Accuracy of delivered airway pressure and work of breathing estimation during proportional assist ventilation: a bench study

Additional file 2: Table S1. Measured and theoretical mean airway pressure during inspiration (imeas and iTh) with different triggers in different respiratory mechanics

Bench testing of a new hyperbaric chamber ventilator at different atmospheric pressures

Purpose: Providing mechanical ventilation is challenging at supra-atmospheric pressure. The higher gas density increases resistance, reducing the flow delivered by the ventilator. A new hyperbaric ventilator (Siaretron IPER 1000) is said to compensate for these effects automatically. The aim of this bench test study was to validate the compensation, define its limits and provide details on the ventilator's output at varied atmospheric pressures. Methods: Experiments were conducted inside a multiplace hyperbaric chamber at 1, 2.2, 2.8 and 4 atmospheres absolute (ATA), with the ventilator connected to a test lung. Transducers were recalibrated at each ATA level. Various ventilator settings were tested in volume and pressure control modes. Measured tidal volumes were compared with theoretical predictions based on gas laws. Results: Results confirmed the ventilator's ability to provide compensation, but also identified its limits. The compensation range could be predicted and depended on the maximal flow attainable, decreasing linearly with increasing atmospheric pressure. With settings inside the range, tidal volumes approximated set values (mean error 10±5%). With settings outside the range, the volume was limited to the predicted maximal value calculated from maximal flow. A practical guide for clinicians is provided. Conclusion: The IPER 1000 ventilator attempted to deliver stable tidal volume by adjusting the opening of the inspiratory valve in proportion to atmospheric pressure. Adequate compensation was observed, albeit only within a predictable range, which can be reliably predicted for each setting and ATA level combination. Setting a tidal volume outside this range can result in an unwanted decrease in minute ventilatio

