Proportional-assist ventilation compared with pressure-support ventilation during exercise in volunteers with external thoracic restriction

Study protocol for a randomized controlled trial of Proportional Assist Ventilation for Minimizing the Duration of Mechanical Ventilation: the PROMIZING study

BACKGROUND

Proportional assist ventilation with load-adjustable gain factors (PAV+) is a mechanical ventilation mode that delivers assistance to breathe in proportion to the patient's effort. The proportional assistance, called the gain, can be adjusted by the clinician to maintain the patient's respiratory effort or workload within a normal range. Short-term and physiological benefits of this mode compared to pressure support ventilation (PSV) include better patient-ventilator synchrony and a more physiological response to changes in ventilatory demand.

METHODS

The objective of this multi-centre randomized controlled trial (RCT) is to determine if, for patients with acute respiratory failure, ventilation with PAV+ will result in a shorter time to successful extubation than with PSV. This multi-centre open-label clinical trial plans to involve approximately 20 sites in several continents. Once eligibility is determined, patients must tolerate a short-term PSV trial and either (1) not meet general weaning criteria or (2) fail a 2-min Zero Continuous Positive Airway Pressure (CPAP) Trial using the rapid shallow breathing index, or (3) fail a spontaneous breathing trial (SBT), in this sequence. Then, participants in this study will be randomized to either PSV or PAV+ in a 1:1 ratio. PAV+ will be set according to a target of muscular pressure. The weaning process will be identical in the two arms. Time to liberation will be the primary outcome; ventilator-free days and other outcomes will be measured.

DISCUSSION

Meta-analyses comparing PAV+ to PSV suggest PAV+ may benefit patients and decrease healthcare costs but no powered study to date has targeted the difficult to wean patient population most likely to benefit from the intervention, or used consistent timing for the implementation of PAV+. Our enrolment strategy, primary outcome measure, and liberation approaches may be useful for studying mechanical ventilation and weaning and can offer important results for patients.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02447692 . Prospectively registered on May 19, 2015.

Proportional-assist ventilation with load-adjustable gain factors for mechanical ventilation: a cost-utility analysis

BACKGROUND

Mechanical ventilation is an important component of patient critical care, but it adds expense to an already high-cost setting. This study evaluates the cost-utility of 2 modes of ventilation: proportional-assist ventilation with load-adjustable gain factors (PAV+ mode) versus pressure-support ventilation (PSV).

METHODS

We adapted a published Markov model to the Canadian hospital-payer perspective with a 1-year time horizon. The patient population modelled includes all patients receiving invasive mechanical ventilation who have completed the acute phase of ventilatory support and have entered the recovery phase. Clinical and cost inputs were informed by a structured literature review, with the comparative effectiveness of PAV+ mode estimated via pragmatic meta-analysis. Primary outcomes of interest were costs, quality-adjusted life years (QALYs) and the (incremental) cost per QALY for patients receiving mechanical ventilation. Results were reported in 2017 Canadian dollars. We conducted probabilistic and scenario analyses to assess model uncertainty.

RESULTS

Over 1 year, PSV had costs of $50 951 and accrued 0.25 QALYs. Use of PAV+ mode was associated with care costs of $43 309 and 0.29 QALYs. Compared to PSV, PAV+ mode was considered likely to be cost-effective, having lower costs (-$7642) and increased QALYs (+0.04) after 1 year. In cost-effectiveness acceptability analysis, 100% of simulations would be cost-effective at a willingness-to-pay threshold of $50 000 per QALY gained.

INTERPRETATION

Use of PAV+ mode is expected to benefit patient care in the intensive care unit (ICU) and be a cost-effective alternative to PSV in the Canadian setting. Canadian hospital payers may therefore consider how best to optimally deliver mechanical ventilation in the ICU as they expand ICU capacity.

Proportional assist ventilation relieves clinically significant dyspnea in critically ill ventilated patients

INTRODUCTION

Dyspnea is common and often severe symptom in mechanically ventilated patients. Proportional assist ventilation (PAV) is an assist ventilatory mode that adjusts the level of assistance to the activity of respiratory muscles. We hypothesized that PAV reduce dyspnea compared to pressure support ventilation (PSV).

