Brochard L
Presse Med. 1998 Jun 20;27(22):1105-7.
The work reported by L'Her et al. in this issue of La Presse Médicale demonstrates the feasibility of applying simple intensive care techniques in situations frequently encountered in emergency care units. These authors used a face mask for continuous positive pressure ventilation in patients over 70 years of age admitted for respiratory distress related to cardiogenic pulmonary edema. In these elderly patients, the authors noted an improvement in blood gases, respiratory rate and heart rate and did not observe any secondary effect. Acute respiratory failure was cured in 90% of the cases without referral to the intensive care unit. The mechanism of action of continuous positive airway pressure, or spontaneous ventilation with positive expiratory pressure, is different from simple oxygen therapy. Two mechanisms are intimately related. The main effect is ventilatory assistance resulting from a "re-aeration" of the pulmonary parenchyma which increases compliance and reduces work required to overcome elastic retraction forces. Likewise the increased pulmonary volume reduces pulmonary resistance. Positive airway pressure also has an effect on left ventricular function. Indeed, after-load is reduced by the reduction in the large negative intrathoracic pressure swing. Lower energy expenditure required for respiration also greatly reduces total oxygen consumption and improved blood gases favor oxygen supply to the myocardium. The contraindications of continuous positive airway pressure are related to abnormal control of the upper airways and major hemodynamic disorders. Prudence is also required in case of shock due to the risk of major respiratory muscle fatigue. The question could also be raised as to the risk in elderly patients where cardiogenic pulmonary edema is often associated with a certain degree of chronic bronchitis. It is now known that these patients have an intrinsic positive expiratory pressure which considerably increases respiratory work. Symptomatic treatment in this type of disorder is mechanical and continuous positive airway pressure diminishes this work. Cardiogenic pulmonary edema in the elderly is thus an excellent indication for spontaneous ventilation with positive expiratory pressure. Improvement in these simple techniques, their widespread use and a better understanding of their limitations remain important challenges for the future.
L'Her等人在本期《法国医学报》上发表的研究表明，在急诊室常见的情况下应用简单的重症监护技术是可行的。这些作者对70岁以上因心源性肺水肿导致呼吸窘迫而入院的患者使用面罩进行持续气道正压通气。在这些老年患者中，作者注意到血气、呼吸频率和心率有所改善，且未观察到任何副作用。90%的病例中急性呼吸衰竭得到治愈，无需转入重症监护病房。持续气道正压通气或呼气末正压自主通气的作用机制不同于单纯的氧疗。两种机制密切相关。主要作用是通过肺实质的“再通气”提供通气辅助，这会增加肺顺应性并减少克服弹性回缩力所需的功。同样，肺容积增加会降低肺阻力。气道正压也对左心室功能有影响。实际上，胸内大的负压波动减小会降低后负荷。呼吸所需的较低能量消耗也大大降低了总氧耗，而改善的血气有利于心肌的氧供应。持续气道正压通气的禁忌症与上气道控制异常和严重的血流动力学紊乱有关。因存在严重呼吸肌疲劳风险，休克时也需谨慎使用。对于老年患者，心源性肺水肿常伴有一定程度的慢性支气管炎，其风险问题也可能被提出。现在已知这些患者存在内在的呼气末正压，这会显著增加呼吸功。在这类疾病中，对症治疗是机械性的，而持续气道正压通气可减少这种功。因此，老年人心源性肺水肿是呼气末正压自主通气的一个极佳适应症。改进这些简单技术、广泛应用它们并更好地理解其局限性，仍是未来的重要挑战。
