Noninvasive Positive Pressure Ventilation*
Successful Outcome in Patients With Acute Lung Injury/ARDS
Graeme M. Rocker, MA, DM;
Mary-Gordon Mackenzie, RN, BSc, MSc, PhD;
Bruce Williams, RRT and
P. Mark Logan, MB
* From the Division of Respirology (Drs. Rocker and Mackenzie), Department
of Respiratory Therapy (Mr. Williams), and Department of Radiology (Dr.
Logan), Dalhousie University and QEII Health Sciences Centre, Halifax, Nova
Scotia, Canada.
 |
Abstract
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Background: There is increasing support for the
use of noninvasive positive pressure ventilation (NPPV) in the
treatment of patients with acute respiratory failure. Highest success
rates are recorded in patients with exacerbation of COPD, particularly
in patients presenting primarily with hypercarbic respiratory failure.
Success has been more limited in patients with acute hypoxemic
respiratory failure, and there are few reports of NPPV in patients with
acute lung injury (ALI) or ARDS.
Objectives: We report
the outcome of 12 episodes of ALI/ARDS in 10 patients treated with
NPPV.
Design: Experiential cohort study.
Setting: Tertiary referral center and university hospital
ICU.
Intervention: Provision of NPPV in patients with
ALI/ARDS.
Results: Group median (range) APACHE (acute
physiology and chronic health evaluation) II score was 16 (11 to 29).
Success rate (avoidance of intubation and no further assisted
ventilation for 72 h) was achieved on six of nine occasions (66%)
when NPPV was used as the initial mode of assisted ventilation. It
failed after three episodes of planned (1) or self (2) extubation.
Duration of successful NPPV was 64.5 h (23.5 to 80.5 h) with
ICU discharge in the next 24 to 48 h for three of six patients.
Unsuccessful episodes lasted 7.3 h (0.1 to 116 h) with need
for conventional ventilation for an additional 5 days (2.7 to 14 days).
Survival (ICU and hospital) for the 10 patients was 70%.
Conclusions: In a group of hemodynamically stable patients
with severe ALI, NPPV had a high success rate. NPPV should be
considered as a treatment option for patients in stable condition in
the early phase of ALI/ARDS.
Abbreviations: ALI = acute lung injury;
APACHE = acute physiology and chronic health evaluation;
CPAP = continuous positive airway pressure; CXR = chest radiograph;
FIO2 = fraction of inspired oxygen;
IPPV = intermittent positive pressure ventilation;
NPPV = noninvasive positive pressure ventilation; PEEP = positive
end-expiratory pressure
Key Words: acute lung injury • noninvasive ventilation • respiratory distress syndrome, adult
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Introduction
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There
is renewed interest in the provision of noninvasive positive pressure
ventilation (NPPV) by face mask for acute respiratory failure, based
mainly on its success in avoidance of intubation in approximately 70%
of patients with exacerbations of COPD.1,2 In
patients with acute hypoxic respiratory failure, experience is less
extensive3 and results are less favorable. A recent
meta-analysis of trials of noninvasive ventilation concluded that its
beneficial effect in acute respiratory failure was restricted to
patients in whom exacerbation of COPD was the cause.4 Data
on the efficacy of NPPV in patients with acute lung injury/acute
respiratory distress syndrome (ALI/ARDS) are very limited. Only 3
patients with ALI/ARDS were included in a total of 158 patients treated
with NPPV2 and 2 in a recent study of proportional assist
ventilation.5 Meanwhile avoidance of barotrauma or
volutrauma, by strategies including the limitation of peak and plateau
airway pressures in the intubated patient, has been a management focus
of ALI/ARDS to receive much recent attention.6,7,8
Mortality from ARDS has long been associated with development of
multiple organ failure9 rather than death from hypoxemic
respiratory failure per se and if intubation could be
avoided in such patients, risk from ventilator-associated lung injury
and/or nosocomial pneumonia/sepsis might be substantially reduced. In
addition, patients would avoid tracheal or laryngeal injury from
conventional intubation or from tracheal stenosis following
tracheostomy.10 In patients with noncardiogenic pulmonary
edema, the addition of continuous positive airway pressure (CPAP) would
provide the beneficial effects of positive end-expiratory pressure
(PEEP) on distribution of extravascular lung water and on alveolar
recruitment and/or inflation. This would reduce the tendency to early
airway closure, a feature of ALI.11 In addition, pressure
support augments spontaneous breaths, further reduces the work of
breathing, and maintains a tidal volume compatible with adequate
alveolar ventilation,12,13 while limiting volume or
barotrauma and the complications of intubation.
