Badal John J, Loeb Robert G, Trujillo Dax K
Department of Anesthesiology, University of Arizona, Tucson, AZ 85724, USA.
Anesth Analg. 2007 Oct;105(4):1048-52, table of contents. doi: 10.1213/01.ane.0000280484.81216.76.
Mixed exhaled CO2 and CO2 excretion (VCO2) are not routinely monitored during anesthesia because they are difficult to measure using standard equipment. We conducted two experiments to test the hypothesis that the ventilator bellows contains mixed exhaled CO2.
In the laboratory experiment, a lung model was assembled with a CO2 source. The gasses were sampled from the bellows and VCO2 was calculated. These values were compared to VCO2 measured by the NICO monitor (Novametrix Medical Systems), a commercially available mainstream capnometer. In the clinical experiment, gasses were sampled from the ventilator bellows in nine subjects under general anesthesia. VCO2 was calculated and compared to values obtained from the NICO monitor.
VCO2 measured from the bellows connected to the lung model resulted in an overall precision of 26 mL/min, bias of -24 mL/min, and average error of -12.0% compared to set CO2 flow. In the clinical trial, calculated VCO2 sampled from the bellows compared to measured VCO2 from the NICO monitor had a bias of -0.15 mL/min, and precision of 33.16 mL/min.
VCO2 calculated from the bellows was not as accurate as NICO VCO2 in the laboratory; however, it can be done using standard anesthesia equipment. Furthermore, in nine anesthetized subjects, the bellows method of VCO2 determination had an overall percent error of 1.34% from NICO VCO2. Given this small percent error between the bellows method and the NICO monitor, we believe that the bellows method of VCO(2) determination is suitable for clinical practice.
麻醉期间通常不会常规监测混合呼出二氧化碳和二氧化碳排出量（VCO2），因为使用标准设备难以测量。我们进行了两项实验，以检验呼吸机风箱中含有混合呼出二氧化碳这一假设。
在实验室实验中，用一个二氧化碳源组装了一个肺模型。从风箱中采集气体并计算VCO2。将这些值与通过NICO监测仪（诺瓦美克斯医疗系统公司）测量的VCO2进行比较，NICO监测仪是一种市售的主流二氧化碳监测仪。在临床实验中，对9名全身麻醉患者的呼吸机风箱中的气体进行采样。计算VCO2并与从NICO监测仪获得的值进行比较。
与设定的二氧化碳流量相比，从连接到肺模型的风箱中测得的VCO2总体精度为26 mL/分钟，偏差为-24 mL/分钟，平均误差为-12.0%。在临床试验中，从风箱中采样计算得到的VCO2与NICO监测仪测得的VCO2相比，偏差为-0.15 mL/分钟，精度为33.16 mL/分钟。
在实验室中，从风箱计算得到的VCO2不如NICO监测仪测得的VCO2准确；然而，使用标准麻醉设备即可完成。此外，在9名麻醉患者中，风箱法测定VCO2与NICO监测仪测得的VCO2相比，总体百分比误差为1.34%。鉴于风箱法与NICO监测仪之间的百分比误差较小，我们认为风箱法测定VCO2适用于临床实践。
