Physiologic response of ventilator-dependent patients with chronic obstructive pulmonary disease to proportional assist ventilation and continuous positive airway pressure

Lung Hyperinflation as Treatable Trait in Chronic Obstructive Pulmonary Disease: A Narrative Review

Lung hyperinflation (LH) is a common clinical feature in patients with chronic obstructive pulmonary disease (COPD). It results from a combination of reduced elastic lung recoil as a consequence of irreversible destruction of lung parenchyma and expiratory airflow limitation. LH is an important determinant of morbidity and mortality in COPD, partially independent of the degree of airflow limitation. Therefore, reducing LH has become a major target in the treatment of COPD over the last decades. Advances were made in the diagnostics of LH and several effective interventions became available. Moreover, there is increasing evidence suggesting that LH is not only an isolated feature in COPD but rather part of a distinct clinical phenotype that may require a more integrated management. This narrative review focuses on the pathophysiology and adverse consequences of LH, the assessment of LH with lung function measurements and imaging techniques and highlights LH as a treatable trait in COPD. Finally, several suggestions regarding future studies in this field are made.

Is positive airway pressure therapy underutilized in chronic obstructive pulmonary disease patients?

INTRODUCTION

The role of noninvasive positive pressure ventilation (NIPPV) in patients with stable chronic obstructive pulmonary disease (COPD) in the home-setting remains controversial. Despite studies suggesting potential benefits, there is an apparent underutilization of such therapy in patients with stable COPD in a domiciliary setting. Areas covered: The reasons for underutilization in the home-setting are multifactorial, and we provide our perspective on the adequacy of scientific evidence and implementation barriers that may underlie the observed underutilization. In this article, we will discuss continuous PAP, bilevel PAP, and non-invasive positive pressure ventilation using a home ventilator (NIPPV). Expert commentary: Many patients with stable COPD and chronic respiratory failure do not receive NIPPV therapy at home despite supportive scientific evidence. Such underutilization suggests that there are barriers to implementation that include provider knowledge, health services, and payor policies. For patients with stable COPD without chronic respiratory failure, there is inadequate scientific evidence to support domiciliary NIPPV or CPAP therapy. In patients with stable COPD without chronic respiratory failure, studies aimed at identifying patient characteristics that determine the effectiveness of domiciliary NIPPV therapy needs further study. Future implementation and health-policy research with appropriate stakeholders are direly needed to help improve patient outcomes.

Non-invasive ventilation: Essential requirements and clinical skills for successful practice

Audits and case reviews of the acute delivery of non-invasive ventilation (NIV) have shown that the results achieved in real life often fall short of those achieved in research trials. Factors include inappropriate selection of patients for NIV and failure to apply NIV correctly. This highlights the need for proper training of all involved individuals. This article addresses the different skills needed in a team to provide an effective NIV service. Some detail is given in each of the key areas but it is not comprehensive and should stimulate further learning (reading, attendance on courses, e-learning, etc.), determined by the needs of the individual.

Evidence Supporting Clinical Use of Proportional Assist Ventilation: A Systematic Review and Meta-Analysis of Clinical Trials

BACKGROUND

While proportional assist ventilation (PAV), generates pressure in proportion to effort without a preselected target, proportional assist ventilation plus (PAV+) measures compliance and resistance, calculates work of breathing, and adjusts support to a preset assistance level.

OBJECTIVE

To summarize randomized controlled trials (RCTs) comparing invasive or noninvasive PAV or PAV+ in critically ill patients. Data Sources: We searched multiple databases to April 2017 without language restrictions and conference proceedings from 5 meetings to identify randomized parallel-group and crossover RCTs that compared invasive or noninvasive PAV or PAV+ to another mode in critically ill adults or children and reported at least 1 clinically important outcome.

RESULTS

We identified 14 RCTs (11 parallel group and 3 crossover) assessing PAV (n = 7) and PAV+ (n = 7) involving 931 adult patients. We found no effect of noninvasive PAV (vs noninvasive pressure support [PS]) on intubation (risk ratio 0.92 [0.59 to 1.43], I² = 0%) or invasive PAV (vs invasive PS) on percentage rapid eye movement sleep (mean difference [MD] -2.93% [-14.20 to ±8.34], I² = 43%). Compared to invasive PS, invasive PAV+ showed a nonsignificant increase in weaning time (MD +0.54 [-0.67 to +1.75] hours, I² = 0%), but no effect on hospital mortality, reintubation, or tracheostomy.

CONCLUSIONS

Current evidence does not support the use of invasive or noninvasive PAV or invasive PAV+ in critically ill adults. Amid low to moderate heterogeneity, we identified 3 promising areas for future research including assessing the role of noninvasive PAV as an initial support strategy in patients with acute respiratory failure, invasive PAV on sleep quality during invasive ventilation, and possibly invasive PAV+ for weaning.

