Gay P C, Rodarte J R, Hubmayr R D
Division of Thoracic Diseases and Internal Medicine, Mayo Clinic, Rochester, MN 55905.
Am Rev Respir Dis. 1989 Mar;139(3):621-6. doi: 10.1164/ajrccm/139.3.621.
The use of continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) has been advocated by some to assist in the weaning process of patients receiving mechanical ventilation for respiratory failure. The efficacy of this technique and its effect on respiratory system mechanics are not well understood. The theoretical advantage of CPAP or PEEP during the weaning process can be obliterated if excessive dynamic hyperinflation is induced. A key determinant of the individual response to this proposed weaning technique is the recognition of the presence or absence of expiratory flow limitation. We studied the effect of progressively increased levels of applied PEEP on isovolume expiratory flow and end-expiratory lung volume in seven patients during controlled mechanical ventilation. In the absence of expiratory flow limitation, passive expiratory flow decreased and end-expiratory lung volume increased when any level of PEEP was applied. In contrast, flow-limited patients did not demonstrate a change in isovolume expiratory flow or end-expiratory lung volume until the applied PEEP reduced the driving pressure for expiratory flow below a critical value. All patients demonstrated dynamic hyperinflation during controlled ventilation as evident by the existence of intrinsic PEEP. The nominal value of applied PEEP that caused a reduction in isovolume expiratory flow was unrelated to the initial level of intrinsic PEEP. The clinical implications of these findings with respect to CPAP therapy during weaning from mechanical ventilation are discussed.
一些人主张使用持续气道正压通气（CPAP）或呼气末正压通气（PEEP）来辅助呼吸衰竭接受机械通气患者的撤机过程。该技术的疗效及其对呼吸系统力学的影响尚未完全明了。如果诱发过度动态肺过度充气，CPAP或PEEP在撤机过程中的理论优势可能会消失。个体对这种撤机技术反应的一个关键决定因素是识别是否存在呼气气流受限。我们研究了在控制机械通气期间，逐步增加PEEP水平对7例患者等容呼气流量和呼气末肺容积的影响。在不存在呼气气流受限时, 施加任何水平的PEEP时，被动呼气流量降低，呼气末肺容积增加。相反，气流受限患者直到施加的PEEP将呼气驱动压力降低到临界值以下时，等容呼气流量或呼气末肺容积才会出现变化。所有患者在控制通气期间均表现出动态肺过度充气，内源性PEEP的存在证明了这一点。导致等容呼气流量降低的施加PEEP标称值与初始内源性PEEP水平无关。讨论了这些发现对于机械通气撤机期间CPAP治疗的临床意义。
