Short-term effects of noisy pressure support ventilation in patients with acute hypoxemic respiratory failure

Heterogeneous impact of Sighs on mortality in patients with acute hypoxemic respiratory failure: insights from the PROTECTION study

BACKGROUND

Sigh breaths may impact outcomes in acute hypoxemic respiratory failure (AHRF) during assisted mechanical ventilation. We investigated whether sigh breaths may impact mortality in predefined subgroups of patients enrolled in the PROTECTION multicenter clinical trial according to: 1.the physiological response in oxygenation to Sigh (responders versus non-responders) and 2.the set levels of positive end-expiratory pressure (PEEP) (High vs. Low-PEEP). If mortality differed between Sigh and No Sigh, we explored physiological daily differences at 7-days.

RESULTS

Patients were randomized to pressure support ventilation (PSV) with Sigh (Sigh group) versus PSV with no sigh (No Sigh group). (1) Sighs were not associated with differences in 28-day mortality in responders to baseline sigh-test. Contrarily-in non-responders-56 patients were randomized to Sigh (55%) and 28-day mortality was lower with sighs (17%vs.36%, log-rank p = 0.031). (2) In patients with PEEP > 8cmH2O no difference in mortality was observed with sighs. With Low-PEEP, 54 patients were randomized to Sigh (48%). Mortality at 28-day was reduced in patients randomised to sighs (13%vs.31%, log-rank p = 0.021). These findings were robust to multivariable adjustments. Tidal volume, respiratory rate and ventilatory ratio decreased with Sigh as compared with No Sigh at 7-days. Ventilatory ratio was associated with mortality and successful extubation in both non-responders and Low-PEEP.

CONCLUSIONS

Addition of Sigh to PSV could reduce mortality in AHRF non-responder to Sigh and exposed to Low-PEEP. Results in non-responders were not expected. Findings in the low PEEP group may indicate that insufficient PEEP was used or that Low PEEP may be used with Sigh. Sigh may reduce mortality by decreasing physiologic dead space and ventilation intensity and/or optimizing ventilation/perfusion mismatch.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov; Identifier: NCT03201263.

Automated characterization of patient-ventilator interaction using surface electromyography

BACKGROUND

Characterizing patient-ventilator interaction in critically ill patients is time-consuming and requires trained staff to evaluate the behavior of the ventilated patient.

METHODS

In this study, we recorded surface electromyography ([Formula: see text]) signals from the diaphragm and intercostal muscles and esophageal pressure ([Formula: see text]) in mechanically ventilated patients with ARDS. The sEMG recordings were preprocessed, and two different algorithms (triangle algorithm and adaptive thresholding algorithm) were used to automatically detect inspiratory patient effort. Based on the detected inspirations, major asynchronies (ineffective, auto-, and double triggers and double efforts), delayed and synchronous triggers were computationally classified. Reverse triggers were not considered in this study. Subsequently, asynchrony indices were calculated. For the validation of detected efforts, two experts manually annotated inspiratory patient activity in [Formula: see text], blinded toward each other, the [Formula: see text] signals, and the algorithmic results. We also classified patient-ventilator interaction and calculated asynchrony indices with manually detected inspirations in [Formula: see text] as a reference for automated asynchrony classification and asynchrony index calculation.

RESULTS

Spontaneous breathing activity was recognized in 22 out of the 36 patients included in the study. Evaluation of the accuracy of the algorithms using 3057 inspiratory efforts in [Formula: see text] demonstrated reliable detection performance for both methods. Across all datasets, we found a high sensitivity (triangle algorithm/adaptive thresholding algorithm: 0.93/0.97) and a high positive predictive value (0.94/0.89) against expert annotations in [Formula: see text]. The average delay of automatically detected inspiratory onset to the [Formula: see text] reference was [Formula: see text]79 ms/29 ms for the two algorithms. Our findings also indicate that automatic asynchrony index prediction is reliable. For both algorithms, we found the same deviation of [Formula: see text] to the [Formula: see text]-based reference.

