Kline J A, Arunachlam M
Department of Emergency Medicine, Carolinas Medical Center, Charlotte, NC 28232, USA.
Ann Emerg Med. 1998 Sep;32(3 Pt 1):289-96. doi: 10.1016/s0196-0644(98)70004-6.
Acute pulmonary embolism (PE) increases alveolar dead space, which can dilute carbon dioxide content in exhaled breath. This study was undertaken to determine whether the capnogram waveform area from patients with PE is decreased compared with that from patients without PE and to examine the potential role of the capnogram waveform area as a screening test for PE.
Studies were conducted on patients from a large, urban emergency department. Steady-state capnograms were collected from subjects breathing room air, and data were electronically stored for later analysis; arterial blood was collected for blood gas analysis. PE was diagnosed or excluded on the basis of appropriate combinations of isotopic ventilation-perfusion lung scanning, lower-extremity venous Doppler ultrasound studies, and pulmonary angiography. Capnogram areas were measured by tracing waveforms on printed copies with an electronic digitizing tablet.
The mean capnogram area from patients with PE (n=19) was 28+/-10 mm Hg x sec, significantly less than for patients without PE (n=120), 53+/-17 mm Hg x sec (95% confidence interval [CI] for a difference of 25 mm Hg x sec, 17 to 33 mm Hg x sec). At a cutoff of 50 mm Hg x sec, the test sensitivity was 100% (95% CI, 82% to 100%), with a negative likelihood ratio (LR-) of .17, and the specificity was 53% (95% CI, 44% to 62%), with a positive likelihood ratio (LR+) of 2.1. At a cutoff of 25 mm Hg x sec, the test sensitivity was 42% (95% CI, 20% to 67%; LR-, .6) and the specificity was 97% (95% CI, 92% to 99%; LR+, 12.3). The area under the smoothed receiver operating characteristic curve for the capnogram area was .896 (95% Cl, .80 to .99).
The capnogram waveform area may be useful in screening for PE in the ED.
急性肺栓塞（PE）会增加肺泡无效腔，这会稀释呼出气体中的二氧化碳含量。本研究旨在确定PE患者的二氧化碳波形图面积与非PE患者相比是否减小，并检验二氧化碳波形图面积作为PE筛查试验的潜在作用。
对来自一家大型城市急诊科的患者进行研究。收集受试者呼吸室内空气时的稳态二氧化碳波形图，并将数据进行电子存储以便后续分析；采集动脉血进行血气分析。根据同位素通气-灌注肺扫描、下肢静脉多普勒超声检查和肺血管造影的适当组合来诊断或排除PE。通过使用电子数字化平板电脑在打印副本上描绘波形来测量二氧化碳波形图面积。
PE患者（n = 19）的平均二氧化碳波形图面积为28±10 mmHg×秒，显著小于非PE患者（n = 120）的53±17 mmHg×秒（差值为25 mmHg×秒的95%置信区间[CI]，17至33 mmHg×秒）。在截断值为50 mmHg×秒时，试验敏感性为100%（95% CI，82%至100%），阴性似然比（LR-）为0.17，特异性为53%（95% CI，44%至62%），阳性似然比（LR+）为2.1。在截断值为25 mmHg×秒时，试验敏感性为42%（95% CI，20%至67%；LR-，0.6），特异性为97%（95% CI，92%至99%；LR+，12.3）。二氧化碳波形图面积的平滑受试者工作特征曲线下面积为0.896（95% Cl，0.80至0.99）。
二氧化碳波形图面积可能有助于在急诊科筛查PE。
