Department of Anaesthesiology, Medical University of Göttingen, University Medical Centre Göttingen, Göttingen, Germany; Department of Anaesthesia and Intensive Care, IRCCS San Raffaele Scientific Institute, Milan, Italy.
Department of Anaesthesiology, Medical University of Göttingen, University Medical Centre Göttingen, Göttingen, Germany.
Br J Anaesth. 2023 Mar;130(3):360-367. doi: 10.1016/j.bja.2022.10.035. Epub 2022 Dec 2.
Ventilatory ratio (VR) has been proposed as an alternative approach to estimate physiological dead space. However, the absolute value of VR, at constant dead space, might be affected by venous admixture and CO volume expired per minute (VCO).
This was a retrospective, observational study of mechanically ventilated patients with acute respiratory distress syndrome (ARDS) in the UK and Italy. Venous admixture was either directly measured or estimated using the surrogate measure Pa/FiO ratio. VCO was estimated through the resting energy expenditure derived from the Harris-Benedict formula.
A total of 641 mechanically ventilated patients with mild (n=65), moderate (n=363), or severe (n=213) ARDS were studied. Venous admixture was measured (n=153 patients) or estimated using the Pa/FiO ratio (n=448). The VR increased exponentially as a function of the dead space, and the absolute values of this relationship were a function of VCO. At a physiological dead space of 0.6, VR was 1.1, 1.4, and 1.7 in patients with VCO equal to 200, 250, and 300, respectively. VR was independently associated with mortality (odds ratio [OR]=2.5; 95% confidence interval [CI], 1.8-3.5), but was not associated when adjusted for V/V, VCO, Pa/FiO (OR=1.2; 95% CI, 0.7-2.1). These three variables remained independent predictors of ICU mortality (V/V [OR=17.9; 95% CI, 1.8-185; P<0.05]; VCO [OR=0.99; 95% CI, 0.99-1.00; P<0.001]; and Pa/FiO (OR=0.99; 95% CI, 0.99-1.00; P<0.001]).
VR is a useful aggregate variable associated with outcome, but variables not associated with ventilation (VCO and venous admixture) strongly contribute to the high values of VR seen in patients with severe illness.
通气比值（VR）已被提议作为一种替代方法来估计生理死腔。然而，在死腔不变的情况下，VR 的绝对值可能会受到静脉血混合和每分钟呼出的二氧化碳量（VCO）的影响。
这是一项在英国和意大利进行的机械通气的急性呼吸窘迫综合征（ARDS）患者的回顾性观察研究。静脉血混合通过直接测量或使用替代指标 Pa/FiO 比值来估计。VCO 通过哈里斯-贝尼迪克特公式得出的静息能量消耗来估计。
共研究了 641 名机械通气的轻度（n=65）、中度（n=363）或重度（n=213）ARDS 患者。静脉血混合通过直接测量（n=153 例）或使用 Pa/FiO 比值估计（n=448 例）。VR 随死腔呈指数增长，而该关系的绝对值与 VCO 有关。在生理死腔为 0.6 时，VCO 分别为 200、250 和 300 的患者的 VR 分别为 1.1、1.4 和 1.7。VR 与死亡率独立相关（比值比[OR]=2.5；95%置信区间[CI]，1.8-3.5），但在调整 V/V、VCO、Pa/FiO 后则不相关（OR=1.2；95% CI，0.7-2.1）。这三个变量仍然是 ICU 死亡率的独立预测因子（V/V [OR=17.9；95% CI，1.8-185；P<0.05]；VCO [OR=0.99；95% CI，0.99-1.00；P<0.001]；和 Pa/FiO [OR=0.99；95% CI，0.99-1.00；P<0.001]）。
VR 是一个与结局相关的有用综合变量，但与通气无关的变量（VCO 和静脉血混合）强烈影响严重疾病患者中看到的高 VR 值。