Neurally adjusted ventilatory assist and proportional assist ventilation both improve patient-ventilator interaction

Introduction

The objective was to compare the impact of three assistance levels of different modes of mechanical ventilation; neurally adjusted ventilatory assist (NAVA), proportional assist ventilation (PAV), and pressure support ventilation (PSV) on major features of patient-ventilator interaction.

Methods

PSV, NAVA, and PAV were set to obtain a tidal volume (V_T) of 6 to 8 ml/kg (PSV₁₀₀, NAVA₁₀₀, and PAV₁₀₀) in 16 intubated patients. Assistance was further decreased by 50% (PSV₅₀, NAVA₅₀, and PAV₅₀) and then increased by 50% (PSV₁₅₀, NAVA₁₅₀, and PAV₁₅₀) with all modes. The three modes were randomly applied. Airway flow and pressure, electrical activity of the diaphragm (EAdi), and blood gases were measured. V_T, peak EAdi, coefficient of variation of V_T and EAdi, and the prevalence of the main patient-ventilator asynchronies were calculated.

Results

PAV and NAVA prevented the increase of V_T with high levels of assistance (median 7.4 (interquartile range (IQR) 5.7 to 10.1) ml/kg and 7.4 (IQR, 5.9 to 10.5) ml/kg with PAV₁₅₀ and NAVA₁₅₀ versus 10.9 (IQR, 8.9 to 12.0) ml/kg with PSV₁₅₀, P <0.05). EAdi was higher with PAV than with PSV at level₁₀₀ and level₁₅₀. The coefficient of variation of V_T was higher with NAVA and PAV (19 (IQR, 14 to 31)% and 21 (IQR 16 to 29)% with NAVA₁₀₀ and PAV₁₀₀ versus 13 (IQR 11 to 18)% with PSV₁₀₀, P <0.05). The prevalence of ineffective triggering was lower with PAV and NAVA than with PSV (P <0.05), but the prevalence of double triggering was higher with NAVA than with PAV and PSV (P <0.05).

Conclusions

PAV and NAVA both prevent overdistention, improve neuromechanical coupling, restore the variability of the breathing pattern, and decrease patient-ventilator asynchrony in fairly similar ways compared with PSV. Further studies are needed to evaluate the possible clinical benefits of NAVA and PAV on clinical outcomes.

Trial registration

Clinicaltrials.gov NCT02056093. Registered 18 December 2013.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0763-6) contains supplementary material, which is available to authorized users.

Physiologic comparison of neurally adjusted ventilator assist, proportional assist and pressure support ventilation in critically ill patients

To compare, in a group of difficult to wean critically ill patients, the short-term effects of neurally adjusted ventilator assist (NAVA), proportional assist (PAV+) and pressure support (PSV) ventilation on patient-ventilator interaction.

METHODS

Seventeen patients were studied during NAVA, PAV+ and PSV with and without artificial increase in ventilator demands (dead space in 10 and chest load in 7 patients). Prior to challenge addition the level of assist in each of the three modes tested was adjusted to get the same level of patient's effort.

RESULTS

Compared to PSV, proportional modes favored tidal volume variability. Patient effort increase after dead space was comparable among the three modes. After chest load, patient effort increased significantly more with NAVA and PSV compared to PAV+. Triggering delay was significantly higher with PAV+. The linear correlation between tidal volume and inspiratory integral of transdiaphragmatic pressure (PTPdi) was weaker with NAVA than with PAV+ and PSV on account of a weaker inspiratory integral of the electrical activity of the diaphragm (∫EAdi)-PTPdi linear correlation during NAVA [median (interquartile range) of r(2), determination of coefficient, 16.2% (1.4-30.9%)].

CONCLUSION

Compared to PSV, proportional modes favored tidal volume variability. The weak ∫EAdi-PTPdi linear relationship during NAVA and poor triggering function during PAV+ may limit the effectiveness of these modes to proportionally assist the inspiratory effort.

New modes of assisted mechanical ventilation

Recent major advances in mechanical ventilation have resulted in new exciting modes of assisted ventilation. Compared to traditional ventilation modes such as assisted-controlled ventilation or pressure support ventilation, these new modes offer a number of physiological advantages derived from the improved patient control over the ventilator. By implementing advanced closed-loop control systems and using information on lung mechanics, respiratory muscle function and respiratory drive, these modes are specifically designed to improve patient-ventilator synchrony and reduce the work of breathing. Depending on their specific operational characteristics, these modes can assist spontaneous breathing efforts synchronically in time and magnitude, adapt to changing patient demands, implement automated weaning protocols, and introduce a more physiological variability in the breathing pattern. Clinicians have now the possibility to individualize and optimize ventilatory assistance during the complex transition from fully controlled to spontaneous assisted ventilation. The growing evidence of the physiological and clinical benefits of these new modes is favoring their progressive introduction into clinical practice. Future clinical trials should improve our understanding of these modes and help determine whether the claimed benefits result in better outcomes.

