Noninvasive positive pressure ventilation (NIPPV)—delivered via a tight-fitting mask rather than via an endotracheal tube or tracheostomy—is one of the most important advances in the management of acute respiratory failure to emerge in the past 2 decades. It is now recommended as the first choice for ventilatory support in selected patients, such as those with exacerbations of chronic obstructive pulmonary disease (COPD) or with cardiogenic pulmonary edema.1–3 In fact, some authors suggest that using NIPPV in more than 20% of COPD patients is a characteristic of respiratory care departments that are “avid for change”4—change being a good thing.
However, NIPPV has not been universally accepted, with wide variations in its utilization. In a 2006 survey, it was being used in only 33% of patients with COPD or congestive heart failure, for which it might be indicated. 5 Some potential reasons for the low rate are that physicians do not know about it, respiratory therapists are not sufficiently trained in it, and hospitals lack the equipment to do it.5
Our goal in this review is to familiarize the reader with how NIPPV has evolved and with its indications and contraindications in specific acute care conditions.
FROM A VACUUM CLEANER TO THE INTENSIVE CARE UNIT
NIPPV appears to have been first tried in 1870 by Chaussier, who used a bag and face mask to resuscitate neonates.6
In 1936, Poulton and Oxon7 described their “pulmonary plus pressure machine,” which used a vacuum cleaner blower and a mask to increase the alveolar pressure and thus counteract the increased intrapulmonary pressure in patients with heart failure, pulmonary edema, Cheyne-Stokes breathing, and asthma.
In the 1940s, intermittent positive pressure breathing devices were developed for use in high-altitude aviation. Motley, Werko, and Cournand8,9 subsequently used these devices to treat acute respiratory failure in pneumonia, pulmonary edema, near-drowning, Guillain-Barré syndrome, and acute severe asthma.
Although NIPPV was shown to be effective for acute conditions, invasive ventilation became preferred, particularly as blood gas analysis and ventilator technologies simultaneously matured, spurred at least in part by the polio epidemics of the 1950s.10
NIPPV reemerged in the 1980s for use in chronic conditions. First, continuous positive airway pressure (CPAP) came into use for obstructive sleep apnea,11 followed by noninvasive positive-pressure volume ventilation in neuromuscular diseases.12 Bilevel positive pressure devices (ie, with separate inspiratory and expiratory pressures) soon followed, again initially for obstructive sleep apnea13 and then for diverse neuromuscular diseases.14
NIPPV is now a mainstream therapy for diverse conditions in acute and chronic care.3 One reason we now use it in acute conditions is to avoid the complications associated with intubation.
Some clinicians initially resisted using NIPPV, concerned that it demanded too much of the nurses’ time15 and was costly.16 However, in a 1997 study in patients with COPD and acute respiratory failure, Nava et al17 found that NIPPV was no more expensive and no more demanding of staff resources than invasive mechanical ventilation in the first 48 hours of ventilation. Further, after the first few days of ventilation, NIPPV put fewer time demands on physicians and nurses than did invasive mechanical ventilation.
THREE MODES: CPAP, PRESSURE-LIMITED, VOLUME-LIMITED
The term “noninvasive ventilation” generally encompasses various forms of positive pressure ventilation. However, negative pressure ventilation, in the form of diaphragm pacing, may regain a foothold in the devices used for respiratory support.18 We therefore favor the term “NIPPV” in this review.
NIPPV IN ACUTE RESPIRATORY FAILURE
The main reasons to use NIPPV instead of invasive ventilation in acute care are to avoid the complications of invasive ventilation, to improve outcomes (eg, reduce mortality rates, decrease hospital length of stay), and to decrease the cost of care.
NIPPV is the standard of care for acute exacerbations of COPD
In a meta-analysis of eight randomized controlled trials,24 the specific advantages of NIPPV compared with usual care in acute exacerbations of COPD included:
- A lower risk of treatment failure, defined as death, need for intubation, or inability to tolerate the treatment (relative risk [RR] 0.51, number needed to treat [NNT] to prevent one treatment failure = 5)
- A lower risk of intubation (RR 0.43, NNT = 5)
- A lower mortality rate (RR 0.41, NNT = 8)
- A lower risk of complications (RR 0.32, NNT = 3)
- A shorter hospital length of stay (by about 3 days).
Mechanisms by which NIPPV may impart these benefits include reducing the work of breathing, unloading the respiratory muscles, lessening diaphragmatic pressure swings, reducing the respiratory rate, eliminating diaphragmatic work, and counteracting the threshold loading effects of auto-positive end-expiratory pressure (auto-PEEP).24–26
Also, if a patient with COPD is intubated, NIPPV seems to help after the tube is removed, preventing postextubation respiratory failure and facilitating weaning from invasive ventilation.27 These topics are discussed below.
A Cochrane systematic review24 concluded that NIPPV should be tried early in the course of respiratory failure, before severe acidosis develops. The patients in the studies in this review all had partial pressure of arterial carbon dioxide (Paco2) levels greater than 45 mm Hg.
In patients with severe respiratory acidosis (pH < 7.25), NIPPV failure rates are greater than 50%. However, trying NIPPV may still be justified, even in the presence of hypercapnic encephalopathy, as long as no other indications for invasive support and facilities for prompt endotracheal intubation are available. 1
However, in another systematic review,26 in patients with mild COPD exacerbations (pH > 7.35), NIPPV was no more effective than standard medical therapy in preventing acute respiratory failure, preventing death, or reducing length of hospitalization. Moreover, nearly 50% of the patients could not tolerate NIPPV.