Patient-ventilator interaction during pressure support ventilation and neurally adjusted ventilatory assist*:

The effects of real-time waveform analysis software on patient ventilator synchronization during pressure support ventilation: a randomized crossover physiological study

BACKGROUND

Patient-ventilator asynchrony commonly occurs during pressure support ventilation (PSV). IntelliSync + software (Hamilton Medical AG, Bonaduz, Switzerland) is a new ventilation technology that continuously analyzes ventilator waveforms to detect the beginning and end of patient inspiration in real time. This study aimed to evaluate the physiological effect of IntelliSync + software on inspiratory trigger delay time, delta airway (Paw) and esophageal (Pes) pressure drop during the trigger phase, airway occlusion pressure at 0.1 s (P0.1), and hemodynamic variables.

METHODS

A randomized crossover physiologic study was conducted in 14 mechanically ventilated patients under PSV. Patients were randomly assigned to receive conventional flow trigger and cycling, inspiratory trigger synchronization (I-sync), cycle synchronization (C-sync), and inspiratory trigger and cycle synchronization (I/C-sync) for 15 min at each step. Other ventilator settings were kept constant. Paw, Pes, airflow, P0.1, respiratory rate, SpO2, and hemodynamic variables were recorded. The primary outcome was inspiratory trigger and cycle delay time between each intervention. Secondary outcomes were delta Paw and Pes drop during the trigger phase, P0.1, SpO2, and hemodynamic variables.

RESULTS

The time to initiate the trigger was significantly shorter with I-sync compared to baseline (208.9±91.7 vs. 301.4±131.7 msec; P = 0.002) and I/C-sync compared to baseline (222.8±94.0 vs. 301.4±131.7 msec; P = 0.005). The I/C-sync group had significantly lower delta Paw and Pes drop during the trigger phase compared to C-sync group (-0.7±0.4 vs. -1.2±0.8 cmH2O; P = 0.028 and - 1.8±2.2 vs. -2.8±3.2 cmH2O; P = 0.011, respectively). No statistically significant differences were found in cycle delay time, P0.1 and other physiological variables between the groups.

CONCLUSIONS

IntelliSync + software reduced inspiratory trigger delay time compared to the conventional flow trigger system during PSV mode. However, no significant improvements in cycle delay time and other physiological variables were observed with IntelliSync + software.

TRIAL REGISTRATION

This study was registered in the Thai Clinical Trial Registry (TCTR20200528003; date of registration 28/05/2020).

Trends in the Incidence of Bronchopulmonary Dysplasia after the Introduction of Neurally Adjusted Ventilatory Assist (NAVA)

OBJECTIVE

This study investigates the difference in the rates of bronchopulmonary dysplasia in very low birth weight infants before and after the introduction of neurally adjusted ventilatory assist (NAVA).

STUDY DESIGN

A retrospective cohort study comparing rates of Bronchopulmonary dysplasia (BPD) before and after implementation of NAVA. Eligibility criteria included all very low birth weight VLBW neonates needing ventilation. For analysis, each cohort was divided into three subgroups based on gestational age. Changes in the rate of BPD, length of stay, tracheostomy rates, invasive ventilator days, and home oxygen therapy were compared.

RESULTS

There were no differences in the incidence of BPD in neonates at 23-25 6/7 weeks' and 29-32 weeks' gestation between the two cohorts. A higher incidence of BPD was seen in the 26-28 5/7 weeks' gestation NAVA subgroup compared to controls (86% vs. 68%, p = 0.05). No significant difference was found for ventilator days, but infants in the 26-28 6/7 subgroup in the NAVA cohort had a longer length of stay (98 ± 34 days vs. 82 ± 24 days, p = 0.02), a higher percentage discharged on home oxygen therapy (45% vs. 18%, respectively, p = 0.006), and higher tracheostomy rates (3/36 vs. 0/60, p = 0.02), compared to the control group.

CONCLUSIONS

The NAVA mode was not associated with a reduction in BPD when compared to other modes of ventilation. Unexpected increases were seen in BPD rates, home oxygen therapy rates, tracheostomy rates, and the length of stay in the NAVA subgroup born at 26-28 6/7 weeks' gestation.

Management of Chronic Obstructive Pulmonary Disease (COPD) Exacerbations in Hospitalized Patients From Admission to Discharge: A Comprehensive Review of Therapeutic Interventions

Chronic obstructive pulmonary disease (COPD) is a common and debilitating condition that often necessitates hospitalization for exacerbations. Since COPD exacerbations can cause significant morbidity and mortality, managing them is crucial for patient care. Effective management of COPD exacerbations is essential to prevent complications, as COPD exacerbations are associated with increased healthcare costs and decreased quality of life. This review aims to comprehensively discuss the management of COPD exacerbations, covering various pharmacologic and non-pharmacologic strategies. These include inhaled bronchodilators, systemic steroids, antibiotics, invasive and non-invasive ventilation, oxygen therapy, smoking cessation, immunization with pneumococcal vaccine, inhalers at discharge, pulmonary rehabilitation, long-term oxygen therapy (LTOT), ambulatory oxygen therapy, short-burst oxygen therapy, extracorporeal membrane oxygenation (ECMO), lung volume reduction surgery (LVRS), endobronchial procedures, and lung transplant. It is drawn upon various sources, including clinical studies, systemic reviews, and observational studies, to provide a comprehensive overview of current practices and identify areas for future research and innovation in managing COPD exacerbations. Addressing these areas of interest can improve patient outcomes and quality of life.

Causes, Consequences, and Treatments of Sleep and Circadian Disruption in the ICU: An Official American Thoracic Society Research Statement

Background: Sleep and circadian disruption (SCD) is common and severe in the ICU. On the basis of rigorous evidence in non-ICU populations and emerging evidence in ICU populations, SCD is likely to have a profound negative impact on patient outcomes. Thus, it is urgent that we establish research priorities to advance understanding of ICU SCD. Methods: We convened a multidisciplinary group with relevant expertise to participate in an American Thoracic Society Workshop. Workshop objectives included identifying ICU SCD subtopics of interest, key knowledge gaps, and research priorities. Members attended remote sessions from March to November 2021. Recorded presentations were prepared and viewed by members before Workshop sessions. Workshop discussion focused on key gaps and related research priorities. The priorities listed herein were selected on the basis of rank as established by a series of anonymous surveys. Results: We identified the following research priorities: establish an ICU SCD definition, further develop rigorous and feasible ICU SCD measures, test associations between ICU SCD domains and outcomes, promote the inclusion of mechanistic and patient-centered outcomes within large clinical studies, leverage implementation science strategies to maximize intervention fidelity and sustainability, and collaborate among investigators to harmonize methods and promote multisite investigation. Conclusions: ICU SCD is a complex and compelling potential target for improving ICU outcomes. Given the influence on all other research priorities, further development of rigorous, feasible ICU SCD measurement is a key next step in advancing the field.

Respiratory drive, inspiratory effort, and work of breathing: review of definitions and non-invasive monitoring tools for intensive care ventilators during pandemic times

Technological advances in mechanical ventilation have been essential to increasing the survival rate in intensive care units. Usually, patients needing mechanical ventilation use controlled ventilation to override the patient’s respiratory muscles and favor lung protection. Weaning from mechanical ventilation implies a transition towards spontaneous breathing, mainly using assisted mechanical ventilation. In this transition, the challenge for clinicians is to avoid under and over assistance and minimize excessive respiratory effort and iatrogenic diaphragmatic and lung damage. Esophageal balloon monitoring allows objective measurements of respiratory muscle activity in real time, but there are still limitations to its routine application in intensive care unit patients using mechanical ventilation. Like the esophageal balloon, respiratory muscle electromyography and diaphragmatic ultrasound are minimally invasive tools requiring specific training that monitor respiratory muscle activity. Particularly during the coronavirus disease pandemic, non invasive tools available on mechanical ventilators to monitor respiratory drive, inspiratory effort, and work of breathing have been extended to individualize mechanical ventilation based on patient’s needs. This review aims to identify the conceptual definitions of respiratory drive, inspiratory effort, and work of breathing and to identify non invasive maneuvers available on intensive care ventilators to measure these parameters. The literature highlights that although respiratory drive, inspiratory effort, and work of breathing are intuitive concepts, even distinguished authors disagree on their definitions.

Neurally Adjusted Ventilatory Assist in Acute Respiratory Failure-A Narrative Review

Maintaining spontaneous breathing has both potentially beneficial and deleterious consequences in patients with acute respiratory failure, depending on the balance that can be obtained between the protecting and damaging effects on the lungs and the diaphragm. Neurally adjusted ventilatory assist (NAVA) is an assist mode, which supplies the respiratory system with a pressure proportional to the integral of the electrical activity of the diaphragm. This proportional mode of ventilation has the theoretical potential to deliver lung- and respiratory-muscle-protective ventilation by preserving the physiologic defense mechanisms against both lung overdistention and ventilator overassistance, as well as reducing the incidence of diaphragm disuse atrophy while maintaining patient–ventilator synchrony. This narrative review presents an overview of NAVA technology, its basic principles, the different methods to set the assist level and the findings of experimental and clinical studies which focused on lung and diaphragm protection, machine–patient interaction and preservation of breathing pattern variability. A summary of the findings of the available clinical trials which investigate the use of NAVA in acute respiratory failure will also be presented and discussed.

Timing of inspiratory muscle activity detected from airway pressure and flow during pressure support ventilation: the waveform method

Background

Whether respiratory efforts and their timing can be reliably detected during pressure support ventilation using standard ventilator waveforms is unclear. This would give the opportunity to assess and improve patient–ventilator interaction without the need of special equipment.

Methods

In 16 patients under invasive pressure support ventilation, flow and pressure waveforms were obtained from proximal sensors and analyzed by three trained physicians and one resident to assess patient’s spontaneous activity. A systematic method (the waveform method) based on explicit rules was adopted. Esophageal pressure tracings were analyzed independently and used as reference. Breaths were classified as assisted or auto-triggered, double-triggered or ineffective. For assisted breaths, trigger delay, early and late cycling (minor asynchronies) were diagnosed. The percentage of breaths with major asynchronies (asynchrony index) and total asynchrony time were computed.

