Brandolese R, Broseghini C, Polese G, Bernasconi M, Brandi G, Milic-Emili J, Rossi A
Dept of Anesthesia and Intensive Care, Padova General Hospital, Italy.
Eur Respir J. 1993 Mar;6(3):358-63.
The aim of the study was to assess the impact of the intrinsic positive end-expiratory pressure (PEEPi) on pulmonary gas exchange in mechanically-ventilated patients, by comparing the effects of similar levels (0.8-0.9 kPa) of positive end-expiratory pressure (PEEP) and PEEPi. Ten patients with acute respiratory failure, without chronic airway disease, were studied with three ventilatory modes: 1) intermittent positive pressure ventilation with zero end-expiratory pressure (ZEEP mode); 2) continuous positive pressure ventilation with PEEP set by the ventilator (PEEP mode); and 3) intrinsic PEEP elicited by adequate shortening of the expiratory time (PEEPi mode). Cardiorespiratory variables (e.g. respiratory compliance and resistance, arterial and mixed venous blood gases, cardiac output, pulmonary capillary pressure, oxygen delivery) were measured during each ventilatory mode. Compared to ZEEP, both PEEP and PEEPi decreased cardiac output while increasing arterial oxygen tension (PaO2). However, the improvement of PaO2 was more consistent (8 out of 10 patients), and larger (+2.1 kPa, on average, p < 0.05) with PEEP than with PEEPi (5 out of 10 patients, and +1.4 kPa, on average, NS). Since the effects of PEEP and PEEPi on ventilation, lung volume, compliance, cardiac output (QT), mixed venous oxygen tension (PvO2) and oxygen consumption (VO2) were similar, we attributed the less favourable impact of PEEPi on PaO2 to a less homogeneous distribution of PEEPi between lung units with different time constant, and hence to a more uneven distribution of the inspired gas.
本研究的目的是通过比较相似水平（0.8 - 0.9 kPa）的呼气末正压（PEEP）和内源性呼气末正压（PEEPi）的作用，评估内源性呼气末正压对机械通气患者肺气体交换的影响。对10例无慢性气道疾病的急性呼吸衰竭患者采用三种通气模式进行研究：1）呼气末压力为零的间歇正压通气（ZEEP模式）；2）呼吸机设置PEEP的持续正压通气（PEEP模式）；3）通过适当缩短呼气时间诱发内源性PEEP（PEEPi模式）。在每种通气模式下测量心肺变量（如呼吸顺应性和阻力、动脉血和混合静脉血气、心输出量、肺毛细血管压力、氧输送）。与ZEEP相比，PEEP和PEEPi均降低心输出量，同时增加动脉血氧张力（PaO2）。然而，PEEP使PaO2的改善更一致（10例患者中有8例）且幅度更大（平均增加2.1 kPa，p < 0.05），而PEEPi使PaO2改善的患者较少（10例患者中有5例）且幅度较小（平均增加1.4 kPa，无统计学意义）。由于PEEP和PEEPi对通气、肺容积、顺应性、心输出量（QT）、混合静脉血氧张力（PvO2）和氧消耗（VO2）的影响相似，我们将PEEPi对PaO2的不利影响归因于不同时间常数肺单位之间PEEPi分布不均匀，从而导致吸入气体分布更不均匀。