CONCLUSIONS

Our study demonstrates the feasibility of automating the quantification of patient-ventilator asynchrony in critically ill patients using noninvasive sEMG. This may facilitate more frequent diagnosis of asynchrony and support improving patient-ventilator interaction.

Variable ventilation versus stepwise lung recruitment manoeuvres for lung recruitment: A comparative study in an experimental model of atelectasis

BACKGROUND

Variable ventilation recruits alveoli in atelectatic lungs, but it is unknown how it compares with conventional recruitment manoeuvres.

OBJECTIVES

To test whether mechanical ventilation with variable tidal volumes and conventional recruitment manoeuvres have comparable effects on lung function.

DESIGN

Randomised crossover study.

SETTING

University hospital research facility.

ANIMALS

Eleven juvenile mechanically ventilated pigs with atelectasis created by saline lung lavage.

INTERVENTIONS

Lung recruitment was performed using two strategies, both with an individualised optimal positive-end expiratory pressure (PEEP) associated with the best respiratory system elastance during a decremental PEEP trial: conventional recruitment manoeuvres (stepwise increase of PEEP) in pressure-controlled mode) followed by 50 min of volume-controlled ventilation (VCV) with constant tidal volume, and variable ventilation, consisting of 50 min of VCV with random variation in tidal volume.

MAIN OUTCOME MEASURES

Before and 50 min after each recruitment manoeuvre strategy, lung aeration was assessed by computed tomography, and relative lung perfusion and ventilation (0% = dorsal, 100% = ventral) were determined by electrical impedance tomography.

RESULTS

After 50 min, variable ventilation and stepwise recruitment manoeuvres decreased the relative mass of poorly and nonaerated lung tissue (percent lung mass: 35.3 ± 6.2 versus 34.2 ± 6.6, P  = 0.303); reduced poorly aerated lung mass compared with baseline (-3.5 ± 4.0%, P  = 0.016, and -5.2 ± 2.8%, P  < 0.001, respectively), and reduced nonaerated lung mass compared with baseline (-7.2 ± 2.5%, P  < 0.001; and -4.7 ± 2.8%, P  < 0.001 respectively), while the distribution of relative perfusion was barely affected (variable ventilation: -0.8 ± 1.1%, P  = 0.044; stepwise recruitment manoeuvres: -0.4 ± 0.9%, P  = 0.167). Compared with baseline, variable ventilation and stepwise recruitment manoeuvres increased Pa O 2 (172 ± 85mmHg, P  = 0.001; and 213 ± 73 mmHg, P  < 0.001, respectively), reduced Pa CO 2 (-9.6 ± 8.1 mmHg, P  = 0.003; and -6.7 ± 4.6 mmHg, P  < 0.001, respectively), and decreased elastance (-11.4 ± 6.3 cmH 2 O, P  < 0.001; and -14.1 ± 3.3 cmH 2 O, P  < 0.001, respectively). Mean arterial pressure decreased during stepwise recruitment manoeuvres (-24 ± 8 mmHg, P  = 0.006), but not variable ventilation.

CONCLUSION

In this model of lung atelectasis, variable ventilation and stepwise recruitment manoeuvres effectively recruited lungs, but only variable ventilation did not adversely affect haemodynamics.

TRIAL REGISTRATION

This study was registered and approved by Landesdirektion Dresden, Germany (DD24-5131/354/64).

Patient-Ventilator Synchrony in Neurally-Adjusted Ventilatory Assist and Variable Pressure Support Ventilation

BACKGROUND

Neurally-adjusted ventilatory assist (NAVA) improves patient-ventilator synchrony and reduces the risk of respiratory over-assistance. Variable pressure support ventilation (PSV) is a recently introduced mode of assisted ventilation that has also shown reduction in patient-ventilator asynchronies. We hypothesized that NAVA would reduce patient-ventilator asynchronies and inspiratory effort compared to variable PSV because breathing variability was intrinsically determined by the patient and not by the ventilator. This study aimed to evaluate patient-ventilator asynchronies and inspiratory effort pressure-time product (PTP) between NAVA and variable PSV in subjects with mild ARDS.

