Prevention of respiratory failure after extubation
Other studies used NIPPV to prevent respiratory failure after extubation rather than wait to apply it after respiratory failure developed.38–41
Nava et al,40 in a trial in patients successfully weaned but considered to be at risk of reintubation, found that fewer of those randomized to NIPPV had to be reintubated than those who received standard care (8% vs 24%), and 10% fewer of them died in the intensive care unit. Risk factors for reintubation (and therefore eligibility criteria for this trial) included a Paco2 higher than 45 mm Hg, more than one consecutive failure of weaning, chronic heart failure, other comorbidity, weak cough, or stridor.
Extubated patients are a heterogeneous group, so if some subgroups benefit from a transition to NIPPV after extubation, it will be important to identify them. For instance, a subgroup analysis of a study by Ferrer et al38 indicated the survival benefit of NIPPV after extubation was limited to patients with chronic respiratory disorders and hypercapnia during a trial of spontaneous breathing.
In a subsequent successful test of this hypothesis, a randomized trial showed that the early use of noninvasive ventilation in patients with hypercapnia after a trial of spontaneous breathing and with chronic respiratory disorders (COPD, chronic bronchitis, bronchiectasis, obesity-hypoventilation, sequelae of tuberculosis, chest wall deformity, or chronic persistent asthma) reduced the risk of respiratory failure after extubation and the risk of death within the first 90 days.39
Others in which this approach may be helpful are obese patients who have high Paco2 levels. Compared with historical controls, 62 patients with a body mass index greater than 35 kg/m2 who received NIPPV in the 48 hours after extubation had a lower rate of respiratory failure, shorter lengths of stay in the intensive care unit and hospital, and, in the subgroup with hypercapnia, a lower hospital mortality rate.41
NIPPV to facilitate weaning
In several studies, mechanically ventilated patients who had failed a trial of spontaneous breathing were randomized to undergo either accelerated weaning, extubation, and NIPPV or conventional weaning with pressure support via mechanical ventilation.42–46 Most patients developed hypercapnia during the spontaneous breathing trials, and most of the patients had COPD.
A meta-analysis47 of the randomized trials of this approach concluded that, compared with continued invasive ventilation, NIPPV decreased the risk of death (relative risk 0.41) and of ventilator-associated pneumonia (relative risk 0.28) and reduced the total duration of mechanical ventilation by a weighted mean difference of 7.33 days. The benefits appeared to be most significant in patients with COPD.
NIPPV IN ASTHMA AND STATUS ASTHMATICUS
Noninvasive ventilation is an attractive alternative to intubation for patients with status asthmaticus, given the challenges and conflicting demands of maintaining ventilation despite severe airway obstruction.
In a 1996 prospective study of 17 episodes of asthma associated with acute respiratory failure, Meduri et al48 showed that NIPPV could progressively improve the pH and the Paco2 over 12 to 24 hours and reduce the respiratory rate.
In a subsequent controlled trial, Soroksky et al49 randomized 30 patients presenting to an emergency room with a severe asthma attack to NIPPV with conventional therapy vs conventional therapy only. The study group had a significantly greater increase in the forced expiratory volume in 1 second compared with the control group (54% vs 29%, respectively) and a lower hospitalization rate (18% vs 63%).
Another randomized trial of NIPPV, in patients with status asthmaticus presenting to an emergency room, was prematurely terminated due to a physician treatment bias that favored NIPPV.50 The preliminary results of that study showed a 7.3% higher intubation rate in the control group than in the NIPPV group, along with trends toward a lower intubation rate, a shorter length of hospital stay, and lower hospital charges in the NIPPV group.
Despite these initial favorable results, a Cochrane review concluded that the use of NIPPV in patients with status asthmaticus is controversial.51 NIPPV can be tried in selected patients such as those with mild to moderate respiratory distress (respiratory rate greater than 25 breaths per minute, use of accessory muscles to breathe, difficulty speaking), an arterial pH of 7.25 to 7.35, and a Paco2 of 45 to 55 mm Hg.52 Patients with impending respiratory failure or the inability to protect the airway should probably not be considered for NIPPV.52
IN ACUTE LUNG INJURY AND ACUTE RESPIRATORY DISTRESS SYNDROME
The most challenging application of NIPPV may be in patients with acute lung injury and the acute respiratory distress syndrome.
Initial trials of NIPPV in this setting have been disappointing, and a meta-analysis of the topic concluded that NIPPV was unlikely to have any significant benefit.53 An earlier study that used CPAP in patients with acute respiratory failure predominantly due to acute lung injury showed early physiologic improvements but no reduction in the need for intubation, no improvement in outcomes, and a higher rate of adverse events, including cardiac arrest, in those randomized to CPAP.54
A subsequent observational cohort specifically identified shock, metabolic acidosis, and severe hypoxemia as predictors of NIPPV failure.55
A more recent prospective study demonstrated that NIPPV improved gas exchange and obviated intubation in 54% of patients, with a consequent reduction in ventilator-associated pneumonia and a lower rate of death in the intensive care unit.56 A Simplified Acute Physiology Score (SAPS) II greater than 34 and a Pao2/Fio2 ratio less than 175 after 1 hour of NIPPV were identified as predicting that NIPPV would fail.56