Department of Anesthesiology, University Medical Center Göttingen, Göttingen, Germany.
Department of Adult Critical Care, Guy's and St Thomas' NHS Foundation Trust, Health Centre for Human and Applied Physiological Sciences, London, United Kingdom.
J Appl Physiol (1985). 2023 Aug 1;135(2):334-342. doi: 10.1152/japplphysiol.00225.2023. Epub 2023 Jun 22.
The conditions of temperature, pressure, and saturation in which respiratory gas volumes are expressed [standard temperature and pressure, dry (STPD), ambient temperature and pressure, saturated (ATPS), or body temperature and pressure, saturated (BTPS)] are physiologically relevant, but often ignored or unknown in clinical practice. In this study, we aimed to investigate whether and at which extent the gas volume corrections, either in natural or artificial lung, may alter key respiratory and metabolic variables and the possible clinical consequences. We primarily referred to the effects of gas volume corrections on three physiological variables: physiological dead space, venous admixture, and total CO production (V̇co) during extracorporeal support. We used three physiological models in which calculations of these variables have been performed with and without correction of gas volumes, both in a theoretical model and in 448 patients. The lack of gas volume correction leads to an error in the computation of physiological dead space fraction between 0.05 and 0.15, both in the theoretical model and in the patient population. The venous admixture was minimally affected by the absence of correction (0.01-0.04 error). During extracorporeal support, if the V̇co of natural and membrane lung is expressed in different conditions, potentially large errors (0%-18.4%) may occur in the computation of total V̇co (V̇co = V̇co + V̇co). This may lead to inappropriate settings of mechanical ventilation with higher plateau pressure. As the dead space and the CO sharing between natural and artificial lung are relevant both as prognostic index and as a guide for appropriate mechanical ventilation, their inappropriate computation may lead to erroneous categorization of the patients and inappropriate mechanical treatment. Gas volume conditions are often ignored or unknown in the clinical practice. However, they could have relevance for the calculation of some key variables in ICU setting. This study shows that gas volume corrections are mostly relevant when assessing CO clearance, both in mechanical ventilation and during extracorporeal support, whereas irrelevant for oxygenation assessment of patients. Knowing when the appropriate corrections are needed allows to better understand patients' clinical conditions and to tailor the treatment.
呼吸气体容积的温度、压力和饱和度条件[标准温度和压力，干燥（STPD）、环境温度和压力，饱和（ATPS）或体温和压力，饱和（BTPS）]在生理学上是相关的，但在临床实践中经常被忽视或未知。在这项研究中，我们旨在研究在何种程度上以及在何种程度上，无论是在天然肺还是人工肺中，气体容积校正可能会改变关键的呼吸和代谢变量以及可能的临床后果。我们主要参考了气体容积校正对三个生理变量的影响：生理无效腔、静脉混合和体外支持期间的总 CO 产生（V̇co）。我们使用了三个生理模型，在这些模型中，无论是否校正气体体积，都在理论模型和 448 名患者中计算了这些变量。如果不校正气体体积，会导致生理无效腔分数的计算错误在 0.05 到 0.15 之间，无论是在理论模型还是在患者人群中都是如此。静脉混合受校正缺失的影响最小（误差为 0.01-0.04）。在体外支持期间，如果天然和膜肺的 V̇co 在不同条件下表达，在总 V̇co（V̇co = V̇co + V̇co）的计算中可能会出现潜在的大误差（0%-18.4%）。这可能导致机械通气的平台压力设置过高。由于无效腔和天然与人工肺之间的 CO 共享都是作为预后指标和适当机械通气指南的相关因素，因此它们的不当计算可能导致患者的错误分类和不当的机械治疗。在临床实践中，气体体积条件经常被忽视或未知。然而，它们可能与 ICU 环境中一些关键变量的计算有关。本研究表明，在评估 CO 清除率时，气体体积校正大多是相关的，无论是在机械通气还是体外支持期间，而对于患者的氧合评估则不相关。了解何时需要适当的校正可以帮助更好地了解患者的临床情况，并调整治疗方案。
