Nik Ab Rahman Nik Hisamuddin, Mamat Amiruddin Fairuz
Int J Emerg Med. 2010 Dec 9;3(4):315-20. doi: 10.1007/s12245-010-0233-5.
Capnometry measures carbon dioxide in expired air and provides the clinician with a noninvasive measure of the systemic metabolism, circulation and ventilation. This study was carried out on patients with acute breathlessness to define the utility and role of capnometry in the emergency department.
THE OBJECTIVES OF THE STUDY WERE: To determine the correlation between end tidal CO(2) and PaCO(2) in non-intubated acutely breathless patients.To determine factors that influence the end tidal carbon dioxide (ETCO(2)).To determine the correlation between ETCO(2) with PaCO(2) in patients presenting with pulmonary disorders.
One hundred fifty acutely breathless patients arriving at the emergency department and fulfilling the inclusion and exclusion criteria were chosen during a 6-month study period. The patients gave written or verbal consent, and were triaged and treated according to their presenting complaints. Demographic data were collected, and the ETCO(2) data were recorded. Arterial blood gas was taken in all patients. The data were compiled and analyzed using various descriptive studies from the Statistics Program for Social Studies (SPSS) version 12. Correlation between ETCO(2) and PaCO(2) was analyzed using the Pearson correlation coefficient. Other variables also were analyzed to determine the correlation using simple linear regression. The agreement and difference between ETCO(2) and PaCO(2) were analyzed using paired sample t-tests.
There is a strong correlation between ETCO(2) and PaCO(2) using the Pearson correlation coefficient: 0.716 and p value of 0.00 (p < 0.05). However, the paired t-test showed a mean difference between the two parameters of 4.303 with a p value < 0.05 (95% CI 2.818, 5.878). There was also a good correlation between ETCO(2) and acidosis state with a Pearson correlation coefficient of 0.374 and p value 0.02 (p < 0.05). A strong correlation was also observed between ETCO(2) and a hypocapnic state, with a Pearson correlation coefficient of 0.738 (p < 0.05). Weak correlation was observed between alkalosis and ETCO(2), with a Pearson correlation coefficient of 0.171 (p < 0.05). A strong negative correlation was present between ETCO(2) and hypercapnic patients presenting with pulmonary disorders, with a Pearson correlation coefficient of -0.738 (p < 0.05) and of -0.336 (p < 0.05), respectively.
This study shows that ETCO(2) can be used to predict the PaCO(2) level when the difference between the PaCO(2) and ETCO(2) is between 2 to 6 mmHg, especially in cases of pure acidosis and hypocapnia. Using ETCO(2) to predict PaCO(2) should be done with caution, especially in cases that involve pulmonary disorders and acid-base imbalance.
二氧化碳监测法可测量呼出气体中的二氧化碳含量，为临床医生提供一种无创的系统性代谢、循环及通气测量方法。本研究针对急性气促患者开展，以明确二氧化碳监测法在急诊科的效用及作用。
本研究的目标如下：确定未插管急性气促患者的呼气末二氧化碳（ETCO₂）与动脉血二氧化碳分压（PaCO₂）之间的相关性。确定影响呼气末二氧化碳（ETCO₂）的因素。确定肺部疾病患者的ETCO₂与PaCO₂之间的相关性。
在为期6个月的研究期间，选取了150名抵达急诊科且符合纳入和排除标准的急性气促患者。患者给予书面或口头同意，并根据其主诉进行分诊和治疗。收集人口统计学数据，并记录ETCO₂数据。所有患者均采集动脉血气。使用社会科学统计程序（SPSS）12版的各种描述性研究对数据进行整理和分析。使用Pearson相关系数分析ETCO₂与PaCO₂之间的相关性。还分析了其他变量，以使用简单线性回归确定相关性。使用配对样本t检验分析ETCO₂与PaCO₂之间的一致性和差异。
使用Pearson相关系数分析显示ETCO₂与PaCO₂之间存在强相关性：相关系数为0.716，p值为0.00（p＜0.05）。然而，配对t检验显示这两个参数之间的平均差值为4.303，p值＜0.05（95%可信区间2.818，5.878）。ETCO₂与酸中毒状态之间也存在良好相关性，Pearson相关系数为0.374，p值为0.02（p＜0.05）。ETCO₂与低碳酸血症状态之间也观察到强相关性，Pearson相关系数为0.738（p＜0.05）。碱中毒与ETCO₂之间观察到弱相关性，Pearson相关系数为0.171（p＜0.05）。ETCO₂与患有肺部疾病的高碳酸血症患者之间存在强负相关性，Pearson相关系数分别为-0.738（p＜0.05）和-0.336（p＜0.05）。
本研究表明，当PaCO₂与ETCO₂之间的差值在2至6mmHg之间时，ETCO₂可用于预测PaCO₂水平，尤其是在单纯酸中毒和低碳酸血症的情况下。使用ETCO₂预测PaCO₂时应谨慎，尤其是在涉及肺部疾病和酸碱失衡的情况下。