METHODS

After 24 h of controlled mechanical ventilation, subjects (P_aO2 /F_IO2 200-300 and PEEP level < 10 cm H₂O) were randomized in sequence 1:1 by using a web-based encrypted platform and assigned to NAVA or variable PSV groups. Both modes of ventilation were consecutively kept for 24 h unless there were clinical changes. The primary aim of this study was to evaluate differences in asynchrony index (AI) between variable PSV and NAVA. Our secondary aims were to evaluate the coefficient of variation (CV) of breathing patterns and inspiratory effort between the groups.

RESULTS

Thirteen subjects were randomized in the NAVA group and 13 subjects in the variable PSV group. AI over time and minute PTP (PTP_min) were not different between NAVA and variable PSV groups (AI t₀P = .52, AI t₁₂P = .27, AI t₂₄P = .12; and PTP_min-t0P = .60, PTP_min-t12P = .57, PTP_min-t24P = .85, respectively). CV for tidal volume (V_T) and pressure support (PS) was lower in variable PSV group over time compared with NAVA group (P < .05).

CONCLUSIONS

In this randomized controlled trial including subjects with mild ARDS, NAVA and variable PSV had comparable effects on patient-ventilator synchronies and PTP. However, variable PSV reduced the variability of V_T and PS when compared with NAVA.

Effects of Different Levels of Variability and Pressure Support Ventilation on Lung Function in Patients With Mild-Moderate Acute Respiratory Distress Syndrome

Background: Variable pressure support ventilation (vPSV) is an assisted ventilation mode that varies the level of pressure support on a breath-by-breath basis to restore the physiological variability of breathing activity. We aimed to compare the effects of vPSV at different levels of variability and pressure support (ΔP_S) in patients with acute respiratory distress syndrome (ARDS).

Methods: This study was a crossover randomized clinical trial. We included patients with mild to moderate ARDS already ventilated in conventional pressure support ventilation (PSV). The study consisted of two blocks of interventions, and variability during vPSV was set as the coefficient of variation of the ΔP_S level. In the first block, the effects of three levels of variability were tested at constant ΔP_S: 0% (PSV_0%, conventional PSV), 15% (vPSV_15%), and 30% (vPSV_30%). In the second block, two levels of variability (0% and variability set to achieve ±5 cmH₂O variability) were tested at two ΔP_S levels (baseline ΔP_S and ΔP_S reduced by 5 cmH₂O from baseline). The following four ventilation strategies were tested in the second block: PSV with baseline ΔP_S and 0% variability (PSV_BL) or ±5 cmH₂O variability (vPSV_BL), PSV with ΔP_S reduced by 5 cmH₂O and 0% variability (PSV₋₅) or ±5 cmH₂O variability (vPSV₋₅). Outcomes included gas exchange, respiratory mechanics, and patient-ventilator asynchronies.

Results: The study enrolled 20 patients. In the first block of interventions, oxygenation and respiratory mechanics parameters did not differ between vPSV_15% and vPSV_30% compared with PSV_0%. The variability of tidal volume (V_T) was higher with vPSV_15% and vPSV_30% compared with PSV_0%. The incidence of asynchronies and the variability of transpulmonary pressure (P_L) were higher with vPSV_30% compared with PSV_0%. In the second block of interventions, different levels of pressure support with and without variability did not change oxygenation. The variability of V_T and P_L was higher with vPSV₋₅ compared with PSV₋₅, but not with vPSV_BL compared with PSV_BL.

Conclusion: In patients with mild-moderate ARDS, the addition of variability did not improve oxygenation at different pressure support levels. Moreover, high variability levels were associated with worse patient-ventilator synchrony.

Clinical Trial Registration:www.clinicaltrials.gov, identifier: NCT01683669.