Results

Out of 4426 analyzed breaths, 94.1% (70.4–99.4) were assisted, 0.0% (0.0–0.2) auto-triggered and 5.8% (0.4–29.6) ineffective. Asynchrony index was 5.9% (0.6–29.6). Total asynchrony time represented 22.4% (16.3–30.1) of recording time and was mainly due to minor asynchronies. Applying the waveform method resulted in an inter-operator agreement of 0.99 (0.98–0.99); 99.5% of efforts were detected on waveforms and agreement with the reference in detecting major asynchronies was 0.99 (0.98–0.99). Timing of respiratory efforts was accurately detected on waveforms: AUC for trigger delay, cycling delay and early cycling was 0.865 (0.853–0.876), 0.903 (0.892–0.914) and 0.983 (0.970–0.991), respectively.

Conclusions

Ventilator waveforms can be used alone to reliably assess patient’s spontaneous activity and patient–ventilator interaction provided that a systematic method is adopted.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03895-4.

Quantifying ventilator unloading in CPAP ventilation

BACKGROUND

The intrinsic (muscular) patient effort driving inspiration in non-invasive ventilation modes, such as continuous positive airway pressure (CPAP) therapy, has not been identified from non-invasive data. Current CPAP settings are based on clinical judgment and assessment of symptoms of respiratory distress. Non-optimal settings, including too much positive end expiratory pressure (PEEP) can cause unintended lung injury and ventilator unloading, where patient effort drops and the CPAP device enables too much work being imposed on the injured lung. Currently, there is no non-invasive means of quantifying or identifying these effects.

METHODS

A novel model-based method of ascertaining intrinsic patient work of breathing (WOB) in CPAP is developed based on linear single compartment and 2nd order b-spline models previously used in invasive ventilation modes. Results are compared to current clinical indications, such as total Imposed WOB from the CPAP device and beak length, the latter of which is the clinical metric used to indicate alveolar overdistension. Intrinsic and Imposed WOB are compared. The hypothesis is that ventilator unloading can be assessed as a decrease in Intrinsic WOB relative to Imposed WOB, as PEEP and associated ventilator unloading rise. This hypothesis is tested using 14 subjects from a CPAP trial of several breathing rates at two PEEP levels.

RESULTS

The ratio of Intrinsic to Imposed WOB, normalised per unit tidal volume, decreased with increasing PEEP (4-7 cm H₂O), capturing the expected trend of ventilator unloading. Ventilator unloading was observed across all breathing rates. Beak length measurements showed no conclusive evidence of capturing overdistension at higher PEEP or ventilator unloading.

CONCLUSIONS

Patient Intrinsic WOB in CPAP was non-invasively quantified using model-based methods, based on pressure and flow measurements. The ratio of Intrinsic to Imposed WOB per unit tidal volume clearly and consistently showed ventilator unloading across all patients and breathing rates, with Intrinsic WOB decreasing with increasing PEEP. This trend was not observed in the current clinical metric of beak length. Non-invasively quantifying Intrinsic WOB and ventilator unloading is the critical first step to objectively optimising clinical CPAP settings, patient care, and outcomes.

Automatic Adjustment of the Inspiratory Trigger and Cycling-Off Criteria Improved Patient-Ventilator Asynchrony During Pressure Support Ventilation

Background: Patient-ventilator asynchrony is common during pressure support ventilation (PSV) because of the constant cycling-off criteria and variation of respiratory system mechanical properties in individual patients. Automatic adjustment of inspiratory triggers and cycling-off criteria based on waveforms might be a useful tool to improve patient-ventilator asynchrony during PSV.

Method: Twenty-four patients were enrolled and were ventilated using PSV with different cycling-off criteria of 10% (PS₁₀), 30% (PS₃₀), 50% (PS₅₀), and automatic adjustment PSV (PS_AUTO). Patient-ventilator interactions were measured.

Results: The total asynchrony index (AI) and NeuroSync index were consistently lower in PS_AUTO when compared with PS₁₀, PS₃₀, and PS₅₀, (P < 0.05). The benefit of PS_AUTO in reducing the total AI was mainly because of the reduction of the micro-AI but not the macro-AI. PS_AUTO significantly improved the relative cycling-off error when compared with prefixed controlled PSV (P < 0.05). PS_AUTO significantly reduced the trigger error and inspiratory effort for the trigger when compared with a prefixed trigger. However, total inspiratory effort, breathing patterns, and respiratory drive were not different among modes.

Conclusions: When compared with fixed cycling-off criteria, an automatic adjustment system improved patient-ventilator asynchrony without changes in breathing patterns during PSV. The automatic adjustment system could be a useful tool to titrate more personalized mechanical ventilation.

Refractory ineffective triggering during pressure support ventilation: effect of proportional assist ventilation with load-adjustable gain factors

Background

Ineffective triggering is frequent during pressure support ventilation (PSV) and may persist despite ventilator adjustment, leading to refractory asynchrony. We aimed to assess the effect of proportional assist ventilation with load-adjustable gain factors (PAV+) on the occurrence of refractory ineffective triggering.

Design

Observational assessment followed by prospective cross-over physiological study.

Setting

Academic medical ICU.

Patients

Ineffective triggering was detected during PSV by a twice-daily inspection of the ventilator’s screen. The impact of pressure support level (PSL) adjustments on the occurrence of asynchrony was recorded. Patients experiencing refractory ineffective triggering, defined as persisting asynchrony at the lowest tolerated PSL, were included in the physiological study.

Interventions

Physiological study: Flow, airway, and esophageal pressures were continuously recorded during 10 min under PSV with the lowest tolerated PSL, and then under PAV+ with the gain adjusted to target a muscle pressure between 5 and 10 cmH₂O.

Measurements

Primary endpoint was the comparison of asynchrony index between PSV and PAV+ after PSL and gain adjustments.

Results

Among 36 patients identified having ineffective triggering under PSV, 21 (58%) exhibited refractory ineffective triggering. The lowest tolerated PSL was higher in patients with refractory asynchrony as compared to patients with non-refractory ineffective triggering. Twelve out of the 21 patients with refractory ineffective triggering were included in the physiological study. The median lowest tolerated PSL was 17 cmH₂O [12–18] with a PEEP of 7 cmH₂O [5–8] and FiO₂ of 40% [39–42]. The median gain during PAV+ was 73% [65–80]. The asynchrony index was significantly lower during PAV+ than PSV (2.7% [1.0–5.4] vs. 22.7% [10.3–40.1], p < 0.001) and consistently decreased in every patient with PAV+. Esophageal pressure–time product (PTPes) did not significantly differ between the two modes (107 cmH₂O/s/min [79–131] under PSV vs. 149 cmH₂O/s/min [129–170] under PAV+, p = 0.092), but the proportion of PTPes lost in ineffective triggering was significantly lower with PAV+ (2 cmH₂O/s/min [1–6] vs. 8 cmH₂O/s/min [3–30], p = 0.012).

Conclusions

Among patients with ineffective triggering under PSV, PSL adjustment failed to eliminate asynchrony in 58% of them (21 of 36 patients). In these patients with refractory ineffective triggering, switching from PSV to PAV+ significantly reduced or even suppressed the incidence of asynchrony.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-021-00935-0.

Patient-Ventilator Dyssynchrony in Critically Ill Patients

Patient–ventilator dyssynchrony is a mismatch between the patient’s respiratory efforts and mechanical ventilator delivery. Dyssynchrony can occur at any phase throughout the respiratory cycle. There are different types of dyssynchrony with different mechanisms and different potential management: trigger dyssynchrony (ineffective efforts, autotriggering, and double triggering); flow dyssynchrony, which happens during the inspiratory phase; and cycling dyssynchrony (premature cycling and delayed cycling). Dyssynchrony has been associated with patient outcomes. Thus, it is important to recognize and address these dyssynchronies at the bedside. Patient–ventilator dyssynchrony can be detected by carefully scrutinizing the airway pressure–time and flow–time waveforms displayed on the ventilator screens along with assessing the patient’s comfort. Clinicians need to know how to depict these dyssynchronies at the bedside. This review aims to define the different types of dyssynchrony and then discuss the evidence for their relationship with patient outcomes and address their potential management.

Comparative effects of neurally adjusted ventilatory assist and variable pressure support on lung and diaphragmatic function in a model of acute respiratory distress syndrome: A randomised animal study

BACKGROUND

Variable assisted mechanical ventilation has been shown to improve lung function and reduce lung injury. However, differences between extrinsic and intrinsic variability are unknown.

OBJECTIVE

To investigate the effects of neurally adjusted ventilatory assist (NAVA, intrinsic variability), variable pressure support ventilation (Noisy PSV, extrinsic variability) and conventional pressure-controlled ventilation (PCV) on lung and diaphragmatic function and damage in experimental acute respiratory distress syndrome (ARDS).

DESIGN

Randomised controlled animal study.

SETTING

University Hospital Research Facility.

SUBJECTS

A total of 24 juvenile female pigs.

INTERVENTIONS

ARDS was induced by repetitive lung lavage and injurious ventilation. Animals were randomly assigned to 24 h of either: 1) NAVA, 2) Noisy PSV or 3) PCV (n=8 per group). Mechanical ventilation settings followed the ARDS Network recommendations.

MEASUREMENTS

The primary outcome was histological lung damage. Secondary outcomes were respiratory variables and patterns, subject-ventilator asynchrony (SVA), pulmonary and diaphragmatic biomarkers, as well as diaphragmatic muscle atrophy and myosin isotypes.

RESULTS

Global alveolar damage did not differ between groups, but NAVA resulted in less interstitial oedema in dorsal lung regions than Noisy PSV. Gas exchange and SVA incidence did not differ between groups. Compared with Noisy PSV, NAVA generated higher coefficients of variation of tidal volume and respiratory rate. During NAVA, only 40.4% of breaths were triggered by the electrical diaphragm signal. The IL-8 concentration in lung tissue was lower after NAVA compared with PCV and Noisy PSV, whereas Noisy PSV yielded lower type III procollagen mRNA expression than NAVA and PCV. Diaphragmatic muscle fibre diameters were smaller after PCV compared with assisted modes, whereas expression of myosin isotypes did not differ between groups.