Comparative evaluation of three interfaces for non-invasive ventilation: a randomized cross-over design physiologic study on healthy volunteers

Introduction

Interface choice is crucial for non-invasive ventilation (NIV) success. We compared a new interface, the helmet next (H_N), with the facial mask (FM) and the standard helmet (H_S) in twelve healthy volunteers.

Methods

In this study, five NIV trials were randomly applied, preceded and followed by a trial of unassisted spontaneous breathing (SB). Baseline settings, for example, 5 cmH₂O of both inspiratory pressure support (PS) and positive end-expiratory pressure (PEEP), were applied through FM, H_S and H_N, while increased settings (PS and PEEP of 8 cmH₂O) were only applied through H_S and H_N. We measured flow, airway, esophageal and gastric pressures, and calculated inspiratory effort indexes and trigger delays. Comfort was assessed with a visual-analog-scale.

Results

We found that FM, H_S and H_N at baseline settings were not significantly different with respect to inspiratory effort indexes and comfort. Inspiratory trigger delay and time of synchrony (TI,synchrony) were significantly improved by FM compared to both helmets, whereas expiratory trigger delay was shorter with FM, as opposed to H_S only. H_N at increased settings performed better than FM in decreasing inspiratory effort measured by pressure-time product of transdiaphragmatic pressure (PTPdi)/breath (10.7 ± 9.9 versus 17.0 ± 11.0 cmH₂O*s), and PTPdi/min (128 ± 96 versus 204 ± 81 cmH₂O*s/min), and PTPdi/L (12.6 ± 9.9 versus 30.2 ± 16.8 cmH₂O*s/L). TI, synchrony was inferior between H_N and H_S at increased settings and FM.

Conclusions

H_N might hold some advantages with respect to interaction and synchrony between subject and ventilator, but studies on patients are needed to confirm these findings.

Trial registration

ClinicalTrials.gov NCT01610960

Partial ventilatory support modalities in acute lung injury and acute respiratory distress syndrome-a systematic review

PURPOSE

The efficacy of partial ventilatory support modes that allow spontaneous breathing in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) is unclear. The objective of this scoping review was to assess the effects of partial ventilatory support on mortality, duration of mechanical ventilation, and both hospital and intensive care unit (ICU) lengths of stay (LOS) for patients with ALI and ARDS; the secondary objective was to describe physiologic effects on hemodynamics, respiratory system and other organ function.

METHODS

MEDLINE (1966-2009), Cochrane, and EmBase (1980-2009) databases were searched using common ventilator modes as keywords and reference lists from retrieved manuscripts hand searched for additional studies. Two researchers independently reviewed and graded the studies using a modified Oxford Centre for Evidence-Based Medicine grading system. Studies in adult ALI/ARDS patients were included for primary objectives and pre-clinical studies for supporting evidence.

RESULTS

Two randomized controlled trials (RCTs) were identified, in addition to six prospective cohort studies, one retrospective cohort study, one case control study, 41 clinical physiologic studies and 28 pre-clinical studies. No study was powered to assess mortality, one RCT showed shorter ICU length of stay, and the other demonstrated more ventilator free days. Beneficial effects of preserved spontaneous breathing were mainly physiological effects demonstrated as improvement of gas exchange, hemodynamics and non-pulmonary organ perfusion and function.

CONCLUSIONS

The use of partial ventilatory support modalities is often feasible in patients with ALI/ARDS, and may be associated with short-term physiological benefits without appreciable impact on clinically important outcomes.

Helmet with specific settings versus facemask for noninvasive ventilation

OBJECTIVE

To compare the physiologic effects of noninvasive pressure-support ventilation (NPSV) delivered by a facemask, a helmet with the same settings, and a helmet with specific settings. Inspiratory muscle effort, gas exchange, patient-ventilator synchrony, and comfort were evaluated.

DESIGN

Prospective crossover study.

SETTING

A 13-bed medical intensive care unit in a university hospital.

PATIENTS

Eleven patients at risk for respiratory distress requiring early NPSV after extubation.

INTERVENTION

One hour after extubation, three 20-minute NPSV periods were delivered in a random order by facemask, helmet, and helmet with 50% increases in both pressure support and positive end-expiratory pressure and with the highest pressurization rate (95% max).

MEASUREMENTS AND MAIN RESULTS

Flow and airway, esophageal, and gastric pressure signals were measured under the three NPSV conditions and during spontaneous breathing. Compared with the facemask, the helmet with the same settings resulted in a greater inspiratory muscle effort, but this difference was abolished by the specific settings (pressure-time product in cm H2O.s.min, 63.8 [27.3-85.9], 81.8 [36.0-111.5], and 58.0 [25.4-79.5], respectively, p < 0.05, compared with 209.3 [29.8-239.6] during spontaneous breathing). Compared with the facemask, the helmet with the same settings worsened patient-ventilator synchrony, as indicated by longer triggering-on and cycling-off delays (0.14 [0.11-0.20] seconds vs. 0.32 [0.26-0.43] seconds, p < 0.05; and 0.20 [0.08-0.24] seconds vs. 0.27 [0.25-0.35] seconds, p < 0.01, respectively). The specific settings significantly improved the triggering-on delay compared with the helmet without specific settings (p < 0.01). Tolerance was the same with the three methods.

