Ito Shoji, Mardimae Alexandra, Han Jay, Duffin James, Wells Greg, Fedorko Ludwik, Minkovich Leonid, Katznelson Rita, Meineri Massimiliano, Arenovich Tamara, Kessler Cathie, Fisher Joseph A
Department of Anaesthesiology, University Health Network, Toronto Canada.
J Physiol. 2008 Aug 1;586(15):3675-82. doi: 10.1113/jphysiol.2008.154716. Epub 2008 Jun 19.
Accurate measurements of arterial P(CO(2)) (P(a,CO(2))) currently require blood sampling because the end-tidal P(CO(2)) (P(ET,CO(2))) of the expired gas often does not accurately reflect the mean alveolar P(CO(2)) and P(a,CO(2)). Differences between P(ET,CO(2)) and P(a,CO(2)) result from regional inhomogeneities in perfusion and gas exchange. We hypothesized that breathing via a sequential gas delivery circuit would reduce these inhomogeneities sufficiently to allow accurate prediction of P(a,CO(2)) from P(ET,CO(2)). We tested this hypothesis in five healthy middle-aged men by comparing their P(ET,CO(2)) values with P(a,CO(2)) values at various combinations of P(ET,CO(2)) (between 35 and 50 mmHg), P(O(2)) (between 70 and 300 mmHg), and breathing frequencies (f; between 6 and 24 breaths min(-1)). Once each individual was in a steady state, P(a,CO(2)) was collected in duplicate by consecutive blood samples to assess its repeatability. The difference between P(ET,CO(2)) and average P(a,CO(2)) was 0.5 +/- 1.7 mmHg (P = 0.53; 95% CI -2.8, 3.8 mmHg) whereas the mean difference between the two measurements of P(a,CO(2)) was -0.1 +/- 1.6 mmHg (95% CI -3.7, 2.6 mmHg). Repeated measures ANOVAs revealed no significant differences between P(ET,CO(2)) and P(a,CO(2)) over the ranges of P(O(2)), f and target P(ET,CO(2)). We conclude that when breathing via a sequential gas delivery circuit, P(ET,CO(2)) provides as accurate a measurement of P(a,CO(2)) as the actual analysis of arterial blood.
目前，准确测量动脉血二氧化碳分压（P(a,CO₂)）需要采集血样，因为呼出气体的呼气末二氧化碳分压（P(ET,CO₂)）往往不能准确反映平均肺泡二氧化碳分压和动脉血二氧化碳分压。P(ET,CO₂)与P(a,CO₂)之间的差异源于灌注和气体交换的区域不均匀性。我们假设，通过顺序式气体输送回路呼吸能够充分减少这些不均匀性，从而根据P(ET,CO₂)准确预测P(a,CO₂)。我们通过比较5名健康中年男性在不同P(ET,CO₂)（35至50 mmHg之间）、P(O₂)（70至300 mmHg之间）和呼吸频率（f；6至24次/分钟之间）组合下的P(ET,CO₂)值与P(a,CO₂)值，对这一假设进行了测试。每个个体达到稳态后，通过连续采集两份血样来收集P(a,CO₂)，以评估其重复性。P(ET,CO₂)与平均P(a,CO₂)之间的差异为0.5±1.7 mmHg（P = 0.53；95%置信区间-2.8, 3.8 mmHg），而P(a,CO₂)两次测量之间的平均差异为-0.1±1.6 mmHg（95%置信区间-3.7, 2.6 mmHg）。重复测量方差分析显示，在P(O₂)、f和目标P(ET,CO₂)的范围内，P(ET,CO₂)与P(a,CO₂)之间无显著差异。我们得出结论，当通过顺序式气体输送回路呼吸时，P(ET,CO₂)对P(a,CO₂)的测量与动脉血实际分析一样准确。
