Automated ventilator technology: More answers and some questions

To the Editors: We have read with interest the recently published editorial by Joosten et al. in Respirology, concerning the trial published by Patout et al. which compared an automated mode (AVAPS-AE) with a standard non-invasive ventilation (NIV) mode. We agree with the authors concerning the modest interest of those automated modes and on the lack of evidence for their use as first intention treatment in patients needing NIV. However, some issues deserve discussion. First, Joosten et al. underline that ‘patients suffering from obesity hypoventilation and sleep apnoea may be treated with CPAP as with NIV’. In fact, recent publications raising this question suggested that both treatments are equally effective only in mildly hypercapnic patients. In Howard et al.’s study, both treatments were equivalent only in patients with PaCO2 < 6.6 kPa. Moreover, in those trials, pressure support (PS) levels used were lower than recommended. Hence, most researchers suggest to reserve CPAP only for patients with mild hypercapnia. In the Patout et al.’s trial, mean PaCO2 was 6.94 0.71 kPa and PS levels applied were higher suggesting that CPAP would have been insufficient. A second issue concerns NIV initiation. Patout et al. introduced NIV in the hospital with a mean stay of 4 days. Joosten et al. consider that ‘it is beyond the scope of normal clinical practice’. Some studies suggested a relationship between modality of NIV initiation and acceptance to treatment. Hence, 4–7 days of in-hospital NIV initiation seem to offer the best compromise. A survey interrogating expert centres showed that NIV initiation is performed in hospital by 79% of respondents with a mean stay of 6 3 days. NIV setting at home need implementing an educational programme, an appropriated logistical and an available trained staff. This might not be possible in most centres providing NIV. Even if some recent trials showed no difference between an in-hospital and home-based NIV, such trials were performed by centres having a large experience and included only stable well-selected patients. The French guidelines established that NIV initiation is only feasible at home under strict conditions in an appropriate framework. The process should be conducted by a competent physician by using a strict monitoring protocol. Patients must preferably live near an expert centre with 24 h availability. Then, apart from clinical trials and except for some specific wellestablished programmes, such complexity is not currently available in clinical practice. Finally, NIV adjustments in the study by Patout et al. were performed by including data obtained from the ventilator built-in software. Joosten et al. stress that such technology and ‘its clinical usefulness in place of polysomnography remain to be established’. However, the accuracy and the clinical interest of some of these built-in monitoring systems has been well studied. A step-by-step adjustment of NIV settings was recommended by clinical experts based on data extracted from built-in software. The systematic use of PSG-based NIV titration, as suggested by Joosten et al., has not proven to improve the outcome and is difficult to achieve in real life. In France, this method is beyond the scope of normal clinical practice. In summary, the trial by Patout et al. not only provides strong evidence in support of the potential interest of these novel ventilator modes, but also highlights the fact that the methodological issues of this study reflect the real-life scenario in most European centres. This further enhances the clinical impact of their results.