A bench study of intensive-care-unit ventilators: new versus old and turbine-based versus compressed gas-based ventilators

Patient-ventilator synchrony under non-invasive ventilation is improved by an automated real time waveform analysis algorithm: a bench study

BACKGROUND

Because of inherent leaks, obtaining good patient-ventilator synchrony during non-invasive ventilation (NIV) is challenging. The IntelliSync + ® software (Hamilton medical, Bonaduz, CH), that can be used together with the NIV mode, performs real-time automated analysis of airway pressure- and flow-time curves to detect the transition between inspiration and expiration. It then controls the ventilator inspiratory and expiratory valves to improve patient-ventilator synchrony. The main goal of this NIV bench study was to evaluate the impact of IntelliSync + ® on synchrony in the presence of leaks of 9 and 20 L/min in the tested ventilator circuit (no face mask used), with normal, obstructive and restrictive respiratory mechanics and two levels of NIV pressure support (PS 8 and 14 cmH2O). For this, the time needed to trigger the ventilator (Td) and the difference between the end of the simulated breath and the termination of pressurization (Tiex) were measured. The number of classical asynchronies and the ventilator pressurization capacity were also assessed.

RESULTS

Compared to NIV delivered with the classical NIV mode (compensating leaks and limiting inspiratory time to 2 s), activating IntelliSync + ® improved Tiex and, to a lesser extent, Td in clinically relevant setups. IntelliSync + ® also showed a trend towards reducing classical asynchronies, particularly directly after leak flow increase. The impact of the system was most significant with high PS levels and pathological respiratory mechanics. Especially, in the obstructive model, in the presence of large leak (20 L/min) and PS 14 cmH2O, Tiex decreased from 0.61 [0.56-0.64] to 0.16 [0.07-0.18] s and Td from 0.07 [0.06-0.08] to 0.06 [0.06-0.08] s. In less challenging situations, IntelliSync + ® was less beneficial. Overall, ventilator pressurization was improved when IntelliSync + ® was activated.

CONCLUSIONS

In this NIV bench model, IntelliSync + ®, used in addition to NIV-PS, improved both expiratory and inspiratory synchrony. It was particularly efficient in the presence of obstructive and restrictive respiratory mechanics and high-pressure support levels. These pre-clinical results tend to support the ability of IntelliSync + ® to improve patient-ventilator synchrony in the presence of leaks and provide pre-clinical data supporting a clinical evaluation of the automated algorithm during NIV.

Spontaneous breathing trials: how and for how long?

PURPOSE OF REVIEW

Guidelines recommend systematic performance of a spontaneous breathing trial (SBT) before extubation in ICUs, the objective being to reduce the risk of reintubation. In theory, a more challenging SBT performed with a T-piece may further reduce the risk of reintubation, whereas a less challenging SBT performed with pressure-support ventilation (PSV) may hasten extubation.

RECENT FINDINGS

Recent findings show that a more challenging SBT with a T-piece or for a prolonged duration do not help to reduce the risk of reintubation. In contrast, a less challenging SBT with PSV is easier to pass than a T-piece, and may hasten extubation without increased risk of reintubation. Although SBT with PSV and additional positive end-expiratory pressure is indeed a less challenging SBT, further studies are needed to generalize such an easy trial in daily practice. Earlier screening for a first SBT may also decrease time to extubation without increased risk of reintubation. Lastly, reconnection to the ventilator for a short period after successful SBT facilitates recovery from the SBT-induced alveolar derecruitment.

SUMMARY

Several recent clinical trials have improved assessment of the most adequate way to perform SBT before extubation.

Spontaneous breathing trials should be adapted for each patient according to the critical illness. A new individualised approach: the GLOBAL WEAN study

PURPOSE

Spontaneous breathing trials (SBT) evaluate the patient's capacity to maintain inspiratory effort after extubation. SBT practices are heterogeneous and not individualised. The objective of this study was to assess which SBT best reproduces inspiratory effort after extubation in five critical illnesses.

METHODS

In this multicentre randomized cross-over study, adult intensive care unit patients under invasive mechanical ventilation for at least 24-h and ready for extubation, underwent three 15-min SBTs in random order: pressure support ventilation level of 7-cmH2O with positive end-expiratory pressure (PEEP) level of 0-cmH2O (PSV7PEEP0), PSV 0-cmH2O with PEEP 0-cmH2O (PSV0PEEP0) and T-piece trial. Primary outcome was the variation of pressure-time-product per minute (PTPmin) between each SBT and 20-min after extubation. Five categories of critical illnesses were selected: abdominal surgery, brain injury, chest trauma, chronic obstructive pulmonary disease (COPD) and miscellaneous.

RESULTS

Five hundred measures of effort from 100 patients were analysed. PTPmin (cmH2O s/min, median and interquartile range, IQR) was 256 (208-321) after extubation, 192 (127-281) at the end of PSV7PEEP0 (p < 0.001 in comparison to after extubation), 291 (235-347) at the end of PSV0PEEP0 and 262 (198-338) at the end of T-piece (both no different from after extubation). One method of SBT in patients with brain injury (PSV0PEEP0), two in abdominal surgery (PSV0PEEP0 and T-piece) and miscellaneous patients (PSV7PEEP0 and T-piece) and all three methods in chest trauma and COPD exacerbation patients replicated reasonably accurately the postextubation effort to breathe.

CONCLUSION

Unassisted SBTs, namely PSV0PEEP0 and T-piece trial, are the most appropriate to replicate the postextubation effort to breathe.

Ventilator performances for non-invasive ventilation: a bench study

INTRODUCTION

A wide range of recent ventilators, dedicated or not, is available for non-invasive ventilation (NIV) in respiratory or intensive care units (ICU). We conducted a bench study to compare their technical performances.

METHODS

Ventilators, including five ICU ventilators with NIV mode on, two dedicated NIV ventilators and one transport ventilator, were evaluated on a test bench for NIV, consisting of a 3D manikin head connected to an ASL 5000 lung model via a non-vented mask. Ventilators were tested according to three simulated lung profiles (normal, obstructive, restrictive), three levels of simulated air leakage (0, 15, 30 L/min), two levels of pressure support (8, 14 cmH2O) and two respiratory rates (15, 25 cycles/min).

RESULTS

The global median Asynchrony Index (AI) was higher with ICU ventilators than with dedicated NIV ventilators (4% (0; 76) vs 0% (0; 15), respectively; p<0.05) and different between all ventilators (p<0.001). The AI was higher with ICU ventilators for the normal and restrictive profiles (p<0.01) and not different between ventilators for the obstructive profile. Auto-triggering represented 43% of all patient-ventilator asynchrony. Triggering delay, cycling delay, inspiratory pressure-time product, pressure rise time and pressure at mask were different between all ventilators (p<0.01). Dedicated NIV ventilators induced a lower pressure-time product than ICU and transport ventilators (p<0.01). There was no difference between ventilators for minute ventilation and peak flow.

CONCLUSION

Despite the integration of NIV algorithms, most recent ICU ventilators appear to be less efficient than dedicated NIV ventilators. Technical performances could change, however, according to the underlying respiratory disease and the level of air leakage.

A new physiological manikin to test and compare ventilation devices during cardiopulmonary resuscitation

Background

There is a lack of bench systems permitting to evaluate ventilation devices in the specific context of cardiac arrest.

Objectives

The objective of the study is to assess if a new physiological manikin may permit to evaluate the performances of medical devices dedicated to ventilation during cardiopulmonary resuscitation (CPR).