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

Objectives To compare, in a group of difficult to wean critically ill patients, the short-term effects of neurally adjusted ventilator assist (NAVA), proportional assist (PAV+) and pressure support (PSV) ventilation on patient-ventilator interaction. MethodsSeventeen patients were studied during NAVA, PAV+ and PSV with and without artificial increase in ventilator demands (dead space in 10 and chest load in 7 patients). Prior to challenge addition the level of assist in each of the three modes tested was adjusted to get the same level of patient's effort.ResultsWithout challenge all modes provided an equal support. Compared to PSV, proportional modes favored tidal volume variability. Patient effort increase after dead space was comparable among the three modes. After chest load, patient effort increased significantly more with NAVA and PSV compared to PAV+. Triggering delay was significantly higher with PAV+. The linear correlation between tidal volume and inspiratory integral of transdiaphragmatic pressure (PTPdi) was weaker with NAVA than with PAV+ and PSV on account of a weaker inspiratory integral of the electrical activity of the diaphragm (∫EAdi)-PTPdi linear correlation during NAVA [median (interquartile range) of r(2), determination of coefficient, 16.2% (1.4-30.9%)].ConclusionCompared to PSV, proportional modes favored tidal volume variability. The weak ∫EAdi-PTPdi linear relationship during NAVA and poor triggering function during PAV+ may limit the effectiveness of these modes to proportionally assist the inspiratory effort.ΣΚΟΠΟΣ Στόχος της μελέτης ήταν να συγκρίνει, σε μία ομάδα δύσκολων στην αποδέσμευση τους από τον αναπνευστήρα βαρέως πασχόντων ασθενών, τις βραχυπρόθεσμες επιπτώσεις του νευρογενώς προσαρμοζόμενου υποβοηθούμενου αερισμού [neurally adjusted ventilator assist (NAVA)], του αναλογικά υποβοηθούμενου αερισμού [proportional assist (PAV+)] και του αερισμού με υποστήριξη πίεσης [ pressure support (PSV)] στην αλληλεπίδραση ασθενή-αναπνευστήρα. ΜΕΘΟΔΟΙ Εξετάσθηκαν δεκαεπτά ασθενείς κατά τη διάρκεια μηχανικού αερισμού με NAVA, PAV+ και PSV πριν και μετά την τεχνητή αύξηση των αναγκών σε αερισμό μέσω είτε τοποθέτησης νεκρού χώρου (σε 10 ασθενείς) είτε ελαστικού φορτίου στο θώρακα και την κοιλία (σε 7 ασθενείς). Πριν την τεχνητή αύξηση των αναγκών σε αερισμό, το επίπεδο υποστήριξης τιτλοποιήθηκε ώστε να ανταποκρίνεται σε ισοδύναμη αναπνευστική προσπάθεια εκ μέρους του ασθενή.ΑΠΟΤΕΛΕΣΜΑΤΑΤα τρία εξεταζόμενα μοντέλα παρείχαν την ίδια υποστήριξη πριν την προθήκη νεκρού χώρου ή ελαστικού φορτίου. Σε σύγκριση με το PSV, τα αναλογικά μοντέλα επέτρεψαν μεγαλύτερη διακύμανση του αναπνεόμενου όγκου. Μετά την προσθήκη νεκρού χώρου η αναπνευστική προσπάθεια αυξήθηκε σε συγκρίσιμο βαθμό και στα τρία μοντέλα αερισμού. Μετά την τοποθέτηση ελαστικού φορτίου, η αναπνευστική προσπάθεια παρουσίασε σημαντικά μεγαλύτερη αύξηση στο NAVA και στο PSV σε σύγκριση με το PAV+. Η διέγερση του αναπνευστήρα παρουσίασε σημαντικά μεγαλύτερη καθυστέρηση με το PAV+. Η γραμμική συσχέτιση μεταξύ του αναπνεόμενου όγκου και της -εκφραζόμενης από το ολοκλήρωμα της δια-διαφραγματικής πίεσης κατά τη διάρκεια της εισπνοής (PTPdi)- εισπνευστικής προσπάθειας ήταν ασθενέστερη με το NAVA σε σύγκριση με το PAV+ και το PSV. Αυτό αποδίδεται σε ασθενέστερη γραμμική συσχέτιση του ολοκληρώματος της ηλεκτρικής δραστηριότητας του διαφράγματος (∫EAdi) με την PTPdi κατά τη διάρκεια του NAVA [median (interquartile range) του r(2), determination of coefficient, 16.2% (1.4-30.9%)].ΣΥΜΠΕΡΑΣΜΑΤΑΣυγκρινόμενα με το PSV, τα αναλογικά μοντέλα επέτρεψαν μεγαλύτερη διακύμανση του αναπνεόμενου όγκου. Η ασθενής ∫EAdi-PTPdi γραμμική συσχέτιση κατά τον αερισμό με NAVA και η καθυστέρηση της διέγερσης του αναπνευστήρα κατά τον αερισμό με PAV+, φαίνεται να περιορίζουν την αποτελεσματικότητα των αναλογικών μοντέλων στην υποστήριξη της εισπνευστικής προσπάθειας του ασθενή. Λόγω των περιορισμών αυτών στη λειτουργία των αναλογικών μοντέλων, στην καθημερινή πράξη, σε δύκολους να αποδεσμευθούν από τον αναπνευστήρα βαρέως πάσχοντες ασθενείς, η κατάλληλα τιτλοποιημένη χορήγηση PSV δε φαίνεται να μειονεκτεί σε σύγκριση με την εφαρμογή PAV+ ή NAVA, εφόσον οι μηχανικές ιδιότητες του αναπνευστικού συστήματος παραμένουν σταθερές

