Richter Torsten, Bellani Giacomo, Scott Harris R, Vidal Melo Marcos F, Winkler Tilo, Venegas Jose G, Musch Guido
Department of Anesthesia and Critical Care, CLN 309, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA.
Am J Respir Crit Care Med. 2005 Aug 15;172(4):480-7. doi: 10.1164/rccm.200501-004OC. Epub 2005 May 18.
The prone position is used to improve gas exchange in patients with acute respiratory distress syndrome. However, the regional mechanism by which the prone position improves gas exchange in acutely injured lungs is still incompletely defined.
We used positron emission tomography imaging of [(13)N]nitrogen to assess the regional distribution of pulmonary shunt, aeration, perfusion, and ventilation in seven surfactant-depleted sheep in supine and prone positions.
In the supine position, the dorsal lung regions had a high shunt fraction, high perfusion, and poor aeration. The prone position was associated with an increase in lung gas content and with a more uniform distribution of aeration, as the increase in aeration in dorsal lung regions was not offset by loss of aeration in ventral regions. Consequently, the shunt fraction decreased in dorsal regions in the prone position without a concomitant impairment of gas exchange in ventral regions, thus leading to a significant increase in the fraction of pulmonary perfusion participating in gas exchange. In addition, the vertical distribution of specific alveolar ventilation became more uniform in the prone position. A biphasic relation between regional shunt fraction and gas fraction showed low shunt for values of gas fraction higher than a threshold, and a steep linear increase in shunt for lower values of gas fraction.
In a surfactant-deficient model of lung injury, the prone position improved gas exchange by restoring aeration and decreasing shunt while preserving perfusion in dorsal lung regions, and by making the distribution of ventilation more uniform.
俯卧位用于改善急性呼吸窘迫综合征患者的气体交换。然而，俯卧位改善急性损伤肺脏气体交换的局部机制仍未完全明确。
我们使用[（13）N]氮正电子发射断层扫描成像来评估7只表面活性剂缺乏的绵羊在仰卧位和俯卧位时肺分流、通气、灌注和通气的区域分布。
在仰卧位时，肺背侧区域分流分数高、灌注高但通气差。俯卧位与肺气体含量增加以及通气分布更均匀相关，因为肺背侧区域通气增加并未被腹侧区域通气丧失所抵消。因此，俯卧位时背侧区域的分流分数降低，而腹侧区域的气体交换并未随之受损，从而导致参与气体交换的肺灌注分数显著增加。此外，特定肺泡通气的垂直分布在俯卧位时变得更加均匀。区域分流分数与气体分数之间呈双相关系，即气体分数高于阈值时分流较低，而气体分数较低时分流呈陡峭线性增加。
在表面活性剂缺乏的肺损伤模型中，俯卧位通过恢复通气、减少分流同时保留肺背侧区域的灌注以及使通气分布更均匀来改善气体交换。
