Hibberd Owen, Hazlerigg Antonia, Cocker Paul John, Wilson Alastair W, Berry Neil, Harris Tim
East Anglian Air Ambulance, Cambridge, UK.
Blizard Institute, Queen Mary University of London, London, UK.
J Intensive Care Soc. 2022 Feb;23(1):11-19. doi: 10.1177/1751143720970356. Epub 2020 Oct 29.
Control of the arterial partial pressure of carbon dioxide (PaCO) is important in the ventilated patient. End-tidal carbon dioxide (ETCO) levels are often used as a proxy, but are clinically limited. The difference between the PaCO and ETCO has been suggested to be 0.5-1.0 kPa. However, this has not been consistently reflected in the physiologically unstable pre-hospital patient. This study aims to elucidate the PaCO-ETCO gradient for pre-hospital intubated patients.
This was a retrospective, cohort study using data identified from the HEMSbase 2 database (Feb 2015-Nov 2018). Patients were included if they had documented ETCO and arterial PaCO measurements. Arterial PaCO data that could not be linked to within 5 minutes of ETCO were excluded. Bland-Altman plots were calculated to describe agreement.
A total of 73 patients were identified. Aetiology was arranged into three categories: 13 (17.8%) medical, 22 (30.1%) traumatic and 38 (52.1%) out-of-hospital cardiac arrest (OHCA). The median PaCO-ETCO gradient was 2.0 [1.3-3.1] kPa. A PaCO-ETCO gradient of 0-1 kPa was seen for only 11 (15.1%) of total patients. The Bland-Altman agreement for all aetiologies was more than the accepted gradient of 0-1 kPa with the largest bias and widest limits of agreement seen for OHCA (-3.2 [0.3 - -6.8]).
The magnitude of the differences between the ETCO and PaCO, levels of variation and inability to predict this suggest that ETCO is not a suitable surrogate upon which to base ventilatory settings in conditions where pH or PaCO require precise control.
控制动脉血二氧化碳分压（PaCO₂）对接受机械通气的患者至关重要。呼气末二氧化碳（ETCO₂）水平常被用作替代指标，但在临床应用中存在局限性。有研究表明，PaCO₂与ETCO₂的差值为0.5 - 1.0 kPa。然而，这一差异在生理状态不稳定的院前患者中并未得到一致体现。本研究旨在阐明院前插管患者的PaCO₂ - ETCO₂梯度。
这是一项回顾性队列研究，使用从HEMSbase 2数据库（2015年2月至2018年11月）中识别的数据。纳入记录了ETCO₂和动脉血PaCO₂测量值的患者。排除与ETCO₂测量时间间隔超过5分钟的动脉血PaCO₂数据。通过计算Bland - Altman图来描述一致性。
共纳入73例患者。病因分为三类：内科疾病13例（17.8%）、创伤22例（30.1%）和院外心脏骤停（OHCA）38例（52.1%）。PaCO₂ - ETCO₂梯度的中位数为2.0 [1.3 - 3.1] kPa。仅11例（15.1%）患者的PaCO₂ - ETCO₂梯度为0 - 1 kPa。所有病因的Bland - Altman一致性均超过公认的0 - 1 kPa梯度，其中OHCA的偏差最大，一致性界限最宽（-3.2 [0.3 - -6.8]）。
ETCO₂与PaCO₂之间差异的大小、变化程度以及无法进行预测表明，在需要精确控制pH值或PaCO₂的情况下，ETCO₂并非确定通气设置的合适替代指标。