CONCLUSIONS

Our results suggest that increasing both the pressure-support level and positive end-expiratory pressure and using the highest pressurization rate may be advisable when providing NPSV via a helmet.

Tracheal pressure regulated volume assist ventilation in acute respiratory failure

PURPOSE

Proportional assist ventilation (PAV) uses volume assist (VAV) and flow assist ventilation (FAV) to reduce elastic and resistive effort, respectively. Proportional assist ventilation may be difficult to apply clinically, particularly due to FAV related considerations. It was hypothesized that regulating tracheal (Ptr) rather than airway opening pressure (Pao), to overcome endotracheal tube related resistive effort, during VAV would provide an effective alternative method of ventilation. We therefore compared the effects of Pao and Ptr regulated VAV on breathing pattern and inspiratory effort.

METHODS

In seven intubated patients, flow, volume, Pao, Ptr, esophageal and transdiaphragmatic pressure were measured during VAV (0-80% respiratory system elastance) using Pao vs Ptr to regulate ventilator applied pressure. Breathing pattern and the pressure-time integral of the inspiratory muscles (integralP(mus) . dt) and diaphragm (integralP(di) . dt) were determined.

RESULTS

Compared to spontaneous breathing, the respiratory rate to tidal volume ratio, or rapid shallow breathing index (RSBI), improved progressively with increasing VAV (130 +/- 64 vs 70 +/- 35, VAV 0 vs 80%; P < 0.05) while inspiratory effort fell (integralP(mus) . dt = 39.6 +/- 7.5 vs 28.5 +/- 7.2 cm H(2)O.sec.L(-1), integralP(di) . dt, = 35.4 +/- 7.8 vs 24.2 +/- 5.9 cm H(2)O.sec.L(-1), VAV 0 vs 80%; P < 0.05) due to a decrease in elastic related effort. At any given level of support, there was further reduction in RSBI, integralP(mus) . dt, and integralP(di) . dt (which averaged 23.6 +/- 2.7, 33.7 +/- 4.4, and 38.5 +/- 5.1%, respectively; P < 0.05) for Ptr compared to Pao regulated VAV due to a decrease in resistive effort.

CONCLUSIONS

Tracheal pressure regulated VAV can be a simple and effective method of partial ventilatory support in acute respiratory failure. Further work will be needed to determine its efficacy and potential benefit relative to PAV and other modes of ventilation in routine clinical practice.

Sleep during proportional-assist ventilation with load-adjustable gain factors in critically ill patients

BACKGROUND

Proportional-assist ventilation with load-adjustable gain factors (PAV+) automatically adjusts the flow and volume assist to represent constant fractions of resistance and elastance of the respiratory system, respectively. Resistance and elastance are calculated at random intervals of 4-10 breaths, by applying a 300 ms pause maneuver at the end of selected inspirations.

OBJECTIVES

To determine whether the large number of end-inspiratory occlusions during PAV+ operation influences sleep quality in critically ill patients who exhibited good patient-ventilator synchrony during pressure support (PS, baseline).

METHODS

One and two nights' polysomnography was performed in sedated (protocol A, n=11) and non-sedated (protocol B, n=9) patients, respectively, while respiratory variables were continuously recorded. In each protocol the patients were ventilated with PAV+ and PS at two levels of assist (baseline and high).

RESULTS

In both protocols sleep quality did not differ between the modes of support or the assist levels. In sedated patients sleep efficiency was slightly but significantly higher with PAV+ than with high PS, while it did not differ between modes in non-sedated patients. The two modes of support had comparable effects on respiratory variables. Independent of the mode of support and particularly at high assist, a significant proportion of patients developed periodic breathing during sleep (27% in protocol A and 44% in protocol B).

CONCLUSION

In patients exhibiting good patient-ventilator synchrony during PS, the large number of short-term end-inspiratory occlusions with PAV+ operation did not adversely influence sleep quality. With both modes high assist may cause unstable breathing during sleep.

Non-invasive ventilation in chronic obstructive pulmonary disease patients: helmet versus facial mask

RATIONALE

The helmet is a new interface with the potential of increasing the success rate of non-invasive ventilation by improving tolerance.

OBJECTIVES

To perform a physiological comparison between the helmet and the conventional facial mask in delivering non-invasive ventilation in hypercapnic patients with chronic obstructive pulmonary disease.

METHODS

Prospective, controlled, randomized study with cross-over design. In 10 patients we evaluated gas exchange, inspiratory effort, patient-ventilator synchrony and patient tolerance after 30 min of non-invasive ventilation delivered either by helmet or facial mask; both trials were preceded by periods of spontaneous unassisted breathing.

