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(Chest. 2004;126:382-388.)
© 2004 American College of Chest Physicians

Tolerance and Physiologic Effects of Nocturnal Mask Pressure Support vs Proportional Assist Ventilation in Chronic Ventilatory Failure*

João Carlos Winck, MD, PhD; Michele Vitacca, MD; António Morais, MD; Luca Barbano, MD; Roberto Porta, MD; Armando Teixeira-Pinto, MD and Nicolino Ambrosino, MD, FCCP

* From the Departments of Pneumology (Drs. Winck and Morais) and Biostatistics and Medical Informatics (Dr. Teixeira-Pinto), Hospital São João, Faculdade de Medicina, Universidade do Porto, Porto, Portugal; Pulmonary Division (Drs. Vitacca, Barbano, and Porta), S. Maugeri Foundation IRCCS, Gussago (BS); and Pulmonary Unit (Dr. Ambrosino), Cardio-Thoracic Department, University of Pisa, Pisa, Italy.

Correspondence to: João Carlos Winck, MD, PhD, Pneumology Department, Hospital São João, Faculdade de Medicina, Universidade do Porto, Porto, Portugal; e-mail: jwinck{at}hsjoao.min-saude.pt


   Abstract
TOP
 Abstract
Introduction
 Methods and Materials
 Results
 Discussion
 Conclusion
 References
 
Study objectives: To compare the tolerance and physiologic effects of a 5-night treatment with either nasal proportional assist ventilation (PAV) or pressure support ventilation (PSV) in patients with chronic ventilatory failure.

Design: Cross-over, randomized, controlled study.

Setting: Rehabilitation units of pneumology department.

Patients or participants: Four patients with COPD and 10 patients with restrictive thoracic diseases with chronic hypercapnia (median baseline PaCO2, 55.1 mm Hg) were studied.

Interventions: In a cross-over study, nasal PAV and PSV set at the patient’s comfort were randomly applied during 5 consecutive nights (with a 2-night washout period).

Measurements and results: Continuous nocturnal pulse oximetric saturation (SpO2) and arterial blood gas results at wake-up were evaluated at baseline during spontaneous breathing and on the fifth day of ventilatory support. Dyspnea, sleep quality, adaptation, and comfort at inspiration and expiration by visual analog scale (VAS) were evaluated every day as well as a side effects score. On the fifth day, there were no significant differences in daytime PaCO2 (median PAV, 53.3 mm Hg; median PSV, 50.2; p = 0.168). Mean nocturnal SpO2 improved significantly with both PAV and PSV without any significant differences between modes (baseline median, 92%; PAV median, 94.5%; PSV median, 95%). The percentage of the study night spent < 90% SpO2 (T90) was slightly but significantly higher with PAV than with PSV (median PAV T90, 4%; median PSV T90, 2%; p = 0.049). The VAS symptom score was similar at day 5 between modes; however, nasal and oral dryness were lower (p = 0.05) and alarm noise was higher (p = 0.037) with PAV.

Conclusions: After 5 days of treatment, both modes had similar tolerance, and were equally effective in reducing daytime hypercapnia and improving nocturnal saturation and symptoms. However, PAV induced less nasal and oral dryness but was associated with higher alarm noise.

Key Words: chronic ventilatory failure • COPD • noninvasive mechanical ventilation • pressure support ventilation • proportional assist ventilation • restrictive disorders


   Introduction
TOP
 Abstract
 Introduction
Methods and Materials
 Results
 Discussion
 Conclusion
 References
 
Noninvasive positive pressure ventilation (NPPV) has gained widespread use in recent years. Nocturnal NPPV has been proposed for patients with hypercapnic chronic ventilatory failure (CVF) in order to rest the respiratory muscles, improve gas exchange, and reset the central respiratory drive.1

Studies in the last decade have shown that NPPV can be effective in improving sleep quality and long-term outcome in patients with restrictive chest wall diseases (RCWDs) and COPD, although, particularly in the latter, evidence of significant clinical benefit is lacking.2345 Pressure support ventilation (PSV) is the most common mode of providing ventilatory assistance in the long-term setting, with or without some level of positive end-expiratory pressure.6 Although the performance of this mode has been considered generally favorable, patient/ventilator asynchrony may sometimes occur.7