Methods

Specific CPR-related features required to reproduce realistic ventilation were implemented into the SAM (Sarthe Anjou Mayenne) manikin. In the first place, the manikin ability to mimic ventilation during CPR was assessed and compared to real-life tracings of airway pressure, flow and capnogram from three out of hospital cardiac arrest (OHCA) patients. In addition, to illustrate the interest of this manikin, ventilation was evaluated during mechanical continuous chest compressions with two devices dedicated to CPR: the Boussignac cardiac arrest device (B-card - Vygon; Ecouen France) and the Impedance Threshold Device (ITD - Zoll; Chelmsford, MA).

Results

The SAM manikin enabled precise replication of ventilation tracings as observed in three OHCA patients during CPR, and it allowed for comparison between two distinct ventilation devices. B-card generated a mean, maximum and minimum intrathoracic pressure of 6.3 (±0.1) cmH2O, 18.9 (±1.1) cmH2O and -0.3 (±0.2) cmH2O respectively; while ITD generated a mean, maximum and minimum intrathoracic pressure of -1.6 (±0.0) cmH2O, 5.7 (±0.1) cmH2O and -4.8 (±0.1) cmH2O respectively during CPR. B-card allowed to increase passive ventilation compared to the ITD which resulted in a dramatic limitation of passive ventilation.

Conclusion

The SAM manikin is an innovative model integrating specific physiological features that permit to accurately evaluate and compare ventilation devices during CPR.

Evaluation of phrenic nerve stimulation trigger lag and synchronization in different modes of ventilation

Phrenic nerve stimulation is currently being investigated for the prevention of diaphragm atrophy in patients with mechanically supported breathing. Patients receiving breathing support from mechanical ventilation are at risk of mismatches between respiratory demand and ventilator support. Our objectives were to determine if a novel phrenic nerve stimulation device provided stimulation during inspiration as intended and did not exacerbate any potential discordances. A benchtop electromechanical simulation model was developed to validate phrenic nerve stimulation with simulated breathing. The phrenic nerve stimulation device was evaluated with a mechanical ventilator attached to a breathing simulator. The trigger ratio and time lag between phrenic nerve stimulation and mechanical ventilation was measured for multiple disease and ventilator parameters. For the 1:1 breath trigger ratio test, 99.79% of intended stimulation breaths received stimulation at the correct time. For the 1:4 breath trigger ratio test, 99.72% of intended stimulation breaths received stimulation at the correct time. For trigger lag times for the inspiratory and expiratory phases, the mean inspiratory lag was 36.10 ± 10.50 ms and 16.61 ± 3.61 ms, respectively. The following discordance scenarios were evaluated in conjunction with simulated phrenic nerve stimulation: asynchrony-false trigger, dyssynchrony-early trigger, dyssynchrony-late trigger, dyssynchrony-early cycling, dyssynchrony-late cycling. Testing demonstrated none of these discordances were exacerbated by the simulated phrenic nerve stimulation. The novel phrenic nerve stimulation device delivered electrical stimulation therapy as intended and did not exacerbate any simulated discordances.

Physiologic Effects of Reconnection to the Ventilator for 1 Hour Following a Successful Spontaneous Breathing Trial

BACKGROUND

Reconnection to the ventilator for 1 h following a successful spontaneous breathing trial (SBT) may reduce reintubation rates compared with direct extubation. However, the physiologic mechanisms leading to this effect are unclear.

RESEARCH QUESTION

Does reconnection to the ventilator for 1 h reverse alveolar derecruitment induced by SBT, and is alveolar derecruitment more pronounced with a T-piece than with pressure-support ventilation (PSV)?

STUDY DESIGN AND METHODS

This is an ancillary study of a randomized clinical trial comparing SBT performed with a T-piece or with PSV. Alveolar recruitment was assessed by using measurement of end-expiratory lung volume (EELV).

RESULTS

Of the 25 patients analyzed following successful SBT, 11 underwent SBT with a T-piece and 14 with PSV. At the end of the SBT, EELV decreased by -30% (95% CI, -37 to -23) compared with baseline prior to the SBT. This reduction was greater with a T-piece than with PSV: -43% (95% CI, -51 to -35) vs -20% (95% CI, -26 to -13); P < .001. Following reconnection to the ventilator for 1 h, EELV accounted for 96% (95% CI, 92 to 101) of baseline EELV and did not significantly differ from prior to the SBT (P = .104). Following 10 min of reconnection to the ventilator, EELV wasted at the end of the SBT was completely recovered using PSV (P = .574), whereas it remained lower than prior to the SBT using a T-piece (P = .010).

INTERPRETATION

Significant alveolar derecruitment was observed at the end of an SBT and was markedly more pronounced with a T-piece than with PSV. Reconnection to the ventilator for 1 h allowed complete recovery of alveolar derecruitment.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov; No.: NCT04227639; URL: www.

CLINICALTRIALS

gov.

Are all ventilators for NIV performing the same? A bench analysis

Global pandemic due to COVID-19 has increased the interest for ventilators´ use worldwide. New devices have been developed and older ones have undergone a renewed interest, but we lack robust evidence about performance of each ventilator to match appropriate device to a given patient and care environment. The aim of this bench study was to investigate the performance of six devices for noninvasive ventilation, and to compare them in terms of volume delivered, trigger response, pressurization capacity and synchronization in volume assisted controlled and pressure support ventilation. All ventilators were tested under thirty-six experimental conditions by using the lung model ASL5000® (IngMar Medical, Pittsburgh, PA). Two leak levels, two muscle inspiratory efforts and three mechanical patterns were combined for simulation. Trigger function was assessed by measurement of trigger-delay time. Pressurization capacity was evaluated as area under the pressure-time curve over the first 500 ms after inspiratory effort onset. Synchronization was evaluated by the asynchrony index and by incidence and type of asynchronies in each condition. All ventilators showed a good performance, even if pressurization capacity was worse than expected. Leak level did not affect their function. Differences were found during low muscle effort and obstructive pattern. In general, Philips Trilogy Evo/EV300 and Hamilton C3 showed the best results. NIV devices successfully compensate air leaks but still underperform with low muscle effort and obstructive lungs. Clinicians´ must have a clear understanding of the goals of NIV both for devices´ choice and set main parameters to achieve therapy success.

Which spontaneous breathing trial to predict effort to breathe after extubation according to five critical illnesses: the cross-over GLOBAL WEAN study protocol

INTRODUCTION

Readiness to be freed from ventilatory support can be evaluated by spontaneous breathing trial (SBT) assessing the patient's ability to sustain respiratory effort after extubation. Current SBT practices are heterogenous and there are few physiological studies on the topic. The objective of this study is to assess which SBT best reproduces inspiratory effort to breathe after extubation depending on the patient's illness.

METHODS AND ANALYSIS

This will be a multicentre randomised cross-over physiological study, in a large population, in the era of modern intensive care units using last generation modern ventilators. Each included patient will perform three 15-minute SBTs in a random order: pressure support ventilation (PSV) level of 7 cmH₂O with positive end expiratory pressure (PEEP) level of 0 cmH₂O, PSV 0 cmH₂O with PEEP 0 cmH₂O and T-piece trial. A rest period of baseline state ventilation will be observed between the SBTs (10 min) and before extubation (30 min). Primary outcome will be the inspiratory muscle effort, reflected by pressure time product per minute (PTPmin). This will be calculated from oesophageal pressure measurements at baseline state, before and after each SBT and 20 min after extubation. Secondary outcomes will be PTPmin at 24 hours and 48 hours after extubation, changes in physiological variables and respiratory parameters at each step, postextubation respiratory management and the rate of successful extubation. One hundred patients with at least 24 hours of invasive mechanical ventilation will be analysed, divided into five categories of critical illness: abdominal surgery, brain injury, chest trauma, chronic obstructive pulmonary disease and miscellaneous (pneumonia, sepsis, heart disease).

ETHICS AND DISSEMINATION

The study project was approved by the appropriate ethics committee (2019-A01063-54, Comité de Protection des Personnes TOURS - Région Centre - Ouest 1, France). Informed consent is required, for all patients or surrogate in case of inability to give consent.

