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While
prospective randomized trials have involved relatively small numbers of
patients (<1000 total), a consistent treatment benefit has been
demonstrated, and noninvasive ventilation has been recommended as
first-line therapy in the management in COPD patients with hypercapnic
respiratory failure. Systematic reviews and meta-analyses have all come to
the same conclusion. Noninvasive ventilation reduces the need for
intubation, mortality, complications, and length of stay in patients with
COPD.
However, the magnitude of the benefit of
noninvasive ventilation differs given some inconsistencies in the included
studies. The largest review concluded that noninvasive ventilation
decreased the intubation rate by 28% (95% confidence interval [CI],
15-40%), in-hospital mortality rate by 10% (95% CI, 5-15%), and absolute
reduction in length of stay by 4.57 days (95% CI, 2.30-6.38 d).5 The
benefit was most pronounced in patients with more severe COPD
exacerbations, defined by an initial pH of less than 7.30. The magnitude
of effect was even more pronounced in this group, with intubation rates decreased
by 34% (95% CI, 22-46%), mortality reduction of 12% (95% CI, 6-18%), and absolute
reduction in the length of stay by 5.59 days (95% CI, 3.66-7.52 d).
Investigations with less severely affected patients did not demonstrate
any benefit in any of these outcomes.
- COPD
is the most suitable condition for noninvasive ventilation.
- Noninvasive
ventilation is most effective in patients with moderate-to-severe
disease
- Hypercapnic
respiratory acidosis may define the best responders (pH 7.20-7.30).
- Noninvasive
ventilation is also effective in patients with a pH of 7.35-7.30,
but no added benefit is appreciated if the pH is greater than 7.35.
- The
lowest threshold of effectiveness is unknown, but success has been
achieved with pH values as low as 7.10.
- Obtunded
COPD patients can be treated, but the success rate is lower.
- Improvement after
a 1- to 2-hour trial may predict success.
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Noninvasive
Ventilation Pulmonary Edema
Respiratory
failure due to cardiogenic
pulmonary edema or congestive
heart failure (CHF) is
another condition that is effectively treated with noninvasive ventilation
(NIV)
This
leads initially to hypoxemic respiratory failure, and patients with CHF
who further deteriorate manifest hypercapnic respiratory
failure. Positive-pressure ventilation is beneficial because it recruits
alveoli, increases functional residual capacity, and allows breathing on
the more compliant portion of the lung's pressure-volume curve, thereby
decreasing the work of breathing, improving ventilation-perfusion
relationships, and eventually correcting hypoxemia and hypercapnia.
Positive intrathoracic pressure also decreases preload and left
ventricular afterload, both beneficial effects in patients with volume
overload.
CPAP
has long been recognized as effective in the management of CHF, but
noninvasive ventilation provided using BiPAP or pressure support
modalities, however, has been mixed.
- Noninvasive
ventilation is well suited for patients with cardiogenic pulmonary
edema.
- CPAP
and BiPAP modalities both are effective, with CPAP possibly being more
effective.
- The
greatest benefits are realized in relief of symptoms and dyspnea.
- A
decrease in intubation and mortality rates is not a universal
experience.
- Patients
with hypercapnic respiratory acidosis may derive the greatest benefit
from noninvasive ventilation.
- Importantly,
adjust to standard therapy, including diuresis.
- Benefit
may be seen with as few as 2 hours of support.
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Postextubation
respiratory insufficiency requiring reintubation can occur in more than
20% of patients.
postextubation
period, including increased respiratory load, hyperinflation,
diaphragmatic dysfunction, and increases in preload and afterload, all of
which can contribute singly or in unison to hypercapnia, hypoxemia, and
eventual respiratory failure. In addition, patients may have incurred some
upper airway trauma with intubation or may have developed upper airway
edema, which, in turn, can contribute to partial upper airway obstruction,
which is another factor contributing to an increased respiratory workload.
Patients
in whom weaning trials have failed or those who do not meet extubation
criteria have been extubated to noninvasive ventilation support as part of
an early extubation approach or as an adjunct to weaning. Early
extubation with noninvasive ventilation support may be able to prevent
some of the complications associated with endotracheal intubation,
specifically nosocomial pneumonia; additionally, it allows for speech with
preservation of oropharyngeal function. Noninvasive ventilation has also
been applied to patients who were suggested to be extubated based on
extubation criteria but then developed postextubation respiratory
distress.