CONCLUSION

Noisy PSV and NAVA did not reduce global lung injury compared with PCV but affected different biomarkers and attenuated diaphragmatic atrophy. NAVA increased the respiratory variability; however, NAVA yielded a similar SVA incidence as Noisy PSV.

TRIAL REGISTRATION

This trial was registered and approved by the Landesdirektion Dresden, Germany (AZ 24-9168.11-1/2012-2).

Neural control of pressure support ventilation improved patient-ventilator synchrony in patients with different respiratory system mechanical properties: a prospective, crossover trial

Background

Conventional pressure support ventilation (PS_P) is triggered and cycled off by pneumatic signals such as flow. Patient-ventilator asynchrony is common during pressure support ventilation, thereby contributing to an increased inspiratory effort. Using diaphragm electrical activity, neurally controlled pressure support (PS_N) could hypothetically eliminate the asynchrony and reduce inspiratory effort. The purpose of this study was to compare the differences between PS_N and PS_P in terms of patient-ventilator synchrony, inspiratory effort, and breathing pattern.

Methods

Eight post-operative patients without respiratory system comorbidity, eight patients with acute respiratory distress syndrome (ARDS) and obvious restrictive acute respiratory failure (ARF), and eight patients with chronic obstructive pulmonary disease (COPD) and mixed restrictive and obstructive ARF were enrolled. Patient-ventilator interactions were analyzed with macro asynchronies (ineffective, double, and auto triggering), micro asynchronies (inspiratory trigger delay, premature, and late cycling), and the total asynchrony index (AI). Inspiratory efforts for triggering and total inspiration were analyzed.

Results

Total AI of PS_N was consistently lower than that of PS_P in COPD (3% vs. 93%, P = 0.012 for 100% support level; 8% vs. 104%, P = 0.012 for 150% support level), ARDS (8% vs. 29%, P = 0.012 for 100% support level; 16% vs. 41%, P = 0.017 for 150% support level), and post-operative patients (21% vs. 35%, P = 0.012 for 100% support level; 15% vs. 50%, P = 0.017 for 150% support level). Improved support levels from 100% to 150% statistically increased total AI during PS_P but not during PS_N in patients with COPD or ARDS. Patients’ inspiratory efforts for triggering and total inspiration were significantly lower during PS_N than during PS_P in patients with COPD or ARDS under both support levels (P < 0.05). There was no difference in breathing patterns between PS_N and PS_P.

Conclusions

PS_N improves patient-ventilator synchrony and generates a respiratory pattern similar to PS_P independently of any level of support in patients with different respiratory system mechanical properties. PS_N, which reduces the trigger and total patient's inspiratory effort in patients with COPD or ARDS, might be an alternative mode for PS_P.

Trial Registration

ClinicalTrials.gov, NCT01979627; https://clinicaltrials.gov/ct2/show/record/NCT01979627.

Prolonged Weaning: S2k Guideline Published by the German Respiratory Society

Mechanical ventilation (MV) is an essential part of modern intensive care medicine. MV is performed in patients with severe respiratory failure caused by respiratory muscle insufficiency and/or lung parenchymal disease; that is, when other treatments such as medication, oxygen administration, secretion management, continuous positive airway pressure (CPAP), or nasal high-flow therapy have failed. MV is required for maintaining gas exchange and allows more time to curatively treat the underlying cause of respiratory failure. In the majority of ventilated patients, liberation or "weaning" from MV is routine, without the occurrence of any major problems. However, approximately 20% of patients require ongoing MV, despite amelioration of the conditions that precipitated the need for it in the first place. Approximately 40-50% of the time spent on MV is required to liberate the patient from the ventilator, a process called "weaning". In addition to acute respiratory failure, numerous factors can influence the duration and success rate of the weaning process; these include age, comorbidities, and conditions and complications acquired during the ICU stay. According to international consensus, "prolonged weaning" is defined as the weaning process in patients who have failed at least 3 weaning attempts, or require more than 7 days of weaning after the first spontaneous breathing trial (SBT). Given that prolonged weaning is a complex process, an interdisciplinary approach is essential for it to be successful. In specialised weaning centres, approximately 50% of patients with initial weaning failure can be liberated from MV after prolonged weaning. However, the heterogeneity of patients undergoing prolonged weaning precludes the direct comparison of individual centres. Patients with persistent weaning failure either die during the weaning process, or are discharged back to their home or to a long-term care facility with ongoing MV. Urged by the growing importance of prolonged weaning, this Sk2 Guideline was first published in 2014 as an initiative of the German Respiratory Society (DGP), in conjunction with other scientific societies involved in prolonged weaning. The emergence of new research, clinical study findings and registry data, as well as the accumulation of experience in daily practice, have made the revision of this guideline necessary. The following topics are dealt with in the present guideline: Definitions, epidemiology, weaning categories, underlying pathophysiology, prevention of prolonged weaning, treatment strategies in prolonged weaning, the weaning unit, discharge from hospital on MV, and recommendations for end-of-life decisions. Special emphasis was placed on the following themes: (1) A new classification of patient sub-groups in prolonged weaning. (2) Important aspects of pulmonary rehabilitation and neurorehabilitation in prolonged weaning. (3) Infrastructure and process organisation in the care of patients in prolonged weaning based on a continuous treatment concept. (4) Changes in therapeutic goals and communication with relatives. Aspects of paediatric weaning are addressed separately within individual chapters. The main aim of the revised guideline was to summarize both current evidence and expert-based knowledge on the topic of "prolonged weaning", and to use this information as a foundation for formulating recommendations related to "prolonged weaning", not only in acute medicine but also in the field of chronic intensive care medicine. The following professionals served as important addressees for this guideline: intensivists, pulmonary medicine specialists, anaesthesiologists, internists, cardiologists, surgeons, neurologists, paediatricians, geriatricians, palliative care clinicians, rehabilitation physicians, intensive/chronic care nurses, physiotherapists, respiratory therapists, speech therapists, medical service of health insurance, and associated ventilator manufacturers.

Abnormal Sleep, Circadian Rhythm Disruption, and Delirium in the ICU: Are They Related?

Delirium is a syndrome characterized by acute brain failure resulting in neurocognitive disturbances affecting attention, awareness, and cognition. It is highly prevalent among critically ill patients and is associated with increased morbidity and mortality. A core domain of delirium is represented by behavioral disturbances in sleep-wake cycle probably related to circadian rhythm disruption. The relationship between sleep, circadian rhythm and intensive care unit (ICU)-acquired delirium is complex and likely bidirectional. In this review, we explore the proposed pathophysiological mechanisms of sleep disruption and circadian dysrhythmia as possible contributing factors in transitioning to delirium in the ICU and highlight some of the most relevant caveats for understanding the relationship between these complex phenomena. Specifically, we will (1) review the physiological consequences of poor sleep quality and efficiency; (2) explore how the neural substrate underlying the circadian clock functions may be disrupted in delirium; (3) discuss the role of sedative drugs as contributors to delirium and chrono-disruption; and, (4) describe the association between abnormal sleep-pathological wakefulness, circadian dysrhythmia, delirium and critical illness. Opportunities to improve sleep and readjust circadian rhythmicity to realign the circadian clock may exist as therapeutic targets in both the prevention and treatment of delirium in the ICU. Further research is required to better define these conditions and understand the underlying physiologic relationship to develop effective prevention and therapeutic strategies.

Neurally adjusted ventilatory assist in acute respiratory failure: a randomized controlled trial

PURPOSE

We hypothesized that neurally adjusted ventilatory assist (NAVA) compared to conventional lung-protective mechanical ventilation (MV) decreases duration of MV and mortality in patients with acute respiratory failure (ARF).

METHODS

We carried out a multicenter, randomized, controlled trial in patients with ARF from several etiologies. Intubated patients ventilated for ≤ 5 days expected to require MV for ≥ 72 h and able to breathe spontaneously were eligible for enrollment. Eligible patients were randomly assigned based on balanced treatment assignments with a computerized randomization allocation sequence to two ventilatory strategies: (1) lung-protective MV (control group), and (2) lung-protective MV with NAVA (NAVA group). Allocation concealment was maintained at all sites during the trial. Primary outcome was the number of ventilator-free days (VFDs) at 28 days. Secondary outcome was all-cause hospital mortality. All analyses were done according to the intention-to-treat principle.

RESULTS

Between March 2014 and October 2019, we enrolled 306 patients and randomly assigned 153 patients to the NAVA group and 153 to the control group. Median VFDs were higher in the NAVA than in the control group (22 vs. 18 days; between-group difference 4 days; 95% confidence interval [CI] 0 to 8 days; p = 0.016). At hospital discharge, 39 (25.5%) patients in the NAVA group and 47 (30.7%) patients in the control group had died (between-group difference - 5.2%, 95% CI - 15.2 to 4.8, p = 0.31). Other clinical, physiological or safety outcomes did not differ significantly between the trial groups.

CONCLUSION

NAVA decreased duration of MV although it did not improve survival in ventilated patients with ARF.

Neurally Adjusted Ventilatory Assist versus Pressure Support Ventilation in Difficult Weaning: A Randomized Trial

BACKGROUND

Difficult weaning frequently develops in ventilated patients and is associated with poor outcome. In neurally adjusted ventilatory assist, the ventilator is controlled by diaphragm electrical activity, which has been shown to improve patient-ventilator interaction. The objective of this study was to compare neurally adjusted ventilatory assist and pressure support ventilation in patients difficult to wean from mechanical ventilation.

METHODS

In this nonblinded randomized clinical trial, difficult-to-wean patients (n = 99) were randomly assigned to neurally adjusted ventilatory assist or pressure support ventilation mode. The primary outcome was the duration of weaning. Secondary outcomes included the proportion of successful weaning, patient-ventilator asynchrony, ventilator-free days, and mortality. Weaning duration was calculated as 28 days for patients under mechanical ventilation at day 28 or deceased before day 28 without successful weaning.