MEASUREMENTS

Arterial blood gases, inspiratory effort, duration of diaphragm contraction and ventilator assistance, effort-to-support delays (at the beginning and at the end of inspiration), number of ineffective efforts, and patient comfort.

MAIN RESULTS

Non-invasive ventilation improved gas exchange (p<0.05) and inspiratory effort (p<0.01) with both interfaces. The helmet, however, was less efficient than the mask in reducing inspiratory effort (p<0.05) and worsened the patient-ventilator synchrony, as indicated by the longer delays to trigger on (p<0.05) and cycle off (p<0.05) the mechanical assistance and by the number of ineffective efforts (p<0.005). Patient comfort was no different with the two interfaces.

CONCLUSIONS

Helmet and facial mask were equally tolerated and both were effective in ameliorating gas exchange and decreasing inspiratory effort. The helmet, however, was less efficient in decreasing inspiratory effort and worsened the patient-ventilator interaction.

Respiratory load compensation during mechanical ventilation—proportional assist ventilation with load-adjustable gain factors versus pressure support

RATIONALE

In mechanically ventilated patients respiratory system impedance may vary from time to time, resulting, with pressure modalities of ventilator support, in changes in the level of assistance. Recently, implementation of a closed-loop adjustment to continuously adapt the level of assistance to changes in respiratory mechanics has been designed to operate with proportional assist ventilation (PAV+).

OBJECTIVES

The aim of this study was to assess, in critically ill patients, the short-term steady-state response of respiratory motor output to added mechanical respiratory load during PAV+ and during pressure support (PS).

PATIENTS AND INTERVENTIONS

In 10 patients respiratory workload was increased and the pattern of respiratory load compensation was examined during both modes of support.

MEASUREMENTS AND RESULTS

Airway and transdiaphragmatic pressures, volume and flow were measured breath by breath. Without load, both modes provided an equal support as indicated by a similar pressure-time product of the diaphragm per breath, per minute and per litre of ventilation. With load, these values were significantly lower (p<0.05) with PAV+ than those with PS (5.1+/-3.7 vs 6.1+/-3.4 cmH2O.s, 120.9+/-77.6 vs 165.6+/-77.5 cmH2O.s/min, and 18.7+/-15.1 vs 24.4+/-16.4 cmH2O.s/l, respectively). Contrary to PS, with PAV+ the ratio of tidal volume (VT) to pressure-time product of the diaphragm per breath (an index of neuroventilatory coupling) remained relatively independent of load. With PAV+ the magnitude of load-induced VT reduction and breathing frequency increase was significantly smaller than that during PS.

CONCLUSION

In critically ill patients the short-term respiratory load compensation is more efficient during proportional assist ventilation with adjustable gain factors than during pressure support.

Physiological response to intrapulmonary percussive ventilation in stable COPD patients

Intrapulmonary percussive ventilation (IPV) is a ventilatory technique that delivers bursts of high-flow respiratory gas into the lung at high rates, intended for treating acute respiratory failure and for mobilization of secretions. We performed a study, aimed at assessing the physiological response to IPV, on patients' breathing pattern, inspiratory effort, lung mechanics and tolerance to ventilation. Ten COPD patients underwent randomized trials of IPV through a face mask at different pressure/frequency combinations (1.2 bar/250 cycles/min; 1.8/250; 1.2/350; 1.8/350), separated by return to baseline (SB), using the IMP2 ventilator. In 5 patients we have also compared the physiological changes of IPV with those obtained during pressure support ventilation (PSV). Minute ventilation did not vary among the trials, but tidal volumes (VT) were significantly greater during 1.2/250, 1.2/350 and 1.8/350 compared to SB. The pressure time product of the diaphragm per minute (PTPdi/min) estimate of the diaphragm oxygen expenditure was also significantly reduced during 1.2/250 and 1.8/250 (209 cmH2O x s/min for SB vs. 143 and 125 for 1.2/250 and 1.8/250, respectively P < 0.05), as well as dynamic intrinsic end-expiratory pressure (PEEPi,dyn). Similar reduction in PTPdi/min were obtained also during PSV. Tolerance to ventilation and oxygen saturation were satisfactory and did not change during the different trials. In 5 normal subjects a prolonged apnea trial lasting > 2 min was also performed, without any significant decrease in SaO2 or subjective discomfort. In conclusion, IPV was able to guarantee an adequate ventilation, while inducing a significant unloading of the diaphragm during the "low-frequency" trials.

Mechanical Ventilation

Mechanical ventilation is the second most frequently performed therapeutic intervention after treatment for cardiac arrhythmias in intensive care units today. Countless lives have been saved with its use despite being associated with a greater than 30% in-hospital mortality rate. As life expectancies increase and people with chronic illnesses survive longer, artificial support with mechanical ventilation is also expected to rise. In one survey, over half of senior internal medicine residents reported their training on mechanical ventilation as inadequate, whereas the majority of critical care nurses reported having received no formal education on its use. Technological advances resulting in the availability of sleeker ventilators with graphic waveform displays and new modes of ventilation have challenged the bedside clinicians to incorporate this new data along with evidenced-based research into their daily practice. A review of current thoughts on mechanical ventilation and weaning is presented.

