Effects of flow triggering on breathing effort during partial ventilatory support

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.

Ventilators, Settings, Autotitration Algorithms

The choice of a ventilator model for a single patient is usually based on parameters such as size (portability), presence or absence of battery and ventilatory modes. However, there are many details within each ventilator model about triggering, pressurisation or autotitration algorithms that may go unnoticed, but may be important or may justify some drawbacks that may occur during their use in individual patients. This review is intended to emphasize these differences. Guidance is also provided on the operation of autotitration algorithms, in which the ventilator is able to take decisions based on a measured or estimated parameter. It is important to know how they work and their potential sources of error. Current evidence on their use is also provided.

Home Non-Invasive Positive Pressure Ventilation in Chronic Obstructive Pulmonary Disease: Why, Who, and How?

Advanced chronic obstructive pulmonary disease (COPD) might result in chronic hypercapnic ventilatory failure. Similar to neuromuscular and restrictive chest wall diseases, long-term non-invasive positive pressure ventilation (NPPV) is increasingly used in chronic hypercapnic COPD. This review describes the methods, patient selection, ventilatory strategies, and therapeutic effects of long-term Home-NPPV based on randomized controlled clinical trials published since 1985 in English language retrieved from the databases PubMed and Scopus. Long-term NPPV is feasible and effective in stable, non-exacerbated COPD patients with daytime hypercapnia with arterial pressure of carbon dioxide (PaCO2) levels ≥50 mm Hg (6.6 kPa), if the applied ventilatory pressures and application times improve baseline hypercapnia by at least 20%. Patients who survived an acute hypercapnic exacerbation might benefit from long-term NPPV if hypercapnia persists 2-4 weeks after resolution of the exacerbation. Pressure-controlled ventilation or pressure-support ventilation with adequate minimum backup breathing frequencies, in combination with nasal masks or oronasal masks have been successfully used in all larger clinical trials. Ventilatory strategies with mean inspiratory pressures of up to 28 cm H2O are well-tolerated by patients, but limitations exist in patients with impaired cardiac performance. Home-NPPV with a PaCO2-reductive approach might be considered as an additional treatment option in patients with stable chronic hypercapnic COPD.

Stepwise Ventilator Waveform Assessment to Diagnose Pulmonary Pathophysiology

Clinicians can use mechanical waveform analysis as a diagnostic tool to identify pulmonary pathophysiology. This review offers an approach to develop a hypothesis of a patient’s lung pathophysiology.

A bench-to-bedside study about trigger asynchronies induced by the introduction of external gas into the non-invasive mechanical ventilation circuit

Treatments that require the introduction of external gas into the non-invasive ventilation (NIV) circuit, such as aerosol and oxygen therapy, may influence the performance of the ventilator trigger system. The aim of the study was to determine the presence and type of asynchronies induced by external gas in the NIV circuit in a bench model and in a group of patients undergoing chronic NIV. Bench study: Four ventilators (one with two different trigger design types) and three gas sources (continuous flow at 4 and 9 l/min and pulsatile flow at 9 l/min) were selected in an active simulator model. The sensitivity of the trigger, the gas introduction position, the ventilatory pattern and the level of effort were also modified. The same ventilators and gas conditions were used in patients undergoing chronic NIV. Bench: the introduction of external gas caused asynchronies in 35.9% of cases (autotriggering 73%, ineffective effort 27%). Significant differences (p < 0.01) were detected according to the ventilator model and the gas source. In seven patients, the introduction of external gas induced asynchrony in 20.4% of situations (77% autotriggering). As in the bench study, there were differences in the occurrence of asynchronies depending on the ventilator model and gas source used. The introduction of external gas produces alterations in the ventilator trigger. These alterations are variable, and depend on the ventilator design and gas source. This phenomenon makes it advisable to monitor the patient at the start of treatment.

Patient-ventilator dyssynchrony in the intensive care unit: A practical approach to diagnosis and management

Patient-ventilator dyssynchrony or asynchrony occurs when, for any parameter of respiration, discordance exists between the patient's spontaneous effort and the ventilator's provided support. If not recognised, it may promote oversedation, prolong the duration of mechanical ventilation, create risk for lung injury, and generally confuse the clinical picture. Seven forms of dyssynchrony are common: (a) ineffective triggering; (b) autotriggering; (c) inadequate flow; (d) too much flow; (e) premature cycling; (f) delayed cycling; and (g) peak pressure apnoea. 'Reverse triggering' also occurs and may mimic premature cycling. Correct diagnosis of these phenomena often permits management by simple ventilator optimisation rather than by less desirable measures.

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.