RESULTS

Weaning duration in all patients was statistically significant shorter in the neurally adjusted ventilatory assist group (n = 47) compared with the pressure support ventilation group (n = 52; 3.0 [1.2 to 8.0] days vs. 7.4 [2.0 to 28.0], mean difference: -5.5 [95% CI, -9.2 to -1.4], P = 0.039). Post hoc sensitivity analysis also showed that the neurally adjusted ventilatory assist group had shorter weaning duration (hazard ratio, 0.58; 95% CI, 0.34 to 0.98). The proportion of patients with successful weaning from invasive mechanical ventilation was higher in neurally adjusted ventilatory assist (33 of 47 patients, 70%) compared with pressure support ventilation (25 of 52 patients, 48%; respiratory rate for neurally adjusted ventilatory assist: 1.46 [95% CI, 1.04 to 2.05], P = 0.026). The number of ventilator-free days at days 14 and 28 was statistically significantly higher in neurally adjusted ventilatory assist compared with pressure support ventilation. Neurally adjusted ventilatory assist improved patient ventilator interaction. Mortality and length of stay in the intensive care unit and in the hospital were similar among groups.

CONCLUSIONS

In patients difficult to wean, neurally adjusted ventilatory assist decreased the duration of weaning and increased ventilator-free days.

Proportional modes of ventilation: technology to assist physiology

Proportional modes of ventilation assist the patient by adapting to his/her effort, which contrasts with all other modes. The two proportional modes are referred to as neurally adjusted ventilatory assist (NAVA) and proportional assist ventilation with load-adjustable gain factors (PAV+): they deliver inspiratory assist in proportion to the patient’s effort, and hence directly respond to changes in ventilatory needs. Due to their working principles, NAVA and PAV+ have the ability to provide self-adjusted lung and diaphragm-protective ventilation. As these proportional modes differ from ‘classical’ modes such as pressure support ventilation (PSV), setting the inspiratory assist level is often puzzling for clinicians at the bedside as it is not based on usual parameters such as tidal volumes and PaCO₂ targets. This paper provides an in-depth overview of the working principles of NAVA and PAV+ and the physiological differences with PSV. Understanding these differences is fundamental for applying any assisted mode at the bedside. We review different methods for setting inspiratory assist during NAVA and PAV+ , and (future) indices for monitoring of patient effort. Last, differences with automated modes are mentioned.

Neurally adjusted ventilatory assist versus pressure support ventilation: a randomized controlled feasibility trial performed in patients at risk of prolonged mechanical ventilation

BACKGROUND

The clinical effectiveness of neurally adjusted ventilatory assist (NAVA) has yet to be demonstrated, and preliminary studies are required. The study aim was to assess the feasibility of a randomized controlled trial (RCT) of NAVA versus pressure support ventilation (PSV) in critically ill adults at risk of prolonged mechanical ventilation (MV).

METHODS

An open-label, parallel, feasibility RCT (n = 78) in four ICUs of one university-affiliated hospital. The primary outcome was mode adherence (percentage of time adherent to assigned mode), and protocol compliance (binary-≥ 65% mode adherence). Secondary exploratory outcomes included ventilator-free days (VFDs), sedation, and mortality.

RESULTS

In the 72 participants who commenced weaning, median (95% CI) mode adherence was 83.1% (64.0-97.1%) and 100% (100-100%), and protocol compliance was 66.7% (50.3-80.0%) and 100% (89.0-100.0%) in the NAVA and PSV groups respectively. Secondary outcomes indicated more VFDs to D28 (median difference 3.0 days, 95% CI 0.0-11.0; p = 0.04) and fewer in-hospital deaths (relative risk 0.5, 95% CI 0.2-0.9; p = 0.032) for NAVA. Although overall sedation was similar, Richmond Agitation and Sedation Scale (RASS) scores were closer to zero in NAVA compared to PSV (p = 0.020). No significant differences were observed in duration of MV, ICU or hospital stay, or ICU, D28, and D90 mortality.

CONCLUSIONS

This feasibility trial demonstrated good adherence to assigned ventilation mode and the ability to meet a priori protocol compliance criteria. Exploratory outcomes suggest some clinical benefit for NAVA compared to PSV. Clinical effectiveness trials of NAVA are potentially feasible and warranted.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01826890. Registered 9 April 2013.

Neurally adjusted ventilatory assist preserves cerebral blood flow velocity in patients recovering from acute brain injury

Neurally adjusted ventilatory assist (NAVA) has never been applied in patients recovering from acute brain injury (ABI) because neural respiratory drive could be affected by intracranial disease with detrimental effects on cerebral blood flow (CBF) velocity. Our primary aim was to assess the impact of NAVA and pressure support ventilation (PSV) on CBF velocity. In fifteen adult patients recovering from ABI and undergoing invasive assisted ventilation, PSV and NAVA were applied over 30-min-lasting trials, in the following sequence: PSV₁, NAVA, and PSV₂. While PSV was set to deliver a tidal volume ranging between 6 and 8 ml kg⁻¹ of predicted body weight, in NAVA the level of assistance was chosen to achieve the same inspiratory peak airway pressure as PSV. At the end of each trial, a sonographic evaluation of CBF mean velocity was bilaterally obtained on the middle cerebral artery and an arterial blood gas sample was taken for analysis. CBF mean velocity was 51.8 [41.9,75.2] cm  s⁻¹ at baseline, 51.9 [43.4,71.0] cm s⁻¹ in PSV₁, 53.6 [40.7,67.7] cm s⁻¹ in NAVA, and 49.5 [42.1,70.8] cm s⁻¹ in PSV₂ (p = 0.0514) on the left and 50.2 [38.0,77.7] cm s⁻¹ at baseline, 47.8 [41.7,68.2] cm s⁻¹ in PSV₁, 53.9 [40.1,78.5] cm s⁻¹ in NAVA, and 55.6 [35.9,74.1] cm s⁻¹ in PSV₂ (p = 0.8240) on the right side. No differences were detected for pH (p = 0.0551), arterial carbon dioxide tension (p = 0.8142), and oxygenation (p = 0.0928) over the entire study duration. NAVA and PSV preserved CBF velocity in patients recovering from ABI.

Trial registration: The present trial was prospectively registered at www.clinicatrials.gov (NCT03721354) on October 18th, 2018.

Effect of Neurally Adjusted Ventilatory Assist on Patient-Ventilator Interaction in Mechanically Ventilated Adults: A Systematic Review and Meta-Analysis

OBJECTIVES

Patient-ventilator asynchrony is common among critically ill patients undergoing mechanical ventilation and has been associated with adverse outcomes. Neurally adjusted ventilatory assist is a ventilatory mode that may lead to improved patient-ventilator synchrony. We conducted a systematic review to determine the impact of neurally adjusted ventilatory assist on patient-ventilator asynchrony, other physiologic variables, and clinical outcomes in adult patients undergoing invasive mechanical ventilation in comparison with conventional pneumatically triggered ventilatory modes.

DATA SOURCES

We searched Medline, EMBASE, Cochrane Database of Systematic Reviews, Cochrane Central, CINAHL, Scopus, Web of Science, conference abstracts, and ClinicalTrials.gov until July 2018.

STUDY SELECTION

Two authors independently screened titles and abstracts for randomized and nonrandomized controlled trials (including crossover design) comparing the occurrence of patient-ventilator asynchrony between neurally adjusted ventilatory assist and pressure support ventilation during mechanical ventilation in critically ill adults. The asynchrony index and severe asynchrony (i.e., asynchrony index > 10%) were the primary outcomes.

DATA EXTRACTION

Two authors independently extracted study characteristics and outcomes and assessed risk of bias of included studies.

DATA SYNTHESIS

Of 11,139 unique citations, 26 studies (522 patients) met the inclusion criteria. Sixteen trials were included in the meta-analysis using random effects models through the generic inverse variance method. In several different clinical scenarios, the use of neurally adjusted ventilatory assist was associated with significantly reduced asynchrony index (mean difference, -8.12; 95% CI, -11.61 to -4.63; very low quality of evidence) and severe asynchrony (odds ratio, 0.42; 95% CI, 0.23-0.76; moderate quality of evidence) as compared with pressure support ventilation. Furthermore, other measurements of asynchrony were consistently improved during neurally adjusted ventilatory assist.

CONCLUSIONS

Neurally adjusted ventilatory assist improves patient-ventilator synchrony; however, its effects on clinical outcomes remain uncertain. Randomized controlled trials are needed to determine whether the physiologic efficiency of neurally adjusted ventilatory assist affects patient-important outcomes in critically ill adults.

Neurally adjusted ventilatory assist vs. pressure support to deliver protective mechanical ventilation in patients with acute respiratory distress syndrome: a randomized crossover trial

Background

Protective mechanical ventilation is recommended for patients with acute respiratory distress syndrome (ARDS), but it usually requires controlled ventilation and sedation. Using neurally adjusted ventilatory assist (NAVA) or pressure support ventilation (PSV) could have additional benefits, including the use of lower sedative doses, improved patient–ventilator interaction and shortened duration of mechanical ventilation. We designed a pilot study to assess the feasibility of keeping tidal volume (V_T) at protective levels with NAVA and PSV in patients with ARDS.

Methods

We conducted a prospective randomized crossover trial in five ICUs from a university hospital in Brazil and included patients with ARDS transitioning from controlled ventilation to partial ventilatory support. NAVA and PSV were applied in random order, for 15 min each, followed by 3 h in NAVA. Flow, peak airway pressure (Paw) and electrical activity of the diaphragm (EAdi) were captured from the ventilator, and a software (Matlab, Mathworks, USA), automatically detected inspiratory efforts and calculated respiratory rate (RR) and V_T. Asynchrony events detection was based on waveform analysis.

