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* From the Division of Pulmonary & Critical Care Medicine, Department of Medicine, Temple University School of Medicine, Philadelphia, PA.
Correspondence to: Gerard J. Criner, MD, FCCP, Professor of Medicine and Director, Pulmonary & Critical Care Medicine, Temple University School of Medicine, 3401 North Broad St, Suite 921, Philadelphia, PA 19140; e-mail: criner{at}astro.ocis.temple.edu
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Abstract |
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 TOP Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Design: Descriptive analysis of prospectively collected clinical data.
Setting: Inpatient noninvasive respiratory care unit and outpatient clinic of university hospital.
Patients: Forty patients with chronic respiratory failure (20 with severe COPD and 20 with restrictive ventilatory disorders).
Interventions and
measurements: All patients were admitted to a noninvasive
respiratory care unit for 20 ± 3 days for inpatient evaluation
consisting of medical treatment, rehabilitation, and NPPV evaluation
and instruction. NPPV was titrated via a ventilatory support system
(BiPAP; Respironics Inc; Monroeville, PA) or a portable volume
ventilator (PLV 102; Lifecare, Inc; Boulder, CO) to achieve a 
20%
increase in baseline minute ventilation while monitoring gas exchange,
expired volume, and clinical evidence of a decrease in the patient's
work of breathing.
Results: The patients' mean age (± SD) was 65 ± 9.7 years, and there was a 3:1 female:male predominance. In the noninvasive respiratory care unit, 36 patients used NPPV for 7.31 ± 0.26 h/night. Four patients (three with COPD, one with restrictive disorder) withdrew from the study during the 3-week inpatient stay because they could not tolerate NPPV. Six patients (5 with COPD, 1 with restrictive disorder) used a portable volume ventilator and 34 patients used BiPAP (15 with COPD, 19 with restrictive disorders). At discharge, compared with at admission, daytime PaO2/fraction of inspired oxygen (FIO2) increased (327 ± 10 vs 283 ± 13 mm Hg; p = 0.01), PaCO2 was reduced (52 ± 2 vs 67 ± 3 mm Hg; p = 0.0001), and functional score increased (4.76 ± 1.16 vs 2.7 ± 1.64 arbitrary units (AUs); p < 0.01). Six months after discharge, improvements in PaO2/FIO2 (317 ± 10 vs 283 ± 13; p = 0.05), PaCO2 (52 ± 2 vs 67 ± 3 mm Hg; p = 0.0001), and functional score (5.66 ± 0.41 vs 2.7 ± 0.3 AUs; p < 0.001) were maintained compared with admission values. FVC, FEV1, and maximum inspired and expired mouth pressures were unchanged before and after long-term NPPV. Ten patients (7 with COPD, 3 with restrictive disorders) discontinued NPPV at 6 months, and 3 progressed to tracheostomy. The remaining 26 patients continued to use NPPV at the 6-month follow-up. They claimed to use NPPV for 7.23 ± 0.24 h/night, but logged metered use was 4.5 ± 0.58 h/night. Problems that required adjustment in either the mask (36%) or ventilator source (36%) included mask leaks (43%), skin irritation (22%), rhinitis (13%), aerophagia (13%), and discomfort from mask headgear (7%).
Conclusion: NPPV acutely and chronically improves gas exchange and functional status in patients with chronic respiratory failure, but a significant number of patients do not tolerate NPPV on a chronic basis. Comprehensive follow-up is required to correct problems with NPPV and ensure optimal patient compliance.