Tracking respiratory mechanics around natural breathing rates via variable ventilation

Measuring respiratory resistance and elastance as a function of time, tidal volume, respiratory rate, and positive end-expiratory pressure can guide mechanical ventilation. However, current measurement techniques are limited since they are assessed intermittently at non-physiological frequencies or involve specialized equipment. To this end, we introduce ZVV, a practical approach to continuously track resistance and elastance during Variable Ventilation (VV), in which frequency and tidal volume vary from breath-to-breath. ZVV segments airway pressure and flow recordings into individual breaths, calculates resistance and elastance for each breath, bins them according to frequency or tidal volume and plots the results against bin means. ZVV's feasibility was assessed clinically in five human patients with acute lung injury, experimentally in five mice ventilated before and after lavage injury, and computationally using a viscoelastic respiratory model. ZVV provided continuous measurements in both settings, while the computational study revealed <2% estimation errors. Our findings support ZVV as a feasible technique to assess respiratory mechanics under physiological conditions. Additionally, in humans, ZVV detected a decrease in resistance and elastance with time by 12.8% and 6.2%, respectively, suggesting that VV can improve lung recruitment in some patients and can therefore potentially serve both as a dual diagnostic and therapeutic tool.

The Effects of Positive End-Expiratory Pressure on Transpulmonary Pressure and Recruitment-Derecruitment During Neurally Adjusted Ventilator Assist: A Continuous Computed Tomography Study in an Animal Model of Acute Respiratory Distress Syndrome

Background

Whether spontaneous breathing (SB) should be used in early acute respiratory distress syndrome (ARDS) is questioned because it may cause ventilator-induced lung injury (VILI) by tidal high strain/stress and recruitment/derecruitment (R/D). However, SB has shown beneficial effects when used appropriately. We hypothesized that high levels of positive end-expiratory pressure (PEEP), during assisted SB, would prevent tidal R/D, reducing ventilatory variation and respiratory rate while potentially increasing transpulmonary pressure (P_TP). The aim was to test this hypothesis in experimental mild ARDS during continuous SB using neurally adjusted ventilator assist (NAVA) and uninterrupted computed tomography (CT) exposure.

Methods

Mild experimental ARDS (PaO₂/F_iO₂-ratio of 250) was induced in anesthetized pigs (n = 5), ventilated using uninterrupted NAVA. PEEP was changed in steps of 3 cmH₂O, from 0 to 15 and back to 0 cmH₂O. Dynamic CT scans, ventilatory parameters, and esophageal pressure were acquired simultaneously. P_TP and R/D were calculated and compared among PEEP levels.

Results

When increasing PEEP from 0 to 15 cmH₂O, tidal R/D decreased from 4.3 ± 5.9 to 1.1 ± 0.7% (p < 0.01), breath-to-breath variability decreased, and P_TP increased from 11.4 ± 3.7 to 29.7 ± 14.1 cmH₂O (R² = 0.96).

Conclusion

This study shows that injurious phenomena like R/D and high P_TP are present in NAVA at the two extremes of the PEEP spectrum. Willing to titrate PEEP to limit these phenomena, the physician must choose the best compromise between restraining the R/D or P_TP.

Patient-ventilator asynchronies during mechanical ventilation: current knowledge and research priorities

BACKGROUND

Mechanical ventilation is common in critically ill patients. This life-saving treatment can cause complications and is also associated with long-term sequelae. Patient-ventilator asynchronies are frequent but underdiagnosed, and they have been associated with worse outcomes.

MAIN BODY

Asynchronies occur when ventilator assistance does not match the patient's demand. Ventilatory overassistance or underassistance translates to different types of asynchronies with different effects on patients. Underassistance can result in an excessive load on respiratory muscles, air hunger, or lung injury due to excessive tidal volumes. Overassistance can result in lower patient inspiratory drive and can lead to reverse triggering, which can also worsen lung injury. Identifying the type of asynchrony and its causes is crucial for effective treatment. Mechanical ventilation and asynchronies can affect hemodynamics. An increase in intrathoracic pressure during ventilation modifies ventricular preload and afterload of ventricles, thereby affecting cardiac output and hemodynamic status. Ineffective efforts can decrease intrathoracic pressure, but double cycling can increase it. Thus, asynchronies can lower the predictive accuracy of some hemodynamic parameters of fluid responsiveness. New research is also exploring the psychological effects of asynchronies. Anxiety and depression are common in survivors of critical illness long after discharge. Patients on mechanical ventilation feel anxiety, fear, agony, and insecurity, which can worsen in the presence of asynchronies. Asynchronies have been associated with worse overall prognosis, but the direct causal relation between poor patient-ventilator interaction and worse outcomes has yet to be clearly demonstrated. Critical care patients generate huge volumes of data that are vastly underexploited. New monitoring systems can analyze waveforms together with other inputs, helping us to detect, analyze, and even predict asynchronies. Big data approaches promise to help us understand asynchronies better and improve their diagnosis and management.

