Rich G F, Sullivan M P, Adams J M
Department of Anesthesiology, University of Virginia, Charlottesville.
Anesthesiology. 1990 Aug;73(2):265-8. doi: 10.1097/00000542-199008000-00013.
The authors compared PaCO2 with end-tidal CO2 (ETCO2) sampled at multiple sites along the endotracheal tube (ETT) in seven anesthetized rabbits (weight, 2.7-3.6 kg) to determine the most convenient, yet accurate, sampling location. Comparisons were made during spontaneous and controlled ventilation with fresh gas flows (FGF) of two and ten times the minute ventilation using a Mapleson D circuit. An Engstrom Eliza analyzer with a continuous sampling rate of 100 ml/min was used to measure ETCO2. A 0.75-mm ID polyethylene tube inserted in the side of the ETT sampled ETCO2 at the distal tip and at the 6-, 12-, and 15-cm marks on the ETT. ETCO2 was also measured at the standard proximal connector. The differences (P less than 0.05) between PaCO2 and ETCO2 at the distal, 6-, 12-, and 15-cm marks were 2.9 +/- 0.4, 3.1 +/- 0.4, 3.6 +/- 0.4, and 4.6 +/- 0.5 mmHg (mean +/- SEM), respectively, and did not change with FGF or mode of ventilation. The difference between PaCO2 and ETCO2 measured at the proximal connector was always large but significantly (P less than 0.05) greater during spontaneous than controlled ventilation (24.2 +/- 1.5 versus 15.0 +/- 1.4 mmHg) and at higher FGF (19.4 +/- 1.3 versus 16.8 +/- 1.6 mmHg). The differences (P less than 0.05) between ETCO2 at the distal tip and ETCO2 at the 6-, 12-, and 15-cm marks were 0.24 +/- 0.07, 0.73 +/- 0.11, and, 1.77 +/- 0.20 mmHg, respectively. This demonstrates that the change in ETCO2 between the distal tip and the 12-cm mark on the ETT is less than 1 mmHg, and that this clinically insignificant difference is independent of FGF and mode of ventilation. The 12 cm-mark is outside of the mouth on a newborn, and sampling ETCO2 at that point, which may be accomplished simply by inserting a small needle in the side of the ETT, may be the most appropriate sampling location.
作者将7只麻醉兔（体重2.7 - 3.6千克）气管内导管（ETT）多个部位采集的呼气末二氧化碳（ETCO2）与动脉血二氧化碳分压（PaCO2）进行比较，以确定最便捷且准确的采样位置。使用Mapleson D回路，在分钟通气量的2倍和10倍新鲜气体流量（FGF）下，于自主通气和控制通气期间进行比较。使用连续采样率为100毫升/分钟的Engstrom Eliza分析仪测量ETCO2。将一根内径0.75毫米的聚乙烯管插入ETT侧面，在ETT远端尖端以及距尖端6厘米、12厘米和15厘米处标记采集ETCO2。还在标准近端接头处测量ETCO2。在远端、6厘米、12厘米和15厘米标记处，PaCO2与ETCO2之间的差异（P < 0.05）分别为2.9±0.4、3.1±0.4、3.6±0.4和4.6±0.5毫米汞柱（均值±标准误），且不随FGF或通气模式改变。在近端接头处测量的PaCO2与ETCO2之间的差异始终很大，但在自主通气时显著（P < 0.05）大于控制通气时（24.2±1.5对15.0±1.4毫米汞柱），且在较高FGF时（19.4±1.3对16.8±1.6毫米汞柱）更大。远端尖端处的ETCO2与6厘米、12厘米和15厘米标记处的ETCO2之间的差异（P < 0.05）分别为0.24±0.07、0.73±0.11和1.77±0.20毫米汞柱。这表明ETT远端尖端与12厘米标记处之间的ETCO2变化小于1毫米汞柱，且这种临床上无显著意义的差异与FGF和通气模式无关。对于新生儿，12厘米标记位于口腔外，在该位置采集ETCO2（可简单地通过在ETT侧面插入一根小针来实现）可能是最合适的采样位置。
