Partial support for patients with respiratory failure can be provided with invasive mechanical ventilation or non-invasive mechanical ventilation. The role of non-invasive positive pressure ventilation (NPPV) in preventing intubation for various conditions has been well studied. Less well studied is the role for NPPV in the weaning and peri-extubation period.
by Dr Brooks A. Fallis and Dr Karen E. A. Burns
Mechanical ventilation is essential for supporting patients through episodes of respiratory failure by unloading respiratory muscles and improving gas exchange. While potentially lifesaving, invasive mechanical ventilation with an endotracheal tube or tracheostomy can be associated with important harm, in part due to complications such as ventilator associated pneumonia (VAP). VAP has been shown to increase morbidity and trends towards increasing mortality [1].
Critical care physicians strive to extubate patients as early as possible, while minimising the risk of re-intubation, which has been shown to be independently associated with increased risk of developing VAP [2]. Spontaneous breathing trials (SBT) are used to decide if a patient has been weaned. An SBT involves a focused assessment of a patient’s ability to breathe on his/her own. If a patient does not demonstrate signs of respiratory failure, fatigue or instability during an SBT, the patient can be evaluated for extubation or liberation from the ventilator.
NPPV can provide partial respiratory support by connecting patients to a ventilator using an interface or mask and obviates the need for an invasive airway. Consequently, NPPV is associated with a reduction in VAP compared to invasive ventilation [3].
Through NPPV, clinicians can administer oxygen to support gas exchange, augment inspired volume, off-load strained respiratory muscles and apply pressure to keep air sacs from collapsing during expiration. With NPPV patients are able to cough and speak, and NPPV can be temporarily removed for eating or to allow periods of spontaneous breathing.
Role of non-invasive ventilation
There is strong evidence to support the use of NPPV as an initial treatment for acute respiratory failure due to acute exacerbations of chronic obstructive pulmonary disease (COPD) and for cardiogenic pulmonary edema in appropriately selected patients [4,5]. However, for patients who have been intubated and placed on invasive mechanical ventilation, the role of NPPV in the weaning and peri-extubation period has not been as well studied.
There are three situations where NPPV might be considered in the peri-extubation period. First, NPPV can be used for weaning, that is by allowing earlier extubation of a patient who is on low ventilator settings, but would otherwise not yet be ready to be liberated from the ventilator, and replacing invasive mechanical support with non-invasive mechanical support. Second, clinicians can apply NPPV prophylactically in patients who are deemed ready for extubation, but who are at high risk of failure to reduce the risk of developing recurrent respiratory failure. Third, NPPV can be used as an alternative to direct re-intubation in a patient who has been extubated, but develops recurrent respiratory failure.
In COPD patients, individual trials of early liberation from mechanical ventilation and immediate application of NPPV for weaning demonstrated reduced rates of VAP, mortality and tracheostomy [6,7,8]. A meta-analysis of 12 small trials, including predominantly patients with COPD, found that compared to invasive weaning, non-invasive weaning had beneficial effects on mortality, VAP and other clinically important outcomes [9].
This meta-analysis also suggested in subgroup analysis that the benefits regarding mortality and weaning failures were not significantly greater in trials enrolling exclusively COPD patients versus mixed populations. Although trials have been conducted in mixed populations, the evidence in non-COPD patients is less clear, and non-invasive weaning should be used with caution in this population [9, 10].
Trials of prophylactic application of NPPV, after elective extubation, have suggested some benefits in high risk patients, especially those who develop hypercapnea during an SBT [11, 12]. The evidence, however, is less clear for high risk patients who do not develop hypercapnea during SBT [11].
The role of NPPV in post-extubation respiratory failure is controversial. Two trials specifically addressing this question were both negative, with one trial demonstrating increased mortality in the NPPV group [13, 14]. However, other trials examining prophylactic NPPV application in high risk patients have used NPPV as a rescue therapy in their control arms, and showed no adverse effect in subgroup analysis [11, 12]. These trials had a significant number of patients with underlying COPD. The role of NPPV in patients with COPD who develop
post-extubation respiratory failure remains to be determined.
Conclusion
NPPV is an important tool in the armamentarium of critical care clinicians. It can be used not only to prevent intubation, but also as a tool in the weaning and peri-extubation period. However, patients must be carefully selected as not all patients are appropriate candidates. In the peri-extubation period, the strongest evidence supports the use of non-invasive weaning in COPD patients and for prophylactic NPPV application in high risk patients, who develop hypercapnea during an SBT. Additional trials are needed to determine the net clinical benefits associated with the use of NPPV in the weaning and peri-extubation period, especially with regard to its role in COPD patients who develop post-extubation respiratory failure.
References
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The authors
Brooks A. Fallis MD, MSc and
Karen E. A. Burns MD, FRCPC, MSc*
University of Toronto, Ontario, Canada
*Corresponding author:
Karen E. A. Burns MD
St Michael’s Hospital
30 Bond Street, 4-045 Queen Wing,
Toronto, Ontario Canada M5B 1 W8
E-mail: burnsk@smh.ca