- Noninvasive
ventilation is effective as a bridge support after early extubation.
- Noninvasive
ventilation is an adjunct to weaning (substitutes noninvasive support
for invasive support).
- Patients
with underlying COPD are most likely to benefit from noninvasive
ventilation after early extubation.
- Noninvasive
ventilation is not as effective in patients with postextubation
respiratory distress.
- COPD
patients are a subgroup who may benefit in that situation.
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Noninvasive
Ventilation Postoperative Patients
Noninvasive
ventilation is likely to be successful in selected patients. The
following highlights the main considerations in each condition.
- Postoperative
hypoxemia related to atelectasis or
pulmonary edema
- Occurrence
following multiple types of surgery (eg, lung, cardiac, abdominal).
- Randomized
trials with postoperative continuous positive airway pressure (CPAP)
demonstrate benefit
- Applied
as prophylactic support or with development of hypoxemia
- Benefit
noted with level CPAP levels in 7.5- to 10-cm water range
- Lower
intubation rates, days in ICU, and pneumonia
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Community-acquired
pneumonia
- Immunocompromised
patients and hypoxemic respiratory failure
- Solid
organ transplantation9
- Single-center
trial, approximately 50 patients
- Subgroup
with cardiogenic pulmonary edema fared best
- Febrile
neutropenic patients
- Single-center
trial, approximately 50 patients
- Mostly
hematologic malignancies or bone marrow transplantations
- Benefit
of noninvasive ventilation in those with an identified cause of
pneumonia
- Severity
of illness relatively modest
- Asthma20
- Similar
pathophysiology to COPD; limited reported experience with
noninvasive ventilation
- Mostly
case series with reported benefit
- Prospective,
randomized studies based on emergency department settings
- Improvement
in spirometry main outcome measure
- Fewer
admissions with noninvasive ventilation; intubation not an outcome
measure
- Hypercapnic
asthma patients not represented in randomized trials
- Noninvasive
ventilation probably beneficial, but experience limited
- Rib
fractures (traumatic, with nonpenetrating chest injuries)
- Older
single report using low-level CPAP (5 cm water)
- Fewer
episodes of pneumonia, duration of hospitalization
- No mortality benefit:
Hernandez et al found that in patients with hypoxemia related to
severe thoracic trauma, noninvasive mechanical ventilation reduced
intubation rates. In a randomized clinical trial, patients with PaO2/FiO2 ratio
of less than 200 for more than 8 hours while receiving oxygen by
high-flow mask within the first 48 hours after thoracic trauma were
randomized to remain on high-flow oxygen mask or to receive
noninvasive mechanical ventilation. The trial was halted after 25
patients were enrolled in each group because the intubation rate was
much higher in controls than in noninvasive mechanical ventilation
patients (40% vs 12%, P =
.02). In addition, length of hospital stay was shorter in
noninvasive mechanical ventilation patients (14 vs 21 d, P =
.001); however, no difference in survival was observed.25
- Do-not-intubate
status (advanced disease or terminal malignancy)26
- Numerous
case series
- COPD
patients comprise most patients
- Most
with hypercapnic respiratory failure
- Report
of 60% success rate, but discharge home rate of 40-50%
- Median
survival following treatment 179 days in one series
- One-year
survival rate of 30%
- Some
with more distress from the mask and noninvasive ventilation than
benefit
- Issues
with resource utilization and prolonging the inevitable
- Better
outcomes in CHF, awake patients, and those with strong cough
(mobilized secretions)
- Benefit
in patients with malignancy if treating reversible condition
- Benefit
in dyspnea relief for patients with terminal malignancy27
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- Acute
respiratory distress syndrome28,29
- Not
recommended as first-line therapy in management
- Limited
experience, but may benefit those who do not require immediate
intubation
- Noninvasive
ventilation provided via mask or helmet; able to avoid intubation in
approximately half
- Ventilator
settings in successful noninvasive ventilation - Pressure support
ventilation of 14 cm water; positive end-expiratory (PEEP) of 7 cm
water
- Successfully treated
patients found to have lower severity of illness (Simplified Acute
Physiology Score II <34 or improvement of PaO2/FIO2 ratio
>175 after 1 h)
- Severe
acute respiratory distress syndrome31
- Successful
treatment with noninvasive ventilation during severe acute
respiratory distress syndrome (SARS) outbreak
- Noninvasive
ventilation able to avoid intubation in 70%
- Patients
hypoxemic with also relatively low severity of illness (Acute
Physiology and Chronic Health Evaluation II [APACHE II] score <6)
The
remaining conditions have had reports of successful noninvasive
ventilation in both acute and chronic respiratory failure. Most of these
processes represent patients with either chronic hypercapnia or relatively
mild hypoxemia. Patients with these diagnoses who may be candidates for
noninvasive ventilation should be evaluated on a case-by-case basis.