PATIENTS AND METHODS

Mechanically ventilated patients with clinically significant dyspnea were included. Dyspnea intensity was assessed by the Dyspnea-Visual Analog Scale (D-VAS) and the Intensive Care-Respiratory Distress Observation Scale (IC-RDOS) at inclusion (PSV-Baseline), after personalization of ventilator settings in order to minimize dyspnea (PSV-Personalization), and after switch to PAV. Respiratory drive was assessed by record of electromyographic activity of inspiratory muscles, the proportion of asynchrony was analyzed.

RESULTS

Thirty-four patients were included (73% males, median age of 66 [57-77] years). The D-VAS score was lower with PSV-Personalization (37 mm [20‒55]) and PAV (31 mm [14‒45]) than with PSV-Baseline (62 mm [28‒76]) (p < 0.05). The IC-RDOS score was lower with PAV (4.2 [2.4‒4.7]) and PSV-Personalization (4.4 [2.4‒4.9]) than with PSV-Baseline (4.8 [4.1‒6.5]) (p < 0.05). The electromyographic activity of parasternal intercostal muscles was lower with PAV and PSV-Personalization than with PSV-Baseline. The asynchrony index was lower with PAV (0% [0‒0.55]) than with PSV-Baseline and PSV-Personalization (0.68% [0‒2.28] and 0.60% [0.31‒1.41], respectively) (p < 0.05).

CONCLUSION

In mechanically ventilated patients exhibiting clinically significant dyspnea with PSV, personalization of PSV settings and PAV results in not different decreased dyspnea and activity of muscles to a similar degree, even though PAV was able to reduce asynchrony more effectively.

Mechanisms of the breathing contribution to bodily self-consciousness in healthy humans: Lessons from machine-assisted breathing?

Previous studies investigated bodily self-consciousness (BSC) by experimentally exposing subjects to multisensory conflicts (i.e., visuo-tactile, audio-tactile, visuo-cardiac) in virtual reality (VR) that involve the participant's torso in a paradigm known as the full-body illusion (FBI). Using a modified FBI paradigm, we found that synchrony of visuo-respiratory stimulation (i.e., a flashing outline surrounding an avatar in VR; the flash intensity depending on breathing), is also able to modulate BSC by increasing self-location and breathing agency toward the virtual body. Our aim was to investigate such visuo-respiratory effects and determine whether respiratory motor commands contributes to BSC, using non-invasive mechanical ventilation (i.e., machine-delivered breathing). Seventeen healthy participants took part in a visuo-respiratory FBI paradigm and performed the FBI during two breathing conditions: (a) "active breathing" (i.e., participants actively initiate machine-delivered breaths) and (b) "passive breathing" (i.e., breaths' timing was determined by the machine). Respiration rate, tidal volume, and their variability were recorded. In line with previous results, participants experienced subjective changes in self-location, breathing agency, and self-identification toward the avatar's body, when presented with synchronous visuo-respiratory stimulation. Moreover, drift in self-location was reduced and tidal volume variability were increased by asynchronous visuo-respiratory stimulations. Such effects were not modulated by breathing control manipulations. Our results extend previous FBI findings showing that visuo-respiratory stimulation affects BSC, independently from breathing motor command initiation. Also, variability of respiratory parameters was influenced by visuo-respiratory feedback and might reduce breathing discomfort. Further exploration of such findings might inform the development of respiratory therapeutic tools using VR in patients.

Non invasive ventilation as an additional tool for exercise training

Recently, there has been increasing interest in the use of non invasive ventilation (NIV) to increase exercise capacity. In individuals with COPD, NIV during exercise reduces dyspnoea and increases exercise tolerance. Different modalities of mechanical ventilation have been used non-invasively as a tool to increase exercise tolerance in COPD, heart failure and lung and thoracic restrictive diseases. Inspiratory support provides symptomatic benefit by unloading the ventilatory muscles, whereas Continuous Positive Airway Pressure (CPAP) counterbalances the intrinsic positive end-expiratory pressure in COPD patients. Severe stable COPD patients undergoing home nocturnal NIV and daytime exercise training showed some benefits. Furthermore, it has been reported that in chronic hypercapnic COPD under long-term ventilatory support, NIV can also be administered during walking. Despite these results, the role of NIV as a routine component of pulmonary rehabilitation is still to be defined.

Comparative effects of proportional assist and variable pressure support ventilation on lung function and damage in experimental lung injury

OBJECTIVE

To investigate the effects of proportional assist ventilation, variable pressure support, and conventional pressure support ventilation on lung function and damage in experimental acute lung injury.

