by 64 ± 42% and 91 ± 72%, respectively) in responders. ∆PPVPLR, expressed either as absolute or as percent relative changes, detected preload responsiveness (area under the receiver operating curve, AUROC: 0.98 ± 0.02 for both). ∆IVCDVPLR detected preload responsiveness only when expressed in absolute changes (AUROC: 0.76 ± 0.10), not in relative changes. ∆PPVVt, expressed as absolute or percent relative changes, detected preload responsiveness (AUROC: 0.98 ± 0.02 and 0.94 ± 0.04, respectively). This was also the case for ∆IVCDVVt, but the diagnostic threshold (1 point or 4%) was below the least significant change of IVCDV (9[3–18]%). During mechanical ventilation with Vt = 6 mL/kg, the effects of PLR can be assessed by changes in PPV. If IVCDV is used, it should be expressed in percent and not absolute changes. The effects of the Vt challenge can be assessed on PPV, but not on IVCDV, since the diagnostic threshold is too small compared to the reproducibility of this variable. Trial registration: Agence Nationale de Sécurité du Médicament et des Produits de santé: ID-RCB: 2016-A00893-48.

中文翻译：

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在低潮气量通气的情况下，被动抬腿和潮气量挑战期间脉压变化和下腔静脉扩张性的变化是否可以检测到前负荷反应？

在潮气量 (Vt) < 8 mL/kg 通气的患者中，脉压变化 (PPV) 以及可能的下腔静脉直径 (IVCDV) 扩张性的变化无法检测到前负荷反应性。在这种情况下，可以使用被动抬腿 (PLR)，但它需要测量心输出量。潮气量 (Vt) 挑战（Vt 从 6 到 8 mL/kg 增加 1 分钟引起的 PPV 变化）是另一种选择，但它需要一条动脉。我们测试了在 Vt = 6 mL/kg 的情况下，PLR 的影响是否可以通过 PPV (ΔPPVPLR) 或 IVCDV (ΔIVCDVPLR) 的变化而不是心输出量的变化来评估，以及 Vt 激发的影响是否可以通过 IVCDV (ΔIVCDVVt) 的变化而不是 PPV (ΔPPVVt) 的变化来评估。在 30 名无自主呼吸和心律失常的危重患者中，以 Vt = 6 mL/kg 通气，我们在 PLR 测试之前/期间和 Vt 挑战之前/期间测量了心脏指数 (CI) (PiCCO2)、IVCDV 和 PPV。PLR 诱导的 CI 增加 ≥ 10% 定义为前负荷反应性。在基线时，IVCDV 在预负荷反应者（n = 15）和无反应者之间没有差异。与无反应者相比， PPV 和 IVCDV 在 PLR 期间降低更多（分别为 − 38 ± 16% 和 − 26 ± 28%），在 Vt 激发期间增加更多（分别为 64 ± 42% 和 91 ± 72%）在响应者中。ΔPPVPLR，表示为绝对或百分比相对变化，检测到预负荷反应（接收器操作曲线下的面积，AUROC：0.98 ± 0.02 两者）。∆IVCDVPLR 仅在以绝对变化（AUROC：0.76 ± 0.10）而非相对变化表示时检测到前负荷反应性。∆PPVVt，表示为绝对或百分比相对变化，检测到的前负荷反应（AUROC：分别为 0.98 ± 0.02 和 0.94 ± 0.04）。这也是 ∆IVCDVVt 的情况，但诊断阈值（1 分或 4%）低于 IVCDV 的最不显着变化（9[3–18]%）。在 Vt = 6 mL/kg 的机械通气期间，可以通过 PPV 的变化来评估 PLR 的影响。如果使用 IVCDV，则应以百分比而非绝对变化表示。可以评估 Vt 激发对 PPV 的影响，但不能对 IVCDV 进行评估，因为与该变量的再现性相比，诊断阈值太小。试验注册：Agence Nationale de Sécurité du Médicament et des Produits de santé：ID-RCB：