Key Words: COPD • hypoventilation • mechanical ventilation • noninvasive positive pressure ventilation • respiratory failure
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In this study we evaluated the acute and chronic effects of NPPV on gas exchange, functional status, and respiratory mechanics in patients with chronic respiratory failure related to COPD or restrictive ventilatory disorders. We also sought to determine the incidence and type of problems that arise with long-term outpatient NPPV therapy so that these problems could be ameliorated in the future to improve long-term compliance. We initiated NPPV in a noninvasive respiratory care unit geared toward the evaluation and treatment of NPPV and followed patients after discharge in a comprehensive outpatient program in order to maximize compliance with chronic NPPV therapy.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Assessment of Functional Status
Functional status of all patients was measured using a 7-point
functional scale, where 1 = impaired cognition; 2 = awake, alert,
oriented; 3 = chairbound; 4 = independent in activities of daily
living; 5 = ambulatory, but homebound; 6 = performs all self-care
activities at home (housework, cooking, etc.); and 7 = performs
activities outside the house. Functional scores are recorded in
arbitrary units (AUs).
NPPV Technique
All patients were evaluated for NPPV via a bilevel positive
pressure ventilatory support device (BiPAP; Respironics, Inc;
Monroeville, PA) or a portable volume ventilator (PLV-102 Volume
Ventilator, Lifecare Inc, Boulder, CO). A description of the BiPAP
ventilatory support device has been previously
described.12
Appropriate settings of inspiratory and
expiratory pressures, volumes, and ventilatory modes (ie,
BiPAP vs portable volume ventilator) were chosen while monitoring
airway pressure, inspiratory and expiratory airflow and changes in
tidal volume (VT). Airway pressures were measured
at the mask pressure port by an in-line pressure transducer (range,
± 100 cm H2O; Validyne; Northridge, CA).
Changes in airflow were measured by an in-line pneumotachograph (Hans
Rudolph, Inc; Kansas City, MO), which was placed between the mask and
the exhalation valve. Inspiratory and expiratory volumes were recorded
by integration of the airflow signal and recorded on a multichannel
strip chart recorder (model ES 1000; Gould Inc). Inspiratory and
expiratory pressures, and ventilator-delivered VT
for patients using BiPAP or volume ventilator, respectively, were
titrated until expired minute ventilation increased 20% above
baseline values while simultaneously improving gas exchange
(ie, increased
PaO2/FIO2
and lower PaCO2) and
ensuring patient-ventilator synchrony. The choice of ventilator
(ie, BiPAP or portable volume ventilator) was determined by
each patient's degree of comfort with each source of ventilation,
coupled with the ability to increase minute ventilation, improve gas
exchange, and diminish the patient's work of breathing. After initial
evaluation, 34 patients received NPPV via BiPAP and 6 patients required
NPPV via the portable volume ventilator.
Choice of Mask for NPPV
NPPV was applied in patients via nasal continuous positive
airway pressure masks (Respironics, Inc), an Adam's Circuit nasal mask
(Puritan Bennett; Carlsbad, CA), an oronasal mask (Respironics, Inc),
and a prototypical total face mask (Respironics, Inc.).
Compliance with NPPV Therapy
Compliance with NPPV therapy for inpatients and outpatients was
recorded as hours per day of use. Patient compliance with NPPV in the
hospital was monitored via direct observation by a respiratory
therapist and recorded in a daily log. After discharge, patient
compliance with NPPV was evaluated both by patients' verbal report and
by review of logged hours of use recorded from the ventilator meter by
the durable home equipment vendor.
Ventilator Rehabilitation Unit
All aspects of inpatient NPPV care were conducted within the
confines of the VRU, a special noninvasive respiratory care unit geared
toward maximizing patients' compliance with noninvasive ventilation.
The VRU is one of four US Health Care Financing Administration Chronic
Ventilator Demonstration sites. This program consists of a
multidisciplinary inpatient and outpatient ventilator-dependent
rehabilitation program that includes pulmonologists, respiratory
therapists, physical therapists, speech therapists, nutritionists,
psychologists, and nursing staff trained in advanced respiratory
treatment of patients with chronic respiratory failure. All patients
had a multidisciplinary approach to their inpatient treatment and
attended a weekly outpatient clinic after discharge. Team meetings were
held each week to assess each patient's progress and plan further
care.