Proportional assist ventilation (PAV) is a new ventilatory mode that was developed to enhance patient/ventilator synchrony, by providing inspiratory flow and pressure in proportion to the patient’s effort.8 PAV provides a higher level of respiratory comfort than PSV in volunteers whose respiratory system compliance has been artificially reduced.9 In the acute setting, nasal PAV has shown more rapid improvement in some physiologic variables and better tolerance than PSV.1011 Application of daytime nasal PAV in patients with stable CVF is effective in improving arterial blood gas results and respiratory muscle function in short-term physiologic studies.1213 However, this theoretic advantage has not altered the clinical application of NPPV. One reason might be that a direct comparison between PAV and PSV was only done in short-term physiologic daytime studies,141516 while home NPPV is usually prescribed at night. In CVF, no comparison of nocturnal application of the two modalities has been performed. Our aim therefore was to compare the tolerance and the physiologic effects of a 5-night treatment with either nasal PAV or PSV of patients with CVF.


   Methods and Materials
TOP
 Abstract
 Introduction
 Methods and Materials
Results
 Discussion
 Conclusion
 References
 
The investigative protocol was approved by the ethics committees of the S. João Hospital and the S. Maugeri Foundation IRCCS. The study was conducted according to the declaration of Helsinki. Patients gave their informed consent to participate in the study.

Patients
Patients with CVF belonging to both institutions and willing to participate in the study were included. From April 1999 to October 2001, 14 patients (4 with COPD and 10 with RCWD) with CVF and admitted for pulmonary rehabilitation were recruited from the Pulmonary Division of the Scientific Institute of Gussago (8 patients) and the Pneumology Department of the São João Hospital, Porto (6 patients). The diagnosis of COPD was made according to the American Thoracic Society standards.17 The diagnosis of CVF was based on the clinical records showing values of PaCO2 > 45 mm Hg during spontaneous room air breathing in the months if not years preceding the study. All patients were in stable clinical condition, as assessed by an arterial pH > 7.35, and they did not have any exacerbations in the preceding 4 weeks. Patients with any other chronic organ failure, cancer, or inability to cooperate were also excluded from the study. All the patients were receiving drug treatment according to the prescriptions of their primary care physicians. In particular, patients with COPD were receiving regular treatment with inhaled bronchodilators, avoiding either systemic or inhaled steroids except for exacerbations. Seven patients (patients 2, 4, 5, 7, 10, 12, and 13) were receiving long-term oxygen therapy, and none had experienced NPPV before. After completion of the study, seven patients (five patients with RCWD and two with COPD) were prescribed home NPPV. The patients’ characteristics according to diagnosis are shown in Table 1 .


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  		Table 1.. Patient Characteristics*

 
Measurements
Static lung volumes were measured by body plethysmograph (6200 Autobox DL; SensorMedics; Yorba Linda, CA) and dynamic lung volumes by mass flow sensor (Vmax229; SensorMedics) with the patients in the seated position according to standard procedure.18 The predicted values of Quanjer19 were used. The inspiratory muscle strength was assessed by measuring maximal inspiratory pressure at the level of functional residual capacity, according to the method of Black and Hyatt.20 The highest of three reproducible attempts was recorded.

Physiologic Data: Overnight pulse oximetric saturation (SpO2) was continuously recorded at baseline using a finger oximeter (Pulsox 3I; Minolta; Osaka, Japan [in Porto] and Pulsox 5; Minolta [in Gussago]) while patients breathed spontaneously with their usual home oxygen supplementation if any. The severity of overnight oxygen desaturation was assessed by calculating the mean and minimum SpO2 and percentage of the study night spent < 90% SpO2 (T90). Resting blood gases were measured at baseline and on the fifth day of treatment, at wake up, from radial artery samples (RapidLab 860; Ciba-Corning; Sudburry, Eng-land).

Tolerance: Visual analog scales (VAS) for dyspnea, quality of sleep, and comfort at inspiration and expiration were evaluated.21 At baseline and every morning after starting both periods of ventilatory support, the patients were asked to indicate their response to the following questions: "How breathless have you felt this morning?", "How well did you sleep last night?", "Was the machine last night comfortable?", and "How comfortable were inspiration and expiration?". In a horizontal line with two anchor points, one at each extreme, the patients drew a line corresponding to the intensity of the symptom (the larger the numerical value, the worse the symptom: 0 is the best, 100 is the worst). On the fifth day of each PSV and PAV study arm, morning arterial blood gases (without the ventilator) and nocturnal monitoring (with ventilatory support) were evaluated.