Results

We randomized 20 patients, but the protocol was interrupted for five (25%) patients for whom we were unable to maintain V_T below 6.5 mL/kg in PSV due to strong inspiratory efforts and for one patient for whom we could not detect EAdi signal. For the 14 patients who completed the protocol, V_T was 5.8 ± 1.1 mL/kg for NAVA and 5.6 ± 1.0 mL/kg for PSV (p = 0.455) and there were no differences in RR (24 ± 7 for NAVA and 23 ± 7 for PSV, p = 0.661). Paw was greater in NAVA (21 ± 3 cmH₂O) than in PSV (19 ± 3 cmH₂O, p = 0.001). Most patients were under continuous sedation during the study. NAVA reduced triggering delay compared to PSV (p = 0.020) and the median asynchrony Index was 0.7% (0–2.7) in PSV and 0% (0–2.2) in NAVA (p = 0.6835).

Conclusions

It was feasible to keep V_T in protective levels with NAVA and PSV for 75% of the patients. NAVA resulted in similar V_T, RR and Paw compared to PSV. Our findings suggest that partial ventilatory assistance with NAVA and PSV is feasible as a protective ventilation strategy in selected ARDS patients under continuous sedation.

Trial registration ClinicalTrials.gov (NCT01519258). Registered 26 January 2012, https://clinicaltrials.gov/ct2/show/NCT01519258

Ventilator- and interface-related factors influencing patient-ventilator asynchrony during noninvasive ventilation

Patient-ventilator asynchrony (PVA) is common in patients receiving noninvasive ventilation (NIV). This occurs primarily when the triggering and cycling-off of ventilatory assistance are not synchronized with the patient's inspiratory efforts and could result in increased work of breathing and niv failure. In general, five types of asynchrony can occur during NIV: ineffective inspiratory efforts, double-triggering, auto-triggering, short-ventilatory cycling, and long-ventilatory cycling. Many factors that affect PVA are mostly related to the degree of air leakage, level of pressure support, and the type and properties of the interface used. Careful monitoring and adjustment of these factors are essential to reduce PVA and improve patient comfort. In this article, we discuss the machine and interface-related factors that influence PVA during NIV and its effect on the respiratory mechanics during pressure support ventilation, which is the ventilatory mode used most commonly during NIV. For that, we critically evaluated studies that assessed ventilator- and interface-related factors that influence PVA during NIV and proposed therapeutic solutions.

The Injurious Effects of Elevated or Nonelevated Respiratory Rate during Mechanical Ventilation

Respiratory rate is one of the key variables that is set and monitored during mechanical ventilation. As part of increasing efforts to optimize mechanical ventilation, it is prudent to expand understanding of the potential harmful effects of not only volume and pressures but also respiratory rate. The mechanisms by which respiratory rate may become injurious during mechanical ventilation can be distinguished in two broad categories. In the first, well-recognized category, concerning both controlled and assisted ventilation, the respiratory rate per se may promote ventilator-induced lung injury, dynamic hyperinflation, ineffective efforts, and respiratory alkalosis. It may also be misinterpreted as distress delaying the weaning process. In the second category, which concerns only assisted ventilation, the respiratory rate may induce injury in a less apparent way by remaining relatively quiescent while being challenged by chemical feedback. By responding minimally to chemical feedback, respiratory rate leaves the control of V. e almost exclusively to inspiratory effort. In such cases, when assist is high, weak inspiratory efforts promote ineffective triggering, periodic breathing, and diaphragmatic atrophy. Conversely, when assist is low, diaphragmatic efforts are intense and increase the risk for respiratory distress, asynchronies, ventilator-induced lung injury, diaphragmatic injury, and cardiovascular complications. This review thoroughly presents the multiple mechanisms by which respiratory rate may induce injury during mechanical ventilation, drawing the attention of critical care physicians to the potential injurious effects of respiratory rate insensitivity to chemical feedback during assisted ventilation.

Extracorporeal Membrane Oxygenation Can Successfully Support Patients With Severe Acute Respiratory Distress Syndrome in Lieu of Mechanical Ventilation

OBJECTIVES

Extracorporeal membrane oxygenation is increasingly used in the management of severe acute respiratory distress syndrome. With extracorporeal membrane oxygenation, select patients with acute respiratory distress syndrome can be managed without mechanical ventilation, sedation, or neuromuscular blockade. Published experience with this approach, specifically with attention to a patient's respiratory drive following cannulation, is limited.

DESIGN

We describe our experience with three consecutive patients with severe acute respiratory distress syndrome supported with right jugular-femoral configuration of venovenous extracorporeal membrane oxygenation without therapeutic anticoagulation as an alternative to lung-protective mechanical ventilation. Outcomes are reported including daily respiratory rate, vital capacities, and follow-up pulmonary function testing.

RESULTS

Following cannulation, patients were extubated within 24 hours. During extracorporeal membrane oxygenation support, all patients were able to maintain a normal respiratory rate and experienced steady improvements in vital capacities. Patients received oral nutrition and ambulated daily. At follow-up, no patients required supplemental oxygen.

CONCLUSIONS

Our results suggest that venovenous extracorporeal membrane oxygenation can provide a safe and effective alternative to lung-protective mechanical ventilation in carefully selected patients. This approach facilitates participation in physical therapy and avoids complications associated with mechanical ventilation.

Neurally adjusted ventilatory assist versus pressure support ventilation in patient-ventilator interaction and clinical outcomes: a meta-analysis of clinical trials

Background

The objective of this study was to conduct a meta-analysis comparing neurally adjusted ventilatory assist (NAVA) with pressure support ventilation (PSV) in adult ventilated patients with patient-ventilator interaction and clinical outcomes.

Methods

The PubMed, the Web of Science, Scopus, and Medline were searched for appropriate clinical trials (CTs) comparing NAVA with PSV for the adult ventilated patients. RevMan 5.3 was performed for comparing NAVA with PSV in asynchrony index (AI), ineffective efforts, auto-triggering, double asynchrony, premature asynchrony, breathing pattern (Peak airway pressure (Paw_peek), mean airway pressure (Paw_mean), tidal volume (V_T, mL/kg), minute volume (MV), respiratory muscle unloading (peak electricity of diaphragm (EAdi_peak), P 0.1, V_T/EAdi), clinical outcomes (ICU mortality, duration of ventilation days, ICU stay time, hospital stay time).

Results

Our meta-analysis included 12 studies involving a total of 331 adult ventilated patients, AI was significantly lower in NAVA group [mean difference (MD) -12.82, 95% confidence interval (CI): -21.20 to -4.44, I²=88%], and using subgroup analysis, grouped by mechanical ventilation, the results showed that NAVA also had lower AI than PSV (Mechanical ventilation, MD -9.52, 95% CI: -17.85 to -1.20, I²=87%), (Non-invasive ventilation (NIV), MD -24.55, 95% CI: -35.40 to -13.70, I²=0%). NAVA was significantly lower than the PSV in auto-triggering (MD -0.28, 95% CI: -0.51 to -0.05, I²=10%), and premature triggering (MD -2.49, 95% CI: -3.77 to -1.21, I²=29%). There were no significant differences in double triggering, ineffective efforts, breathing pattern (Paw_mean, Paw_peak, V_T, MV), and respiratory muscle unloading (EAdi_peak, P 0.1, V_T/EAdi). For clinical outcomes, NAVA was significantly lower than the PSV (MD -2.82, 95% CI: -5.55 to -0.08, I²=0%) in the duration of ventilation, but two groups did not show significant differences in ICU mortality, ICU stay time, and hospital stay time.

Conclusions

NAVA is more beneficial in patient-ventilator interaction than PSV, and could decrease the duration of ventilation.

Neural Offset Time Evaluation in Surface Respiratory Signals during Controlled Respiration

The electrical activity of the diaphragm measured by surface electromyography (sEMGdi) provides indirect information on neural respiratory drive. Moreover, it allows evaluating the ventilatory pattern from the onset and offset (ntoff) estimation of the neural inspiratory time. sEMGdi amplitude variation was quantified using the fixed sample entropy (fSampEn), a less sensitive method to the interference from cardiac activity. The detection of the ntoff is controversial, since it is located in an intermediate point between the maximum value and the cessation of sEMGdi inspiratory activity, evaluated by the fSampEn. In this work ntoff detection has been analyzed using thresholds between 40% and 100 % of the fSampEn peak. Furthermore, fSampEn was evaluated analyzing the r parameter from 0.05 to 0.6, using a m equal to 1 and a sliding window size equal to 250 ms. The ntoff has been compared to the offset time (toff) obtained from the airflow during a controlled respiratory protocol varying the fractional inspiratory time from 0.54 to 0.18 whilst the respiratory rate was constant at 16 bpm. Results show that the optimal threshold values were between 66.0 % to 77.0 % of the fSampEn peak value. r values between 0.25 to 0.50 were found suitable to be used with the fSampEn.

Patient-ventilator asynchrony in adult critically ill patients

INTRODUCTION

Patient-ventilator asynchrony is considered a major clinical problem for mechanically ventilated patients. It occurs during partial ventilatory support, when the respiratory muscles and the ventilator interact to contribute generating the volume output. In this review article, we consider all studies published on patient-ventilator asynchrony in the last 25 years.

EVIDENCE ACQUISITION

We selected 62 studies. The different forms of asynchrony are first defined and classified. We also describe the methods used for detecting and quantifying asynchronies. We then outline the outcome variables considered for evaluating the clinical consequences of asynchronies. The methodology for detection and quantification of patient-ventilator asynchrony are quite heterogeneous. In particular, the Asynchrony Index is calculated differently among studies.

EVIDENCE SYNTHESIS

Sixteen studies established some relationship between asynchronies and one or more clinical outcomes, such as duration of mechanical ventilation (seven studies), mortality (five studies), length of intensive care and hospital stay (four studies), patient comfort (four studies), quality of sleep (three studies), and rate of tracheotomy (three studies). In patients with severe patient-ventilator asynchrony, four of seven studies (57%) report prolonged duration of mechanical ventilation, one of five (20%) increased mortality, one of four (25%) longer intensive care and hospital lengths of stay, four of four (100%) worsened comfort, three of four (75%) deteriorated quality of sleep, and one of three (33%) increased rate of tracheotomy.

CONCLUSIONS

Given the varying outcomes considered and the erratic results, it remains unclear whether asynchronies really affects patient outcome, and the relationship between asynchronies and outcome is causative or associative.