Noninvasive pressure support versus proportional assist ventilation in acute respiratory failure

BACKGROUND

Although conventional pressure ventilation (PSV) decreases the rate of intubation in acute respiratory failure, patient-ventilator dyssynchrony is a frequent cause of failure. In proportional assist ventilation (PAV), pressure is applied by the ventilator in proportion to the patient-generated volume and flow; therefore, there is automatic synchrony between the patient's effort and the ventilatory cycle.

OBJECTIVE

The aim of this study was to compare the effects of PSV and PAV during noninvasive ventilation in the treatment of acute respiratory failure.

DESIGN

Prospective randomised study.

SETTING

A multidisciplinary 24-bed intensive care unit of an acute-care teaching hospital in Alicante, Spain. PATIENTS. This study included 117 consecutive adult patients with acute respiratory failure randomised to noninvasive ventilation delivered by PSV ( n = 59) or PAV ( n = 58).

MEASUREMENTS AND RESULTS

There were no statistically significant differences between patients assigned to each mode of ventilation with regard to baseline parameters and aetiological diagnoses of acute respiratory failure. With regard to outcome data, no significant differences were observed between PSV and PAV in the frequency of intubation (37% vs 34%), mortality rate (29% vs 28%), and mean length of stay. Subjective comfort (0-10 visual analogue scale) was rated higher and intolerance occurred less frequently (3.4% vs 15%, P = 0.03) in the PAV than in the PSV mode.

CONCLUSIONS

Although PAV seems more comfortable and intolerance occurred less frequently, no major differences exist in terms of physiological improvement or in terms of outcomes when comparing PSV and PAV.

Respiratory muscle workload in intubated, spontaneously breathing patients without COPD: pressure support vs proportional assist ventilation

OBJECTIVE

To compare the respiratory muscle workload associated with pressure support ventilation (PSV) and proportional assist ventilation (PAV) in intubated and spontaneously breathing patients without COPD.

DESIGN AND SETTING

Prospective study, intensive care unit university hospital.

INTERVENTIONS

Twenty intubated patients, during early weaning, PSV settings made by clinician in charge of the patient, and two levels of PAV, set to counterbalance 80% (PAV 80) and 50% (PAV 50) of both elastic and resistive loads, respectively. The patients were ventilated in the following order: 1) PSV; 2) PAV 50 or PAV 80; 3) PSV; 4) PAV 80 or PAV 50; 5) PSV. PSV settings were kept constant.

MEASUREMENTS

Arterial blood gases, breathing pattern and respiratory effort parameters at the end of each of the five steps.

MAIN RESULTS

PSV and PAV 80 had the same effects on work of breathing (WOB). The pressure-time product (PTP) was significantly higher during PAV 80 than during PSV (90+/-76 and 61+/-56 cmH(2)O.s.min(-1), respectively, P <0.05). Tidal volume was comparable, albeit more variable with PAV 80 than with PSV (variation coefficient, 43% vs 25%, respectively, P <0.05). PAV 50 entailed a higher respiratory rate, lower tidal volume, and higher WOB and PTP than PSV and PAV 80. PaO(2)/FiO(2) and SaO(2) were lower with PAV 50 than with PSV and PAV 80.

CONCLUSION

In a group of intubated spontaneously breathing non-COPD patients, PAV 80 and PSV were associated with comparable levels WOB, whereas PTP was higher during PAV 80. PAV 50 provided insufficient respiratory assistance.

New modes of mechanical ventilation: proportional assist ventilation, neurally adjusted ventilatory assist, and fractal ventilation

Increased knowledge of the mechanisms that determine respiratory failure has led to the development of new technologies aimed at improving ventilatory treatment. Proportional assist ventilation and neurally adjusted ventilatory assist have been designed with the goal of improving patient-ventilator interaction by matching the ventilator support with the neural output of the respiratory centers. With proportional assist ventilation, the support is continuously readjusted in proportion to the predicted inspiratory effort. Neurally adjusted ventilatory assist is an experimental mode in which the assistance is delivered in proportion to the electrical activity of the diaphragm, assessed by means of an esophageal electrode. Biologically variable (or fractal) ventilation is a new, volume-targeted, controlled ventilation mode aimed at improving oxygenation; it incorporates the breath-to-breath variability that characterizes a natural breathing pattern.

Mask proportional assist vs pressure support ventilation in patients in clinically stable condition with chronic ventilatory failure

OBJECTIVE

To compare the short-term physiologic effects of mask pressure support ventilation (PSV) and proportional assist ventilation (PAV) in patients in clinically stable condition with chronic ventilatory failure (CVF).

DESIGN

Randomized, controlled physiologic study.

SETTING

Lung function units of two pulmonary rehabilitation centers.