To be enrolled into this program, patients must have demonstrated a willingness to actively participate in self-care and have an interested support person. Approximately 65% of the patients referred for enrollment into the program came from within the primary practice of Temple Hospital, and 35% were referred from outside hospitals.
Data Collection Protocol
An algorithm of the data collection protocol is shown in Figure 1 . Baseline measurements of arterial blood gas tensions, respiratory
mechanics, and functional status were obtained in all patients at VRU
entry. All patients then underwent titration of pressure (BiPAP) or
volume (PLV-102 ventilator) ventilators to achieve ventilation goals as
previously outlined. The duration of NPPV use per day was increased in
progressive fashion until patients were able to tolerate at least
6 h of NPPV treatment per night. During the patients' stay in the
VRU, they were evaluated by all members of the multidisciplinary team.
Prior to discharge, patients and their families underwent additional
NPPV instruction. At the time of discharge, repeat measurements of
arterial blood gas tensions, respiratory mechanics, and functional
score were obtained.
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Measurements of arterial blood gas tensions, respiratory mechanics, and functional status were then repeated approximately 6 months after discharge. During the follow-up period, patients underwent adjustments in NPPV masks or ventilator settings if needed in order to maintain patient-ventilator synchrony and optimize gas exchange and functional status.
Statistical Analysis
A one-way analysis of variance with repeated measures was used
to compare ventilatory variables, and arterial blood gases on
admission, at discharge, and during outpatient follow-up. Separate
analyses were done between COPD and restrictive ventilatory disorder
subsets. The Student's t test was used to determine whether
a significant relationship existed between respiratory mechanics before
and after the institution of NPPV therapy. Demographic data are shown
as mean ± SD; other results are expressed as mean ± SEM. A
probability value of 0.05 was considered statistically significant.
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In all patients who started NPPV, 34 used BiPAP (15 with COPD, 19 with restrictive disorders) and 6 required a portable volume ventilator (5 with COPD, 1 with restrictive disorder) in order to achieve ventilation goals. The average level of inspiratory positive airway pressure was 17 ± 4 cm H2O, and expiratory positive airway pressure was 3 ± 2 cm H2O with a mean pressure boost of 14 ± 3 cm H2O. The average delivered expired VT was 725 ± 140 mL with a rate of 22 ± 4 breaths/min in patients receiving NPPV via the portable volume ventilator.
Arterial blood gas analysis in all compliant patients was obtained while the patients were breathing spontaneously at the time of admission, while using NPPV at the optimum settings, during spontaneous breathing at discharge, and while spontaneously breathing at a follow-up visit approximately 23 ± 5 weeks after discharge, as shown in Figure 2 . Mean PaO2/FIO2 values while using NPPV were higher than admission values (329 ± 17 vs 283 ± 13; p = 0.015); mean PaCO2 was significantly lower during NPPV than at admission (51 ± 2 vs 67 ± 3 mm Hg; p = 0.0001); and pH was greater during NPPV than at admission (7.41 ± 0.01 vs 7.35 ± 0.01; p = 0.0001). In compliant patients, the improvements in gas exchange (327 ± 10 vs 283 ± 13; p = 0.01), PaCO2 (52 ± 2 vs 67 ± 3; p = 0.0001), and pH 7.38 ± 0.01 vs 7.35 ± 0.01; p = 0.007) were maintained during spontaneous breathing, both at discharge and at follow-up (Fig 2) .
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To determine whether NPPV had an independent effect on the improvement observed in gas exchange, arterial blood gas values at discharge and follow-up were compared in patients who complied with NPPV vs patients who were noncompliant with NPPV. As shown in Figure 4 , PaO2/FIO2 tended to decrease (294 ± 12 to 259 ± 16; p = 0.10) and PaCO2 tended to rise (54 ± 2 to 60 ± 4 mm Hg; p = 0.19) in the noncompliant group, but remained stable in patients who complied with NPPV.