TRIAL REGISTRATION NUMBER

NCT04222569.

Developing of an open-source low-cost ventilator based on turbine technology

The COVID-19 pandemic has revealed numerous global health system deficits, even in developed countries. The high cost and shortage of treatment, health care, and medical devices are the reasons. Aside from new mutations, the availability of respirators is an urgent concern, especially in developing countries. Even after the pandemic, respiratory diseases are among the most prevalent diseases. Researchers can help reduce treatment costs by offering scalable, open-source solutions that are manufacturable. Since March 2020, serious efforts have been made to reduce the problems caused by the lack of respirators at the lowest possible cost. In this research paper, a unique and integrated solution for a fully automatic ventilator is presented and described. The design considers the cost, speed of assembly, safety, ease of use, robustness, portability issues, and scalability to fit all requirements for emergency ventilation. Furthermore, the device was developed using turbine technology to generate air pressure. The work describes a low-cost alternative ventilator that uses a novel proportional-valve approach to control oxygen mixing process, control circuit, and control algorithm. The current software supports pressure mode controllers, and it can be upgraded to volume-mode or dual mode without any modifications in the hardware. In addition, the hardware, particularly the electronic circuit, has idle input/output ports for further development. Based on the evaluations of the developed ventilator using an artificial lung, the system exhibited acceptable accuracy regarding to the pressure, leak compensation, and oxygen concentration levels. The designated safety conditions have been met, and the safety alarms tripped according to any violations. Moreover, all design files are provided with clear instructions to rebuild the device, despite the complexity of electronics assembly. The system can be described as a development kit, which can shorten the time for researchers/manufacturers to develop a device equivalent to the expensive devices available in the market.

Pre-clinical validation of a turbine-based ventilator for invasive ventilation-The ACUTE-19 ventilator

BACKGROUND

The Severe Acute Respiratory Syndrome (SARS)-Coronavirus 2 (CoV-2) pandemic pressure on healthcare systems can exhaust ventilator resources, especially where resources are restricted. Our objective was a rapid preclinical evaluation of a newly developed turbine-based ventilator, named the ACUTE-19, for invasive ventilation.

METHODS

Validation consisted of (a) testing tidal volume (V_T) delivery in 11 simulated models, with various resistances and compliances; (b) comparison with a commercial ventilator (VIVO-50) adapting the United Kingdom Medicines and Healthcare products Regulatory Agency-recommendations for rapidly manufactured ventilators; and (c) in vivo testing in a sheep before and after inducing acute respiratory distress syndrome (ARDS) by saline lavage.

RESULTS

Differences in V_T in the simulated models were marginally different (largest difference 33ml [95%-confidence interval (CI) 31-36]; P<.001ml). Plateau pressure (P_plat) was not different (-0.3cmH₂O [95%-CI -0.9 to 0.3]; P=.409), and positive end-expiratory pressure (PEEP) was marginally different (0.3 cmH₂O [95%-CI 0.2 to 0.3]; P<.001) between the ACUTE-19 and the commercial ventilator. Bland-Altman analyses showed good agreement (mean bias, -0.29, [limits of agreement, 0.82 to -1.42], and mean bias 0.56 [limits of agreement, 1.94 to -0.81], at a P_plat of 15 and 30cmH₂O, respectively). The ACUTE-19 achieved optimal oxygenation and ventilation before and after ARDS induction.

CONCLUSIONS

The ACUTE-19 performed accurately in simulated and animal models yielding a comparable performance with a VIVO-50 commercial device. The acute 19 can provide the basis for the development of a future affordable commercial ventilator.

Testing of pandemic ventilators under early and agile development

Aiming to address clinical requirements subsequent to SARS-CoV-2-related pulmonary disease, multiple research groups and industry groups carried out intensive studies to develop pandemic ventilators (PDVs). In vitro testing to critically evaluate the specific performance of the developed apparatuses is an essential requirement. This study presents a test protocol which promotes a test-oriented, iterative, and agile assessment and consecutive development of such PDVs. It allows for fast identification of specific characteristics of each PDV in the individual test features. The test protocol includes an evaluation of the accuracy of control systems and instruments at changing parameters, the oxygen dynamics, and the response to trigger signals. The test environment is a mechanical lung, which allows reproducing various lung mechanics and to simulate active breathing cycles. A total of three PDVs that are under development were iteratively tested, with a Hamilton T1 as a reference. Continuous testing of the PDVs under development enables quick identification of critical application aspects that deserve further improved. Based on the present test protocol, the ventilators demonstrate a promising performance justifying continued development.

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.

Noninvasive ventilation in children: A review for the pediatric anesthesiologist

Preserving adequate respiratory function is essential in the perioperative period. Mechanical ventilation with endotracheal intubation is widely used for this purpose. In select patients, noninvasive ventilation (NIV) may be an alternative to invasive ventilation or may complement respiratory management. NIV is used to provide ventilatory support and increase gas exchange at the alveolar level without the use of an invasive artificial airway such as an endotracheal tube or tracheostomy. NIV includes both continuous positive airway pressure (CPAP) and noninvasive positive pressure ventilation. Indications for NIV range from acute hypoxic respiratory failure in the intensive care unit or the emergency department, to chronic respiratory failure in patients with neuromuscular disease with nocturnal hypoventilation. In the perioperative setting, NIV is commonly applied as CPAP, and bilevel positive airway pressure (BPAP). There are limited data on the role of NIV in children in the perioperative setting, and there are no clear guidelines regarding optimal timing of use and pressure settings of perioperative NIV. Contraindications to the use of NIV include reduced level of consciousness, apnea, severe respiratory distress, and inability to maintain upper airway patency or airway protective reflexes. Common problems encountered during NIV involve airway leaks and asynchrony with auto-triggering. High-flow nasal oxygen (HFNO) has emerged as an alternative to NIV when trying to decrease the work of breathing and improve oxygenation in children. HFNO delivers humidified and heated oxygen at rates between 2 and 70 L/min using specific nasal cannulas, and flows are determined by the patient's weight and clinical needs. HFNO can be useful as a method for preoxygenation in infants and children by prolonging apnea time before desaturation, yet in children with decreased minute ventilation or apnea HFNO does not improve alveolar gas exchange. Clinicians experienced with these devices, such as pediatric intensivists and pulmonary medicine specialists, can be useful resources for the pediatric anesthesiologist caring for complex patients on NIV.

A Multiple Emergency Ventilator as Backup Solution in Pandemic: A Specifically Designed and Dimensioned Device

Goal: To provide a Multiple Emergency Ventilator (MEV) as backup in case of shortage of ICU ventilators and for use in camp hospitals. Methods: MEV provides the same oxygen mixture and peak inspiratory pressure (PIP) to 10 patients. These specifications were fixed: i) gas supply and plugs to double-limb intubation sets compatible to existing systems; ii) fluid-dynamics with no pressure drop and almost complete patients’ uncoupling; iii) individual monitoring of inspiratory and expiratory pressures and flows and control of their timing; iv) easy stocking, transport, installation with self-supporting pipes. Results: A Bell-Jar System (BJS) design permitted to safely fix PIP based on Archimedes’ law. The main distribution line was based on 2” stainless steel pipes assuring the required mechanical properties and over-dimensioned for fluidics. The Windkessel of the BJS and pipeline dead-volumes is 75.65 L and in the worst case of the instantaneous demand of 5 L by 10 patients (0.5 L each) shows an adiabatic PIP drop limited to –6.18%, confirming the needed uncoupling. Consequently, patients’ asynchrony is permitted as needed by pressure-controlled volume-guaranteed and assisted-ventilation. Conclusions: Although MEV is proposed as a backup system, its features may cover the whole set of ventilation modes required by ICU ventilation.

