Performance characteristics of five new anesthesia ventilators and four intensive care ventilators in pressure-support mode: a comparative bench study

Bench assessment of PC-CMVs modes in transport and emergency ventilators under ICU conditions

Although there has been an increase in bench test evaluation of mechanical ventilators in recent years, a publication gap remains in assessing Pressure Control Continuous Mandatory Ventilation Modes with a set point targeting scheme PC-CMVs. This study evaluates the operational variability in PC-CMVs of eleven transport and emergency ventilators used in ICU units in Brazil during the COVID-19 pandemic. The assessment involved a comprehensive set of test scenarios derived from existing literature and the NBR ISO 80601-2-12:2014 standard. Nine parameters were computed for five consecutive breaths, offering a comprehensive characterization of pressure and flow waveforms. Most ventilators had Inspiratory pressure and PEEP values that fell outside of the tolerance ranges. Notably, three mechanical ventilators failed to reach the target pressures within the specified inspiratory times during test scenarios with a higher time constant (τ). We observed significant differences among emergency and transport ventilators in all assessed parameters, indicating a performance difference in PC-CMVs modes. The current results might help clinicians determine which ventilator models are suitable for specific clinical situations, particularly when unfavorable circumstances compel doctors to use ventilators that may not provide adequate support for patients in intensive care units.

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.

Separation of cardiogenic oscillations from airflow waveforms using singular spectrum analysis

BACKGROUND AND OBJECTIVE

Airflow fluctuations caused by cardiac contraction can trigger inappropriate ventilator pressure support in anesthesia machines and intensive care unit mechanical ventilators. Removal of this cardiogenic artifact from the airflow signal would improve ventilator function. The application of singular spectrum analysis (SSA) to remove cardiogenic oscillations from ventilator airflow signals recorded from intubated, mechanically ventilated patients under general anesthesia was evaluated in this study.

METHODS

Airflow (liters/minute) and CO₂ (mmHg) data were collected at a sampling rate of 125 Hz from the intraoperative monitoring systems using special-purpose software. Simultaneous electrocardiogram signals (mV) were also collected at a sampling rate of 250 Hz. One-dimensional SSA was performed offline on normalized airflow signals using a window length sufficient to span one period of typical respiratory variation. The main components of the airflow waveform are respiratory excursions and cardiogenic oscillations, with respiratory excursions more slowly varying and of higher magnitude. The smooth respiratory waveform was formed from elementary reconstructed series corresponding to the highest singular values obtained with SSA analysis. The quality of respiratory waveform extraction with SSA was determined by calculating the weighted correlation between the selected elementary reconstructed series.

RESULTS

Airflow data was recorded from 6 patients. The respiratory component of the airflow signal without cardiogenic oscillations was reconstructed from elementary series corresponding to singular values of highest magnitude. The weighted correlations obtained were greater than 0.96 in the majority of patients studied. Cardiogenic oscillations were reconstructed from elementary reconstructed series corresponding to singular values of lower magnitude.

CONCLUSIONS

SSA is effective in extracting higher amplitude respiratory excursions while excluding lower amplitude cardiogenic oscillations and noise from the airflow signal. This study demonstrates that suppression of the cardiogenic artefact with SSA is computationally feasible to augment ventilator performance.

[Anesthesia and intensive care ventilators: differences and usability in COVID-19 patients]