PATIENTS

Eighteen patients with CVF caused by COPD (11 patients) and restrictive chest wall diseases (RCWDs) [7 patients].

METHODS

Assessment of breathing pattern and minute ventilation (E), respiratory muscles and lung mechanics, and patient/ventilator interaction during both unassisted and assisted ventilation. After baseline assessment during spontaneous breathing (SB), mask PSV and PAV were randomly applied at the patient's comfort, with the addition of the same level of continuous positive airway pressure (2 cm H2O or 4 cm H2O in all patients), for 30 min each, with a 20-min interval of SB between periods of assisted ventilation.

RESULTS

A longer time was spent to set PAV than PSV (663 +/- 179 s and 246 +/- 58 s, respectively; p < 0.001). Mean airway opening pressure (Pao) computed over a period of 1 min, but not peak Pao, was significantly lower with PAV than with PSV (151 +/- 45 cm H2O/s/min and 207 +/- 73 cm H2O/s/min, respectively; p < 0.002). Tidal volume (VT) exhibited a greater variability with PAV than with PSV (variation coefficient, 16.3% +/- 10.5% vs 11.6% +/- 7.7%, respectively; p < 0.05). Compared with SB, both modalities resulted in a significant increase in VT (by 40% and 36% with PAV and PSV, respectively, on average) and E (by 37% and 35%) with unchanged breathing frequency and duty cycle. Both modalities significantly reduced esophageal (by 39% and 51%) and diaphragmatic (by 42% and 63%) pressure-time products, respectively. Ineffective efforts were observed with neither modes of assistance in any patient.

CONCLUSIONS

In resting, awake patients in clinically stable condition with CVF caused by either COPD or RCWD, noninvasive application of PAV, set at the patient's comfort, was not superior to PSV either in increasing VT and E or in unloading the inspiratory muscles. We failed to find any difference in patient/ventilator interaction between ventilatory modes.

Proportional assist ventilation (PAV): a significant advance or a futile struggle between logic and practice?

Proportional assist ventilation is a promising addition to other more conventional modes of mechanical ventilation with the theoretical advantage of improving patient-ventilator interaction. It may also be of use as a diagnostic tool in the control of breathing in mechanically ventilated patients.

Noninvasive proportional assist ventilation for acute respiratory insufficiency. Comparison with pressure support ventilation

Noninvasive positive pressure ventilation (NPPV) is usually applied using pressure support ventilation (PSV). Proportional assist ventilation (PAV) is a newer mode that delivers assisted ventilation in proportion to patient effort. We hypothesized that PAV for NPPV would support gas exchange and avoid intubation as well as PSV and be more comfortable and tolerable for patients. Adult patients with acute respiratory insufficiency were randomized to receive NPPV with PAV delivered using the Respironics Vision ventilator or PSV using a Puritan-Bennett 7200ae critical care ventilator. Each mode was adjusted to relieve dyspnea and improve gas exchange until patients met weaning or intubation criteria, died, or refused to continue. Twenty-one and 23 patients were entered into the PAV and PSV groups, respectively, and had similar diagnoses and baseline characteristics, although pH was slightly lower in the PAV group (7.30 versus 7.35, p = 0.02). Mortality and intubation rates were similar, but refusal rate was lower, reduction in respiratory rate was more rapid, and there were fewer complications in the PAV group. We conclude that use of the PAV mode is feasible for noninvasive therapy of acute respiratory insufficiency. Compared with PSV delivered with the Puritan-Bennett 7200ae, PAV is associated with more rapid improvements in some physiologic variables and is better tolerated.

Oscillatory resistance measured during noninvasive proportional assist ventilation

Setting proportional assist ventilation (PAV) requires the measurement of patient resistance and elastance. To avoid patient sedation/paralysis or the use of an esophageal balloon, noninvasive PAV is indirectly set by the "runaway" method or in accordance with patient comfort. The aim of this study was to ascertain whether the forced oscillation technique (FOT) applied by the ventilator during noninvasive PAV is useful in assessing patient respiratory resistance. Nasal PAV was applied to 14 patients with severe chronic obstructive pulmonary disease. During PAV a modified ventilator applied a 5-Hz pressure oscillation to noninvasively assess FOT resistance (Rrs). Lung resistance (RL) was measured in seven of the patients by using an esophageal balloon. Moreover, measurements were also performed in five of the patients when PAV was applied through the mouth. Rrs was close to RL both during nasal (Rrs = 8.9 +/- 3.1, RL = 9.0 +/- 2.6; cm H(2)O x s/L; n = 7, p > 0.05) and mouth (Rrs = 5.6 +/- 2.1, RL = 5.8 +/- 1.4; cm H(2)O x s/L; n = 5, p > 0.05) breathing. Rrs was slightly greater than the maximum value of flow assistance applied during the setting of PAV (FAmax): 11.1 +/- 5.4 and 9.5 +/- 2.9 cm H(2)O x s/L, respectively (n = 14, p > 0.05), both variables being significantly correlated (r = 0.72, p < 0.05). FOT applied by the PAV ventilator allowed the assessment of patient resistance. These results suggest that FOT could be useful in setting PAV flow assistance and in automatically and continuously updating this setting in accordance with patient resistance.