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

Respiratory drive: a journey from health to disease

Abstract Respiratory drive is defined as the intensity of respiratory centers output during the breath and is primarily affected by cortical and chemical feedback mechanisms. During the involuntary act of breathing, chemical feedback, primarily mediated through CO2, is the main determinant of respiratory drive. Respiratory drive travels through neural pathways to respiratory muscles, which execute the breathing process and generate inspiratory flow (inspiratory flow-generation pathway). In a healthy state, inspiratory flow-generation pathway is intact, and thus respiratory drive is satisfied by the rate of volume increase, expressed by mean inspiratory flow, which in turn determines tidal volume. In this review, we will explain the pathophysiology of altered respiratory drive by analyzing the respiratory centers response to arterial partial pressure of CO2 (PaCO2) changes. Both high and low respiratory drive have been associated with several adverse effects in critically ill patients. Hence, it is crucial to understand what alters the respiratory drive. Changes in respiratory drive can be explained by simultaneously considering the (1) ventilatory demands, as dictated by respiratory centers activity to CO2 (brain curve); (2) actual ventilatory response to CO2 (ventilation curve); and (3) metabolic hyperbola. During critical illness, multiple mechanisms affect the brain and ventilation curves, as well as metabolic hyperbola, leading to considerable alterations in respiratory drive. In critically ill patients the inspiratory flow-generation pathway is invariably compromised at various levels. Consequently, mean inspiratory flow and tidal volume do not correspond to respiratory drive, and at a given PaCO2, the actual ventilation is less than ventilatory demands, creating a dissociation between brain and ventilation curves. Since the metabolic hyperbola is one of the two variables that determine PaCO2 (the other being the ventilation curve), its upward or downward movements increase or decrease respiratory drive, respectively. Mechanical ventilation indirectly influences respiratory drive by modifying PaCO2 levels through alterations in various parameters of the ventilation curve and metabolic hyperbola. Understanding the diverse factors that modulate respiratory drive at the bedside could enhance clinical assessment and the management of both the patient and the ventilator

Accuracy of delivered airway pressure and work of breathing estimation during proportional assist ventilation: a bench study

Abstract Background Proportional assist ventilation+ (PAV+) delivers airway pressure (P aw) in proportion to patient effort (P mus) by using the equation of motion of the respiratory system. PAV+ calculates automatically respiratory mechanics (elastance and resistance); the work of breathing (WOB) is estimated by the ventilator. The accuracy of P mus estimation and hence accuracy of the delivered P aw and WOB calculation have not been assessed. This study aimed at assessing the accuracy of delivered P aw and calculated WOB by PAV+ and examining the factors influencing this accuracy. Methods Using an active lung model with different respiratory mechanics, we compared (1) the actual delivered P aw by the ventilator to the theoretical P aw as defined by the equation of motion and (2) the WOB value displayed by the ventilator to the WOB measured from a Campbell diagram. Results Irrespective of respiratory mechanics and gain, the ventilator provided a P aw approximately 25 % lower than expected. This underassistance was greatest at the beginning of the inspiration. Intrinsic PEEP (PEEPi), associated with an increase in trigger delay, was a major factor affecting PAV+ accuracy. The absolute value of total WOB displayed by the ventilator was underestimated, but the changes in WOB were accurately detected by the ventilator. Conclusion The assistance provided by PAV+ well follows P mus but with a constant underassistance. This is associated with an underestimation by the ventilator of the WOB. PEEPi can be a major factor contributing to PAV+ inaccuracy. Clinical recommendations should include using a high trigger sensitivity and a careful PEEP titration

The Role of Noninvasive Respiratory Management in Patients with Severe COVID-19 Pneumonia

Acute hypoxemic respiratory failure is the principal cause of hospitalization, invasive mechanical ventilation and death in severe COVID-19 infection. Nearly half of intubated patients with COVID-19 eventually die. High-Flow Nasal Oxygen (HFNO) and Noninvasive Ventilation (NIV) constitute valuable tools to avert endotracheal intubation in patients with severe COVID-19 pneumonia who do not respond to conventional oxygen treatment. Sparing Intensive Care Unit beds and reducing intubation-related complications may save lives in the pandemic era. The main drawback of HFNO and/or NIV is intubation delay. Cautious selection of patients with severe hypoxemia due to COVID-19 disease, close monitoring and appropriate employment and titration of HFNO and/or NIV can increase the rate of success and eliminate the risk of intubation delay. At the same time, all precautions to protect the healthcare personnel from viral transmission should be taken. In this review, we summarize the evidence supporting the application of HFNO and NIV in severe COVID-19 hypoxemic respiratory failure, analyse the risks associated with their use and provide a path for their proper implementation