Validación preclínica de un respirador de turbina para la ventilación invasiva: el respirador ACUTE-19

Antecedentes

La pandemia producida por el síndrome respiratorio agudo severo por coronavirus 2 puede agotar los recursos sanitarios, especialmente de respiradores, en situaciones de escasez de recursos sanitarios. Nuestro objetivo fue realizar una evaluación preclínica rápida de un prototipo de respirador de turbina para la ventilación invasiva denominado ACUTE-19.

Métodos

La validación consistió en: a) evaluación de la administración de un volumen corriente en 11 modelos pulmonares simulados, con diversas resistencias y compliancias; b) comparación con un ventilador comercial (VIVO-50) adaptando las recomendaciones de la Agencia Reguladora de Medicamentos y Productos Sanitarios del Reino Unido para ventiladores de fabricación rápida, y c) realización de pruebas in vivo en una oveja antes y después de inducir el síndrome de distrés respiratorio agudo mediante lavado salino.

Resultados

Las diferencias de volumen corriente en los modelos simulados fueron mínimamente diferentes (la mayor diferencia fue de 33 ml [IC 95%: 31 a 36]; p < 0,001). La presión de meseta no fue diferente (−0,3 cmH₂O [IC 95%: −0,9 a 0,3]; p = 0,409), y la presión positiva al final de la espiración fue levemente diferente (0,3 cmH₂O [IC 95%: 0,2 a 0,3]; p < 0,001) comparando el ACUTE-19 y el ventilador comercial. El análisis de Bland-Altman mostró una buena concordancia (sesgo medio −0,29 [límites de concordancia 0,82 a −1,42], y sesgo medio 0,56 [límites de concordancia 1,94 a −0,81], a una presión de meseta de 15 y 30 cmH₂O, respectivamente). El ACUTE-19 consiguió una oxigenación y ventilación óptimas antes y después de la inducción del síndrome de distrés respiratorio agudo en el modelo animal.

Conclusiones

El ACUTE-19 se comportó con precisión en los modelos simulados y animales, con un rendimiento comparable al del dispositivo comercial VIVO-50. El ACUTE-19 puede servir de base para el desarrollo de un futuro ventilador comercial asequible.

1-hour t-piece spontaneous breathing trial vs 1-hour zero pressure support spontaneous breathing trial and reintubation at day 7: A non-inferiority approach

PURPOSE

Physiological data suggest that T-piece and zero pressure support (PS0) ventilation both accurately reflect spontaneous breathing conditions after extubation. These two types of spontaneous breathing trials (SBTs) are used in our Intensive Care Unit to evaluate patients for extubation readiness and success but have rarely been compared in clinical studies.

MATERIALS AND METHODS

We performed a prospective observational study to confirm the hypothesis that 1-hour T-piece SBT and 1-h PS0 zero PEEP (ZEEP) SBT are associated with similar rates of reintubation at day 7 after extubation. A non-inferiority approach was used for sample size calculation.

RESULTS

The cohort consisted of 529 subjects invasively ventilated for more than 24 h and extubated after successful 1-hour T-piece SBT (n = 303, 57%) or 1-h PS0 ZEEP SBT (n = 226, 43%). The reintubation rate at day 7 was 14.6% with PS0 ZEEP and 17.5% with T-piece (difference - 2.6% [95% confidence interval, -8.3% to 4.3%]; p = 0.40). The reasons for reintubation did not differ significantly when compared between patients with 1-h PS0 ZEEP SBT and patients with 1-hour T-piece SBT.

CONCLUSION

Our results suggest that successful 1-hour T-piece and 1-h PSO ZEEP SBTs are associated with similar reintubation rates at day 7.

Patient–Ventilator Interaction Testing Using the Electromechanical Lung Simulator xPULM™ during V/A-C and PSV Ventilation Mode

During mechanical ventilation, a disparity between flow, pressure and volume demands of the patient and the assistance delivered by the mechanical ventilator often occurs. This paper introduces an alternative approach of simulating and evaluating patient–ventilator interactions with high fidelity using the electromechanical lung simulator xPULM™. The xPULM™ approximates respiratory activities of a patient during alternating phases of spontaneous breathing and apnea intervals while connected to a mechanical ventilator. Focusing on different triggering events, volume assist-control (V/A-C) and pressure support ventilation (PSV) modes were chosen to test patient–ventilator interactions. In V/A-C mode, a double-triggering was detected every third breathing cycle, leading to an asynchrony index of 16.67%, which is classified as severe. This asynchrony causes a significant increase of peak inspiratory pressure (7.96 ± 6.38 vs. 11.09 ± 0.49 cmH2O, p < 0.01)) and peak expiratory flow (−25.57 ± 8.93 vs. 32.90 ± 0.54 L/min, p < 0.01) when compared to synchronous phases of the breathing simulation. Additionally, events of premature cycling were observed during PSV mode. In this mode, the peak delivered volume during simulated spontaneous breathing phases increased significantly (917.09 ± 45.74 vs. 468.40 ± 31.79 mL, p < 0.01) compared to apnea phases. Various dynamic clinical situations can be approximated using this approach and thereby could help to identify undesired patient–ventilation interactions in the future. Rapidly manufactured ventilator systems could also be tested using this approach.

Respiratory Support Adjustments and Monitoring of Mechanically Ventilated Patients Performing Early Mobilization: A Scoping Review

This scoping review is aimed to summarize current knowledge on respiratory support adjustments and monitoring of metabolic and respiratory variables in mechanically ventilated adult patients performing early mobilization.

DATA SOURCES

Eight electronic databases were searched from inception to February 2021, using a predefined search strategy.

STUDY SELECTION

Two blinded reviewers performed document selection by title, abstract, and full text according to the following criteria: mechanically ventilated adult patients performing any mobilization intervention, respiratory support adjustments, and/or monitoring of metabolic/respiratory real-time variables.

DATA EXTRACTION

Four physiotherapists extracted relevant information using a prespecified template.

DATA SYNTHESIS

From 1,208 references screened, 35 documents were selected for analysis, where 20 (57%) were published between 2016 and 2020. Respiratory support settings (ventilatory modes or respiratory variables) were reported in 21 documents (60%). Reported modes were assisted (n = 11) and assist-control (n = 9). Adjustment of variables and modes were identified in only seven documents (20%). The most frequent respiratory variable was the Fio2, and only four studies modified the level of ventilatory support. Mechanical ventilator brand/model used was not specified in 26 documents (74%). Monitoring of respiratory, metabolic, and both variables were reported in 22 documents (63%), four documents (11%) and 10 documents (29%), respectively. These variables were reported to assess the physiologic response (n = 21) or safety (n = 13). Monitored variables were mostly respiratory rate (n = 26), pulse oximetry (n = 22), and oxygen consumption (n = 9). Remarkably, no study assessed the work of breathing or effort during mobilization.

CONCLUSIONS

Little information on respiratory support adjustments during mobilization of mechanically ventilated patients was identified. Monitoring of metabolic and respiratory variables is also scant. More studies on the effects of adjustments of the level/mode of ventilatory support on exercise performance and respiratory muscle activity monitoring for safe and efficient implementation of early mobilization in mechanically ventilated patients are needed.

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.

Reliability and limits of transport-ventilators to safely ventilate severe patients in special surge situations

BACKGROUND

Intensive Care Units (ICU) have sometimes been overwhelmed by the surge of COVID-19 patients. Extending ICU capacity can be limited by the lack of air and oxygen pressure sources available. Transport ventilators requiring only one O₂ source may be used in such places.

OBJECTIVE

To evaluate the performances of four transport ventilators and an ICU ventilator in simulated severe respiratory conditions.