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In contrast to the improvements in gas exchange and functional status, spirometry (FEV1 and FVC) and respiratory muscle strength (PImax and PEmax) before and after approximately 6 months of NPPV therapy were not significantly different in patients with COPD or restrictive disorders (Fig 5 , 6 ).
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Our observations that NPPV improves gas exchange and functional status in patients with restrictive ventilatory disorders corroborate the findings of others4 12 14 19 20 21 . As a whole, when noninvasive ventilation is used in patients with restrictive ventilatory disorders, the data uniformly show an improvement in patient symptoms and gas exchange,4 19 20 28 and occasionally demonstrate an improvement in respiratory muscle function20 28 and spirometric values.20 Although NPPV improves gas exchange and symptoms in patients with restrictive ventilatory disorders, its effect on respiratory muscle strength and spirometry is variable.20 23 25 28 Our findings are in agreement with those of others23 25 28 that improvements in gas exchange and functional status need not be accompanied by any change in spirometry or respiratory muscle strength.
Results of noninvasive ventilation in COPD patients with chronic respiratory failure have been even more inconsistent. Strumpf et al15 and Gay et al13 have shown that NPPV in patients with chronic, stable, moderately severe COPD has no significant effect on gas exchange, functional status, or the patients' quality of life. In contrast, other investigators have demonstrated that NPPV used daily for 1 week to 3 months had significant beneficial effects on gas exchange, sleep quality, exercise tolerance, and quality of life.5 6 7 14 17
Why different investigators have found varying results in using NPPV in COPD patients, in contrast to patients with restrictive disorders, is not known, but several theories exist. First, patients with restrictive ventilatory disorders and hypercapnia suffer primarily from hypoventilation resulting from either respiratory muscle weakness or chronic resetting of the CO2 threshold. Application of noninvasive ventilation in this patient group improves nocturnal ventilation and acts to reset the CNS CO2 threshold. Some have suggested that the use of noninvasive ventilation provides intermittent chronic respiratory muscle resting and/or improves lung and chest wall compliance, thereby resulting in an improvement in respiratory mechanics that improves respiratory function, gas exchange, and functional status.20 The latter mechanisms appear less tenable because the presence of respiratory muscle fatigue has never been shown to exist in a chronic state in any patient group; also, several studies have failed to document an improvement in spirometric values or respiratory muscle strength, suggesting that NPPV does not improve respiratory mechanics.
COPD patients develop hypercapnia by very different mechanisms than patients who become hypercapnic because of restrictive ventilatory disorders. Most commonly, hypercapnia exists in this patient group because of an increase in physiologic dead space secondary to a ventilation/perfusion imbalance induced by bronchospasm or by the effect of emphysema altering CO2 elimination across a significantly reduced alveolar capillary bed. In COPD patients, therefore, hypercapnia does not always signify hypoventilation, but may signify high physiologic dead space as a result of either reactive airways disease or structural changes in the lung. The application of NPPV in this scenario would be much less likely to uniformly improve gas exchange or functional tolerance. Moreover, the application of NPPV in patients with COPD whose lungs are severely hyperinflated and obstructed may further worsen the development of hyperinflation, thereby contributing to poorer tolerance of NPPV in contrast to patients with restrictive ventilatory disorders.
Although the above reasons support the notion that COPD patients do not tolerate NPPV as well as patients with restrictive disorders, some COPD patients chronically use NPPV for long periods of time and appear to derive physiologic and functional benefit. What makes this patient group distinct from other patient groups with COPD is currently unknown, but several hypotheses could be put forth.