We report the outcome of provision of NPPV in the treatment of 10
patients with ALI/ARDS who underwent a trial of NPPV on 12 occasions.
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Materials and Methods
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Between August 1, 1994, and July 31, 1996, the efficacy of NPPV
was assessed on 108 occasions in patients with acute hypoxemic and/or
hypercapnic respiratory failure at the Victoria General Site of the QE
II Health Sciences Centre, Halifax, Nova Scotia, a tertiary referral
center for the Maritime Provinces of Eastern Canada. Ten patients (3
male, 7 female, mean age 47 years, range 25 to 89 years) met the
American-European diagnostic criteria for ALI/ARDS6 and
received NPPV on 12 occasions. In addition NPPV was provided for acute
respiratory failure on 96 other occasions as follows (COPD, n = 30;
cardiogenic pulmonary edema/fluid overload, n = 25; pneumonia,
n = 19; postoperative atelectasis, n = 9; interstitial lung
disease, n = 8; and neuromuscular disorders, n = 5). For patients
with ALI/ARDS, a radiologist blinded to the clinical course scored all
patients according to extent of interstitial and/or alveolar pulmonary
edema14 at initiation of NPPV and subsequently assessed
chest radiographs (CXRs) for evidence of barotrauma. Demographic
details, risk factor for ARDS, oxygenation fraction
(PaO2/FIO2), CXR score,
and APACHE (acute physiology and chronic health evaluation) II score
can be found in Table 1.
Details of duration of NPPV, its success or failure, sedation
requirements, length of intermittent positive pressure ventilation
(IPPV) beyond NPPV failure, length of ICU stay, and ICU and hospital
mortality can be found in Table 2.
Patients were treated with NPPV via a full face mask connected to a
ventilator (Puritan Bennett 7200a; Lawrenceville, GA) in CPAP mode with
added pressure support. CPAP was adjusted to maintain
FIO2 at < 60% with arterial oxyhemoglobin
saturation of > 90% when possible. Pressure support was adjusted in
efforts to maintain a tidal volume > 5 mL/kg and a respiratory rate
of < 30 breaths/min. Success was defined as a withdrawal of face mask
ventilation without the need for further assisted ventilation for an
additional 72 h. Failure was defined as the need for conventional
intubation or the further provision of NPPV within a 72-h period from
the end of a previous NPPV trial. In seven patients, NPPV was
instituted as a primary mode of respiratory support. For three patients
with ARDS, NPPV was provided after self-extubation (n = 2) and on one
occasion following progressive respiratory failure after planned
extubation. One patient did not have intubation or other
cardiopulmonary resuscitation (patient 11, Table 1) and one additional
patient refused conventional intubation and mechanical ventilation and
chose face mask ventilation as a more acceptable alternative on two
occasions (No. 4 and 5, Table 1). Data are expressed throughout as
median (range).
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Results
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Overall patient survival was 70% (7 of 10) with three ICU deaths
occurring 5, 8, and 16 days after ICU admission. Overall success rate
for NPPV trials was 6 of 12 (50%). When used as a de novo
therapy, it was more successful (six of nine occasions), with failure
in all three patients in whom NPPV was tried following self-extubation
(n = 2) after 0.1 and 1.15 h and once after planned extubation.
Two patients underwent a trial of NPPV on two occasions with one
success and one failure at the second attempt. On 11 of 12 occasions,
baseline PaO2/FIO2
prior to starting NPPV was < 120. In response to NPPV,
PaO2/FIO2 was available
in 10 patients (patients 1 and 7 failed too quickly), it remained
< 200 in 7, but improved by > 25% in 9 patients, and was unchanged
in 1 (Table 1). Group median (range) APACHE II score was 16 (11 to 29).