MATERIALS AND METHODS

Two pneumatic transport ventilators, (Oxylog 3000, Draeger; Osiris 3, Air Liquide Medical Systems), two turbine transport ventilators (Elisee 350, ResMed; Monnal T60, Air Liquide Medical Systems) and an ICU ventilator (Engström Carestation-GE Healthcare) were evaluated on a Michigan test lung. We tested each ventilator with different set volumes (Vt_set = 350, 450, 550 ml) and compliances (20 or 50 ml/cmH₂O) and a resistance of 15 cmH₂O/l/s based on values described in COVID-19 Acute Respiratory Distress Syndrome. Volume error (percentage of Vt_set) with P_0.1 of 4 cmH₂O and trigger delay during assist-control ventilation simulating spontaneous breathing activity with P_0.1 of 4 cmH₂O and 8 cmH₂O were measured.

RESULTS

Grouping all conditions, the volume error was 2.9 ± 2.2% for Engström Carestation; 3.6 ± 3.9% for Osiris 3; 2.5 ± 2.1% for Oxylog 3000; 5.4 ± 2.7% for Monnal T60 and 8.8 ± 4.8% for Elisee 350. Grouping all conditions (P_0.1 of 4 cmH₂O and 8 cmH₂O), trigger delay was 50 ± 11 ms, 71 ± 8 ms, 132 ± 22 ms, 60 ± 12 and 67 ± 6 ms for Engström Carestation, Osiris 3, Oxylog 3000, Monnal T60 and Elisee 350, respectively.

CONCLUSIONS

In surge situations such as COVID-19 pandemic, transport ventilators may be used to accurately control delivered volumes in locations, where only oxygen pressure supply is available. Performances regarding triggering function are acceptable for three out of the four transport ventilators tested.

A Novel Low-Cost Ventilator for Use in a Worldwide Pandemic: The Portsmouth Ventilator

The ongoing severe acute respiratory syndrome coronavirus 2 or coronavirus disease 2019 pandemic has demonstrated the potential need for a low-cost, rapidly deployable ventilator. Based on this premise, we sought to design a ventilator with the following criteria: 1) standard components that are accessible to the public, 2) "open-source" compatibility to allow anyone to easily recreate the system, 3) ability to ventilate in acute respiratory distress syndrome, and 4) lowest possible cost to provide adequate oxygenation and ventilation.

Design

We pursued development of a pneumatic-type ventilator. The basic design involves three electrically controlled solenoid valves, a pressure chamber, the patient breathing circuit, a positive end-expiratory pressure valve, and an electronics control system. Multiple safety elements were built into the design. The user-friendly interface allows simple control of ventilator settings. The ventilator delivers a hybrid form of pneumatic, assist-control ventilation, with predicted tidal volumes of 300-800 mL, positive end-expiratory pressure 0-20 cm H₂O, and Fio₂ 21-100%.

Main Results

The ventilator was extensively tested with two separate high-fidelity lung simulators and a porcine in vivo model. Both lung simulators were able to simulate a variety of pathologic states, including obstructive lung disease and acute respiratory distress syndrome. The ventilator performed well across all simulated scenarios. Similarly, a porcine in vivo model was used to assess performance in live tissue, with a specific emphasis on gas exchange. The ventilator performed well in vivo and demonstrated noninferior ventilation and oxygenation when compared with the standard ventilator.

Conclusions

The Portsmouth Ventilator was able to perform well across all simulated pathologies and in vivo. All components may be acquired by the public for a cost of approximately $250 U.S.D. Although this ventilator has limited functionality compared with modern ventilators, the simple design appears to be safe and would allow for rapid mass production if ventilator surge demand exceeded supply.

Airway Occlusion Pressure As an Estimate of Respiratory Drive and Inspiratory Effort during Assisted Ventilation

Rationale: Monitoring and controlling respiratory drive and effort may help to minimize lung and diaphragm injury. Airway occlusion pressure (P0.1) is a noninvasive measure of respiratory drive.Objectives: To determine 1) the validity of "ventilator" P0.1 (P0.1vent) displayed on the screen as a measure of drive, 2) the ability of P0.1 to detect potentially injurious levels of effort, and 3) how P0.1vent displayed by different ventilators compares to a "reference" P0.1 (P0.1ref) measured from airway pressure recording during an occlusion.Methods: Analysis of three studies in patients, one in healthy subjects, under assisted ventilation, and a bench study with six ventilators. P0.1vent was validated against measures of drive (electrical activity of the diaphragm and muscular pressure over time) and P0.1ref. Performance of P0.1ref and P0.1vent to detect predefined potentially injurious effort was tested using derivation and validation datasets using esophageal pressure-time product as the reference standard.Measurements and Main Results: P0.1vent correlated well with measures of drive and with the esophageal pressure-time product (within-subjects R² = 0.8). P0.1ref >3.5 cm H₂O was 80% sensitive and 77% specific for detecting high effort (≥200 cm H₂O ⋅ s ⋅ min^-1); P0.1ref ≤1.0 cm H₂O was 100% sensitive and 92% specific for low effort (≤50 cm H₂O ⋅ s ⋅ min^-1). The area under the receiver operating characteristics curve for P0.1vent to detect potentially high and low effort were 0.81 and 0.92, respectively. Bench experiments showed a low mean bias for P0.1vent compared with P0.1ref for most ventilators but precision varied; in patients, precision was lower. Ventilators estimating P0.1vent without occlusions could underestimate P0.1ref.Conclusions: P0.1 is a reliable bedside tool to assess respiratory drive and detect potentially injurious inspiratory effort.

Static and Dynamic Transpulmonary Driving Pressures Affect Lung and Diaphragm Injury during Pressure-controlled versus Pressure-support Ventilation in Experimental Mild Lung Injury in Rats

BACKGROUND

Pressure-support ventilation may worsen lung damage due to increased dynamic transpulmonary driving pressure. The authors hypothesized that, at the same tidal volume (VT) and dynamic transpulmonary driving pressure, pressure-support and pressure-controlled ventilation would yield comparable lung damage in mild lung injury.

METHODS

Male Wistar rats received endotoxin intratracheally and, after 24 h, were ventilated in pressure-support mode. Rats were then randomized to 2 h of pressure-controlled ventilation with VT, dynamic transpulmonary driving pressure, dynamic transpulmonary driving pressure, and inspiratory time similar to those of pressure-support ventilation. The primary outcome was the difference in dynamic transpulmonary driving pressure between pressure-support and pressure-controlled ventilation at similar VT; secondary outcomes were lung and diaphragm damage.

RESULTS

At VT = 6 ml/kg, dynamic transpulmonary driving pressure was higher in pressure-support than pressure-controlled ventilation (12.0 ± 2.2 vs. 8.0 ± 1.8 cm H2O), whereas static transpulmonary driving pressure did not differ (6.7 ± 0.6 vs. 7.0 ± 0.3 cm H2O). Diffuse alveolar damage score and gene expression of markers associated with lung inflammation (interleukin-6), alveolar-stretch (amphiregulin), epithelial cell damage (club cell protein 16), and fibrogenesis (metalloproteinase-9 and type III procollagen), as well as diaphragm inflammation (tumor necrosis factor-α) and proteolysis (muscle RING-finger-1) were comparable between groups. At similar dynamic transpulmonary driving pressure, as well as dynamic transpulmonary driving pressure and inspiratory time, pressure-controlled ventilation increased VT, static transpulmonary driving pressure, diffuse alveolar damage score, and gene expression of markers of lung inflammation, alveolar stretch, fibrogenesis, diaphragm inflammation, and proteolysis compared to pressure-support ventilation.

CONCLUSIONS

In the mild lung injury model use herein, at the same VT, pressure-support compared to pressure-controlled ventilation did not affect biologic markers. However, pressure-support ventilation was associated with a major difference between static and dynamic transpulmonary driving pressure; when the same dynamic transpulmonary driving pressure and inspiratory time were used for pressure-controlled ventilation, greater lung and diaphragm injury occurred compared to pressure-support ventilation.