A rational approach on the use of extracorporeal membrane oxygenation in severe hypoxemia: advanced technology is not a panacea

Veno-venous extracorporeal membrane oxygenation (ECMO) is a helpful intervention in patients with severe refractory hypoxemia either because mechanical ventilation cannot ensure adequate oxygenation or because lung protective ventilation is not feasible. Since ECMO is a highly invasive procedure with several, potentially devastating complications and its implementation is complex and expensive, simpler and less invasive therapeutic options should be first exploited. Low tidal volume and driving pressure ventilation, prone position, neuromuscular blocking agents and individualized ventilation based on transpulmonary pressure measurements have been demonstrated to successfully treat the vast majority of mechanically ventilated patients with severe hypoxemia. Veno-venous ECMO has a place in the small portion of severely hypoxemic patients in whom these strategies fail. A combined analysis of recent ARDS trials revealed that ECMO was used in only 2.15% of patients (n = 145/6736). Nevertheless, ECMO use has sharply increased in the last decade, raising questions regarding its thoughtful use. Such a policy could be harmful both for patients as well as for the ECMO technique itself. This narrative review attempts to describe together the practical approaches that can be offered to the sickest patients before going to ECMO, as well as the rationale and the limitations of ECMO. The benefit and the drawbacks associated with ECMO use along with a direct comparison with less invasive therapeutic strategies will be analyzed

The oesophageal balloon for respiratory monitoring in ventilated patients: updated clinical review and practical aspects

There is a well-recognised importance for personalising mechanical ventilation settings to protect the lungs and the diaphragm for each individual patient. Measurement of oesophageal pressure (Poes) as an estimate of pleural pressure allows assessment of partitioned respiratory mechanics and quantification of lung stress, which helps our understanding of the patient's respiratory physiology and could guide individualisation of ventilator settings. Oesophageal manometry also allows breathing effort quantification, which could contribute to improving settings during assisted ventilation and mechanical ventilation weaning. In parallel with technological improvements, Poes monitoring is now available for daily clinical practice. This review provides a fundamental understanding of the relevant physiological concepts that can be assessed using Poes measurements, both during spontaneous breathing and mechanical ventilation. We also present a practical approach for implementing oesophageal manometry at the bedside. While more clinical data are awaited to confirm the benefits of Poes-guided mechanical ventilation and to determine optimal targets under different conditions, we discuss potential practical approaches, including positive end-expiratory pressure setting in controlled ventilation and assessment of inspiratory effort during assisted modes

The Role of Noninvasive Respiratory Management in Patients with Severe COVID-19 Pneumonia

Acute hypoxemic respiratory failure is the principal cause of hospitalization, invasive mechanical ventilation and death in severe COVID-19 infection. Nearly half of intubated patients with COVID-19 eventually die. High-Flow Nasal Oxygen (HFNO) and Noninvasive Ventilation (NIV) constitute valuable tools to avert endotracheal intubation in patients with severe COVID-19 pneumonia who do not respond to conventional oxygen treatment. Sparing Intensive Care Unit beds and reducing intubation-related complications may save lives in the pandemic era. The main drawback of HFNO and/or NIV is intubation delay. Cautious selection of patients with severe hypoxemia due to COVID-19 disease, close monitoring and appropriate employment and titration of HFNO and/or NIV can increase the rate of success and eliminate the risk of intubation delay. At the same time, all precautions to protect the healthcare personnel from viral transmission should be taken. In this review, we summarize the evidence supporting the application of HFNO and NIV in severe COVID-19 hypoxemic respiratory failure, analyse the risks associated with their use and provide a path for their proper implementation