Die aktuelle Coronavirus-Krankheit 2019 (Covid-19)-Pandemie ist eine dynamische Situation mit therapeutischen Herausforderungen und logistischen Unwägbarkeiten. Ein Mangel an medizinischer Schutzausrüstung und Intensivrespiratoren ist je nach Wirkung der „Flatten-the-Curve“ Maßnahmen zu erwarten. Gleichzeitig besteht bei vielen Ärzten und Pflegekräften eine hohe Unsicherheit bezüglich der Möglichkeiten und Limitationen verschiedener Gerätetypen. Intensivrespiratoren wurden speziell für die Behandlung von Patienten mit pathologischer Lungenmechanik entwickelt. Gleichwohl liefern aktuelle Narkosegeräte den Intensivbeatmungsgeräten ähnliche Leistungen und bieten meist viele Beatmungstypen inklusive unterstützender Spontanatmungsmodi. Trotz ausreichender technischer Voraussetzungen bestehen im Vergleich zu Intensivrespiratoren jedoch wesentliche konzeptionelle Unterschiede. Diese bedingen bei der Nutzung zur Langzeitbeatmung einen deutlich größeren Überwachungsaufwand. Moderne Transportbeatmungsgeräte eignen sich v.a. zur kurzfristen Überbrückung da bei Geräten mit Raumluftzufuhr immer eine Verwendung mit 100 % Sauerstoff in kontaminierter Umgebung erfolgen sollte. In den sozialen Medien zuletzt vielfach präsentierte unkonventionelle Beatmungskonzepte zur Beatmung mehrerer Patienten mit einer Beatmungsmaschine, sog. „Ventilator-Splittung“ ist nicht zu empfehlen. Ziel dieser Übersichtsarbeit ist es, dem Leser einen Überblick über die konzeptionellen und technischen Unterschiede verschiedener Typen von Beatmungsgeräten zu geben.

Pressure support ventilation-pro decreases propofol consumption and improves postoperative oxygenation index compared with pressure-controlled ventilation in children undergoing ambulatory surgery: a randomized controlled trial

PURPOSE

The PSVPro mode is increasingly being used for surgeries under laryngeal mask airway owing to improved ventilator-patient synchrony and decreased work of breathing. We hypothesized that PSVPro ventilation mode would reduce consumption of anesthetic agents compared with pressure control ventilation (PCV).

METHODS

Seventy children between three and eight years of age undergoing elective lower abdominal and urological surgery were randomized into PCV group (n = 35) or PSVPro group (n = 35). General anesthesia was induced with sevoflurane and a Proseal LMA™ was inserted. Anesthesia was maintained with propofol infusion to maintain the entropy values between 40 and 60. In the PCV mode, the inspiratory pressure was adjusted to obtain an expiratory tidal volume of 8 mL·kg-1 and a respiratory rate of 12-20/min. In the PSVPRO group, the flow trigger was set at 0.4 L·min-1 and pressure support was adjusted to obtain expiratory tidal volume of 8 mL·kg-1. Consumption of anesthetic agent was recorded as the primary outcome. Emergence time and discharge time were recorded as secondary outcomes.

RESULTS

The PSVPro group showed significant reduction in propofol consumption compared with the PCV group (mean difference, 33.3 µg-1·kg-1·min-1; 95% confidence interval [CI], 24.2 to 42.2). There was decrease in the emergence time in the PSVPro group compared with the PCV group (mean difference, 3.5 min; 95% CI, 2.8 to 4.2) and in time to achieve modified Aldrete score > 9 (mean difference, 3.6 min; 95% CI, 1.9 to 5.2).

CONCLUSION

The PSVPro mode decreases propofol consumption and emergence time, and improves oxygenation index in children undergoing ambulatory surgery.

TRIAL REGISTRATION

Clinical Trial Registry of India (CTRI/2017/12/010942); registered 21 December, 2017.

The addition of a humidifier device to a circuit and its impact on home ventilator performance: a bench study

INTRODUCTION AND OBJECTIVES

Humidification and non-invasive ventilation are frequently used together, despite the lack of precise recommendations regarding this practice. We aimed to analyse the impact of active external and built-in humidifiers on the performance of home ventilators, focusing on their pressurization efficacy and their behaviour under different inspiratory efforts.

METHODS

We designed a bench study of a lung simulator programmed to emulate mechanical conditions similar to those experienced by real respiratory patients and to simulate three different levels of inspiratory effort: five different commonly used home NIV devices and active humidifiers attached to the latter (internal or "built-in") or to the circuit (external). To test ventilator pressurization under different humidification and effort settings, pressure-time products in the first 300ms and 500ms of the respiratory cycle were calculated in the 45 situations simulated. Inferential statistical analysis was performed.

RESULTS

A significant reduction of PTP 300 and PTP 500 was observed with the external humidifier in three of the devices. The same pattern was noted for another device with an internal humidifier, and only one device showed no significant changes. This impact on pressurization was commonly higher under high inspiratory effort.

CONCLUSIONS

These results indicate the need to monitor pressure changes in the use of external humidification devices in some home NIV ventilators.

