Hedenstierna G, Santesson J, Bindslev L, Baehrendtz S, Klingstedt C, Norlander O
Acta Anaesthesiol Scand. 1982 Oct;26(5):429-34. doi: 10.1111/j.1399-6576.1982.tb01794.x.
Anaesthesia and most frequently acute respiratory failure are accompanied by a lowered functional residual capacity (FRC). This lowering promotes airway closure in dependent lung units and forces ventilation to non-dependent regions. Perfusion, on the other hand, is forced towards dependent lung units. A ventilation-perfusion mismatch is created and hypoxaemia may develop. General PEEP counters airway closure, but impedes cardiac output and forces perfusion further to dependent regions. In addition, barotrauma may occur. Improved matching of ventilation and perfusion can be achieved by: (1) positioning the subject in the lateral posture; (2) ventilating each lung separately in proportion to its perfusion (differential ventilation); and (3) applying PEEP only to the dependent lung (selective PEEP). Because of less overall intrathoracic pressure and lung expansion, interference with the total lung blood flow and the danger of barotrauma should be less than with general PEEP. Improved gas exchange with a 50-100% increase in PaO2 has been observed in a limited number of patients with acute bilateral lung disease studied so far during differential ventilation and selective PEEP.
麻醉以及最常见的急性呼吸衰竭常伴有功能残气量（FRC）降低。这种降低促使肺低垂部位的气道关闭，并迫使通气转向非低垂区域。另一方面，灌注则被迫流向肺低垂部位。从而造成通气-灌注不匹配，可能会出现低氧血症。常规呼气末正压通气（PEEP）可对抗气道关闭，但会阻碍心输出量，并迫使灌注进一步流向低垂区域。此外，还可能发生气压伤。通过以下方法可改善通气与灌注的匹配：（1）使患者处于侧卧位；（2）根据每个肺的灌注情况分别进行通气（差异通气）；（3）仅对低垂肺应用PEEP（选择性PEEP）。由于胸腔内总压力和肺扩张程度较小，与常规PEEP相比，对全肺血流的干扰以及气压伤的风险应该更小。在目前已研究的少数急性双侧肺部疾病患者中，在差异通气和选择性PEEP期间观察到，动脉血氧分压（PaO2）提高了50% - 100%，气体交换得到改善。