First, some COPD patients have been shown to have an
overlapping syndrome (ie, combination of COPD and
obstructive sleep apnea syndrome) that may benefit from the use of
nocturnal ventilation.29
This patient group may,
therefore, favorably influence the beneficial effects of NPPV in
chronic respiratory failure and COPD. Most studies that tend to
demonstrate an improvement in symptoms and gas exchange with NPPV in
severe COPD have included patients with moderate to severe hypercapnia
on implementation. Indeed, our patients had higher levels of
PaCO2 than did any other
patients in whom NPPV has been applied on a chronic basis. Our results
are similar to those of Meecham-Jones et al,17
who showed
a benefit in 12 patients with severe COPD whose mean
PaCO2 was 55 mm Hg. In
contrast, Strumpf et al15
and Gay et al13
failed to show any benefit with NPPV in COPD patients whose average
PaCO2 levels were 
45 mm
Hg. Perhaps COPD patients with severe hypercapnia represent a subgroup
of patients in whom hypoventilation is a component of their disease,
and thus they benefit from chronic NPPV application.
Our data suffer from the standpoint that the study did not have
an appropriate control arm of patients who only received long-term
oxygen or low levels of continuous positive airway pressure. We believe
that this would not have been appropriate for those patients with
restrictive ventilatory disorders because many studies have now shown
the beneficial effects of NPPV therapy in this patient group. Our COPD
patient group, as a whole, was extremely ill (ie, COPD
patients were acidemic, 40% had cor pulmonale, and one third
had been intubated 6 months prior to study entry) and had already
failed maximal standard therapy. Despite the absence of an adequate
control group, however, the observation that patients who were
noncompliant with NPPV tend to showed a worsening in gas exchange
and functional status supports our notion that NPPV had a important
therapeutic role in those who complied with therapy.
Our chronic NPPV therapy compliance rate of 65% occurred in a comprehensive outpatient program that was geared toward maximizing patient comfort and the efficacy of NPPV application with frequent face mask changes or ventilator settings to optimize patient comfort and gas exchange. In the patients who were compliant with NPPV, they underestimated their use of noninvasive ventilation at least 45% of the time as compared with objective meter logs. This highlights the problems of prior studies that have commented on the efficacy of NPPV. Some patients who were previously reported not to have benefited from NPPV may have failed not because of lack of clinical efficacy, but rather because of noncompliance with prescribed NPPV therapy. Future studies must address the issue of efficacy vs compliance and ensure that objective parameters of NPPV use are measured.
It should also be recognized that patients with COPD developed a set of complications when they used NPPV that differed from those developed by patients with restrictive ventilatory disorders. The development of tracheobronchitis, with an increase in airway secretions, dynamic development of worsened airways obstruction, and the need for additional medications such as bronchodilators, poses problems in the application of NPPV therapy to this group. Obviously, worsening secretions or bronchospasm affect gas exchange and require an alteration in the application of NPPV. Furthermore, the development of worsening hyperinflation or the need for concomitant use of other medications may negatively influence patient compliance with NPPV, such that only the most motivated patient who perceives benefit will continue with therapy.
Our data are strengthened by the fact that they were collected prospectively in a comprehensive inpatient and outpatient program that was optimized to provide maximal medical therapy (including pulmonary rehabilitation) and compliance with NPPV treatment (ie, adjustments of face mask and ventilator settings to maximize ventilatory support). Nonetheless, even in such a comprehensive program, we found that only approximately 50% of our patients with COPD could tolerate NPPV, in contrast to 75% of patients with restrictive ventilatory disorders.
In summary, our data corroborate prior studies that show an important beneficial effect of NPPV on gas exchange and functional status in patients with chronic respiratory failure secondary to COPD or restrictive ventilatory disorders. However, in our study, only 75% of patients with restrictive ventilatory disorders and 50% of patients with COPD continued to use NPPV during prolonged follow-up of approximately 6 months, despite enrollment in a comprehensive inpatient and outpatient program. Future studies, preferably conducted in a prospective, randomized, and controlled fashion, are required to determine the subgroups of COPD patients who may best benefit from NPPV therapy.
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Footnotes |
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Supported in part by grant No. 29-P-99401/3–01 from the Health Care Financing Administration.
Received for publication October 9, 1997. Accepted for publication April 16, 1999.
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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