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.

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.

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.

Effects of pressure support ventilation mode on emergence time and intra-operative ventilatory function: a randomized controlled trial

We tested the hypothesis that pressure-support ventilation (PSV) allows a reduction in emergence time and laryngeal mask airway (LMA) removal time after general anesthesia compared to volume-controlled mechanical ventilation (CMV). Because spontaneous breathing (SB) is often used with LMA under general anesthesia, patients were allocated randomly to three groups (CMV, SB and PSV). Thirty-six consecutive ASA I-II patients scheduled for knee arthroscopic surgery under general anesthesia with a LMA and breathing throughout the ventilator circuit were included. Hemodynamic and ventilatory variables were recorded before and 10-min after general anesthesia-induction, at the surgical incision, at the end of anaesthetic drugs infusion and when the patient was totally awake (which defines emergence time). LMA removal time, drug consumption were recorded at the end of the surgical procedure. Leak fraction around the LMA was also evaluated. LMA removal time was significantly higher in the CMV-group (18 ± 6 min) compared to both SB (8 ± 4 min) and PSV (7 ± 4 min, P < 0.05) groups as well as for emergence time: CMV-group (32 ± 12 min), SB (17 ± 7 min) and PSV (13 ± 6 min, P < 0.05) groups. Total propofol consumption was significantly lower in the PSV-group (610 ± 180 mg) than in both CMV (852 ± 330 mg) and SB (734 ± 246 mg, P < 0.05) groups. Air leaks around the LMA was significantly higher in the CMV-group than in the SB and PSV groups (16% vs 3% and 7%, all P<0.05). In conclusion, in knee arthroscopic surgery, in comparison to CMV, PSV use during general anesthesia in unparalyzed patients decreases LMA removal time, propofol consumption and leaks around LMA while improving ventilatory variables without adverse effects.

TRIAL REGISTRATION

Controlled-Trials.com ISRCTN17382426.

An ADARPEF survey on respiratory management in pediatric anesthesia

BACKGROUND

There have been recent changes with regard to tools and concepts for respiratory management of children undergoing general anesthesia.

OBJECTIVES

To determine the practice of pediatric anesthetists concerning: preoxygenation, breathing systems, ventilation modes, anesthetic agent and airway device, strategies for a general anaesthetic of less than 30 min using spontaneous respiration, and opinion about technical aspects of ventilation.

METHODS

Online questionnaire sent by e-mail to all the anesthetists registered on the mailing list of the French-speaking Pediatric Anesthetists and Intensivists Association (ADARPEF).

RESULTS

232 questionnaires (46%) were returned. More than 25% of anesthetists surveyed declared that they do not perform preoxygenation before induction for children <15 years old, apart from neonates and clinical specific situations. When performed, <65% chose a FiO2 higher than 80%. Inhalational induction with sevoflurane is the preferred mode of induction set at 6% or 8%, respectively, 69% [62-75] vs 25% [18-31]. For induction, the circle system was the most popular circuit used in all ages. The accessory breathing system-Mapleson B type-was predominantly used for neonates (44% [37-54]). For maintenance of an anesthesia lasting <30 min in spontaneous breathing, the use of laryngeal mask increased with age, and the endotracheal tube was reserved for neonates (40% [33-48]). Pressure support ventilation was rarely used from the beginning of induction but was widely used for maintenance, whatever the age-group. Results differed according to the type of institution.

CONCLUSION

Ventilation management depends on the age and institutions in terms of circuit, airway device or ventilation mode, and specific differences exist for neonates.

Continuous positive airway pressure/pressure support pre-oxygenation of morbidly obese patients

BACKGROUND

Morbidly obese patients are more prone to desaturation of arterial blood during apnea with induction of anesthesia than are non-obese. This study aimed to assess the effect of low-pressure continuous positive airway pressure (CPAP) with pressure support ventilation (PSV) during pre-oxygenation on partial oxygen pressure in arterial blood (PaO2 ) immediately after tracheal intubation (post-intubation PaO2).

