Gas Exchange during Controlled Ventilation in Children with Normal and Abnormal Pulmonary Circulation: A Study Using the Single Breath Test for Carbon Dioxide
Gas Exchange during Controlled Ventilation in Children with Normal and Abnormal Pulmonary Circulation: A Study Using the Single Breath Test for Carbon Dioxide
复制标题
肺循环正常和异常的儿童受控通气期间的气体交换：使用二氧化碳单次呼吸测试的研究
作者：
R. Fletcher;L. Niklason;B. Drefeldt
对42例开胸手术患儿在麻醉和控制性通气时进行二氧化碳单次呼吸试验（SBT-CO_2）。使用基于Servo呼吸机的计算机化系统进行测试。该系统对压缩体积、装置死腔和再呼吸进行在线校正。肺循环正常的儿童具有良好的气体交换，PaO 2值较高，平均肺泡死腔分数（VDalv/VTalv）为0.10，SBT-CO 2的III相平缓倾斜。由于房间隔缺损或室间隔缺损导致肺过度灌注（左向右分流）的儿童PaO 2值显著较低，III相斜率较陡，VDalv/VTalv值的速度较大。肺动脉狭窄合并心内右向左分流导致肺灌注不足的儿童PaO 2值极低，VDalv/VTalv的“成人”值也极低。他们需要增加通气以维持CO2稳态。在合并的材料中，气道死腔与身高、体重和年龄密切相关。当潮气量增加37%，呼吸频率同时减少30%时，气道死腔不受影响，这是一种使肺泡通气量保持不变的方法。这可能是因为使用了吸气末暂停;当频率降低时，吸气末暂停的长度增加，允许肺泡/新鲜气体界面的近端扩散。
Carbon dioxide single breath tests (SBT-CO2) were obtained during anesthesia and controlled ventilation in 42 children about to undergo thoracic surgery. The tests were obtained with a computerized system based on the Servo ventilator. The system made on-line corrections for compressed volume, apparatus deadspace, and rebreathing. Children with normal pulmonary circulation had excellent gas exchange with high PaO2 values, a mean alveolar deadspace fraction (VDalv/VTalv) of 0.10, and a gently sloping phase III of SBT-CO2 Children with pulmonary hyperperfusion (left to right shunting) due to an atrial septal defect or a ventrical septal defect had significantly lower PaO2 values, steeper phase III slopes, and a greater spead of values for VDalvlVTalv. Children with pulmonary hypoperfusion due to pulmonary stenosis in combination with intracardiac right to left shunting had extremely low PaO2 values, and “adult” values for VDalv/VTalv. They required increased ventilation to maintain CO2 homeostasis. In the pooled material, the airway deadspace was strongly correlated to height, weight, and age. The airway deadspace was unaffected when tidal volume was increased by 37%, and ventilatory frequency simultaneously reduced by 30%, a maneuver that left alveolar ventilation unchanged. This is probably because an end-inspiratory pause was used; when frequency is reduced the length of the end-inspiratory pause increases, allowing proximal diffusion of the alveolar/fresh gas interface.