EPISYNC study: predictors of patient-ventilator asynchrony in a prospective cohort of patients under invasive mechanical ventilation - study protocol.

INTRODUCTION: Patient-ventilator asynchrony is common during the entire period of invasive mechanical ventilation (MV) and is associated with worse clinical outcomes. However, risk factors associated with asynchrony are not completely understood. The main objectives of this study are to estimate the incidence of asynchrony during invasive MV and its association with respiratory mechanics and other baseline patient characteristics. METHODS AND ANALYSIS: We designed a prospective cohort study of patients admitted to the intensive care unit (ICU) of a university hospital. Inclusion criteria are adult patients under invasive MV initiated for less than 72 hours, and with expectation of remaining under MV for more than 24 hours. Exclusion criteria are high flow bronchopleural fistula, inability to measure respiratory mechanics and previous tracheostomy. Baseline assessment includes clinical characteristics of patients at ICU admission, including severity of illness, reason for initiation of MV, and measurement of static mechanics of the respiratory system. We will capture ventilator waveforms during the entire MV period that will be analysed with dedicated software (Better Care, Barcelona, Spain), which automatically identifies several types of asynchrony and calculates the asynchrony index (AI). We will use a linear regression model to identify risk factors associated with AI. To assess the relationship between survival and AI we will use Kaplan-Meier curves, log rank tests and Cox regression. The calculated sample size is 103 patients. The statistical analysis will be performed by the software R Programming (www.R-project.org) and will be considered statistically significant if the p value is less than 0.05. ETHICS AND DISSEMINATION: The study was approved by the Ethics Committee of Instituto do Coração, School of Medicine, University of São Paulo, Brazil, and informed consent was waived due to the observational nature of the study. We aim to disseminate the study findings through peer-reviewed publications and national and international conference presentations. TRIAL REGISTRATION NUMBER: NCT02687802; Pre-results.

Management of refractory hypoxemia in ARDS.

Severe hypoxemia is the hallmark of ARDS. However, unmanageable refractory hypoxemia fortunately is a rare occurrence in patients with ARDS and an infrequent cause of death in ARDS. However, in some patients, in spite of the application of lung protective ventilation with moderate to high levels of end-expiratory pressure (PEEP), refractory hypoxemia remains unresolved. When refractory hypoxemia persists, we first recommend the use of lung recruitment maneuvers and a decremental PEEP trial, if this does not resolve the refractory hypoxemia prone positioning should be attempted. The use of aerosolized pulmonary vasodilators can be used to buy time when these approaches fail as the patient is transitioned to extracorporeal membrane oxygenation. We also find that there is now sufficient evidence to recommend against the use of high frequency oscillation in the management of refractory hypoxemia.

Jet or intensive care unit ventilator during simulated percutaneous transtracheal ventilation: a lung model study.

BACKGROUND: Percutaneous transtracheal ventilation (PTV) via a jet ventilator (PTJV) is considered a rescue technique in difficult airway management. However, whether a conventional ventilator can generate adequate ventilation via PTV is not known. Our goal was to evaluate the tidal volume (V(T)) generated by a conventional ventilator during simulated PTV compared with PTJV in a lung model. METHODS: A lung model simulating an adult lung was used. A catheter was inserted through the artificial trachea and connected to either a jet ventilator or a conventional ventilator. The direction of catheter insertion was perpendicular to the trachea, pointing towards the lung and away from the lung. The jet ventilator was operated at 344.7 kPa. The conventional ventilator was operated in the pressure mode at peak inspiratory pressures of 40-90 cm H(2)O. RESULTS: The jet ventilator generated larger V(T) [817 (336) ml] when the catheter was pointing towards the lung than when pointing away from the lung or perpendicular to the trachea [121 (41) and 69 (24) ml, respectively, P<0.01]. With the conventional ventilator, changes in V(T) at different direction of catheter insertion were much less [222 (81) ml catheter pointing towards the lung, 229 (121) ml perpendicular to the trachea, and 187 (97) ml away from the lung]. CONCLUSIONS: Our result demonstrated that PTJV was effective only when the catheter was pointing towards the lung and requires high operating pressure. A conventional ventilator can generate reasonable minute ventilation through the transtracheal catheter less dependent on directions of catheter insertion and should be considered during emergent PTV.