METHODS

Forty-four adult patients scheduled for laparoscopic gastric bypass surgery were pre-oxygenated with 80% O2 for 2 min, randomized either to CPAP 5 cm H2O + PSV 5 cm H2O (CPAP/PSV, n = 22) or neutral-pressure breathing without CPAP/PSV (control, n = 22). Anesthesia was induced in a rapid-sequence protocol and the trachea was intubated without prior mask ventilation. Arterial blood gases were measured before pre-oxygenation, before induction of anesthesia, and immediately following intubation, before the first positive pressure breath.

RESULTS

After pre-oxygenation, partial carbondioxide pressure was significantly lower in the CPAP/PSV group (4.9 ± 0.5 kPa), (mean ± standard deviation) than in the control group (5.2 ± 0.7 kPa) (P = 0.025). Post-preoxygenation PaO2 did not differ between the groups, but post-intubation PaO2 was significantly higher in the CPAP/PSV group (32.2 ± 4.1 kPa) than in the control group (23.8 ± 8.8 kPa) (P < 0.001). In the control group, nadir oxygen saturation was lower (median 98%, range 83-99%) than in the CPAP/PSV group (median 99%, range 97-99%, P = 0.011).

CONCLUSIONS

In morbidly obese patients, low-pressure CPAP combined with low-pressure PSV during pre-oxygenation resulted in better oxygenation, compared with neutral-pressure breathing, and prevented desaturation episodes.

How to choose an anesthesia ventilator?

During the past few years, many manufacturers have developed a new generation anesthesia ventilators or anesthesia workstations with innovative technology and introduced so-called new ventilatory modes in the operating room. The aim of this article is to briefly explain how an anesthesia ventilator works, to describe the main differences between the technologies used, to describe the main criteria for evaluating technical and pneumatic performances and to list key elements not to be forgotten during the process of acquiring an anesthesia ventilator.

[The choice of a pediatric anesthesia ventilator]

The technology of anesthesia ventilators has substantially progressed during last years. The choice of a pediatric anesthesia ventilator needs to be led by multiple parameters: requirement, technical (pneumatic performance, velocity of halogenated or oxygen delivery), cost (purchase, in operation, preventive and curative maintenance), reliability, ergonomy, upgradability, and compatibility. The demonstration of the interest of pressure support mode during maintenance of spontaneous ventilation anesthesia makes this mode essential in pediatrics. In contrast, the financial impact of target controlled inhalation of halogenated has not be studied in pediatrics. Paradoxically, complex and various available technologies had not been much prospectively studied. Anesthesia ventilators performances in pediatrics need to be clarified in further clinical and bench test studies.

[Risk of barotrauma when using non-reinhalation Waters valves: a comparative study on bench test]

OBJECTIVE

Manual ventilation is delivered in the operating room or the intensive care unit to intubated or non-intubated patients, using non-rebreathing systems such as the Waters valve. New generation Waters valves are progressively replacing the historic Waters valve. The aim of this study was to evaluate maximal pressure delivered by these 2 valves.

TYPE OF STUDY

Bench test.

MATERIAL AND METHOD

Thirty-two different conditions were tested, according to 2 oxygen flow rates (10 and 20L/min), without (static condition) or with manual insufflations (dynamic condition) and 4 valve expiratory opening pressures. The primary endpoint was maximal pressure measured at the exit of the valve, connected to a model lung and a bench test.

RESULTS

Measured pressures were different for most evaluated conditions. Increasing oxygen flow from 10 to 20L/min increased maximal pressure for both valves. Increasing valve expiratory opening pressure induced a significant increase in maximal pressure for the new generation valve (from 4 to 61cmH2O in static conditions and from 18 to 68cmH2O in dynamic conditions). For the historic valve, maximal pressure increased significantly but remained below 15cmH2O in both static and dynamic conditions.

CONCLUSION

Use of new generation Waters valves should be different from historic Waters valves. Indeed, barotrauma could be caused by badly adapted valve expiratory opening pressure settings.

Bench studies evaluating devices for non-invasive ventilation: critical analysis and future perspectives

PURPOSE

Because non-invasive mechanical ventilation (NIV) is increasingly used, new devices, both ventilators and interfaces, have been continuously proposed for clinical use in recent years. To provide the clinicians with valuable information about ventilators and interfaces for NIV, several bench studies evaluating and comparing the performance of NIV devices have been concomitantly published, which may influence the choice in equipment acquisition. As these comparisons, however, may be problematic and sometimes lacking in consistency, in the present article we review and discuss those technical aspects that may explain discrepancies.

