Branson R D, Campbell R S, Davis K, Porembka D T
Department of Surgery, University of Cincinnati Medical Center, Ohio 45267-0558, USA.
Anaesth Intensive Care. 1998 Apr;26(2):178-83. doi: 10.1177/0310057X9802600208.
We compared the effects of humidity delivered by the circle system at low fresh gas flows (FGF) with a conventional two-limb and coaxial circuit on the structure and function of the tracheobronchial epithelium in dogs. Animals were anaesthetized and mechanically ventilated using an anaesthesia ventilator to maintain normocarbia. Group I (control) animals received a FGF equal to the required minute ventilation mimicking an open circuit technique. Group II and III animals had FGF set at 20% of the required minute ventilation. Group II used a two-limb circuit and Group III used a coaxial circuit. Relative humidity and temperature of inspired gases were measured at baseline and hourly afterwards. In the first experiment, biopsies of the tracheobronchial tree were obtained bronchoscopically at baseline and then hourly for six hours. Microscopic examination of these samples allowed calculation of mean ciliary length. In the second experiment, tracheal mucus flow velocity (TMFV) was measured at baseline and hourly afterward, using a cinebroncho-fibrescopic method. Delivered absolute humidity was greatest with low FGF and the coaxial circuit, followed by low FGF and a conventional circuit, and high FGF (15 +/- 1.4 vs 9 +/- 0.8 vs 5 +/- 0.4 mg H2O, P < 0.01) after two hours. Mean cilia length (micron) and TMFV (mm/min) fell during the first hour in all three groups. At hour two TMFV returned to baseline in Group III and was significantly greater than Groups I and II (0.8 +/- 0.4 vs 8.6 +/- 1.1 vs 15.4 +/- 2.1, P < 0.001). Mean ciliary length demonstrated a similar pattern with reductions from baseline in all three groups for the first two hours. Groups II and III had an increase in cilia length beginning at hour three and were both significantly greater than Group I at hours 3 through 6 (1.3 +/- 0.5 vs 3.2 +/- 1.1 vs 4.2 +/- 0.8, P < 0.001). Alterations in tracheobronchial structure and function result from exposure to dry gases and are amplified by the duration of exposure. Our findings suggest a minimum of 12 to 15 mg H2O/l is necessary to prevent these alterations. In this study, the combination of low FGF and a coaxial anaesthesia circuit reached this minimum threshold more quickly than a conventional two-limb circuit.
我们比较了在低新鲜气体流量（FGF）下循环系统输送的湿度与传统双管和同轴回路对犬气管支气管上皮结构和功能的影响。动物经麻醉后使用麻醉呼吸机进行机械通气以维持正常碳酸血症。第一组（对照组）动物接受的FGF等于所需的分钟通气量，模拟开放回路技术。第二组和第三组动物的FGF设置为所需分钟通气量的20%。第二组使用双管回路，第三组使用同轴回路。在基线时及之后每小时测量吸入气体的相对湿度和温度。在第一个实验中，在基线时通过支气管镜获取气管支气管树的活检样本，然后每小时获取一次，共持续6小时。对这些样本进行显微镜检查可计算平均纤毛长度。在第二个实验中，使用电影支气管纤维镜检查法在基线时及之后每小时测量气管黏液流速（TMFV）。两小时后，低FGF和同轴回路输送的绝对湿度最大，其次是低FGF和传统回路，高FGF时最低（15±1.4 vs 9±0.8 vs 5±0.4 mg H₂O，P<0.01）。在所有三组中，平均纤毛长度（微米）和TMFV（毫米/分钟）在第一小时内均下降。在第二小时，第三组的TMFV恢复到基线水平，且显著高于第一组和第二组（0.8±0.4 vs 8.6±1.1 vs 15.4±2.1，P<0.001）。平均纤毛长度呈现类似模式，在最初两小时内所有三组均较基线水平降低。第二组和第三组从第三小时开始纤毛长度增加，在第3至6小时均显著高于第一组（1.3±0.5 vs 3.2±1.1 vs 4.2±0.8，P<0.001）。气管支气管结构和功能的改变是由于暴露于干燥气体所致，且暴露时间越长影响越大。我们的研究结果表明，至少需要12至15 mg H₂O/l才能防止这些改变。在本研究中，低FGF与同轴麻醉回路的组合比传统双管回路更快达到这一最低阈值。