The American-European Consensus Conference definition of the acute respiratory distress syndrome is dead, long live positive end-expiratory pressure!

In 1994, an American-European Consensus Conference (AECC) formalized the criteria for the diagnosis of the acute respiratory distress syndrome (ARDS). Although that definition is simple to apply in the clinical setting, it has been challenged over the years in several studies since the assessment of the oxygenation defect does not require standardized ventilatory support. We were the first to propose new guidelines, based on a specific, standard method of evaluating oxygenation status, a proposal that was later advocated by others. To address the limitations of the AECC definition, a modified ARDS definition has been proposed by a task force panel of experts, referred to as the Berlin Defintion, using a terminology similar to that we previously proposed. However, that proposal has several methodological flaws. Since all ARDS patients start off with terrible oxygenation, the Berlin Definition offers no room for stratifying and identifyng true ARDS patients since there is no further re-evaluation of the hypoxemia under standard ventilator setting in a specific time period. In this Point of View, we review the history of the definition of ARDS and discussed the methodological concerns regarding adopting this new, revised ARDS definition.

[Interpretation of ventilator curves in patients with acute respiratory failure]. / Interpretación de las curvas del respirador en pacientes con insuficiencia respiratoria aguda.

Mechanical ventilation is a therapeutic intervention involving the temporary replacement of ventilatory function with the purpose of improving symptoms in patients with acute respiratory failure. Technological advances have facilitated the development of sophisticated ventilators for viewing and recording the respiratory waveforms, which are a valuable source of information for the clinician. The correct interpretation of these curves is crucial for the correct diagnosis and early detection of anomalies, and for understanding physiological aspects related to mechanical ventilation and patient-ventilator interaction. The present study offers a guide for the interpretation of the airway pressure and flow and volume curves of the ventilator, through the analysis of different clinical scenarios.

Lung recruitment maneuvers during acute respiratory distress syndrome: is it useful?

Although significant advances have been made in approaches to manage the acute respiratory distress syndrome (ARDS), reported overall mortality for ARDS is still high. Recruitment maneuvers (RM) have been recommended by some as potential adjuncts to lung protective ventilatory approaches in ARDS. In this point of view issues surrounding the use of RM in ARDS are addressed. Specifically, the ability of RM to open the lung, the safety of RM, and their affect on outcome are addressed. Finally, a specific approach to performing RM with the use of a decremental PEEP trial is outlined.

Peak pressure during volume history and pressure-volume curve measurement affects analysis.

A previous volume history should be established prior to pressure- volume (P-V) curve measurement, however the effect of the volume history and the peak inspiratory pressure (PIP) during the P-V measurement has not been explored. Lung injury was created by lavage in nine sheep (25-35 kg). After stabilization, four P-V curves were sequentially obtained with PIP of 40, 50, 60, and 40 cm H2O. Prior to each P-V measurement the PIP delivered for 1 min was the same as during P-V measurement. We compared the lower inflection point (Pflex), upper inflection point (UIP), compliance below Pflex (Cstart), compliance between Pflex and UIP (Cinf), and compliance between UIP and peak pressure (Cend) for the inflation limb, and the point of maximum curvature on the deflation limb (PMC), compliance between peak pressure and PMC (Ctop), and maximum compliance (Cdef) for the deflation limb. In two sheep, Pflex at PIP 40 cm H2O could not be identified but appeared when PIP was raised. Pflex, Cstart, Cend, and Ctop were not affected by the PIP. However, UIP, PMC, Cinf, and Cdef increased as the PIP increased. Volume history and the PIP during P-V curve measurements affect both the inflation and deflation P-V curves.

Repetitive high-pressure recruitment maneuvers required to maximally recruit lung in a sheep model of acute respiratory distress syndrome.