CONCLUSIONS

Although our understanding of asynchronies has increased in recent years, many questions remain to be answered. Evolving concepts in asynchronies, lung crosstalk with other organs, and the difficulties of data management make more efforts necessary in this field.

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.

Comparison of different degrees of variability in tidal volume to prevent deterioration of respiratory system elastance in experimental acute lung inflammation

BACKGROUND

Variable ventilation improves respiratory function, but it is not known whether the amount of variability in tidal volume (VT) can be reduced in recruited lungs without a deterioration of respiratory system elastance.

METHODS

Acute lung inflammation was induced by intratracheal instillation of lipopolysaccharide in 35 Wistar rats. Twenty-eight animals were anaesthetized and ventilated in volume-controlled mode. Lungs were recruited by random variation of VT (mean 6 ml kg(-1), coefficient of variation 30%, normal distribution) for 30 min. Animals were randomly assigned to different amounts of VT variability (n=7 for 90 min per group): 30, 15, 7.5, or 0%. Lung function, diffuse alveolar damage, and gene expression of biological markers associated with cell mechanical stress, inflammation, and fibrogenesis were assessed. Seven animals were not ventilated and served as controls for post-mortem analyses.

RESULTS

A VT variability of 30%, but not 15, 7.5, or 0%, prevented deterioration of respiratory system elastance [Mean (SD) -7.5 (8.7%), P<0.05; 21.1 (9.6%), P<0.05; 43.3 (25.9), P<0.05; and 41.2 (16.4), P<0.05, respectively]. Diffuse alveolar damage was lower with a VT variability of 30% than with 0% and without ventilation, because of reduced oedema and haemorrhage. A VT variability of 30, 15, or 7.5% reduced the gene expression of amphiregulin, cytokine-induced neutrophil chemoattractant-1, and tumour necrosis factor α compared with a VT variability of 0%.

CONCLUSIONS

In this model of acute lung inflammation, a VT variability of 30%, compared with 15 and 7.5%, was necessary to avoid deterioration of respiratory system elastance and was not associated with lung histological damage.

Variable mechanical ventilation

Objective

To review the literature on the use of variable mechanical ventilation and the main outcomes of this technique.

Methods

Search, selection, and analysis of all original articles on variable ventilation, without restriction on the period of publication and language, available in the electronic databases LILACS, MEDLINE^®, and PubMed, by searching the terms "variable ventilation" OR "noisy ventilation" OR "biologically variable ventilation".

Results

A total of 36 studies were selected. Of these, 24 were original studies, including 21 experimental studies and three clinical studies.

Conclusion

Several experimental studies reported the beneficial effects of distinct variable ventilation strategies on lung function using different models of lung injury and healthy lungs. Variable ventilation seems to be a viable strategy for improving gas exchange and respiratory mechanics and preventing lung injury associated with mechanical ventilation. However, further clinical studies are necessary to assess the potential of variable ventilation strategies for the clinical improvement of patients undergoing mechanical ventilation.

Systems Biology and Clinical Practice in Respiratory Medicine. The Twain Shall Meet

