Anaesthesia Research Group, Fisher and Paykel Healthcare Ltd, Auckland, New Zealand.
Robert White Centre for Airway Voice and Swallowing, Poole Hospital NHS Foundation Trust, Poole, UK.
Anaesthesia. 2019 Apr;74(4):441-449. doi: 10.1111/anae.14541. Epub 2019 Feb 15.
Clinical observations suggest that compared with standard apnoeic oxygenation, transnasal humidified rapid-insufflation ventilatory exchange using high-flow nasal oxygenation reduces the rate of carbon dioxide accumulation in patients who are anaesthetised and apnoeic. This suggests that active gas exchange takes place, but the mechanisms by which it may occur have not been described. We used three laboratory airway models to investigate mechanisms of carbon dioxide clearance in apnoeic patients. We determined flow patterns using particle image velocimetry in a two-dimensional model using particle-seeded fluorescent solution; visualised gas clearance in a three-dimensional printed trachea model in air; and measured intra-tracheal turbulence levels and carbon dioxide clearance rates using a three-dimensional printed model in air mounted on a lung simulator. Cardiogenic oscillations were simulated in all experiments. The visualisation experiments indicated that gaseous mixing was occurring in the trachea. With no cardiogenic oscillations applied, mean (SD) carbon dioxide clearance increased from 0.29 (0.04) ml.min to 1.34 (0.14) ml.min as the transnasal humidified rapid-insufflation ventilatory exchange flow rate was increased from 20 l.min to 70 l.min (p = 0.0001). With a cardiogenic oscillation of 20 ml.beat applied, carbon dioxide clearance increased from 11.9 (0.50) ml.min to 17.4 (1.2) ml.min as the transnasal humidified rapid-insufflation ventilatory exchange flow rate was increased from 20 l.min to 70 l.min (p = 0.0014). These findings suggest that enhanced carbon dioxide clearance observed under apnoeic conditions with transnasal humidified rapid-insufflation ventilatory exchange, as compared with classical apnoeic oxygenation, may be explained by an interaction between entrained and highly turbulent supraglottic flow vortices created by high-flow nasal oxygen and cardiogenic oscillations.
临床观察表明，与标准的窒息给氧相比，使用高流量鼻氧进行经鼻湿化快速充气通气交换可降低麻醉和窒息患者二氧化碳积聚的速度。这表明发生了主动气体交换，但尚未描述其发生的机制。我们使用三种实验室气道模型来研究窒息患者的二氧化碳清除机制。我们使用二维模型中的粒子图像测速法在种子荧光溶液中确定流型；在空气中的三维打印气管模型中可视化气体清除；并在空气中的三维打印模型上测量气道内湍流水平和二氧化碳清除率，该模型安装在肺模拟器上。在所有实验中都模拟了心源性振动。在没有心源性振动的情况下，当经鼻湿化快速充气通气交换流量从 20 l.min 增加到 70 l.min 时，平均（SD）二氧化碳清除率从 0.29（0.04）ml.min 增加到 1.34（0.14）ml.min（p=0.0001）。当应用 20 ml.beat 的心源性振动时，当经鼻湿化快速充气通气交换流量从 20 l.min 增加到 70 l.min 时，二氧化碳清除率从 11.9（0.50）ml.min 增加到 17.4（1.2）ml.min（p=0.0014）。这些发现表明，与经典的窒息给氧相比，在经鼻湿化快速充气通气交换的窒息条件下观察到的增强的二氧化碳清除可能是由高流量鼻氧和心源性振动产生的夹带和高湍流的会厌上气流涡旋之间的相互作用解释的。