Additional Expiratory Resistance Elevates Airway Pressure and Lung Volume during High-Flow Tracheal Oxygen via Tracheostomy

The standard high-flow tracheal (HFT) interface was modified by adding a 5-cm H₂O/L/s resistor to the expiratory port. First, in a test lung simulating spontaneous breathing, we found that the modified HFT caused an elevation in airway pressure as a power function of flow. Then, three tracheal oxygen treatments (T-piece oxygen at 10 L/min, HFT and modified HFT at 40 L/min) were delivered in a random crossover fashion to six tracheostomized pigs before and after the induction of lung injury. The modified HFT induced a significantly higher airway pressure compared with that in either T-piece or HFT (p < 0.001). Expiratory resistance significantly increased during modified HFT (p < 0.05) to a mean value of 4.9 to 6.7 cm H₂O/L/s. The modified HFT induced significant augmentation in end-expiratory lung volume (p < 0.05) and improved oxygenation for lung injury model (p = 0.038) compared with the HFT and T-piece. There was no significant difference in esophageal pressure swings, transpulmonary driving pressure or pressure time product among the three treatments (p > 0.05). In conclusion, the modified HFT with additional expiratory resistance generated a clinically relevant elevation in airway pressure and lung volume. Although expiratory resistance increased, inspiratory effort, lung stress and work of breathing remained within an acceptable range.

Accuracy of P0.1 measurements performed by ICU ventilators: a bench study

BACKGROUND

Occlusion pressure at 100 ms (P0.1), defined as the negative pressure measured 100 ms after the initiation of an inspiratory effort performed against a closed respiratory circuit, has been shown to be well correlated with central respiratory drive and respiratory effort. Automated P0.1 measurement is available on modern ventilators. However, the reliability of this measurement has never been studied. This bench study aimed at assessing the accuracy of P0.1 measurements automatically performed by different ICU ventilators.

METHODS

Five ventilators set in pressure support mode were tested using a two-chamber test lung model simulating spontaneous breathing. P0.1 automatically displayed on the ventilator screen (P0.1_vent) was recorded at three levels of simulated inspiratory effort corresponding to P0.1 of 2.5, 5 and 10 cm H₂O measured directly at the test lung and considered as the reference values of P0.1 (P0.1_ref). The pressure drop after 100 ms was measured offline on the airway pressure-time curves recorded during the automated P0.1 measurements (P0.1_aw). P0.1_vent was compared to P0.1_ref and to P0.1_aw. To assess the potential impact of the circuit length, P0.1 were also measured with circuits of different lengths (P0.1_circuit).

RESULTS

Variations of P0.1_vent correlated well with variations of P0.1_ref. Overall, P0.1_vent underestimated P0.1_ref except for the Löwenstein^® ventilator at P0.1_ref 2.5 cm H₂O and for the Getinge group^® ventilator at P0.1_ref 10 cm H₂O. The agreement between P0.1_vent and P0.1_ref assessed with the Bland-Altman method gave a mean bias of - 1.3 cm H₂O (limits of agreement: 1 and - 3.7 cm H₂O). Analysis of airway pressure-time and flow-time curves showed that all the tested ventilators except the Getinge group^® ventilator performed an occlusion of at least 100 ms to measure P0.1. The agreement between P0.1_vent and P0.1_aw assessed with the Bland-Altman method gave a mean bias of 0.5 cm H₂O (limits of agreement: 2.4 and - 1.4 cm H₂O). The circuit's length impacted P0.1 measurements' values. A longer circuit was associated with lower P0.1_circuit values.

CONCLUSION

P0.1_vent relative changes are well correlated to P0.1_ref changes in all the tested ventilators. Accuracy of absolute values of P0.1_vent varies according to the ventilator model. Overall, P0.1_vent underestimates P0.1_ref. The length of the circuit may partially explain P0.1_vent underestimation.

Beatmung bei COPD: von der Präklinik bis zur außerklinischen Beatmung. Eine Übersicht des Arbeitskreises für Beatmung und Intensivmedizin der österreichischen Gesellschaft für Pneumologie

This paper was created by the Austrian Society of Pneumology (Working group Ventilation and Intensive Care) to summarize the specific characteristics of mechanical ventilation in patients presenting with chronic obstructive pulmonary disease (COPD). The main differences in pathophysiology and mechanical ventilation are shown, including acute respiratory failure and out-of-hospital mechanical ventilation.

Effect of inspiratory rise time on sputum movement during ventilator hyperinflation in a test lung model

OBJECTIVES

Physiotherapists may use ventilator hyperinflation to enhance secretion clearance for intubated patients. This study investigated the effects of altering percentage inspiratory rise time (IRT) on sputum movement, ratio of peak inspiratory to expiratory flow rate (PIF:PEF ratio) and net peak expiratory flow (PEF) during ventilator hyperinflation in a test lung model.

DESIGN

Laboratory-based bench study.

INTERVENTIONS

Simulated sputum (two viscosities) was inserted into clean, clear tubing and connected between a ventilator and a resuscitation bag. Thirty-six ventilator hyperinflation breaths were applied for each 5% incremental increase in IRT between 0% and 20%.

MAIN OUTCOME MEASURES

The primary outcome was sputum displacement (cm). Secondary outcomes included PIF:PEF ratio and net PEF.

RESULTS

Significant cephalad sputum movement of 2.42cm (1.59 to 3.94) occurred with IRT between 5% and 20%, compared with caudad movement of 0.53 cm (0.31 to 1.53) at 0% IRT (median sputum movement difference 3.7cm, 95% confidence interval 2.2 to 4.8, P<0.001). Incremental increases in IRT percentage produced linear enhancements in PIF:PEF ratio and net PEF for both sputum concentrations (P<0.001). However, once the critical threshold for PIF:PEF ratio of 0.9 was achieved, the distance of sputum movement remained consistent for all IRT values exceeding 5%.

CONCLUSIONS

Significant increases in sputum movement occurred when IRT percentage was lengthened to achieve the optimal PIF:PEF ratio, irrespective of sputum viscosity. This provides a theoretical rationale for therapists to consider this technique when treating mechanically ventilated patients. As no additional sputum movement was seen beyond the critical PIF:PEF ratio threshold, a low IRT percentage may potentially be used to achieve effective sputum movement.

How should we monitor patients with acute respiratory failure treated with noninvasive ventilation?

Noninvasive ventilation (NIV) is currently one of the most commonly used support methods in hypoxaemic and hypercapnic acute respiratory failure (ARF). With advancing technology and increasing experience, not only are indications for NIV getting broader, but more severe patients are treated with NIV. Depending on disease type and clinical status, NIV can be applied both in the general ward and in high-dependency/intensive care unit settings with different environmental opportunities. However, it is important to remember that patients with ARF are always very fragile with possible high mortality risk. The delay in recognition of unresponsiveness to NIV, progression of respiratory failure or new-onset complications may result in devastating and fatal outcomes. Therefore, it is crucial to understand that timely action taken according to monitoring variables is one of the key elements for NIV success. The purpose of this review is to outline basic and advanced monitoring techniques for NIV during an ARF episode.

Design of a new artificial breathing system for simulating the human respiratory activities

The purpose of this work is the conception and implementation of an artificial active respiratory system that allows the simulation of human respiratory activities. The system consists of two modules, mechanical and electronical. The first one represents a cylindrical lung adjustable in resistance and compliance. This lung is located inside a transparent thoracic box, connected to a piston that generates variable respiratory efforts. The parameters of the system, which are pressure, flow and volume, are measured by the second module. A computer application was developed to control the whole system, and enables the display of the parameters. A series of tests were made to evaluate the respiratory efforts, resistances and compliances. The results were compared to the bibliographical studies, allowing the validation of the proposed system.