Side Effects: side effects (dry nose/mouth, nasal blockage, mask discomfort, gastric distension, and noise alarms) were recorded every day during both ventilatory modes. For each side effect a 0 (no symptoms) to 10 (highest symptoms) VAS was used, and the final score was the average of the 5 days.

Ventilatory Settings
Patients were adapted to both ventilatory modes in a short session (1 h) on the day of randomization. A commercial nasal mask of adequate size for each patient’s nose was used (Softseries or GoldSeal masks; Respironics; Murrysville, PA). For each patient, both modalities were delivered by means of the same portable ventilator able to compensate for leaks and to operate in the CPAP, PSV, and PAV modes (BiPAP Vision; Respironics). The ventilator circuit was equipped with a nonrebreathing valve.22

PAV: The ventilator delivers pressure according to the equation of motion, generating pressure in proportion to the patient’s spontaneous effort.8 A portion of the total mechanical workload, ie, elastance and resistance, is taken over according to a level of assistance, which has been decided by the caregiver and can specifically unload the resistive burden (flow assist [FA]) and the elastic burden (volume assist [VA]). VA and FA were set separately; VA and FA were set initially at the minimum value of 2 cm H2O/L and 1 cm H2O/L/s, respectively, in all patients. Then, leaving FA unchanged, VA was increased slowly by increments of 2 cm H2O/L until the patient indicated that breathing was uncomfortable. Then, that level of assist was decreased by 2 cm H2O/L. This last level was defined as the "maximum tolerated." To set FA, a similar stepwise approach was used, by keeping VA at 2 cm H2O/L and slowly increasing FA from 1 cm H2O/L/s by small increments of 1 cm H2O/L/s until the patient indicated that he/she felt uncomfortable with that level of assistance. Then, that level of assist was decreased by 1 cm H2O/L/s. This last level was defined as the maximum tolerated. The values of VA and FA actually applied to patients during the study were set at 80% of those "maximal individual tolerated" values.13

PSV: The level of inspiratory pressure support was increased slowly by 2 cm H2O increments starting from 2 cm H2O, until the patients indicated that breathing was uncomfortable. Hence, that level of inspiratory pressure support was decreased by 2 cm H2O, and the resultant level was applied.

No preset CPAP level was added to RCWD except the 2 cm H2O delivered by default by the ventilator. In patients with COPD, 4 cm H2O of CPAP was added to counteract the intrinsic positive end-expiratory pressure. No respiratory backup rate was used during both modes.

In patients receiving long-term oxygen therapy, oxygen was delivered at the fraction of inspired oxygen (FIO2) able to maintain a SpO2 > 92% during the run-in period of adaptation to ventilatory support maintaining the same FIO2 on both modes (Table 2 ). Supplemental oxygen was obtained through internal blending (oxygen module of the BiPAP Vision [Respironics]) so that the selection of FIO2 was accurate.


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  		Table 2.. Ventilator Settings*

 
Experimental Procedures
This study used a randomized crossover design. Randomization was obtained with a generated randomized sequence for each center. Seven patients started with PAV, while the other seven patients started with PSV. After baseline measurements were obtained, PAV or PSV were applied in random order, during two periods of 5 consecutive nights each. Between the two periods, patients had an interval of 2 nights during which the treatment was withheld (washout). Measurements were also performed at the end of each ventilatory support period. All patients were treated in the hospital, and a technician supervised compliance with the ventilatory support, ensuring at least 6 h of use per night.

Statistical Analysis
Statistical analysis was carried out using SPSS 10.0 (SPSS; Chicago, IL). Results are expressed as median and interquartile range (IQR). Due to the distribution skewness of the observed variables, the data were analyzed using nonparametric methods.

Comparisons between baseline, PAV, and PSV were made using the Friedman test for all continuous variables. The Wilcoxon test was also used for pairwise comparisons, whenever the Friedman test was found to be significant. Changes in the mode settings during protocol were compared using the McNemar test; p ≤ 0.05 was considered significant.