Respiratory diseases are highly complex, being driven by host-environment interactions and manifested by inflammatory, structural, and functional abnormalities that vary over time. Traditional reductionist approaches have contributed vastly to our knowledge of biological systems in health and disease to date; however, they are insufficient to provide an understanding of the behavior of the system as a whole. In this Pulmonary Perspective, we discuss systems biology approaches, especially but not limited to the study of the lung as a complex system. Such integrative approaches take into account the large number of dynamic subunits and their interactions found in biological systems. Borrowing methods from physics and mathematics, it is possible to study the collective behavior of these systems over time and in a multidimensional manner. We first examine the physiological basis for complexity in the respiratory system and its implications for disease. We then expand on the potential applications of systems biology methods to study complex systems, within the context of diagnosis and monitoring of respiratory diseases including asthma, chronic obstructive pulmonary disease (COPD), and critical illness. We summarize the significant advances made in recent years using systems approaches for disease phenotyping, applied to data ranging from the molecular to clinical level, obtained from large-scale asthma and COPD networks. We describe new studies using temporal complexity patterns to characterize asthma and COPD and predict exacerbations as well as predict adverse outcomes in critical care. We highlight new methods that are emerging with this approach and discuss remaining questions that merit greater attention in the field.

Multicenter study on the prognosis associated with respiratory support for children with acute hypoxic respiratory failure

The objective of the present study was to explore the factors influencing the outcomes related to respiratory support of children with acute hypoxic respiratory failure (AHRF) in 30 hospitals. This was a non-controlled prospective and collaborative multicenter clinical study conducted from June, 2010 to May, 2011 (each hospital for 12 consecutive months). Children aged from 29 days to 6 years and who met the diagnostic standards of AHRF were enrolled as subjects for the study. After patients were enrolled, general parameters including disease diagnosis, treatment and prognosis were recorded. Then we analyzed the differences in prognosis and respiratory therapy of patients with AHRF. During the study period, 13,906 cases of AHRF were admitted among the 30 hospitals, accounting for 75.3% of the total number of patients with AHRF. The proportion in different hospitals ranged from 16 to 98%. A total of 492 children with hypoxic respiratory failure were admitted among the 30 hospitals. The prevalence rate was 3.54%, and the incidence of AHRF in each hospital was 4.54%. Tidal volume and respiratory support treatment were compared with the results from a 2006 study, and the differences were statistically significant in positive end-expiratory pressure (5 vs. 4, P=0.018), fraction of inspire O₂ (0.5 vs. 0.4, P<0.001), pressure of artery O₂ (70 vs. 60 mmHg, P<0.001) and peak inspiratory pressure (20 vs. 24 cm H₂Ο, P<0.001). In conclusion, academic background and the level of regional economic development are factors which influence the prognosis of children with AHRF. On the basis of unapparent differences between academic background and the level of regional economic development, there is a substantial difference in the prognosis from different forms of respiratory support management for AHRF. Therefore, it is essential to develop respiratory support and the level of critical management of pediatric intensive care units.

Variable ventilation from bench to bedside

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency medicine 2016. Other selected articles can be found online at http://www.biomedcentral.com/collections/annualupdate2016. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Approaches to ventilation in intensive care

BACKGROUND

Mechanical ventilation is a common and often life-saving intervention in intensive care medicine. About 35% of all patients in intensive care are mechanically ventilated; about 15% of these patients develop a ventilation-associated pneumonia. The goal of ventilation therapy is to lessen the work of respiration and pulmonary gas exchange and thereby maintain or restore an adequate oxygen supply to the body's tissues. Mechanical ventilation can be carried out in many different modes; the avoidance of ventilation-induced lung damage through protective ventilation strategies is currently a major focus of clinical interest.

METHOD

This review is based on pertinent articles retrieved by a selective literature search.

RESULTS

Compared to conventional lung-protecting modes of mechanical ventilation, the modern modes of ventilation presented here are further developments that optimize lung protection while improving pulmonary function and the synchrony of the patient with the ventilator. In high-frequency ventilation, tidal volumes of 1-2 mL/kgBW (body weight) are given, at a respiratory rate of up to 12 Hz. Assisted forms of spontaneous respiration are also in use, such as proportional assist ventilation (PAV), neurally adjusted ventilatory assist (NAVA), and variable pressure-support ventilation. Computer-guided closed-loop ventilation systems enable automated ventilation; according to a recent meta-analysis, they shorten weaning times by 32% .

CONCLUSION

The currently available scientific evidence with respect to clinically relevant endpoints is inadequate for all of these newer modes of ventilation. It appears, however, that they can lower both the invasiveness and the duration of mechanical ventilation, and thus improve the care of patients who need ventilation. Randomized trials with clinically relevant endpoints must be carried out before any final judgments can be made.

