Noninvasive ventilation strategy for weaning from mechanical ventilation for underlying COPD: How to get to be great being little?

Sir,

We read with interest the article by Mishra et al.[1] on using noninvasive ventilation (NIV) to wean patients from mechanical ventilation (MV) and congratulate the authors on their study. There have been conflicting results reported in the literature in recent years, with regard to the use of NIV in weaning patients from MV.[23] We feel that this study provides important information in this area.

The authors have reported improved outcomes in patients failing a conventional spontaneous breathing trial (SBT), who were subsequently extubated and put on NIV compared to those who were continued on MV and weaned via the reducing pressure support.[1] All patients recruited had severe COPD, as evidenced by the poor Forced Expiratory Volume (FEV1) ratios, and the study group received NIV for long periods, at high pressures, following extubation from MV.

There are, however, some limitations to the study that need some considerations. First, the study contained a very small numbers of patients and had a high attrition rate from the initial screening of patients for inclusion. This seems to be largely due to the strict inclusion criteria, where patients with several significant related comorbidities or coexisting hypoxia were excluded from the study. This effectively created a very select subgroup of patients for inclusion, and thus, only a very select group of patients in everyday clinical practice, to whom the results of this study may be applied. Second, the study group also included a high proportion of patients, who had been intubated without a preceding trial of NIV, and therefore, may have included some patients in whom MV could possibly have been avoided altogether.

Third, the authors report improved outcomes in the NIV group in terms of length of Intensive Care Unit (ICU) stay, time spent on MV, and rates of ventilator-associated pneumonia, but do not provide any information on long-term measures, such as hospital or one-year survival. Therefore, we do not know if the early positive effects of using NIV to wean patients are sustained beyond patient discharge from the ICU.

Finally, it is notable that the NIV group had significantly lower rates of ventilator-associated pneumonia (VAP) than the controls, who were weaned using invasive PS weaning. It is possible that the benefits demonstrated by the authors are a reflection of the impact of reducing the incidence of VAP rather than benefits of NIV per se. It has been suggested from previous studies that the mortality benefits of using NIV in immunocompromised patients are mainly due to a reduction of the risks of developing VAP,[4] and perhaps we are just seeing another example of this effect in patients with COPD. The high mortality rate seen in the control group may also be a reflection of the incidence and impact of VAP in ventilated COPD patients.

The current study reflects the findings from a recent large meta-analysis of 16 studies, in which NIV was used to wean patients from MV,[5] which demonstrated a mortality benefit and reduction in rates of VAP with NIV use. This effect was pronounced in a subgroup analysis of patients with COPD compared to groups with respiratory failure of mixed etiology. Although a recent large randomized controlled trial of patients, predominantly, but not exclusively with COPD, did not demonstrate any benefit from weaning with NIV over MV,[3] it is evident that NIV has an important role to play in weaning patients from MV, especially those with underlying COPD. We feel that the current study provides further evidence that NIV weaning must be strongly considered in all COPD patients ready to start the weaning process, but who are not suitable for immediate extubation.