DESIGN

: Randomized experimental study.

SETTING

University hospital research facility.

SUBJECTS

: Twenty-four juvenile pigs.

INTERVENTIONS

Pigs were anesthetized, intubated, and mechanically ventilated. Acute lung injury was induced by saline lung lavage. After resuming of spontaneous breathing, animals were randomly assigned to 6 hrs of assisted ventilation with pressure support ventilation, proportional assist ventilation, or variable pressure support (n = 8 per group). Mean tidal volume was kept at ≈6 mL/kg in all modes.

MEASUREMENTS AND MAIN RESULTS

Lung functional parameters, distribution of ventilation by electrical impedance tomography, and breathing patterns were analyzed. Histological lung damage and pulmonary inflammatory response were determined postmortem. Variable -pressure support and proportional assist ventilation improved oxygenation and venous admixture compared with pressure support ventilation. Proportional assist ventilation led to higher esophageal pressure time product than variable pressure support and pressure support ventilation, and redistributed ventilation from central to dorsal lung regions compared to pressure support ventilation. Variable pressure support and proportional assist ventilation yielded higher tidal volume variability than pressure support ventilation. Such pattern was deterministic (self-organized) during proportional assist ventilation and stochastic (random) during variable pressure support. Subject-ventilator synchrony as well as pulmonary inflammatory response and damage did not differ among groups.

CONCLUSIONS

In a lung lavage model of acute lung injury, both variable pressure support and proportional assist ventilation increased the variability of tidal volume and improved oxygenation and venous admixture, without influencing subject-ventilator synchrony or affecting lung injury compared with pressure support ventilation. However, variable pressure support yielded less inspiratory effort than proportional assist ventilation at comparable mean tidal volumes of 6 mL/kg.

Effort-adapted modes of assisted breathing

PURPOSE OF REVIEW

New developments in mechanical ventilation have focused on increasing the patient's control of the ventilator by implementing information on lung mechanics and respiratory drive. Effort-adapted modes of assisted breathing are presented and their potential advantages are discussed.

RECENT FINDINGS

Adaptive support ventilation, proportional assist ventilation with load adjustable gain factors and neurally adjusted ventilatory assist are ventilatory modes that follow the concept of adapting the assist to a defined target, instantaneous changes in respiratory drive or lung mechanics. Improved patient ventilator interaction, sufficient unloading of the respiratory muscles and increased comfort have been recently associated with these ventilator modalities. There are, however, scarce data with regard to outcome improvement, such as length of mechanical ventilation, ICU stay or mortality (commonly accepted targets to demonstrate clinical superiority).

SUMMARY

Within recent years, a major step forward in the evolution of assisted (effort-adapted) modes of mechanical ventilation was accomplished. There is growing evidence that supports the physiological concept of closed-loop effort-adapted assisted modes of mechanical ventilation. However, at present, the translation into a clear outcome benefit remains to be proven. In order to fill the knowledge gap that impedes the broader application, larger randomized controlled trials are urgently needed. However, with clearly proven drawbacks of conventional assisted modes such as pressure support ventilation, it is probably about time to leave these modes introduced decades ago behind.

Advanced closed loops during mechanical ventilation (PAV, NAVA, ASV, SmartCare)

New modes of mechanical ventilation with advanced closed loops are now available, and in the future these could assume a greater role in supporting critically ill patients in intensive care units (ICUs) for several reasons. Two modes of ventilation--proportional assist ventilation and neurally adjusted ventilatory assist--deliver assisted ventilation proportional to the patient's effort, improving patient-ventilator synchrony. Also, a few systems that automate the medical reasoning with advanced closed-loops, such as SmartCare and adaptive support ventilation, have the potential to improve knowledge transfer by continuously implementing automated protocols. Moreover, they may improve patient-ventilator interactions and outcomes, and provide a partial solution to the forecast clinician shortages by reducing ICU-related costs, time spent on mechanical ventilation, and staff workload. Preliminary studies are promising, and initial systems are currently being refined with increasing clinical experience. A new era of mechanical ventilation should emerge with these systems.

Helmet ventilation and carbon dioxide rebreathing: effects of adding a leak at the helmet ports

OBJECTIVE

We examined whether additional helmet flow obtained by a single-circuit and a modified plateau valve applied at the helmet expiratory port (open-circuit ventilators) improves CO(2) wash-out by increasing helmet airflow.

