Bhavani-Shankar K, Kumar A Y, Moseley H S, Ahyee-Hallsworth R
Department of Anesthesiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
J Clin Monit. 1995 May;11(3):175-82. doi: 10.1007/BF01617719.
The carbon dioxide (CO2) trace versus time (time capnography) is convenient and adequate for clinical use. This is the method most commonly utilized in capnography. However, the current terminology in time capnography has not yet been standardized and is, therefore, a potential source of confusion. Standard terminology that is based on convention and logic to represent the various phases of a time capnogram is essential. The time capnogram should be considered as two segments: an inspiratory segment and an expiratory segment. The inspiratory segment is termed as phase ); the expiratory segment is divided into phases I, II, III, and, occasionally, IV. Phase I represents the CO2-free gas from the airways (anatomical dead space); phase II consists of a rapid S-shaped upswing on the tracing due to mixing of dead space gas with alveolar gas; and phase III, the alveolar plateau, represents CO2-rich gas from the alveoli. The physiologic basis of phase IV, the terminal upswing at the end of phase III, which is observed in capnograms recorded under certain circumstances (such as in pregnant subjects and obese subjects) is discussed in detail. The clinical implications of the alpha angle, which is the angle between phases II and III, and the beta angle, which is the angle between phases III and the descending limb of phase 0, are outlined. The subtle but important limitations of time capnography are reviewed; its current status as well as its future potential are explored.
二氧化碳（CO₂）浓度随时间变化曲线（实时二氧化碳图）便于临床使用且足够准确。这是二氧化碳图中最常用的方法。然而，目前实时二氧化碳图的术语尚未标准化，因此是一个潜在的混淆来源。基于惯例和逻辑来表示实时二氧化碳图各个阶段的标准术语至关重要。实时二氧化碳图应被视为两个部分：吸气段和呼气段。吸气段称为相位 ；呼气段分为I、II、III期，偶尔还有IV期。I期代表气道中的无CO₂气体（解剖无效腔）；II期由于无效腔气体与肺泡气体混合，在描记图上呈现快速的S形上升；III期，即肺泡平台期，代表来自肺泡的富含CO₂的气体。在某些情况下（如孕妇和肥胖受试者）记录的二氧化碳图中观察到的III期末端上升，即IV期的生理基础将进行详细讨论。还概述了II期和III期之间的夹角α角以及III期与0期下降支之间的夹角β角的临床意义。回顾了实时二氧化碳图细微但重要的局限性；探讨了其当前状况及其未来潜力。