Effects of ultraprotective ventilation, extracorporeal carbon dioxide removal, and spontaneous breathing on lung morphofunction and inflammation in experimental severe acute respiratory distress syndrome

BACKGROUND

To investigate the role of ultraprotective mechanical ventilation (UP-MV) and extracorporeal carbon dioxide removal with and without spontaneous breathing (SB) to improve respiratory function and lung protection in experimental severe acute respiratory distress syndrome.

METHODS

Severe acute respiratory distress syndrome was induced by saline lung lavage and mechanical ventilation (MV) with higher tidal volume (VT) in 28 anesthetized pigs (32.8 to 52.5 kg). Animals (n = 7 per group) were randomly assigned to 6 h of MV (airway pressure release ventilation) with: (1) conventional P-MV with VT ≈6 ml/kg (P-MVcontr); (2) UP-MV with VT ≈3 ml/kg (UP-MVcontr); (3) UP-MV with VT ≈3 ml/kg and SB (UP-MVspont); and (4) UP-MV with VT ≈3 ml/kg and pressure supported SB (UP-MVPS). In UP-MV groups, extracorporeal carbon dioxide removal was used.

RESULTS

The authors found that: (1) UP-MVcontr reduced diffuse alveolar damage score in dorsal lung zones (median[interquartile]) (12.0 [7.0 to 16.8] vs. 22.5 [13.8 to 40.8]), but worsened oxygenation and intrapulmonary shunt, compared to P-MVcontr; (2) UP-MVspont and UP-MVPS improved oxygenation and intrapulmonary shunt, and redistributed ventilation towards dorsal areas, as compared to UP-MVcontr; (3) compared to P-MVcontr, UP-MVcontr and UP-MVspont, UP-MVPS yielded higher levels of tumor necrosis factor-α (6.9 [6.5 to 10.1] vs. 2.8 [2.2 to 3.0], 3.6 [3.0 to 4.7] and 4.0 [2.8 to 4.4] pg/mg, respectively) and interleukin-8 (216.8 [113.5 to 343.5] vs. 59.8 [45.3 to 66.7], 37.6 [18.8 to 52.0], and 59.5 [36.1 to 79.7] pg/mg, respectively) in dorsal lung zones.

CONCLUSIONS

In this model of severe acute respiratory distress syndrome, MV with VT ≈3 ml/kg and extracorporeal carbon dioxide removal without SB slightly reduced lung histologic damage, but not inflammation, as compared to MV with VT = 4 to 6 ml/kg. During UP-MV, pressure supported SB increased lung inflammation.

Relationship of tidal volume to peak flow, breath rate, I: E and plateau time: mock study

BACKGROUND

The purpose of this study was to determine the functional relationship between tidal volume (VT) and 4 other ventilator parameters.

METHODS

The following parameters were collected from an AVEA ventilator operating in the volume-controlled ventilation mode: VT (in L), peak flow (Vmax, in L/min), breath rate (f, in bpm), inspiratory-to-expiratory time ratio (I:E) and plateau time (TP, in s). The relationship between VT and each of the other variables was determined.

RESULTS

When the other parameters were held constant, VT was positively correlated with Vmax and I:E, but negatively correlated with f and TP. When the velocity versus time curve was a 50% linearly decreasing wave, the functional relationship among the 5 parameters was governed by the equation: VT = 180 Vmax (60f - 60f [1 + I:E] - TP).

CONCLUSIONS

The functional relationship among the 5 parameters for the AVEA ventilator in the volume-controlled ventilation mode was determined. The parameters should be controlled in accordance with the patient's pathophysiological needs.

Electrical impedance tomography imaging of the cardiopulmonary system

PURPOSE OF REVIEW

This review article summarizes the recent advances in electrical impedance tomography (EIT) related to cardiopulmonary imaging and monitoring on the background of the 30-year development of this technology.