Neurally adjusted ventilatory assist (NAVA) versus pressure support ventilation: patient-ventilator interaction during invasive ventilation delivered by tracheostomy

BACKGROUND

Prolonged weaning is a major issue in intensive care patients and tracheostomy is one of the last resort options. Optimized patient-ventilator interaction is essential to weaning. The purpose of this study was to compare patient-ventilator synchrony between pressure support ventilation (PSV) and neurally adjusted ventilatory assist (NAVA) in a selected population of tracheostomised patients.

METHODS

We performed a prospective, sequential, non-randomized and single-centre study. Two recording periods of 60 min of airway pressure, flow, and electrical activity of the diaphragm during PSV and NAVA were recorded in a random assignment and eight periods of 1 min were analysed for each mode. We searched for macro-asynchronies (ineffective, double, and auto-triggering) and micro-asynchronies (inspiratory trigger delay, premature, and late cycling). The number and type of asynchrony events per minute and asynchrony index (AI) were determined. The two respiratory phases were compared using the non-parametric Wilcoxon test after testing the equality of the two variances (F-Test).

RESULTS

Among the 61 patients analysed, the total AI was lower in NAVA than in PSV mode: 2.1% vs 14% (p < 0.0001). This was mainly due to a decrease in the micro-asynchronies index: 0.35% vs 9.8% (p < 0.0001). The occurrence of macro-asynchronies was similar in both ventilator modes except for double triggering, which increased in NAVA. The tidal volume (ml/kg) was lower in NAVA than in PSV (5.8 vs 6.2, p < 0.001), and the respiratory rate was higher in NAVA than in PSV (28 vs 26, p < 0.05).

CONCLUSION

NAVA appears to be a promising ventilator mode in tracheotomised patients, especially for those requiring prolonged weaning due to the decrease in asynchronies.

Proportional modes versus pressure support ventilation: a systematic review and meta-analysis

Background

Proportional modes (proportional assist ventilation, PAV, and neurally adjusted ventilatory assist, NAVA) could improve patient–ventilator interaction and consequently may be efficient as a weaning mode. The purpose of this systematic review is to examine whether proportional modes improved patient–ventilator interaction and whether they had an impact on the weaning success and length of mechanical ventilation, in comparison with PSV.

Methods

We searched PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials from inception through May 13, 2018. We included both parallel-group and crossover randomized studies that examined the efficacy of proportional modes in comparison with PSV in mechanically ventilated adults. The primary outcomes were (1) asynchrony index (AI), (2) weaning failure, and (3) duration of mechanical ventilation.

Results

We included 15 studies (four evaluated PAV, ten evaluated NAVA, and one evaluated both modes). Although the use of proportional modes was not associated with a reduction in AI (WMD − 1.43; 95% CI − 3.11 to 0.25; p = 0.096; PAV—one study, and NAVA—seven studies), the use of proportional modes was associated with a reduction in patients with AI > 10% (RR 0.15; 95% CI 0.04–0.58; p = 0.006; PAV—two studies, and NAVA—five studies), compared with PSV. There was a significant heterogeneity among studies for AI, especially with NAVA. Compared with PSV, use of proportional modes was associated with a reduction in weaning failure (RR 0.44; 95% CI 0.26–0.75; p = 0.003; PAV—three studies) and duration of mechanical ventilation (WMD − 1.78 days; 95% CI − 3.24 to − 0.32; p = 0.017; PAV—three studies, and NAVA—two studies). Reduced duration of mechanical ventilation was found with PAV but not with NAVA.

Conclusion

The use of proportional modes was associated with a reduction in the incidence with AI > 10%, weaning failure and duration of mechanical ventilation, compared with PSV. However, reduced weaning failure and duration of mechanical ventilation were found with only PAV. Due to a significant heterogeneity among studies and an insufficient number of studies, further investigation seems warranted to better understand the impact of proportional modes.

Clinical trial registration PROSPERO registration number, CRD42017059791. Registered 20 March 2017

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0470-y) contains supplementary material, which is available to authorized users.

Patient-ventilator asynchrony

Patient-v entilator asynchrony (PVA) is a mismatch between the patient, regarding time, flow, volume, or pressure demands of the patient respiratory system, and the ventilator, which supplies such demands, during mechanical ventilation (MV). It is a common phenomenon, with incidence rates ranging from 10% to 85%. PVA might be due to factors related to the patient, to the ventilator, or both. The most common PVA types are those related to triggering, such as ineffective effort, auto-triggering, and double triggering; those related to premature or delayed cycling; and those related to insufficient or excessive flow. Each of these types can be detected by visual inspection of volume, flow, and pressure waveforms on the mechanical ventilator display. Specific ventilatory strategies can be used in combination with clinical management, such as controlling patient pain, anxiety, fever, etc. Deep sedation should be avoided whenever possible. PVA has been associated with unwanted outcomes, such as discomfort, dyspnea, worsening of pulmonary gas exchange, increased work of breathing, diaphragmatic injury, sleep impairment, and increased use of sedation or neuromuscular blockade, as well as increases in the duration of MV, weaning time, and mortality. Proportional assist ventilation and neurally adjusted ventilatory assist are modalities of partial ventilatory support that reduce PVA and have shown promise. This article reviews the literature on the types and causes of PVA, as well as the methods used in its evaluation, its potential implications in the recovery process of critically ill patients, and strategies for its resolution.

Real-time chest-wall-motion tracking by a single optical fibre grating: a prospective method for ventilator triggering

OBJECTIVE

The ventilators involved in non-invasive mechanical ventilation commonly provide ventilator support via a facemask. The interface of the mask with a patient promotes air leaks that cause errors in the feedback information provided by a pneumatic sensor and hence patient-ventilator asynchrony with multiple negative consequences. Our objective is to test the possibility of using chest-wall motion measured by an optical fibre-grating sensor as a more accurate non-invasive ventilator triggering mechanism.

APPROACH

The basic premise of our approach is that the measurement accuracy can be improved by using a triggering signal that precedes pneumatic triggering in the neuro-ventilatory coupling sequence. We propose a technique that uses the measurement of chest-wall curvature by a long-period fibre-grating sensor. The sensor was applied externally to the rib-cage and interrogated in the lateral (edge) filtering scheme. The study was performed on 34 healthy volunteers. Statistical data analysis of the time lag between the fibre-grating sensor and the reference pneumotachograph was preceded by the removal of the unwanted heartbeat signal by wavelet transform processing.

MAIN RESULTS

The results show a consistent fibre-grating signal advance with respect to the standard pneumatic signal by (230  ±  100) ms in both the inspiratory and expiratory phases. We further show that heart activity removal yields a tremendous improvement in sensor accuracy by reducing it from 60 ml to 0.3 ml.

SIGNIFICANCE

The results indicate that the proposed measurement technique may lead to a more reliable triggering decision. Its imperviousness to air leaks, non-invasiveness, low-cost and ease of implementation offer good prospects for applications in both clinical and homecare ventilation.

Assessing mechanical ventilation asynchrony through iterative airway pressure reconstruction

BACKGROUND AND OBJECTIVE

Respiratory mechanics estimation can be used to guide mechanical ventilation (MV) but is severely compromised when asynchronous breathing occurs. In addition, asynchrony during MV is often not monitored and little is known about the impact or magnitude of asynchronous breathing towards recovery. Thus, it is important to monitor and quantify asynchronous breathing over every breath in an automated fashion, enabling the ability to overcome the limitations of model-based respiratory mechanics estimation during asynchronous breathing ventilation.

METHODS

An iterative airway pressure reconstruction (IPR) method is used to reconstruct asynchronous airway pressure waveforms to better match passive breathing airway waveforms using a single compartment model. The reconstructed pressure enables estimation of respiratory mechanics of airway pressure waveform essentially free from asynchrony. Reconstruction enables real-time breath-to-breath monitoring and quantification of the magnitude of the asynchrony (M_Asyn).

RESULTS AND DISCUSSION

Over 100,000 breathing cycles from MV patients with known asynchronous breathing were analyzed. The IPR was able to reconstruct different types of asynchronous breathing. The resulting respiratory mechanics estimated using pressure reconstruction were more consistent with smaller interquartile range (IQR) compared to respiratory mechanics estimated using asynchronous pressure. Comparing reconstructed pressure with asynchronous pressure waveforms quantifies the magnitude of asynchronous breathing, which has a median value M_Asyn for the entire dataset of 3.8%.

CONCLUSION

The iterative pressure reconstruction method is capable of identifying asynchronous breaths and improving respiratory mechanics estimation consistency compared to conventional model-based methods. It provides an opportunity to automate real-time quantification of asynchronous breathing frequency and magnitude that was previously limited to invasively method only.

Neurally Adjusted Ventilatory Assist Is Associated with Greater Initial Extubation Success in Postoperative Congenital Heart Disease Patients when Compared to Conventional Mechanical Ventilation

Extubation failure is associated with considerable morbidity and mortality in postoperative patients with congenital heart disease (CHD). The study purpose was to investigate initial extubation success utilizing neurally adjusted ventilatory assist (NAVA) compared with pressure-regulated volume controlled, synchronized intermittent mandatory ventilation with pressure support (SIMV-PRVC + PS) for ventilatory weaning in patients who required prolonged mechanical ventilation (MV). Also, total days on MV, inotropes, sedation, analgesia, and pediatric intensive care unit (PICU) length of stay (LOS) between both groups were compared. This was a non-randomized pilot study utilizing historical controls (SIMV-PRVC + PS; n  = 40) compared with a prospective study population (NAVA; n  = 35) in a Level I PICU and was implemented to help future trial designs. All patients ( n  = 75) required prolonged MV ≥96 hours due to their complex postoperative course. Ventilator weaning initiation and management was standardized between both groups. Ninety-seven percent of the NAVA group was successfully extubated on the initial attempt, while 80% were in the SIMV-PRVC + PS group ( p  = 0.0317). Patients placed on NAVA were eight times more likely to have successful initial extubation (odds ratio [OR]: 8.50, 95% confidence interval [CI]: 1.01, 71.82). The NAVA group demonstrated a shorter median duration on MV (9.0 vs. 11.0 days, p  = 0.032), PICU LOS (9.0 vs. 13.5 days, p  < 0.0001), and shorter median duration of days on dopamine (8.0 vs. 11.0 days, p  = 0.0022), milrinone (9.0 vs. 12.0 days, p  = 0.0002), midazolam (8.0 vs. 12.0 days, p  < 0.0001), and fentanyl (9.0 vs. 12.5 days, p  < 0.0001) compared with the SIMV-PRVC + PS group. NAVA compared with SIMV-PRVC + PS was associated with a greater initial extubation success rate. NAVA should be considered as a mechanical ventilator weaning strategy in postoperative congenital heart disease (CHD) patients and warrants further investigation.