The APACHE II score was 17 (11 to 29) when NPPV failed and 14 (12 to
20) when it succeeded. Duration of successful NPPV was 64.5 h
(23.5 to 80.5 h) with ICU discharge in the next 24 to 48 h
for three of six patients. Unsuccessful episodes lasted 7.3 h (0.1
to 116 h) with need for conventional ventilation for an additional
5 days (2.7 to 14 days). Length of ICU stay after NPPV was 3.7 days (1
to 19 days) when successful and 7 days (4 to 15 days) when it failed.
None of these group differences achieved significance. No patients
developed complications related to the use of NPPV such as skin
necrosis, gastric distention, nosocomial pneumonia, or evidence of
barotrauma (pneumothorax, pneumomediastinum, pneumoperitoneum, or
pulmonary interstitial emphysema). No patients vomited and/or aspirated
after initiation of NPPV. Levels of sedation used during NPPV are
recorded in Table 2. Two patients (patients 10 and 12) underwent IPPV
following unsuccessful provision of NPPV for > 2 h. In patient 12,
levels of sedation were morphine, 1.0 mg/h vs 1.0 mg/h and midazolam, 0
mg/h vs 0.4 mg/h during comparable preintubation and post-intubation
periods (approximately 12 h). For patient 10 (with severe
mucositis), hydromorphone was used at 1.6 mg/h (equivalent to morphine,
8 mg/h) before, and at 2.7 mg/h (morphine, 13.5 mg/h) after intubation.
Infusion doses of midazolam were 2.5 mg/h before and 7.5 mg/h after
intubation.
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Discussion
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Within the constraints of an experiential pilot study, this report
describes a surprisingly high success rate of NPPV (with pressure
support) in patients with ALI/ARDS. Since the description by Ashbaugh
et al15 of acute respiratory distress in adults and its
treatment with PEEP, the conventional approach to assisted ventilation
in patients with ALI/ARDS has been the provision of endotracheal
intubation and IPPV. Both of these interventions are associated with
several potential complications related to intubation of the
airway,10 barotrauma and/or volutrauma,7 and
the development of subsequent nosocomial pneumonia in a setting of
ALI16 with its implications for sepsis and multiple organ
failure. The prevention of barotrauma or volutrauma has been one aspect
of conventional management of ARDS to receive much recent
attention.7,8 Strategies to limit ventilator-associated
lung injury have included limitation of peak and plateau airway
pressures in accordance with recent consensus conference
guidelines.6 To our knowledge, significant problems
related to barotrauma or volutrauma due to NPPV have not been reported.
NPPV allows patients to determine their own breathing pattern within
ventilator parameters that limit the imposed pressure effects at
alveolar level. Face mask ventilation can provide the beneficial
effects of both PEEP on distribution of extravascular lung water,
alveolar recruitment, and/or prevention of alveolar collapse (through
CPAP) plus the augmentation of spontaneous tidal breathing with added
inspiratory pressure support. This reduces the work of
breathing,12,13 preserves a tidal volume compatible with
adequate alveolar ventilation, while potentially limiting barotrauma or
volutrauma and the complications of intubation. If this can be achieved
in the early stages of ALI, the compounding problems of dependent
pulmonary edema, dorsal airway closure, surfactant inactivation, and
substantial ventilation/perfusion mismatch might be avoided or at least
ameliorated. Once established on pressure support ventilation, patients
who respond should benefit from improvements in respiratory rate,
respiratory muscle activity, and gas exchange as reported in several
previous studies.1,2,12,13,17
Face mask ventilation is not without hazard. Complications include risk
of skin necrosis at the bridge of the nose that increases with duration
of NPPV, lack of immediate access to the airway, which precludes its
use in patients unable to protect the airway and in those with
significant secretions. There are feelings of claustrophobia and a low
risk of gastric distention. In a major study evaluating the efficacy of
NPPV,2 the overall complication rate was low (16%). Only
two episodes of nosocomial pneumonia were reported in > 200 patients
treated with NPPV2 and in a recent prospective study,
incidence density of nosocomial pneumonia was significantly lower in
patients treated noninvasively by comparison with conventional
intubation and positive pressure ventilation.18 Low rates
of infectious and other complications have also been confirmed in
randomized studies of NPPV.1,17,19 This is in contrast to
reported rates of nosocomial pneumonia in intubated patients that may
approach 30%.16 There were no significant adverse effects
of NPPV in our study. For the patient who refused intubation despite
severe postpartum acute respiratory failure, it was necessary to
maintain adequate sedation to allow her to tolerate face mask
ventilation for two consecutive but well-separated episodes of 56 and
73 h, respectively. The successful outcome in this particular
patient with an APACHE II score of 20 gave us particular encouragement
in the early stages of our experience of NPPV to consider its use under
other circumstances.