Proportional assist ventilation may improve exercise performance in severe chronic obstructive pulmonary disease

PURPOSE

Exercise tolerance is impaired in chronic obstructive pulmonary disease (COPD), in part because of a reduction in ventilatory capacity and excessive dyspnea experienced. The authors reasoned that proportional assist ventilation (PAV), a ventilator mode in which the level of support varies proportionately with patient effort, could be used during exercise to assist ventilation. The purpose of this study was to evaluate the efficacy of PAV to improve exercise endurance and related physiologic parameters in COPD.

METHODS

In 8 patients (age = 62.8 years mean, +/- 6.9 standard deviation) with severe COPD (forced expiratory volume in 1 second = 0.70 +/- 0.21 L) flow, volume, dyspnea, leg fatigue, arterial blood gases, and gas exchange were measured during constant workrate exercise (37 +/- 18 watts; i.e., 80% previously determined maximum oxygen consumption). Crossover exercise trials were performed in random order: while spontaneously breathing through the experimental circuit without assistance (control trial) and with PAV (using 9.8 +/- 2.1 cm H2O/L and 3.3 +/- 1.0 cm H2O/L/sec of volume assist and flow assist, respectively).

RESULTS

The application of PAV during exercise was well tolerated by each subject. Compared with the control measurement at equivalent time during exercise, PAV improved breathing pattern and arterial blood gases while dyspnea was reduced. Consequently, there was a significant increase in exercise duration with PAV (323 +/- 245 seconds during the control trial compared with 507 +/- 334 seconds with PAV, P = 0.02).

CONCLUSIONS

Proportional assist ventilation can improve performance during constant workrate exercise in severe COPD.

Clinical relevance of monitoring respiratory mechanics in the ventilator-supported patient: an update (1995–2000)

The introduction of mechanical ventilation in the intensive care unit environment had the merit of putting a potent life-saving tool in the physicians' hands in a number of situations; however, like most sophisticated technologies, it can cause severe side effects and eventually increase mortality if improperly applied. Assessment of respiratory mechanics serves as an aid in understanding the patient-ventilator interactions with the aim to obtain a better performance of the existing ventilator modalities. It has also provided a better understanding of patients' pathophysiology. Thanks to it, new ventilatory strategies and modalities have been developed. Finally, on-line monitoring of respiratory mechanics parameters is going to be more than a future perspective.

Physiologic effects of early administered mask proportional assist ventilation in patients with chronic obstructive pulmonary disease and acute respiratory failure

OBJECTIVE

To evaluate the physiologic short-term effects of noninvasive proportional assist ventilation (PAV) in patients with acute exacerbation of chronic obstructive pulmonary disease (COPD).

DESIGN

Prospective, physiologic study.

SETTING

Respiratory intermediate intensive care unit.

PATIENTS

Seven patients with acute respiratory failure requiring noninvasive mechanical ventilation because of exacerbation of COPD.

INTERVENTIONS

PAV was administered by nasal mask as first ventilatory intervention. The setting of PAV involved a procedure to adjust volume assist and flow assist to levels corresponding to patient comfort. Volume assist was also set by means of the "run-away" procedure. Continuous positive airway pressure (CPAP) amounting to 2 cm H2O was always set by the ventilator. This setting of assistance (PAV) was applied for 45 mins. Thereafter, CPAP was increased to 5 cm H2O (PAV + CPAP-5) without any change in the PAV setting and was administered for 20 mins. Oxygen was delivered through a port of the mask in the attempt to maintain a target SaO2 >90%.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gases, breathing pattern, and inspiratory effort were measured during unsupported breathing and at the end of PAV, and breathing pattern and inspiratory effort were measured after 20 mins of PAV + CPAP-5. PAV determined a significant increase in tidal volume and minute ventilation (+64% and +25% on average, respectively) with unchanged breathing frequency and a significant improvement in arterial blood gases (PaO2 with the same oxygen supply, from 65 +/- 15 torr to 97 +/- 36 torr; PaCO2, from 80 +/- 11 torr to 76 +/- 13 torr; pH, from 7.30 +/- 0.02 to 7.32 +/- 0.03). The pressure-time product calculated over a period of 1 min (from 318 +/- 87 to 205 +/- 145 cm H2O x sec x min(-1)) was significantly reduced. PAV + CPAP-5 resulted in a further although not significant decrease in the pressure-time product calculated over a period of 1 min (to 183 +/- 110 cm H2O x sec x min(-1)), without additional changes in the breathing pattern.

CONCLUSIONS

Noninvasive PAV is able to improve arterial blood gases while unloading inspiratory muscles in patients with acute exacerbation of COPD.