A study of noninvasive positive-pressure mechanical ventilation in the treatment of acute lung injury with a complex critical care ventilator. Is it the best choice?

Dear Sir,

I have read with attention the article by Zhang et al. ¹ in which the authors attempt to demonstrate that the use of noninvasive positive-pressure mechanical ventilation in acute lung injury, using a ventilator designed for critical care, produces better results than the use of a mini-ventilator.

The authors presented a hybrid study consisting of a prospective part and a retrospective part. In the prospective part of the study, patients were divided into three groups. Participants in the first group were treated with a mini-ventilator (BREAS iSleep 22 BIPAP, Breas Medical AB, Mölnlycke, Sweden), in the second group were ventilated with a large critical care ventilator (Galileo Gold, Hamilton Medical AG, Bonaduz, Switzerland) in spontaneous mode (pressure support ventilation plus positive end expiratory pressure), and in the third group were ventilated with the same critical care ventilator in DuoPAP mode (bilevel positive airway pressure plus pressure support ventilation). A total of 17 patients were analysed in each group.

However, there are some weaknesses in the study. The mean respiratory rate, arterial carbon dioxide partial pressure and acute lung injury score were different in the three groups being compared. In addition, a sophisticated critical care ventilator was compared with a mini-ventilator, which has fewer functions for the ventilation of patients with lung injury and acute respiratory distress syndrome.

Modern noninvasive mechanical ventilation systems have automatic compensation for leakage and have yielded varying results in different degrees of severity of acute respiratory distress syndrome.^2,3 In contrast, double-circuit critical care ventilators (such as the one in this study) have a limited capacity to compensate for leaks.^4–6 However, the authors do not provide data on the highest levels of pressures used, nor the percentage of leaks. ⁷

In the retrospective part of this study, the authors compared nine patients in the third group (Galileo Gold ventilator with DuoPAP and pressure support ventilation) using a facial mask with nine patients receiving mechanical ventilation using the same ventilator but with endotracheal intubation. The authors do not provide information concerning the matching of the two sets of patients nor any data on power calculations or sample size estimation. ⁸

We believe that these issues should be taken into account when analysing this study. The correct choice of ventilator is crucial for the success of the technique; inadequate equipment may lead to poor tolerance and excessive leakage and increases the chances of failure.^9–11