Some practical issues need to be addressed. The levels of sedation
administered to allow NPPV to proceed were variable (Table 2). Patients
were rousable. Doses of sedative drugs used in some patients were less
than might have been expected for intubated patients. The time spent by
respiratory technicians initiating and maintaining NPPV was not
formally assessed. However, it was our impression that an increasing
familiarity with NPPV tended to offset any tendency to increased time
spent at the bedside by the respiratory therapists at initiation of
NPPV, by comparison with their input with ventilated patients. One
recent study has addressed this issue in patients with exacerbations of
COPD. Similar input was required from members of the health-care team
in patients, whether treated noninvasively or with conventional
intubation and IPPV.20 In terms of duration of noninvasive
ventilation, our successful patients tolerated the face mask for a
median of 64 h. Meduri et al2 reported a mean of
25 h, and others have reported longer usage in the acute
situation.21 These reports did not focus on patients with
ALI/ARDS whose requirements for assisted ventilation might be expected
to be longer due to the added complexities of increased pulmonary
capillary permeability, surfactant inactivation, and worsening
ventilation perfusion mismatch on presentation.
With the exception of patient 1, whose tolerance of NPPV was short
lived (1.5 h) and whose death from multiple organ failure followed
within 8 days, most patients in this study had organ failure limited to
the lungs and/or one other system. It is unlikely that NPPV would be
successful in patients with multiple organ failure (only two patients
in our study had an APACHE II score > 20, both of whom subsequently
died). While accepting that the patients described did not have
multiple organ failure, the CXR score and degree of hypoxemia (before
and after NPPV) indicate severe ALI in most patients. Whether initial
use of NPPV contributed to a successful outcome is difficult to state
with certainty. Mortality from ARDS is decreasing,22 but
even within this setting, the mortality rate of this relatively small
group (30%) is lower than is usually reported in the literature and
the success rate for NPPV is similar or higher than that reported in
patients with other causes of acute respiratory failure.3
This study has limitations due to the size of the population reported
and the lack of a control group. It was believed inappropriate to
include any historical control group for comparison. Our patients might
not be representative of patients with ALI/ARDS. However, the
proportion of patients with acute respiratory failure in whom we tried
NPPV for ALI/ARDS is very similar to the reported incidence (9 to 18%)
of ARDS in ICU patients in general.23 The relatively small
numbers of patients included imposed limited value to statistical
analysis of group differences between patients in whom NPPV succeeded
or failed. Consequently no difference was detected for age, APACHE II
score, baseline
PaO2/FIO2, duration of
NPPV, or length of ICU stay. This not withstanding, if it were possible
to identify a subgroup of patients with ALI that might be quickly
reversible, noninvasive ventilation via a face mask might be a safe and
effective treatment option. As yet, there is no variable at
presentation that identifies those patients with acute hypoxemic
respiratory failure who will succeed with NPPV.2 In the
meantime, it would not be appropriate to use NPPV for patients with
life-threatening refractory hypoxemia, ie, a
PaO2/FIO2 ratio
< 60.2
In 197624 and 1977,25 there were reports of
the successful use of CPAP in patients with acute respiratory distress.
In one patient, noncardiogenic pulmonary edema (from renal failure) was
managed successfully without intubation.24 The increasing
experience with and current availability of noninvasive ventilation,
including proportional assist ventilation, and the relative success of
NPPV in our patients with ALI/ARDS, provides support for current
ongoing randomized studies of the efficacy of noninvasive ventilation
in patients with acute hypoxemic respiratory failure secondary to ALI.
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Footnotes
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The Lung Association of Nova Scotia provided support.
Correspondence to: G.M. Rocker, MA, DM, Division of Respirology,
4457 New Halifax Infirmary, 1796 Summer St, Halifax, Nova Scotia,
Canada B3H 3A7; e-mail: gmrocker@is.dal.ca
Received for publication January 13, 1998.
Accepted for publication July 28, 1998.
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TOP
Abstract
Introduction