OBJECTIVE: To compare the effects of two different recruitment maneuvers repeated multiple times on gas exchange lung injury, hemodynamic, and lung mechanics. DESIGN: Randomized prospective comparison. SETTINGS: Animal research laboratory. SUBJECT: Nineteen fasted Hampshire sheep. INTERVENTIONS: In 15 27-kg sheep with saline lavage lung injury, we compared the effects of two recruitment maneuvers: 40 cm H2O continuous positive airway pressure for 60 secs and 40 cm H2O positive end-expiratory pressure with 20 cm H2O pressure control, rate 10 breaths/min, inspiratory to expiratory ratio 1:1 for 2 mins. Each recruitment maneuver was repeated four times, every 30 mins after a 30-sec ventilator disconnection. An additional group received no recruitment maneuvers. Animals were assigned randomly to the three groups and ventilated with 20 cm H2O positive end-expiratory pressure, pressure control 15 cm H2O, rate 20 breaths/min, inspiratory to expiratory ratio 1:1, and Fio2 1.0 between recruitment maneuver periods. MEASUREMENTS AND MAIN RESULTS: Significant and marked increases in Pao2 were observed in the pressure control recruitment maneuver group but only after the second recruitment maneuver. In both the control group and continuous positive airway pressure groups, Pao2 did not significantly increase after any recruitment maneuver compared with baseline injury. There was a significant decrease in cardiac output immediately after some continuous positive airway pressure recruitment maneuvers and a significant increase in mean pulmonary artery pressure in both continuous positive airway pressure and pressure control groups immediately after recruitment maneuvers, but these changes resolved within 10 mins. There were no marked histologic differences between groups and no volutrauma. CONCLUSION: In this model, maximal lung recruitment was obtained with 40 cm H2O positive end-expiratory pressure and 20 cm H2O pressure control applied repetitively every 30 mins for 2 mins without physiologic or histologic harm. Multiple recruitment maneuvers in some animals were required for maximum effect.

Optimal mean airway pressure during high-frequency oscillation: predicted by the pressure-volume curve.

BACKGROUND: A number of groups have recommended setting positive end-expiratory pressure during conventional mechanical ventilation in adults at 2 cm H2O above the lower corner pressure (P(CL)) of the inspiratory pressure-volume (P-V) curve of the respiratory system. No equivalent recommendations for the setting of the mean airway pressure (Paw) during high-frequency oscillation (HFO) exist. The authors questioned if the Paw resulting in the best oxygenation without hemodynamic compromise during HFO is related to the static P-V curve in a large animal model of acute respiratory distress syndrome. METHODS: Saline lung lavage was performed in seven sheep (28+/-5 kg, mean +/- SD) until the arterial oxygen partial pressure/fraction of inspired oxygen ratio decreased to 85+/-27 mmHg at a positive end-expiratory pressure of 5 cm H2O (initial injury). The PCL (20+/-1 cm H2O) on the inflation limb and the point of maximum curvature change (PMC; 26+/-1 cm H2O) on the deflation limb of the static P-V curve were determined. The sheep were subjected to four 1-h cycles of HFO at different levels of Paw (P(CL) + 2, + 6, + 10, + 14 cm H2O), applied in random order. Each cycle was preceded by a recruitment maneuver at a sustained Paw of 50 cm H2O for 60 s. RESULTS: High-frequency oscillation with a Paw of 6 cm H2O above P(CL) (P(CL) + 6) resulted in a significant improvement in oxygenation (P < 0.01 vs. initial injury). No further improvement in oxygenation was observed with higher Paw, but cardiac output decreased, pulmonary vascular resistance increased, and oxygen delivery decreased at Paw greater than P(CL) + 6. The PMC on the deflation limb of the P-V curve was equal to the P(CL) + 6 (r = 0.77, P < 0.05). CONCLUSION: In this model of acute respiratory distress syndrome, optimal Paw during HFO is equal to P(CL) + 6, which correlates with the PMC.

Evaluation of inspiratory rise time and inspiration termination criteria in new-generation mechanical ventilators: a lung model study.

