Raemer D B, Calalang I
Department of Anesthesia, Brigham and Women's Hospital, Boston, MA 02115.
J Clin Monit. 1991 Apr;7(2):195-208. doi: 10.1007/BF01618124.
Substantial mean differences between arterial carbon dioxide tension (PaCO2) and end-tidal carbon dioxide tension (PETCO2) in anesthesia and intensive care settings have been demonstrated by a number of investigators. We have explored the technical causes of error in the measurement of PETCO2 that could contribute to the observed differences. In a clinical setting, the measurement of PETCO2 is accomplished with one of three types of instruments, infrared analyzers, mass spectrometers, and Raman spectrometers, whose specified accuracies are typically +/- 2, +/- 1.5, and +/- 0.5 mm Hg, respectively. We examined potential errors in PETCO2 measurement with respect to the analyzer, sampling system, environment, and instrument. Various analyzer error sources were measured, including stability, warm-up time, interference from nitrous oxide and oxygen, pressure, noise, and response time. Other error sources, including calibration, resistance in the sample catheter, pressure changes, water vapor, liquid water, and end-tidal detection algorithms, were considered and are discussed. On the basis of our measurements and analysis, we estimate the magnitude of the major potential errors for an uncompensated infrared analyzer as: inaccuracy, 2 mm Hg; resolution, 0.5 mm Hg; noise, 2 mm Hg; instability (12 hours), 3 mm Hg; miscalibration, 1 mm Hg; selectivity (70% nitrous oxide), 6.5 mm Hg; selectivity (100% oxygen), -2.5 mm Hg; atmospheric pressure change, less than 1 mm Hg; airway pressure at 30 cm H2O, 2 mm Hg; positive end-expiratory pressure or continuous positive airway pressure at 20 cm H2O, 1.5 mm Hg; sampling system resistance, less than 1 mm Hg; and water vapor, 2.5 mm Hg. In addition to these errors, other systematic mistakes such as an inaccurate end-tidal detection algorithm, poor calibration technique, or liquid water contamination can lead to gross inaccuracies. In a clinical setting, unless the user is confident that all of the technical error sources have been eliminated and the physiologic factors are known, depending on PETCO2 to determine PaCO2 is not advised.
许多研究者已证实在麻醉和重症监护环境中，动脉血二氧化碳分压（PaCO2）与呼气末二氧化碳分压（PETCO2）之间存在显著的平均差异。我们探究了可能导致观察到的差异的PETCO2测量中的技术误差原因。在临床环境中，PETCO2的测量通过三种类型的仪器之一完成，即红外分析仪、质谱仪和拉曼光谱仪，其规定的准确度通常分别为±2、±1.5和±0.5 mmHg。我们从分析仪、采样系统、环境和仪器方面检查了PETCO2测量中的潜在误差。测量了各种分析仪误差源，包括稳定性、预热时间、氧化亚氮和氧气的干扰、压力、噪声和响应时间。还考虑并讨论了其他误差源，包括校准、样品导管中的阻力、压力变化、水蒸气、液态水和呼气末检测算法。根据我们的测量和分析，我们估计未补偿红外分析仪的主要潜在误差大小为：不准确度，2 mmHg；分辨率，0.5 mmHg；噪声，2 mmHg；不稳定性（12小时），3 mmHg；校准错误，1 mmHg；选择性（70%氧化亚氮），6.5 mmHg；选择性（100%氧气），-2.5 mmHg；大气压力变化，小于1 mmHg；气道压力30 cm H2O时，2 mmHg；呼气末正压或气道持续正压20 cm H2O时，1.5 mmHg；采样系统阻力，小于1 mmHg；以及水蒸气，2.5 mmHg。除了这些误差外，其他系统性错误，如呼气末检测算法不准确、校准技术不佳或液态水污染，可能导致严重不准确。在临床环境中，除非使用者确信所有技术误差源已消除且生理因素已知，否则不建议根据PETCO2来确定PaCO2。