DESIGN AND SETTING

Randomized physiological study in a university research laboratory.

PARTICIPANTS

Ten healthy volunteers.

INTERVENTIONS

Helmet continuous positive airway pressure and pressure support ventilation delivered by an ICU ventilator (closed-circuit ventilator) and two open-circuit ventilators equipped with a plateau valve placed either at the inspiratory or at the helmet expiratory port.

MEASUREMENTS AND RESULTS

We measured helmet air leaks, breathing pattern, helmet minute ventilation (Eh)), minute ventilation washing the helmet (Ewh)), CO(2) wash-out, and ventilator inspiratory assistance. Air leaks were small and similar in all conditions. Breathing pattern was similar among the different ventilators. Inspiratory and end-tidal CO(2) were lower, while (Eh) and (Ewh) were higher only using open-circuit ventilators with the plateau valve placed at the helmet expiratory port. This occurred notwithstanding these ventilators delivered a lower inspiratory assistance.

CONCLUSIONS

Additional helmet flow provided by open-circuit ventilators can lower helmet CO(2) rebreathing. However, inspiratory pressure assistance significantly decreases using open-circuit ventilators, still casting doubts on the choice of the optimal helmet ventilation setup.

New Approaches in Pulmonary Rehabilitation

Patients who have mild to severe chronic obstructive pulmonary disease may obtain improvement in dyspnea, exercise capacity, and health-related quality of life as a result of exercise training. The type and intensity of training is of key importance in determining outcomes. High-intensity aerobic training leads to physiologic gains in aerobic fitness. Nevertheless, extreme breathlessness or peripheral muscle fatigue may prevent some patients from performing high-intensity exercise; therefore, new tools are needed to improve the effectiveness of pulmonary rehabilitation.

Closed-loop ventilation: an emerging standard of care?

The rational for using closed loop ventilation is becoming strong and stronger. Studies are now available supporting the hypothesis that patient outcome is improved by using closed loop ventilation. In the highly sophisticated ICU world driven by the triumvirate of cost-efficiency, quality, and safety, closed loop ventilation will become definitely unavoidable. The challenge is how to make that change effortless, "friendly" and as fast as possible. Introducing novel graphical user interfaces and providing data displays that are pertinent, integrative and dynamic will reduce cognitive resources of the clinician and have the potential to make ventilation safer. They may be the key to adopt closed loop ventilation in everyday 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.

Modulation and treatment of patient–ventilator dyssynchrony

PURPOSE OF REVIEW

The coupling between ventilator delivered inspiratory flow and patient's demands both in terms of timing and drive is a challenging task that has become largely feasible in recent years. This review addresses the new advances to modulate and treat patient-ventilator dyssynchrony.

RECENT FINDINGS

Patient-ventilator dyssynchrony is a common phenomenon with conventional modes of mechanical ventilation which influence the duration of mechanical ventilation. Inspection of pressure, volume and flow waveforms represents a valuable tool for the physician to recognize and take the appropriate action to improve patient-ventilator synchrony. New developments have been introduced aiming to improve patient ventilator synchrony by modulating the triggering function and the variables that control the flow delivery and the cycling off.

SUMMARY

Patient-ventilator dyssynchrony may affect patients' outcome. New modes of assisted mechanical ventilation have been introduced and represent a major step forward in modulating patient-ventilator dyssynchrony.

Airway management and artificial ventilation in intensive care

PURPOSE OF REVIEW

This article defines the indication for airway-securing measures and describes the actual state of knowledge about the available techniques. Various modes of ventilation and their rationale are presented.

RECENT FINDINGS

New techniques in airway management and ventilation strategy are presented, explained and evaluated.

SUMMARY

Respiratory failure is a major confounding factor of morbidity and mortality in critical care patients and contributes considerably to prolonged intensive-care unit stay. When respiratory impairment is acute, rapid assessment of essential respiratory functions such as airway patency, gas exchange, and cough function have the highest priority in patients in life-threatening conditions. Securing the airway is a basic and vital procedure that has to be applied either in an elective or an emergency situation. Various levels of difficulty in laryngoscopy, intubation and maintaining oxygenation can occur and require standardized protocols, an adequate level of expertise and appropriate equipment. In intubated patients as well as in patients without secured airway, ventilatory assistance of various degrees and invasivities may be required. In this article all clinically applied forms of ventilation, their advantages and disadvantages as well as the relevant settings are extensively presented and discussed.

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.