Best practices for noninvasive ventilation

Failure of noninvasive ventilation

Patients in whom noninvasive ventilation fails tend to have worse outcomes, probably because of delayed definitive care. Therefore, continuous positive airway pressure by mask is not recommended for patients who have acute lung injury. The association with serious adverse events such as cardiac arrest, which appears to reflect delayed endotracheal intubation, is not balanced by a reduction in mortality or rate of endotracheal intubation. Similarly, in a multi-centre observational study, Demoule and coauthors reported an association between failure of noninvasive ventilation, defined as subsequent endotracheal intubation or death before intubation, with an increased length of stay among patients with a severe exacerbation of COPD or acute pulmonary edema, and an increase in the rate of death from other causes of acute respiratory failure.4

Failure of noninvasive ventilation needs to be detected early, followed by rapid access to safe endotracheal intubation or palliation. In patients with exacerbation of COPD, failure of noninvasive ventilation is associated with failure to improve hypercapnic acidosis or respiratory rate in the first few hours of treatment, high acuity of illness and lack of patient cooperation.5 However, using metaregression analysis, Peter and Moran found that the log odds ratio of intubation is inversely related to the severity of hypercapnic acidosis.6 In other words, within the limited range of severity studied, patients with more severe hypercapnic acidosis are more likely to benefit from noninvasive positive-pressure ventilation, but the ventilation is also more likely to fail. Therefore, the use of noninvasive positive-pressure ventilation is recommended for patients who have a severe exacerbation of COPD and an arterial pH of less than 7.35. It is not helpful for those with an arterial pH of 7.35 or higher because of the lack of evidence of benefit.

Early detection of failed noninvasive ventilation requires careful monitoring of the patient’s vital signs and blood gas levels. Rapid access to conventional mechanical ventilation will depend on the local health care setting and where the noninvasive ventilation is being administered. In a multicentre randomized controlled trial, Plant and colleagues showed that noninvasive ventilation in patients with a severe exacerbation of COPD was safe and effective in the general ward setting.7 However, outcomes of patients in general wards who had more severe disease (arterial pH < 7.307) were not as good as those reported for patients in acute care locations,8 where more sophisticated equipment and individual titration of ventilator settings were available.

Effective implementation

Many factors appear to influence the effective implementation of noninvasive ventilation. These factors include an experienced team of health care staff able to provide 24-hour service and detailed attention to mask interface and leaks, choice of equipment, ventilator settings, inspired oxygen levels, glottic function and clearance of secretions. Failure of the ventilator to match changing patient demand can occur at the start, during and at the end of inspiration. This patient–ventilator dyssynchrony is common, often goes unrecognized and contributes to the failure of noninvasive ventilation. Appropriate monitoring is essential, along with staffing schedules that recognize the usually high nursing workload in the first six to eight hours.9 The role of humidification and the optimal period of rest from noninvasive ventilation to allow oral intake and speech remain under investigation.

Given the increasing demand for critical care beds, not all patients receiving noninvasive ventilation may be cared for in intensive care units or emergency departments. Adequate monitoring is required wherever the patient is located. To facilitate the rescue of patients in whom noninvasive ventilation fails, and to maximize overall benefits of noninvasive ventilation programs, monitoring of patients is best done in partnership with the many services and specialties caring for acutely ill patients.

For these guidelines2 to change clinical practice, they have to be supported by appropriate education, implementation and review. Helping clinicians know when and when not to use noninvasive ventilation is perhaps the most important role for these guidelines.

Key points

• Successful implementation of programs for noninvasive ventilation requires 24-hour availability of an experienced team and appropriate selection of patients.

• Patients in whom noninvasive ventilation fails tend to have worse outcomes, probably because of delayed definitive care.

• Any program must include adequate monitoring of patients to ensure a rapid response when noninvasive ventilation fails.