METHODS

Studies concerning bench evaluations of devices for NIV were reviewed, focusing on some specific technical aspects: lung models and simulation of inspiratory demand and effort, mechanical properties of the virtual respiratory system, generation and quantification of air leaks, ventilator modes and settings, assessment of the interface-ventilator unit performance.

RESULTS

The impact of the use of different test lung models is not clear and warrants elucidation; standard references for simulated demand and effort, mode of generation and extent of air leaks, resistance and compliance of the virtual respiratory system, and ventilator settings are lacking; the criteria for assessment of inspiratory trigger function, inspiration-to-expiration (I:E) cycling, and pressurization rate vary among studies; finally, the terminology utilized is inconsistent, which may also lead to confusion.

CONCLUSIONS

Consistent experimental settings, uniform terminology, and standard measurement criteria are deemed to be useful to enhance bench assessment of characteristics and comparison of performance of ventilators and interfaces for NIV.

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

OBJECTIVE

To compare 13 commercially available, new-generation, intensive-care-unit (ICU) ventilators in terms of trigger function, pressurization capacity during pressure-support ventilation (PSV), accuracy of pressure measurements, and expiratory resistance.

DESIGN AND SETTING

Bench study at a research laboratory in a university hospital.

METHODS

Four turbine-based ventilators and nine conventional servo-valve compressed-gas ventilators were tested using a two-compartment lung model. Three levels of effort were simulated. Each ventilator was evaluated at four PSV levels (5, 10, 15, and 20 cm H2O), with and without positive end-expiratory pressure (5 cm H2O). Trigger function was assessed as the time from effort onset to detectable pressurization. Pressurization capacity was evaluated using the airway pressure-time product computed as the net area under the pressure-time curve over the first 0.3 s after inspiratory effort onset. Expiratory resistance was evaluated by measuring trapped volume in controlled ventilation.

RESULTS

Significant differences were found across the ventilators, with a range of triggering delays from 42 to 88 ms for all conditions averaged (P < 0.001). Under difficult conditions, the triggering delay was longer than 100 ms and the pressurization was poor for five ventilators at PSV5 and three at PSV10, suggesting an inability to unload patient's effort. On average, turbine-based ventilators performed better than conventional ventilators, which showed no improvement compared to a bench comparison in 2000.

CONCLUSION

Technical performance of trigger function, pressurization capacity, and expiratory resistance differs considerably across new-generation ICU ventilators. ICU ventilators seem to have reached a technical ceiling in recent years, and some ventilators still perform inadequately.

[Helium-sevoflurane association: a rescue treatment in case of acute severe asthma]

We report the case of a severe acute asthma, which required, after optimal medical therapy, helium and sevoflurane CO-administration after tracheal intubation. The Anesthetic Conserving Device allowed sevoflurane use with intensive care unit's ventilator. The helium-sevoflurane association was maintained during 9 days to decrease the bronchospasm, waiting for the efficiency of an aetiologic treatment. We discuss the suitability of this association to treat severe acute asthma, and its administration modalities.

The effectiveness of noninvasive positive pressure ventilation to enhance preoxygenation in morbidly obese patients: a randomized controlled study

BACKGROUND

Noninvasive positive-pressure ventilation (NPPV) with pressure support-ventilation and positive end-expiratory pressure are effective in providing oxygenation during intubation in hypoxemic patients. We hypothesized administration of oxygen (O2) using NPPV would more rapidly increase the end-tidal O2 concentration (ETO2) than preoxygenation using spontaneous ventilation (SV) in morbidly obese patients.

METHODS

Twenty-eight morbidly obese patients were enrolled in this prospective randomized study. Administration of O2 for 5 min was performed either with SV group or with NPPV (pressure support = 8 cm H2O, positive end-expiratory pressure = 6 cm H2O) (NPPV group). ETO2 was measured using the anesthesia breathing circuit, and is expressed as a fraction of atmospheric concentration. The primary end-point was the number of patients with an ETo(2) >95% at the end of O2 administration. Secondary end-points included the time to reach the maximal ETO2 and the ETO2 at the conclusion of O2 administration.