   Results
TOP
 Abstract
 Introduction
 Methods and Materials
 Results
Discussion
 Conclusion
 References
 
All patients completed the study, and their demographic characteristics and ventilator settings are depicted in Tables 1, 2. Daytime arterial blood gas measurements at spontaneous breathing, baseline, and at the end of each series of assisted ventilation, as well as nocturnal SpO2 parameters at baseline and during the last night of each modality of assisted ventilation are shown in Table 3 . There were no significant improvements in daytime PaCO2 on the fifth day for PAV or PSV. There were also no significant differences in PaCO2 on the fifth day between PAV and PSV. Daytime PaO2 did not increase significantly by the fifth day with both modes, and again without any significant differences between the modes.


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  		Table 3.. Arterial Blood Gas Results and Nocturnal Saturation at Baseline and on the Fifth Day of PAV and PSV

 
Nocturnal mean SpO2 improved significantly with both PAV (p = 0.006) and PSV (p = 0.008), without any significant differences between the modes (p = 0.124). At the baseline night, the median T90 was 9%. This fell to 4% with PAV and to 2% with PSV. All the differences in T90 were found to be statistically significant, including PSV vs PAV (p = 0.049) [Table 3].

Results of VAS representing comfort, dyspnea, and sleep quality are shown in Figure 1 . Dyspnea and quality of sleep did not improve significantly after 5 days of ventilatory support, and all symptom scores were similar at day 5 between modes. However, comfort was initially better with PSV.



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  		Figure 1.. Median VAS scores (1 to 100 mm) for comfort (upper panel), sleep (middle panel), and dyspnea (lower panel) during 5 days of nocturnal nasal PAV (black line) and PSV (gray line). Dyspnea and quality of sleep did not improve significantly after 5 days of ventilatory support, and all symptom scores were similar at day 5 between modes (p = not significant) However, comfort was initially better with PSV. *p < 0.05, PAV vs PSV on the first day.

 
Ten patients (6 patients in the PAV study arm, and 4 patients in the PSV study arm) needed adjustments to ventilatory settings (reduction of 1 to 3 cm H2O/L of VA and 1 to 2 cm H2O/L/s of FA, or reduction of 2 to 4 cm H2O of inspiratory positive airway pressure) during the protocol in order to maintain compliance with therapy, but there were not any differences in the number of adjustments between the modes (p = 0.549). Concerning side effects, dry nose and mouth scores were lower (p = 0.05) with PAV, but the patients rated the noise from the ventilator alarms significantly higher (p = 0.037) with this mode (Table 4 ).


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  		Table 4.. Median Side Effects Score

 

   Discussion
TOP
 Abstract
 Introduction
 Methods and Materials
 Results
 Discussion
Conclusion
 References
 
This is the first controlled night study comparing nasal PAV and PSV in patients with CVF over a short-term period. We found that a 5-night application of nasal PAV has similar effects compared to PSV with respect to daytime hypercapnia, nocturnal saturation, and symptoms. However, nasal PAV induced less nasal and oral dryness than PSV but was associated with higher alarm noise.

There is now evidence suggesting a role for NPPV in selected patients with CVF.23 The price and portability has encouraged the widespread use of bilevel ventilators, making PSV one of the most used modes.24 However, uniform agreement is still lacking on the best mode or settings to apply in patients with CVF.23 Previous studies,2526 comparing 2-h administration of pressure vs volume preset ventilators or 1-night application of nasal PSV vs assist/control ventilation, have shown equivalent results in stable patients with CVF.

PAV is a mode that may have some theoretical advantages over PSV.8 Initial studies27 in intubated patients have shown that PAV compared to PSV can improve synchrony. More recently, application of PAV through a facial mask has proven to have physiologic and clinical benefit in acute respiratory failure as well as in CVF.101112131415 Short-term clinical and physiologic comparisons of nasal PAV with PSV have been carried out in patients with acute respiratory failure101128 or in CVF patients only in daytime studies.1415 In these studies, both modalities were equivalent in improving clinical and physiologic parameters, although PAV appeared better tolerated.101128 Recently, Porta et al14 showed that in resting, awake, stable patients with CVF due to either COPD or RCWD, noninvasive applications of both PAV and PSV set at the patient’s comfort improved the breathing pattern and minute ventilation while unloading the inspiratory muscles with excellent patient/ventilator interaction. However, in terms of differences between PSV and PAV, the latter achieved those physiologic benefits at a lower level of mean airway pressure but required more time to set the ventilator. Also, in our nighttime study in CVF patients naïve to ventilatory support, both modes resulted to be equivalent in terms of blood gas changes, nocturnal oxygenation, and tolerance. The finding of less nasal and oral dryness with nasal PAV in our study is in accordance with the study of Gay et al10 in acute patients, in which avoidance of excessive airway pressure with nasal PAV may reduce air leaks, one of the main causes of increased upper airway resistance.29