Cystic fibrosis - May be useful as a
bridge to lung transplantation and as an adjunct to oxygen therapy alone
during sleep to improve gas exchange32
- Neuromuscular
respiratory disease33,34
- Nocturnal
use may be especially effective for daytime hypercapnia
- Avoid
in bulbar dysfunction or excess secretions
- Effective
in patients with muscular dystrophy, kyphoscoliosis, and postpolio
syndrome
- Some
may be able to be treated with negative-pressure ventilators
- Obesity-hypoventilation
(or decompensated obstructive sleep apnea) - Corrects hypercapnia,
facilitates diuresis, and provides opportunity for restorative sleep30
- Upper
airway obstruction (partial) - Caution if potential for complete
obstruction
- Mild Pneumocystis
carinii pneumonia
- Case series; may avoid intubation in selected patients
- Support
during invasive procedures - Bronchoscopy, percutaneous gastrostomy30,35
- Idiopathic
pulmonary fibrosis
- Generally
poor response to invasive ventilation, much less noninvasive
ventilation
- Successfully
treated patients with a rapidly reversible cause of respiratory
failure
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Complications
of noninvasive ventilation
- Facial
and nasal pressure injury and sores
- Result
of tight mask seals used to attain adequate inspiratory volumes
- Minimize
pressure by intermittent application of noninvasive ventilation
- Schedule breaks
(30-90 min) to minimize effects of mask pressure
- Balance
strap tension to minimize mask leaks without excessive mask
pressures
- Cover vulnerable
areas (erythematous points of contact) with protective dressings
- Gastric
distension
- Rarely
a problem
- Avoid
by limiting peak inspiratory pressures to less than 25 cm water
- Nasogastric
tubes can be placed but can worsen leaks from the mask
- Nasogastric
tube also bypasses the lower esophageal sphincter and permits reflux
- Dry
mucous membranes and thick secretions
- Seen
in patients with extended use of noninvasive ventilation
- Provide
humidification for noninvasive ventilation devices
- Provide
daily oral care
- Aspiration
of gastric contents
- Especially
if emesis during noninvasive ventilation
- Avoid
noninvasive ventilation in patient with ongoing emesis or
hematemesis
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Complications
of both noninvasive and invasive ventilation
- Barotrauma (significantly
less risk with noninvasive ventilation)
- Hypotension
related to positive intrathoracic pressure (support with fluids)
Complications
avoided by noninvasive ventilation
- Ventilator-associated
pneumonia
- Sinusitis
- Reduction
in need for sedative agents - Sedatives used in less than 15% of
noninvasive ventilation patients in one survey
Other Issues
Cost-analysis of noninvasive
ventilation
- Avoids
costs of endotracheal intubation and mechanical ventilation
Shorter
ICU and hospital stays
Eliminates
costs associated with infectious complications - Episodes of
ventilator-associated pneumonia reduced by half or more
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Author: Guy W Soo Hoo, MD, MPH, Clinical
Professor of Medicine, Geffen School of Medicine at the University of
California at Los Angeles; Director, Medical Intensive Care Unit,
Pulmonary and Critical Care Section, West Los Angeles Healthcare Center,
Veteran Affairs Greater Los Angeles Healthcare System
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