Cardiogenic Pulmonary Edema: A Multicenter Randomized Trial

Studies employing noninvasive pressure support ventilation in cardiogenic pulmonary edema have been performed in the intensive care unit when overt respiratory failure is already present and in small groups of patients. In this multicenter study, performed in emergency departments, 130 patients with acute respiratory failure were randomized to receive medical therapy plus O2 (65 patients) or noninvasive pressure support ventilation (65 patients). The primary end point was the need for intubation; secondary end points were in-hospital mortality and changes in some physiological variables. Noninvasive pressure support ventilation improved Pa^sub O^sub 2^^/FI^sub O^sub 2^^, respiratory rate, and dyspnea significantly faster. Intubation rate, hospital mortality, and duration of hospital stay were similar in the two groups. In the subgroup of hypercapnic patients noninvasive pressure support ventilation improved Pa^sub CO^sub 2^^ significantly faster and reduced the intubation rate compared with medical therapy (2 of 33 versus 9 of 31; p = 0.015). Adverse events, including myocardial infarction, were evenly distributed in the two groups. We conclude that during acute respiratory failure due to cardiogenic pulmonary edema the early use of noninvasive pressure support ventilation accelerates the improvement in Pa^sub O^sub 2^^/FI^sub O^sub 2^^, Pa^sub CO^sub 2^^, dyspnea, and respiratory rate, but does not affect the overall clinical outcome. Noninvasive pressure support ventilation does, however, reduce the intubation rate in the subgroup of hypercapnic patients.

The rationale for using continuous positive airway pressure (CPAP) in acute pulmonary edema is based on the fact that it may limit the decrease in functional residual capacity, improve respiratory mechanics and oxygenation, and decrease left ventricular afterload (1, 2). The best therapy for treating an episode of acute respiratory failure due to cardiogenic pulmonary edema is, however, controversial. A systematic review on the effect of CPAP on mortality and need for intubation of patients with cardiogenic pulmonary edema (3) concluded that experimental evidence exists to support its use in these patients, although the potential for harm has not been excluded; the widespread use of this ventilatory technique is, however, still not recommended by major clinical guidelines (4-6). Indeed, all randomized controlled trials using CPAP (3) excluded a priori the patients with preexisting hypercapnic chronic obstructive pulmonary disease (COPD), whereas one study included patients with a Pa^sub CO^sub 2^^ greater than 45 mm Hg, but without chronic airflow obstruction (7).

A physiologic study demonstrated that noninvasive pressure support ventilation (NPSV) was more effective at unloading the respiratory muscles than CPAP alone in patients with acute cardiogenic pulmonary edema (8).

In patients affected by COPD and hypercapnia and recovering from an acute exacerbation of their disease, the addition of an inspiratory aid (NPSV) to CPAP has been shown to further reduce inspiratory muscle effort (9), so that the application of NPSV may be particularly useful in patients with cardiogenic pulmonary edema and signs of pump failure (i.e., hypercapnia).

In one uncontrolled study using NPSV it was noted that patients who responded to NPSV had a higher baseline carbon dioxide pressure than those who did not respond, suggesting that this strategy is of potential benefit only in patients affected by chronic pulmonary diseases or by disorders in which respiratory muscles are likely to be fatigued (10). In a similar population not balanced for subgroups according to the value of Pa^sub CO^sub 2^^, Masip and coworkers (11) reported that NPSV was superior to conventional oxygen therapy in reducing the intubation rate and more rapidly improving oxygenation. As a matter of fact, four of six patients (66%) requiring intubation in the conventional therapy group were hypercapnic, whereas no hypercapnic patients in the NPSV-treated group required intubation. Unfortunately, the small sample size did not allow a subgroup analysis of the impact of the different degrees of hypercapnia (Pa^sub CO^sub 2^^ greater than or less than 45 mm Hg) on the main outcomes. Indeed, most of the previous investigations, employing either CPAP or NPSV (7, 12-14), were performed in single, specialized centers (usually in an intensive care unit [ICU]), whereas first-line interventions are often carried out in emergency departments (15). The use of noninvasive ventilation directly in this environment could theoretically allow earlier use of this ventilatory technique and at the same time widen its use, because a consistent portion of patients are already intubated when they are admitted to the ICU. We designed a large, multicenter, randomized, prospective study in the setting of emergency rooms, comparing NPSV with conventional oxygen therapy in the treatment of acute cardiogenic pulmonary edema. The aim was to assess the feasibility of NPSV outside the ICU and to detect any differences in mortality, intubation rate, and some physiological variables such as dyspnea and respiratory rate. We also analyzed separately the subgroups of patients with and without hypercapnia, because this latter group is more likely to receive a greater benefit from the application of NPSV

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