Compared to the daytime studies of PAV in stable patients with CVF by Ambrosino et al12 and Polese et al,13 the mean VA and FA in our study were equivalent, and in those studies1213 that level of partial assistance was physiologically effective. Whether this level of assistance will have better clinical long-term outcomes remains to be proven. The levels of inspiratory pressure support in our study were also chosen on the basis of the patient’s comfort, and they were similar to those found by Vitacca et al.30 In that study, these levels were found to be effective in unloading inspiratory muscles in COPD patients with CVF.

Our study is the first to evaluate daily symptoms related to adaptation to nocturnal NPPV. Although there is a trend for faster adaptation with PSV, symptoms did not improve significantly at the end of each study arm, suggesting that 5 days may be a short time for successful patient adaptation. This information together with the need for ventilatory setting adjustment (minor assistance reductions) in 10 cases may have some implications in the best way of tailoring NPPV. Our data, together with the work by Criner et al,31 who showed the same degree of ventilatory adjustments, suggest the need of careful supervision to maximize patient compliance with NPPV at the beginning of treatment.

Both PAV and PSV were effective in improving night oxygenation, but T90 was longer with PAV. Although we did not perform full polysomnography (which may be seen as a limitation of the study), differences in sleep quality as measured by VAS did not occur. Accordingly, the data from our study do not support the concerns about the occurrence of "runaway" due to leaks during sleep, with consequent sleep fragmentation.12 However, this should be looked at in more detail by performing sleep studies with continuous leak measurement.32 If the studies in normal individuals translate into patients with CVF, PAV may have the potential to induce less periodic breathing during sleep.33

Our study can be viewed as a pilot study, and may warrant long-term studies to define the exact role of nasal PAV, especially with a new ventilator designed for home ventilatory support, without the inconvenience of alarms that can induce some sleep fragmentation.10 Sophisticated alarms, like those of the BiPAP Vision (Respironics) responsive to pressure, flow, or respiratory rate may be needed in the acute setting,34 and in some patients with increased ventilator dependence; however, less severe patients may not need such ventilator alarms that needlessly awake them at night during transient air leaking.1 Future technology research is needed to address this important problem. However, as judged by VAS, sleep quality scores, and the supervision of the technicians during nighttime, the performance of PAV during sleep seems to be equivalent to PSV without any significant period of leakage-related "runaways."12


   Conclusion
TOP
 Abstract
 Introduction
 Methods and Materials
 Results
 Discussion
 Conclusion
References
 
We could not identify any significant physiologic or tolerance differences between a 5-day application of either nocturnal nasal PAV or PSV, suggesting that PAV may also be suitable in patients with stable CVF. Less nasal/oral dryness with PAV may translate into better compliance in the long-term since mask leaks and nasal complaints are some of the major problems with NPPV.3132 However, if this mode is to be applied during home mechanical ventilation, the monitoring system may need technological improvement to avoid nocturnal disturbance caused by alarm noise.


   Footnotes
 
Abbreviations: CPAP = continuous positive airway pressure; CVF = chronic ventilatory failure; FA = flow assist; FIO2 = fraction of inspired oxygen; IQR = interquartile range; NPPV = noninvasive positive pressure ventilation; PAV = proportional assist ventilation; PSV = pressure support ventilation; RCWD = restrictive chest wall disease; SpO2 = pulse oximetric saturation; T90 = percentage of the study night spent < 90% SpO2; VA = volume assist; VAS = visual analog scale

Received for publication October 2, 2003. Accepted for publication March 25, 2004.


   References
TOP
 Abstract
 Introduction
 Methods and Materials
 Results
 Discussion
 Conclusion
 References
 

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