RESULTS

A larger proportion of patients achieved a 95% ETO2 at 5 min with NPPV than SV (13/14 vs 7/14, P = 0.01). The time to reach the maximal ETO2 was significantly less in the NPPV than in the SV group (185 +/- 46 vs 222 +/- 42 s, P = 0.02). The mean ETO2 at the conclusion of O2 administration was larger in the NPPV group than the SV group (96.9 +/- 1.3 vs 94.1 +/- 2.0%, P < 0.001). A modest, although significant, increase in gastric distension was observed in the NPPV group. No adverse effects were observed in either group.

CONCLUSION

Administration of O2 via a facemask with NPPV in the operating room is safe, feasible, and efficient in morbidly obese patients. In this population NPPV provides a more rapid O2 administration, achieving a higher ETO2.

A prospective study on the user-friendliness of four anaesthesia workstations

BACKGROUND AND OBJECTIVES

Unlike for intensive care unit and home mechanical ventilators, no study has evaluated the user-friendliness of the recently introduced new anaesthesia workstations.

METHODS

We performed a prospective study to evaluate the user-friendliness of four anaesthesia workstations, which were categorized into two groups: first-generation (Kion) and second-generation (Avance, Felix and Primus). Twenty users (12 nurse-anaesthetists and 8 anaesthesiologists) from three different anaesthesia departments at the same univeristy hospital participated in the study. The user-friendliness scale evaluated 10 criteria, including two design and monitoring criteria, four maintenance criteria and four ventilation use criteria. Each criterion was evaluated from 0 (poor) to 10 (excellent).

RESULTS

The mean score obtained for the first-generation workstation was lower than those obtained for the three second-generation workstations (P < 0.05). No significant differences in the overall user-friendliness score was observed for the three second-generation workstations. The first-generation workstation obtained a significantly lower score than the three second-generation workstations for the design criteria (P < 0.01). For the screen criteria, the highest score was obtained by Felix, which has the largest screen and associated characters. For the main maintenance criteria, Kion and Felix obtained the lowest scores. No significant differences between the four anaesthesia workstations were found for only three of the user-friendliness criteria (self-test, alarms and settings).

CONCLUSIONS

Anaesthesia machines have benefited from considerable advances in design and technology. This novel user-friendliness scale revealed that the most recent workstations were more appreciated by users than the first-generation of anaesthesia workstations. This user-friendliness scale may help the anaesthetic staff to 'consensually' choose the future workstation for their anaesthesia department.

Programming pressure support ventilation in pediatric patients in ambulatory surgery with a laryngeal mask airway

BACKGROUND

Anesthesia workstations with pressure support ventilation (PSV) are available, but there are few studies published on how to program flow-triggered PSV using a laryngeal mask airway (LMA) under general anesthesia in pediatric patients.

METHODS

We studied 60 ASA I and II patients, from 2 mo to 14 yr, scheduled for ambulatory surgery under combined general and regional anesthesia with a LMA. Patients were classified according to their body weight as follows: Group A < or =10 kg, Group B 11-20 kg, and Group C >20 kg. All were ventilated in PSV using the following settings: positive end-expiratory pressure of 4 cm H2O, the minimum flow-trigger without provoking auto-triggering, and the minimum level of pressure support to obtain 10 mL/kg of tidal volume.

RESULTS

The flow-trigger most frequently used in our study was 0.4 L/min, ranging from 0.2 to 0.6 L/min. We found no correlation between the flow-trigger setting and the patient's age, weight, compliance, resistance, or respiratory rate. There was a good correlation between the level of pressure support (Group A = 15 cm H2O, Group B = 10 cm H2O and Group C = 9 cm H2O) and age (P < 0.001), weight (P < 0.001), dynamic compliance (P < 0.001), and airway resistances (P < 0.001).

CONCLUSIONS

PSV with a Proseal LMA in outpatient pediatric anesthesia can be programmed simply using the common clinical noninvasive variables studied. However, more studies are needed to estimate the level of pressure support that may be required in other clinical situations (respiratory pathology, endotracheal tubes, or other types of surgeries) or with other anesthesia workstations.