Patient-ventilator asynchrony

Patient-v entilator asynchrony (PVA) is a mismatch between the patient, regarding time, flow, volume, or pressure demands of the patient respiratory system, and the ventilator, which supplies such demands, during mechanical ventilation (MV). It is a common phenomenon, with incidence rates ranging from 10% to 85%. PVA might be due to factors related to the patient, to the ventilator, or both. The most common PVA types are those related to triggering, such as ineffective effort, auto-triggering, and double triggering; those related to premature or delayed cycling; and those related to insufficient or excessive flow. Each of these types can be detected by visual inspection of volume, flow, and pressure waveforms on the mechanical ventilator display. Specific ventilatory strategies can be used in combination with clinical management, such as controlling patient pain, anxiety, fever, etc. Deep sedation should be avoided whenever possible. PVA has been associated with unwanted outcomes, such as discomfort, dyspnea, worsening of pulmonary gas exchange, increased work of breathing, diaphragmatic injury, sleep impairment, and increased use of sedation or neuromuscular blockade, as well as increases in the duration of MV, weaning time, and mortality. Proportional assist ventilation and neurally adjusted ventilatory assist are modalities of partial ventilatory support that reduce PVA and have shown promise. This article reviews the literature on the types and causes of PVA, as well as the methods used in its evaluation, its potential implications in the recovery process of critically ill patients, and strategies for its resolution.

Neural Breathing Pattern and Patient-Ventilator Interaction During Neurally Adjusted Ventilatory Assist and Conventional Ventilation in Newborns

OBJECTIVE

To compare neurally adjusted ventilatory assist and conventional ventilation on patient-ventilator interaction and neural breathing patterns, with a focus on central apnea in preterm infants.

DESIGN

Prospective, observational cross-over study of intubated and ventilated newborns. Data were collected while infants were successively ventilated with three different ventilator conditions (30 min each period): 1) synchronized intermittent mandatory ventilation (SIMV) combined with pressure support at the clinically prescribed, SIMV with baseline settings (SIMVBL), 2) neurally adjusted ventilatory assist, 3) same as SIMVBL, but with an adjustment of the inspiratory time of the mandatory breaths (SIMV with adjusted settings [SIMVADJ]) using feedback from the electrical activity of the diaphragm).

SETTING

Regional perinatal center neonatal ICU.

PATIENTS

Neonates admitted in the neonatal ICU requiring invasive mechanical ventilation.

MEASUREMENTS AND MAIN RESULTS

Twenty-three infants were studied, with median (range) gestational age at birth 27 weeks (24-41 wk), birth weight 780 g (490-3,610 g), and 7 days old (1-87 d old). Patient ventilator asynchrony, as quantified by the NeuroSync index, was lower during neurally adjusted ventilatory assist (18.3% ± 6.3%) compared with SIMVBL (46.5% ±11.7%; p < 0.05) and SIMVADJ (45.8% ± 9.4%; p < 0.05). There were no significant differences in neural breathing parameters, or vital signs, except for the end-expiratory electrical activity of the diaphragm, which was lower during neurally adjusted ventilatory assist. Central apnea, defined as a flat electrical activity of the diaphragm more than 5 seconds, was significantly reduced during neurally adjusted ventilatory assist compared with both SIMV periods. These results were comparable for term and preterm infants.

CONCLUSIONS

Patient-ventilator interaction appears to be improved with neurally adjusted ventilatory assist. Analysis of the neural breathing pattern revealed a reduction in central apnea during neurally adjusted ventilatory assist use.

Patient-Ventilator Dyssynchrony

In mechanically ventilated patients, assisted mechanical ventilation (MV) is employed early, following the acute phase of critical illness, in order to eliminate the detrimental effects of controlled MV, most notably the development of ventilator-induced diaphragmatic dysfunction. Nevertheless, the benefits of assisted MV are often counteracted by the development of patient-ventilator dyssynchrony. Patient-ventilator dyssynchrony occurs when either the initiation and/or termination of mechanical breath is not in time agreement with the initiation and termination of neural inspiration, respectively, or if the magnitude of mechanical assist does not respond to the patient's respiratory demand. As patient-ventilator dyssynchrony has been associated with several adverse effects and can adversely influence patient outcome, every effort should be made to recognize and correct this occurrence at bedside. To detect patient-ventilator dyssynchronies, the physician should assess patient comfort and carefully inspect the pressure- and flow-time waveforms, available on the ventilator screen of all modern ventilators. Modern ventilators offer several modifiable settings to improve patient-ventilator interaction. New proportional modes of ventilation are also very helpful in improving patient-ventilator interaction.

Prevalence and Prognosis Impact of Patient-Ventilator Asynchrony in Early Phase of Weaning according to Two Detection Methods

BACKGROUND

Patient-ventilator asynchrony is associated with a poorer outcome. The prevalence and severity of asynchrony during the early phase of weaning has never been specifically described. The authors' first aim was to evaluate the prognosis impact and the factors associated with asynchrony. Their second aim was to compare the prevalence of asynchrony according to two methods of detection: a visual inspection of signals and a computerized method integrating electromyographic activity of the diaphragm.

METHODS

This was an ancillary study of a multicenter, randomized controlled trial comparing neurally adjusted ventilatory assist to pressure support ventilation. Asynchrony was quantified at 12, 24, 36, and 48 h after switching from controlled ventilation to a partial mode of ventilatory assistance according to the two methods. An asynchrony index greater than or equal to 10% defined severe asynchrony.

RESULTS

A total of 103 patients ventilated for a median duration of 5 days (interquartile range, 3 to 9 days) were included. Whatever the method used for quantification, severe patient-ventilator asynchrony was not associated with an alteration of the outcome. No factor was associated with severe asynchrony. The prevalence of asynchrony was significantly lower when the quantification was based on flow and pressure than when it was based on the electromyographic activity of the diaphragm at 0.3 min (interquartile range, 0.2 to 0.8 min) and 4.7 min (interquartile range, 3.2 to 7.7 min; P < 0.0001), respectively.

CONCLUSIONS

During the early phase of weaning in patients receiving a partial ventilatory mode, severe patient-ventilator asynchrony was not associated with adverse clinical outcome, although the prevalence of patient-ventilator asynchrony varies according to the definitions and methods used for detection.

Neurally Adjusted Ventilatory Assist (NAVA) or Pressure Support Ventilation (PSV) during spontaneous breathing trials in critically ill patients: a crossover trial

Background

Neurally Adjusted Ventilatory Assist (NAVA) is a proportional ventilatory mode that uses the electrical activity of the diaphragm (EAdi) to offer ventilatory assistance in proportion to patient effort. NAVA has been increasingly used for critically ill patients, but it has not been evaluated during spontaneous breathing trials (SBT). We designed a pilot trial to assess the feasibility of using NAVA during SBTs, and to compare the breathing pattern and patient-ventilator asynchrony of NAVA with Pressure Support (PSV) during SBTs.

Methods

We conducted a crossover trial in the ICU of a university hospital in Brazil and included mechanically ventilated patients considered ready to undergo an SBT on the day of the study. Patients underwent two SBTs in randomized order: 30 min in PSV of 5 cmH₂O or NAVA titrated to generate equivalent peak airway pressure (Paw), with a positive end-expiratory pressure of 5 cmH₂O. The ICU team, blinded to ventilatory mode, evaluated whether patients passed each SBT. We captured flow, Paw and electrical activity of the diaphragm (EAdi) from the ventilator and used it to calculate respiratory rate (RR), tidal volume (VT), and EAdi. Detection of asynchrony events used waveform analysis and we calculated the asynchrony index as the number of asynchrony events divided by the number of neural cycles.

Results

We included 20 patients in the study. All patients passed the SBT in PSV, and three failed the SBT in NAVA. Five patients were reintubated and the extubation failure rate was 25% (95% CI 9–49%). Respiratory parameters were similar in the two modes: VT = 6.1 (5.5–6.5) mL/Kg in NAVA vs. 5.5 (4.8–6.1) mL/Kg in PSV (p = 0.076) and RR = 27 (17–30) rpm in NAVA vs. 26 (20–30) rpm in PSV, p = 0.55. NAVA reduced AI, with a median of 11.5% (4.2–19.7) compared to 24.3% (6.3–34.3) in PSV (p = 0.033).

Conclusions

NAVA reduces patient-ventilator asynchrony index and generates a respiratory pattern similar to PSV during SBTs. Patients considered ready for mechanical ventilation liberation may be submitted to an SBT in NAVA using the same objective criteria used for SBTs in PSV.

Trial registration

ClinicalTrials.gov (NCT01337271), registered April 12, 2011.

Electronic supplementary material

The online version of this article (10.1186/s12890-017-0484-5) contains supplementary material, which is available to authorized users.