RECENT FINDINGS

EIT is expected to become a bedside tool for monitoring and guiding ventilator therapy. In this context, several studies applied EIT to determine spatial ventilation distribution during different ventilation modes and settings. EIT was increasingly combined with other signals, such as airway pressure, enabling the assessment of regional respiratory system mechanics. EIT was for the first time used prospectively to define ventilator settings in an experimental and a clinical study. Increased neonatal and paediatric use of EIT was noted. Only few studies focused on cardiac function and lung perfusion. Advanced radiological imaging techniques were applied to assess EIT performance in detecting regional lung ventilation. New approaches to improve the quality of thoracic EIT images were proposed.

SUMMARY

EIT is not routinely used in a clinical setting, but the interest in EIT is evident. The major task for EIT research is to provide the clinicians with guidelines how to conduct, analyse and interpret EIT examinations and combine them with other medical techniques so as to meaningfully impact the clinical decision-making.

Advances in ventilator-associated lung injury: prevention is the target

Mechanical ventilation (MV) is the main supportive treatment in respiratory failure due to different etiologies. However, MV might aggravate ventilator-associated lung injury (VALI). Four main mechanisms leading to VALI are: 1) increased stress and strain, induced by high tidal volume (VT); 2) increased shear stress, i.e. opening and closing, of previously atelectatic alveolar units; 3) distribution of perfusion and 4) biotrauma. In severe acute respiratory distress syndrome patients, low VT, higher levels of positive end expiratory pressure, long duration prone position and neuromuscular blockade within the first 48 hours are associated to a better outcome. VALI can also occur by using high VT in previously non injured lungs. We believe that prevention is the target to minimize injurious effects of MV. This review aims to describe pathophysiology of VALI, the possible prevention and treatment as well as monitoring MV to minimize VALI.

Year in review 2013: Critical Care--respirology

This review documents important progress made in 2013 in the field of critical care respirology, in particular with regard to acute respiratory failure and acute respiratory distress syndrome. Twenty-five original articles published in the respirology and critical care sections of Critical Care are discussed in the following categories: pre-clinical studies, protective lung ventilation – how low can we go, non-invasive ventilation for respiratory failure, diagnosis and prognosis in acute respiratory distress syndrome and respiratory failure, and promising interventions for acute respiratory distress syndrome.

Low tidal volume pressure support versus controlled ventilation in early experimental sepsis in pigs

Background

In moderate acute respiratory distress syndrome (ARDS) several studies support the usage of assisted spontaneous breathing modes. Only limited data, however, focus on the application in systemic sepsis and developing lung injury. The present study examines the effects of immediate initiation of pressure support ventilation (PSV) in a model of sepsis-induced ARDS.

Methods

18 anesthetized pigs received a two-staged continuous lipopolysaccharide infusion to induce lung injury. The animals were randomly assigned to PSV or volume controlled (VCV) lung protective ventilation (tidal volume each 6 ml kg^-1, n = 2x9) over six hours. Gas exchange parameters, hemodynamics, systemic inflammation, and ventilation distribution by multiple inert gas elimination and electrical impedance tomography were assessed. The post mortem analysis included histopathological scoring, wet to dry ratio, and alveolar protein content.

Results

Within six hours both groups developed a mild to moderate ARDS with comparable systemic inflammatory response and without signs of improving gas exchange parameters during PSV. The PSV group showed signs of more homogenous ventilation distribution by electrical impedance tomography, but only slightly less hyperinflated lung compartments by multiple inert gas elimination. Post mortem and histopathological assessment yielded no significant intergroup differences.

Conclusions

In a porcine model of sepsis-induced mild ARDS immediate PSV was not superior to VCV. This contrasts with several experimental studies from non-septic mild to moderate ARDS. The present study therefore assumes that not only severity, but also etiology of lung injury considerably influences the response to early initiation of PSV.

Should we breathe quiet or noisy?

External noise is introduced by computer-generated random levels of pressure assistance during noisy pressure support ventilation (PSV). In patients, noisy PSV was associated with higher tidal volume variability but not improved cardio-pulmonary function compared with conventional PSV. The potential role of noisy PSV in the management of critically ill patients requiring ventilatory support has to be explored further.