INTRODUCTION: Inspiratory rise time adjustment during pressure ventilation and inspiration termination criteria adjustment during pressure support ventilation are available on some of the newest mechanical ventilators. Both are designed to improve patient-ventilator synchrony. However, the function of these adjuncts during pressure ventilation on these ventilators has not been evaluated. METHODS: Three inspiratory rise times (minimum, medium, and maximum) were evaluated in 5 new-generation mechanical ventilators (Hamilton Galileo, Siemens 300A, Puritan Bennett 840, BEAR 1000, and Dräger Evita 4) during pressure support and pressure assist/control. Three inspiration termination criteria settings (minimum, medium, and maximum) were also evaluated in 2 mechanical ventilators (Hamilton Galileo and Puritan Bennett 840) during pressure support. All evaluations were performed with a spontaneous breathing lung model (compliance 50 mL/cm H2O, resistance 8.2 cm H2O/L/s, respiratory rate 12 breaths/min, inspiratory time 1.0 s, and lung model peak inspiratory flow 60 L/min). Throughout the evaluation, inspiratory pressure was set at 15 cm H2O and positive end-expiratory pressure at 5 cm H2O, resulting in a peak airway pressure of 20 cm H2O. RESULTS: Significant (p < 0.05) and important (> 10%) differences were found among the ventilators at similar rise times (minimum, medium, and maximum) and for each ventilator as rise time was varied. Also, significant (p < 0.05) and important (> 10%) differences were observed between ventilators and within each ventilator when inspiration termination criteria were varied. There were significant (p < 0.05) differences between pressure support and pressure assist/control, but most were < 10%, except those associated with expiration. CONCLUSIONS: Major differences exist for each ventilator as rise time or inspiration termination criteria are varied and among ventilators at similar settings. Inspiration termination criteria adjustment markedly affects transition to exhalation in the Puritan Bennett 840.

Strategies to optimize alveolar recruitment.

Low tidal volume (4-8 mL/kg) during mechanical ventilation in adult respiratory distress syndrome is the standard of care. However, there are questions regarding the approach to setting positive end-expiratory pressure and the use of recruitment maneuvers in patients with adult respiratory distress syndrome. Animal data and preliminary patient data suggest that lung recruitment maneuvers can markedly improve arterial oxygen tension (PaO2). Prone positioning has also become established a method of recruiting lung and improving PaO2 in those with adult respiratory distress syndrome. The data suggest that recruitment maneuvers in the prone position are most effective in improving PaO2 and that the positive end-expiratory pressure level required to sustain the improved PaO2 is less in the prone position than in the supine position.

Heliox delivery with noninvasive positive pressure ventilation: a laboratory study.

BACKGROUND: There is clinical interest in the use of heliox (helium-oxygen mixture) during noninvasive positive pressure ventilation (NPPV), but delivery of heliox with ventilators designed for NPPV has not been reported. We studied helium concentration ([He]) when an 80%:20% helium:oxygen mixture (heliox) was used with 5 NPPV ventilators (Knightstar, Quantum, BiPAP S/T-D30, Sullivan, and BiPAP Vision). METHODS: A simulated spontaneous breathing lung model was connected to the ventilators with a circuit incorporating a standard leak. Heliox flows of 0, 5, 10, and 18 L/min and oxygen flows of 0 and 10 L/min were titrated into the system at either a proximal position near the lung model or a distal position near the ventilator (titration method). Because the BiPAP Vision has an oxygen delivery module, it was also studied using heliox connected to the air inlet of an oxygen blender, with the blender outlet connected to the oxygen module of the ventilator (blender method). All ventilators were evaluated in spontaneous/timed mode at inspiratory/expiratory pressures of 10/5, 15/5, and 20/5 cm H(2)O. After 5 minutes, [He], oxygen concentration, and pressure in the lung model were recorded. RESULTS: Heliox flow, NPPV settings, site of heliox infusion, and type of ventilator significantly (p < 0.05) affected [He]. [He] was > 60% when heliox flow was 18 L/min in some combinations of settings. The BiPAP S/T-D30 and Quantum occasionally functioned erratically. The BiPAP Vision (blender method) ventilator performed erratically with heliox unless the exhalation port test was bypassed on startup. The addition of heliox flow had no important effect on inspiratory or expiratory positive airway pressure on those breaths during which the ventilators functioned correctly. CONCLUSION: Heliox flow was the most important determinant of [He] when using heliox with NPPV. With heliox there was a potential for ventilator malfunction in some conditions. The clinical implications of these findings remain to be determined.