Spontaneous breathing: a double-edged sword to handle with care

In acute hypoxemic respiratory failure (AHRF) and acute respiratory distress syndrome (ARDS) patients, spontaneous breathing is associated with multiple physiologic benefits: it prevents muscles atrophy, avoids paralysis, decreases sedation needs and is associated with improved hemodynamics. On the other hand, in the presence of uncontrolled inspiratory effort, severe lung injury and asynchronies, spontaneous ventilation might also worsen lung edema, induce diaphragm dysfunction and lead to muscles exhaustion and prolonged weaning. In the present review article, we present physiologic mechanisms driving spontaneous breathing, with emphasis on how to implement basic and advanced respiratory monitoring to assess lung protection during spontaneous assisted ventilation. Then, key benefits and risks associated with spontaneous ventilation are described. Finally, we propose some clinical means to promote protective spontaneous breathing at the bedside. In summary, early switch to spontaneous assisted breathing of acutely hypoxemic patients is more respectful of physiology and might yield several advantages. Nonetheless, risk of additional lung injury is not completely avoided during spontaneous breathing and careful monitoring of target physiologic variables such as tidal volume (Vt) and driving transpulmonary pressure should be applied routinely. In clinical practice, multiple interventions such as extracorporeal CO₂ removal exist to maintain inspiratory effort, Vt and driving transpulmonary pressure within safe limits but more studies are needed to assess their long-term efficacy.

Can proportional ventilation modes facilitate exercise in critically ill patients? A physiological cross-over study : Pressure support versus proportional ventilation during lower limb exercise in ventilated critically ill patients

Background

Early exercise of critically ill patients may have beneficial effects on muscle strength, mass and systemic inflammation. During pressure support ventilation (PSV), a mismatch between demand and assist could increase work of breathing and limit exercise. A better exercise tolerance is possible with a proportional mode of ventilation (Proportional Assist Ventilation, PAV+ and Neurally Adjusted Ventilatory Assist, NAVA). We examined whether, in critically ill patients, PSV and proportional ventilation have different effects on respiratory muscles unloading and work efficiency during exercise.

Methods

Prospective pilot randomized cross-over study performed in a medico-surgical ICU. Patients requiring mechanical ventilation >48 h were enrolled. At initiation, the patients underwent an incremental workload test on a cycloergometer to determine the maximum level capacity. The next day, 2 15-min exercise, at 60% of the maximum capacity, were performed while patients were randomly ventilated with PSV and PAV+ or NAVA. The change in oxygen consumption (ΔVO₂, indirect calorimetry) and the work efficiency (ratio of ΔVO₂ per mean power) were computed.

Results

Ten patients were examined, 6 ventilated with PSV/PAV+ and 4 with PSV/NAVA. Despite the same mean inspiratory pressure at baseline between the modes, baseline VO₂ (median, IQR) was higher during proportional ventilation (301 ml/min, 270–342) compared to PSV (249 ml/min, 206–353). Exercise with PSV was associated with a significant increase in VO₂ (ΔVO₂, median, IQR) (77.6 ml/min, 59.9–96.5), while VO₂ did not significantly change during exercise with proportional modes (46.3 ml/min, 5.7–63.7, p < 0.05). As a result, exercise with proportional modes was associated with a better work efficiency than with PSV. The ventilator modes did not affect patient’s dyspnea, limb fatigue, distance, hemodynamics and breathing pattern.

Conclusions

Proportional ventilation during exercise results in higher work efficiency and less increase in VO₂ compared to ventilation with PSV. These preliminary findings suggest that proportional ventilation could enhance the training effect and facilitate rehabilitation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-017-0289-y) contains supplementary material, which is available to authorized users.

Effects of neurally adjusted ventilatory assist on air distribution and dead space in patients with acute exacerbation of chronic obstructive pulmonary disease

Background

Neurally adjusted ventilatory assist (NAVA) could improve patient-ventilator interaction; its effects on ventilation distribution and dead space are still unknown. The aim of this study was to evaluate the effects of varying levels of assist during NAVA and pressure support ventilation (PSV) on ventilation distribution and dead space in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD).

Methods

Fifteen mechanically ventilated patients with AECOPD were included in the study. The initial PSV levels were set to 10 cmH₂O for 10 min. Thereafter, the ventilator mode was changed to NAVA for another 10 min with the same electrical activity of the diaphragm as during PSV. Furthermore, the ventilation mode was switched between PSV and NAVA every 10 min in the following order: PSV 5 cmH₂O; NAVA 50%; PSV 15 cmH₂O; and NAVA 150% (relative to the initial NAVA support level). Ventilation distribution in the lung was evaluated in percentages in regions of interest (ROI) of four anteroposterior segments of equal height (ROI1 to ROI4 represents ventral, mid-ventral, mid-dorsal, and dorsal, respectively). Blood gases, ventilation distribution (electrical impedance tomography), diaphragm activity (B-mode ultrasonography), and dead space fraction (PeCO₂ and PaCO₂) were measured.

Results

The trigger and cycle delays were lower during NAVA than during PSV. The work of trigger was significantly lower during NAVA compared to PSV. The diaphragm activities based on ultrasonography were higher during NAVA compared to the same support level during PSV. The ventilation distribution in ROI4 increased significantly (P < 0.05) during NAVA compared to PSV (except for a support level of 50%). Similar results were found in ROI3 + 4. NAVA reduced dead space fraction compared to the corresponding support level of PSV.

Conclusions

NAVA was superior to PSV in AECOPD for increasing ventilation distribution in ROI4 and reducing dead space.

Trial registration

Clinicaltrials.gov, NCT02289573. Registered on 12 November 2014.

Respiratory monitoring in adult intensive care unit

INTRODUCTION

The mortality of patients with respiratory failure has steadily decreased with the advancements in protective ventilation and treatment options. Although respiratory monitoring per se has not been proven to affect the mortality of critically ill patients, it plays a crucial role in patients' care, as it helps to titrate the ventilatory support. Several new monitoring techniques have recently been made available at the bedside. The goals of monitoring comprise alerting physicians to detect the change in the patients' conditions, to improve the understanding of pathophysiology to guide the diagnosis and provide cost-effective clinical management. Areas covered: We performed a review of the recent scientific literature to provide an overview of the different methods used for respiratory monitoring in adult intensive care units, including bedside imaging techniques such as ultrasound and electrical impedance tomography. Expert commentary: Appropriate respiratory monitoring plays an important role in patients with and without respiratory failure as a guiding tool for the optimization of ventilation support, avoiding further complications and decreasing morbidity and mortality. The physician should tailor the monitoring strategy for each individual patient and know how to correctly interpret the data.

A diaphragmatic electrical activity-based optimization strategy during pressure support ventilation improves synchronization but does not impact work of breathing

Background

Poor patient-ventilator synchronization is often observed during pressure support ventilation (PSV) and has been associated with prolonged duration of mechanical ventilation and poor outcome. Diaphragmatic electrical activity (Eadi) recorded using specialized nasogastric tubes is a surrogate of respiratory brain stem output. This study aimed at testing whether adapting ventilator settings during PSV using a protocolized Eadi-based optimization strategy, or Eadi-triggered and -cycled assisted pressure ventilation (or PSV_N) could (1) improve patient-ventilator interaction and (2) reduce or normalize patient respiratory effort as estimated by the work of breathing (WOB) and the pressure time product (PTP).

Methods

This was a prospective cross-over study. Patients with a known chronic pulmonary obstructive or restrictive disease, asynchronies or suspected intrinsic positive end-expiratory pressure (PEEP) who were ventilated using PSV were enrolled in the study. Four different ventilator settings were sequentially applied for 15 minutes (step 1: baseline PSV as set by the clinician, step 2: Eadi-optimized PSV to adjust PS level, inspiratory trigger, and cycling settings, step 3: step 2 + PEEP adjustment, step 4: PSV_N). The same settings as step 3 were applied again after step 4 to rule out a potential effect of time. Breathing pattern, trigger delay (T_d), inspiratory time in excess (T_iex), pressure-time product (PTP), and work of breathing (WOB) were measured at the end of each step.

Results

Eleven patients were enrolled in the study. Eadi-optimized PSV reduced T_d without altering T_iex in comparison with baseline PSV. PSV_N reduced T_d and T_iex in comparison with baseline and Eadi-optimized PSV. Respiratory pattern did not change during the four steps. The improvement in patient-ventilator interaction did not lead to changes in WOB or PTP.

Conclusions

Eadi-optimized PSV allows improving patient ventilator interaction but does not alter patient effort in patients with mild asynchrony.

Trial registration

Clinicaltrials.gov identifier: NCT 02067403. Registered 7 February 2014.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1599-z) contains supplementary material, which is available to authorized users.

Assisted Ventilation

Controlled Mechanical Ventilation may be essential in the setting of severe respiratory failure but consequences to the patient including increased use of sedation and neuromuscular blockade may contribute to delirium, atelectasis, and diaphragm dysfunction. Assisted ventilation allows spontaneous breathing activity to restore physiological displacement of the diaphragm and recruit better perfused lung regions. Pressure Support Ventilation is the most frequently used mode of assisted mechanical ventilation. However, this mode continues to provide a monotonous pattern of support for respiration which is normally a dynamic process. Noisy Pressure Support Ventilation where tidal volume is varied randomly by the ventilator may improve ventilation and perfusion matching but the degree of support is still determined by the ventilator. Two more recent modes of ventilation, Proportional Assist Ventilation and Neurally Adjusted Ventilatory Assist (NAVA), allow patient determination of the pattern and depth of ventilation. Proposed advantages of Proportional Assist Ventilation and NAVA include decrease in patient ventilator asynchrony and improved adaptation of ventilator support to changing patient demand. Work of breathing can be normalized with these modes as well. To date, however, a clear pattern of clinical benefit has not been demonstrated. Existing challenges for both of the newer assist modes include monitoring patients with dynamic hyperinflation (auto-positive end expiratory pressure), obstructive lung disease, and air leaks in the ventilator system. NAVA is dependent on consistent transduction of diaphragm activity by an electrode system placed in the esophagus. Longevity of effective support with this technique is unclear.

Patient-Ventilator Interactions

Ventilatory muscle fatigue is a reversible loss of the ability to generate force or velocity of contraction in response to increased elastic and resistive loads. Mechanical ventilation should provide support without imposing additional loads from the ventilator (dys-synchrony). Interactive breaths optimize this relationship but require that patient effort and the ventilator response be synchronous during breath initiation, flow delivery, and termination. Proper delivery considers all 3 phases and uses clinical data, ventilator graphics, and sometimes a trial-and-error approach to optimize patient-ventilator interactions. Newer modes optimize interactions but await good clinical outcome data before routine use.