A new global and comprehensive model for ICU ventilator performances evaluation

Background

This study aimed to provide a new global and comprehensive evaluation of recent ICU ventilators taking into account both technical performances and ergonomics.

Methods

Six recent ICU ventilators were evaluated. Technical performances were assessed under two FIO₂ levels (100%, 50%), three respiratory mechanics combinations (Normal: compliance [C] = 70 mL cmH₂O⁻¹/resistance [R] = 5 cmH₂O L⁻¹ s⁻¹; Restrictive: C = 30/R = 10; Obstructive: C = 120/R = 20), four exponential levels of leaks (from 0 to 12.5 L min⁻¹) and three levels of inspiratory effort (P0.1 = 2, 4 and 8 cmH₂O), using an automated test lung. Ergonomics were evaluated by 20 ICU physicians using a global and comprehensive model involving physiological response to stress measurements (heart rate, respiratory rate, tidal volume variability and eye tracking), psycho-cognitive scales (SUS and NASA-TLX) and objective tasks completion.

Results

Few differences in terms of technical performance were observed between devices. Non-invasive ventilation modes had a huge influence on asynchrony occurrence. Using our global model, either objective tasks completion, psycho-cognitive scales and/or physiological measurements were able to depict significant differences in terms of devices’ usability. The level of failure that was observed with some devices depicted the lack of adaptation of device’s development to end users’ requests.

Conclusions

Despite similar technical performance, some ICU ventilators exhibit low ergonomics performance and a high risk of misusage.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-017-0285-2) contains supplementary material, which is available to authorized users.

Trends in mechanical ventilation: are we ventilating our patients in the best possible way?

This review addresses how the combination of physiology, medicine and engineering principles contributed to the development and advancement of mechanical ventilation, emphasising the most urgent needs for improvement and the most promising directions of future development. Several aspects of mechanical ventilation are introduced, highlighting on one side the importance of interdisciplinary research for further development and, on the other, the importance of training physicians sufficiently on the technological aspects of modern devices to exploit properly the great complexity and potentials of this treatment.

EDUCATIONAL AIMS

To learn how mechanical ventilation developed in recent decades and to provide a better understanding of the actual technology and practice.To learn how and why interdisciplinary research and competences are necessary for providing the best ventilation treatment to patients.To understand which are the most relevant technical limitations in modern mechanical ventilators that can affect their performance in delivery of the treatment.To better understand and classify ventilation modes.To learn the classification, benefits, drawbacks and future perspectives of automatic ventilation tailoring algorithms.

FLOW-i ventilator performance in the presence of a circle system leak

Recently, the FLOW-i anaesthesia ventilator was developed based on the SERVO-i intensive care ventilator. The aim of this study was to test the FLOW-i's tidal volume delivery in the presence of a leak in the breathing circuit. We ventilated a test lung model in volume-, pressure-, and pressure-regulated volume-controlled modes (VC, PC, and PRVC, respectively) with a FLOW-i. First, the circuit remained airtight and the ventilator was tested with fresh gas flows of 6, 1, and 0.3 L/min in VC, PC, and PRVC modes and facing 4 combinations of different resistive and elastic loads. Second, a fixed leak in the breathing circuit was introduced and the measurements repeated. In the airtight system, FLOW-i maintained tidal volume (VT) and circuit pressure at approximately the set values, independently of respiratory mode, load, or fresh gas flow. In the leaking circuit, set VT = 500 mL, FLOW-i delivered higher VTs in PC (about 460 mL) than in VC and PRVC, where VTs were substantially less than 500 mL. Interestingly, VT did not differ appreciably from 6 to 0.3 L/min of fresh air flow among the 3 ventilatory modes. In the absence of leakage, peak inspiratory pressures were similar, while they were 35-45 % smaller in PRVC and VC than in PC mode in the presence of leaks. In conclusion, FLOW-i maintained VT (down to fresh gas flows of 0.3 L/min) to 90 % of its preset value in PC mode, which was 4-5 times greater than in VC or PRVC modes.

Spontaneous breathing trial and post-extubation work of breathing in morbidly obese critically ill patients

Background

Predicting whether an obese critically ill patient can be successfully extubated may be specially challenging. Several weaning tests have been described but no physiological study has evaluated the weaning test that would best reflect the post-extubation inspiratory effort.

Methods

This was a physiological randomized crossover study in a medical and surgical single-center Intensive Care Unit, in patients with body mass index (BMI) >35 kg/m² who were mechanically ventilated for more than 24 h and underwent a weaning test. After randomization, 17 patients were explored using five settings : pressure support ventilation (PSV) 7 and positive end-expiratory pressure (PEEP) 7 cmH2O; PSV 0 and PEEP 7cmH2O; PSV 7 and PEEP 0 cmH2O; PSV 0 and PEEP 0 cmH2O; and a T piece, and after extubation. To further minimize interaction between each setting, a period of baseline ventilation was performed between each step of the study. We hypothesized that the post-extubation work of breathing (WOB) would be similar to the T-tube WOB.

Results

Respiratory variables and esophageal and gastric pressure were recorded. Inspiratory muscle effort was calculated as the esophageal and trans-diaphragmatic pressure time products and WOB. Sixteen obese patients (BMI 44 kg/m² ± 8) were included and successfully extubated. Post-extubation inspiratory effort, calculated by WOB, was 1.56 J/L ± 0.50, not statistically different from the T piece (1.57 J/L ± 0.56) or PSV 0 and PEEP 0 cmH₂O (1.58 J/L ± 0.57), whatever the index of inspiratory effort. The three tests that maintained pressure support statistically underestimated post-extubation inspiratory effort (WOB 0.69 J/L ± 0.31, 1.15 J/L ± 0.39 and 1.09 J/L ± 0.49, respectively, p < 0.001). Respiratory mechanics and arterial blood gases did not differ between the five tests and the post-extubation condition.

Conclusions

In obese patients, inspiratory effort measured during weaning tests with either a T-piece or a PSV 0 and PEEP 0 was not different to post-extubation inspiratory effort. In contrast, weaning tests with positive pressure overestimated post-extubation inspiratory effort.

Trial registration

Clinical trial.gov (reference NCT01616901), 2012, June 4th

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1457-4) contains supplementary material, which is available to authorized users.

Accuracy of tidal volume delivered by home mechanical ventilation during mouthpiece ventilation: A bench evaluation

The aim of our study was to evaluate efficacy and reliability of currently available ventilators for mouthpiece ventilation (MPV). Five life-support home ventilators were assessed in a bench test using different settings simulating the specificities of MPV, such as intermittent circuit disconnection and presence of continuous leaks. The intermittent disconnection of the circuit caused relevant swings in the delivered tidal volume ( V_T), showing a V_T overshoot during the disconnection periods and a V_T decrease when the interface was reconnected to the test lung. The five ventilators showed substantial differences in the number of respiratory cycles necessary to reach a stable V_T in the volume-controlled setting, ranging from 1.3 ± 0.6 to 7.3 ± 1.2 cycles. These differences were less accentuated in the volume-assisted setting (MPV-dedicated mode, when available). Our data show large differences in the capacity of the different ventilators to deal with the rapidly changing respiratory load features that characterize MPV, which can be further accentuated according to the used ventilator setting. The dedicated MPV modes allow improvement in the performance of ventilators only in some defined situations. This has practical consequences for the choice of the ventilator to be used for MPV in a specific patient.

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

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.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-016-0131-y) contains supplementary material, which is available to authorized users.

