[Use of non-invasive positive pressure ventilation for cardiogenic pulmonary edema in emergency care units].

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.