ABSTRACT & COMMENTARY
Weaning with Noninvasive Ventilation in COPD
By Richard H. Kallet, MS, RRT, FAARC, FCCM
Director of Quality Assurance, Respiratory Care Services, San Francisco General Hospital
Mr. Kallet reports no financial relationships relevant to this field of study.
SYNOPSIS: Managing COPD with noninvasive ventilation following early extubation resulted in significant improvements in several patient-centered outcomes compared to current weaning practices.
Burns KEA, et al. Noninvasive ventilation as a weaning strategy for mechanical ventilation in adults with respiratory failure: A Cochrane systematic review. CMAJ 2014;186:E112-E122.
This updated systematic review analyzed 16 randomized and quasi-randomized studies examining the efficacy of aggressive extubation and management with noninvasive ventilation (NIV) in patients who had failed at least one spontaneous breathing trial (SBT). By combing the studies in the meta-analysis there were 994 patients, the majority of whom had respiratory failure from an acute exacerbation of chronic obstructive pulmonary disease (COPD). Overall quality of the included studies was moderate to good. NIV was accomplished with a variety of interfaces (e.g., nasal mask, face mask, helmet) and modes (such as pressure support [PS], bi-level, or proportional-assist ventilation). In the control arm of the studies, patients tended to be managed with PS, sometimes in conjunction with intermittent mandatory ventilation.
Among the 994 patients, the relative risk (RR) for mortality was significantly reduced in the NIV cohort (RR, 0.53; 95% confidence interval [CI], 0.36-0.80). However, the results were statistically significant only in those studies focused either exclusively on COPD (RR, 0.36; 95%CI, 0.24-0.56) or in which at least 50% of the patients had COPD (RR, 0.47; 95%CI, 0.29-0.76). NIV also significantly reduced both weaning failure (RR, 0.63; 95%CI, 0.42-0.95) and ventilator-associated pneumonia (RR, 0.25; 95%CI, 0.15-0.43). All of the above results were associated with moderate levels of heterogeneity.
Other results were associated with either variable or considerable heterogeneity. The former included significantly lower rates of extubation failure (RR, 0.65; 95%CI, 0.44-0.97) and tracheostomy (RR, 0.27; 95%CI, 0.16-0.45) in the NIV cohort. The latter included reduced median duration (MD) of invasive mechanical ventilation (MV) (MD, -7.4; 95%CI, -10.3 to -4.6 days) and length-of-stay both in the ICU (MD, -5.6; 95%CI, -7.9 to -3.3 days) and hospital (MD, -6.0; 95%CI, -9.2 to -2.9 days) favoring NIV.
COMMENTARY
This updated systematic review reinforces the impression that patients with COPD receiving MV can be successfully managed without an endotracheal tube once they meet standard weaning readiness criteria. This is an important finding, as these patients have traditionally been viewed as difficult to wean. In consequence, there has been justifiable skepticism whether early, aggressive extubation and reliance on NIV is a prudent approach. Concerns about NIV center on three issues: limited practical driving airway pressure (e.g., < 20 cm H2O) to overcome altered chest impedance, adequate circuit wash-out of carbon dioxide, and finding an effective mask-interface that promotes patient comfort while minimizing circuit leaks and ineffective triggering.
As encouraging as these findings are, problems associated with both clinical and methodological variability among the studies may inhibit clinicians from fully embracing this bold approach to weaning. For example, there was variability among the clinical trials in how patients were assessed for weaning readiness, as well as the implementation and consistent use of weaning protocols. Also, in only one trial was a sedation protocol used. Furthermore, findings regarding the duration of total MV, invasive MV, and weaning were based on subgroup analyses representing 39%, 72%, and 65% of the total number of enrolled patients, respectively.
There are several potential reasons why only patients with COPD exacerbation might benefit from early extubation to NIV. First, these patients typically have reduced respiratory muscle strength due to altered length-tension relationship, malnutrition, and loss of muscle mass, and therefore are more susceptible to acute fatigue. Full recovery from acute fatigue may require up to 48 hours.1 This may be enough time for other therapies (such as corticosteroids, antibiotics, bronchodilators, and pulmonary hygiene) to reverse inflammation, mobilize secretions, and improve chest mechanics. We have observed that COPD patients requiring invasive MV meet weaning-readiness criteria quickly (mean of 2.3 days) and can pass a 2-hour SBT without difficulty (mean of 1.3 days). Moreover, the minute ventilation requirement of these patients to maintain an acceptable pH of 7.30 is modest (6-7 L/min).1
The endotracheal tube is the primary source of resistance during invasive MV and requires 5-8 cm H2O of PS to overcome. When minute ventilation (a primary determinant of both respiratory muscle power and output) is relatively low, it is reasonable to extubate COPD patients who fail an initial SBT. By using a similar level of PS noninvasively to counter the intrinsic muscle loads (from altered chest mechanics) rather than the imposed load from the artificial airway, patients may receive adequate support to sustain spontaneous breathing. These conditions are often absent in other causes of respiratory failure (e.g., acute respiratory distress syndrome), while minute ventilation demand is higher and chest compliance is both lower and improves more slowly in such conditions.
REFERENCE
- Kallet RH. Patient-ventilator interaction during acute lung injury and the role of spontaneous breathing. Part 1. Respiratory muscle function during critical illness. Respir Care 2011;56:181-189.