Technology for noninvasive mechanical ventilation: looking into the black box

Current devices for providing noninvasive respiratory support contain sensors and built-in intelligence for automatically modifying ventilation according to the patient's needs. These devices, including automatic continuous positive airway pressure devices and noninvasive ventilators, are technologically complex and offer a considerable number of different modes of ventilation and setting options, the details of which are sometimes difficult to capture by the user. Therefore, better predicting and interpreting the actual performance of these ventilation devices in clinical application requires understanding their functioning principles and assessing their performance under well controlled bench test conditions with simulated patients. This concise review presents an updated perspective of the theoretical basis of intelligent continuous positive airway pressure and noninvasive ventilation devices, and of the tools available for assessing how these devices respond under specific ventilation phenotypes in patients requiring breathing support.

Current devices for intelligent noninvasive ventilation should be tested to better understand clinical performance http://ow.ly/XAS6Z

Multifaceted bench comparative evaluation of latest intensive care unit ventilators

BACKGROUND

Independent bench studies using specific ventilation scenarios allow testing of the performance of ventilators in conditions similar to clinical settings. The aims of this study were to determine the accuracy of the latest generation ventilators to deliver chosen parameters in various typical conditions and to provide clinicians with a comprehensive report on their performance.

METHODS

Thirteen modern intensive care unit ventilators were evaluated on the ASL5000 test lung with and without leakage for: (i) accuracy to deliver exact tidal volume (VT) and PEEP in assist-control ventilation (ACV); (ii) performance of trigger and pressurization in pressure support ventilation (PSV); and (iii) quality of non-invasive ventilation algorithms.

RESULTS

In ACV, only six ventilators delivered an accurate VT and nine an accurate PEEP. Eleven devices failed to compensate VT and four the PEEP in leakage conditions. Inspiratory delays differed significantly among ventilators in invasive PSV (range 75-149 ms, P=0.03) and non-invasive PSV (range 78-165 ms, P<0.001). The percentage of the ideal curve (concomitantly evaluating the pressurization speed and the levels of pressure reached) also differed significantly (range 57-86% for invasive PSV, P=0.04; and 60-90% for non-invasive PSV, P<0.001). Non-invasive ventilation algorithms efficiently prevented the decrease in pressurization capacities and PEEP levels induced by leaks in, respectively, 10 and 12 out of the 13 ventilators.

CONCLUSIONS

We observed real heterogeneity of performance amongst the latest generation of intensive care unit ventilators. Although non-invasive ventilation algorithms appear to maintain adequate pressurization efficiently in the case of leakage, basic functions, such as delivered VT in ACV and pressurization in PSV, are often less reliable than the values displayed by the device suggest.

Proceedings of the fourth international conference on central hypoventilation

Central hypoventilation syndromes (CHS) are rare diseases of central autonomic respiratory control associated with autonomous nervous dysfunction. Severe central hypoventilation is the hallmark and the most life-threatening feature. CHS is a group of not-fully defined disorders. Congenital CHS (CCHS) (ORPHA661) is clinically and genetically well-characterized, with the disease-causing gene identified in 2003. CCHS presents at birth in most cases, and associated with Hirschsprung's disease (ORPHA99803) and neural crest tumours in 20% and 5% of cases, respectively. The incidence of CCHS is estimated to be 1 of 200,000 live births in France, yet remains unknown for the rest of the world. In contrast, late-onset CHS includes a group of not yet fully delineated diseases. Overlap with CCHS is likely, as a subset of patients harbours PHOX2B mutations. Another subset of patients present with associated hypothalamic dysfunction. The number of these patients is unknown (less than 60 cases reported worldwide). Treatment of CHS is palliative using advanced techniques of ventilation support during lifetime. Research is ongoing to better understand physiopathological mechanisms and identify potential treatment pathways.The Fourth International Conference on Central Hypoventilation was organised in Warsaw, Poland, April 13-15, 2012, under the patronage of the European Agency for Health and Consumers and Public Health European Agency of European Community. The conference provided a state-of-the-art update of knowledge on all the genetic, molecular, cellular, and clinical aspects of these rare diseases.

Bench-test comparison of 26 emergency and transport ventilators

Introduction

Numerous emergency and transport ventilators are commercialized and new generations arise constantly. The aim of this study was to evaluate a large panel of ventilators to allow clinicians to choose a device, taking into account their specificities of use.

Methods

This experimental bench-test took into account general characteristics and technical performances. Performances were assessed under different levels of FIO₂ (100%, 50% or Air-Mix), respiratory mechanics (compliance 30,70,120 mL/cmH₂O; resistance 5,10,20 cmH₂O/mL/s), and levels of leaks (3.5 to 12.5 L/min), using a test lung.

Results

In total 26 emergency and transport ventilators were analyzed and classified into four categories (ICU-like, n = 5; Sophisticated, n = 10; Simple, n = 9; Mass-casualty and military, n = 2). Oxygen consumption (7.1 to 15.8 L/min at F_IO₂ 100%) and the Air-Mix mode (F_IO₂ 45 to 86%) differed from one device to the other. Triggering performance was heterogeneous, but several sophisticated ventilators depicted triggering capabilities as efficient as ICU-like ventilators. Pressurization was not adequate for all devices. At baseline, all the ventilators were able to synchronize, but with variations among respiratory conditions. Leak compensation in most ICU-like and 4/10 sophisticated devices was able to correct at least partially for system leaks, but with variations among ventilators.

Conclusion

Major differences were observed between devices and categories, either in terms of general characteristics or technical reliability, across the spectrum of operation. Huge variability of tidal volume delivery with some devices in response to modifications in respiratory mechanics and F_IO₂ should make clinicians question their use in the clinical setting.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0506-0) contains supplementary material, which is available to authorized users.

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

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.

METHODS

Seventeen 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.

RESULTS

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%)].

CONCLUSION

Compared 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.

Comparing surrogates of oxygenation and ventilation between airway pressure release ventilation and biphasic airway pressure in a mechanical model of adult respiratory distress syndrome

BACKGROUND

No objective data directly comparing the 2 modes are available. Based on a simple mathematical model, APRV and BIPAP can presumably be set to achieve the same mean airway pressure (mPaw), end expiratory pressure, and tidal volume (V(T)). Herein, we tested this hypothesis when using a real ventilator and clinically relevant settings based on expiratory time constants.

METHODS

A spontaneously breathing acute respiratory distress syndrome patient was modeled with a lung simulator. Mode settings: P high and the number of releases were the same in both modes; T low=1 time constant in APRV (expected auto-positive end-expiratory pressure [PEEP], ≈9 cmH(2)O) and 5 time constants in BIPAP; P low, 0 cmH(2)O in APRV and 9 cmH(2)O in BIPAP (equal to the expected auto-PEEP in APRV). The mean mandatory release volumes, minute ventilation [V(E)], mPaw, and total PEEP were compared with t-tests using a P value of 0.05 to reject the null hypothesis.

RESULTS

APRV yielded significantly higher mPaw than did BIPAP. Minute ventilation was significantly higher in BIPAP. The total PEEP was significantly higher in APRV; the total PEEP was significantly higher than expected.

CONCLUSION

We found that neither mode was superior to the other, and that a real ventilator does not behave like a mathematical model. Extreme prolongation of T high generated a higher mPaw at the expense of V(E), and vice versa. The lower V(T) with APRV was due to the higher total PEEP, which was higher than expected. Setting the T low according to the respiratory system time constant for either mode resulted in an unpredictable total PEEP.

Healthcare Technology Management (HTM) of mechanical ventilators by clinical engineers

Mechanical ventilator failures expose patients to unacceptable risks, and maintaining mechanical ventilator safety is an important issue. We examined the usefulness of maintaining mechanical ventilators by clinical engineers (CEs) using a specialized calibrator. These evaluations and the ability to make in-house repairs proved useful for obviating the need to rent ventilators which, in turn, might prove faulty themselves. The CEs' involvement in maintaining mechanical ventilators is desirable, ensures prompt service, and, most importantly, enhances safe management of mechanical ventilators.