ISCCM Guidelines for the Use of Non-invasive Ventilation in Acute Respiratory Failure in Adult ICUs

A. ACUTE HYPERCAPNIC RESPIRATORY FAILURE A1. Acute Exacerbation of COPD: Recommendations: NIV should be used in management of acute exacerbation of COPD in patients with acute or acute-on-chronic respiratory acidosis (pH = 7.25-7.35). (1A) NIV should be attempted in patients with acute exacerbation of COPD (pH <7.25 & PaCO2 ≥ 45) before initiating invasive mechanical ventilation (IMV) except in patients requiring immediate intubation. (2A). Lower the pH higher the chance of failure of NIV. (2B) NIV should not to be used routinely in normo- or mildly hyper-capneic patients with acute exacerbation of COPD, without acidosis (pH > 7.35). (2B) A2. NIV in ARF due to Chest wall deformities/Neuromuscular diseases: Recommendations: NIV may be used in patients of ARF due to chest wall deformity/Neuromuscular diseases. (PaCO2 ≥ 45) (UPP) A3. NIV in ARF due to Obesity hypoventilation syndrome (OHS): Recommendations: NIV may be used in AHRF in OHS patients when they present with acute hypercapnic or acute on chronic respiratory failure (pH 45). (3B) NIV/CPAP may be used in obese, hypercapnic patients with OHS and/or right heart failure in the absence of acidosis. (UPP) B. NIV IN ACUTE HYPOXEMIC RESPIRATORY FAILURE: B1. NIV in Acute Cardiogenic Pulmonary Oedema: Recommendations: NIV is recommended in hospital patients with ARF, due to Cardiogenic pulmonary edema. (1A). NIV should be used in patients with acute heart failure/ cardiogenic pulmonary edema, right from emergency department itself. (1B) Both CPAP and BiPAP modes are safe and effective in patients with cardiogenic pulmonary edema. (1A). However, BPAP (NIV-PS) should be preferred in cardiogenic pulmonary edema with hypercapnia. (3A) B2. NIV in acute hypoxemic respiratory failure: Recommendations: NIV may be used over conventional oxygen therapy in mild early acute hypoxemic respiratory failure (P/F ratio <300 and >200 mmHg), under close supervision. (2B) We strongly recommend against a trial of NIV in patients with acute hypoxemic failure with P/F ratio <150. (2A) B3. NIV in ARF due to Chest Trauma: Recommendations: NIV may be used in traumatic flail chest along with adequate pain relief. (3B) B4. NIV in Immunocompromised Host: Recommendations: In Immunocompromised patients with early ARF, we may consider NIV over conventional oxygen. (2B). B5. NIV in Palliative Care: Recommendations: We strongly recommend use of NIV for reducing dyspnea in palliative care setting. (2A) B6. NIV in post-operative cases: Recommendations: NIV should be used in patients with post-operative acute respiratory failure. (2A) B6a. NIV in abdominal surgery: Recommendations: NIV may be used in patients with ARF following abdominal surgeries. (2A) B6b. NIV in bariatric surgery: Recommendations: NIV may be used in post-bariatric surgery patients with pre-existent OSA or OHS. (3A) B6c. NIV in Thoracic surgery: Recommendations: In cardiothoracic surgeries, use of NIV is recommended post operatively for acute respiratory failure to improve oxygenation and reduce chance of reintubation. (2A) NIV should not be used in patients undergoing esophageal surgery. (UPP) B6d. NIV in post lung transplant: Recommendations: NIV may be used for shortening weaning time and to avoid re-intubation following lung transplantation. (2B) B7. NIV during Procedures (ETI/Bronchoscopy/TEE/Endoscopy): Recommendations: NIV may be used for pre-oxygenation before intubation. (2B) NIV with appropriate interface may be used in patients of ARF during Bronchoscopy/Endoscopy to improve oxygenation. (3B) B8. NIV in Viral Pneumonitis ARDS: Recommendations: NIV cannot be considered as a treatment of choice for patients with acute respiratory failure with H1N1 pneumonia. However, it may be reasonable to use NIV in selected patients with single organ involvement, in a strictly controlled environment with close monitoring. (2B) B9. NIV and Acute exacerbation of Pulmonary Tuberculosis: Recommendations: Careful use of NIV in patients with acute Tuberculosis may be considered, with effective infection control precautions to prevent air-borne transmission. (3B) B10. NIV after planned extubation in high risk patients: Recommendation: We recommend that NIV may be used to wean high risk patients from invasive mechanical ventilation as it reduces re-intubation rate. (2B) B11. NIV for respiratory distress post extubation: Recommendations: We recommend that NIV therapy should not be used to manage respiratory distress post-extubation in high risk patients. (2B) C. APPLICATION OF NIV: Recommendation: Choice of mode should be mainly decided by factors like disease etiology and severity, the breathing effort by the patient and the operator familiarity and experience. (UPP) We suggest using flow trigger over pressure triggering in assisted modes, as it provides better patient ventilator synchrony. Especially in COPD patients, flow triggering has been found to benefit auto PEEP. (3B) D. MANAGEMENT OF PATIENT ON NIV: D1. Sedation: Recommendations: A non-pharmacological approach to calm the patient (Reassuring the patient, proper environment) should always be tried before administrating sedatives. (UPP) In patients on NIV, sedation may be used with extremely close monitoring and only in an ICU setting with lookout for signs of NIV failure. (UPP) E. EQUIPMENT: Recommendations: We recommend that portable bilevel ventilators or specifically designed ICU ventilators with non-invasive mode should be used for delivering Non–invasive ventilation in critically ill patients. (UPP) Both critical care ventilators with leak compensation and bi-level ventilators have been equally effective in decreasing the WOB, RR, and PaCO2. (3B) Currently, Oronasal mask is the most preferred interface for non-invasive ventilation for acute respiratory failure. (3B) F. WEANING: Recommendations: We recommend that weaning from NIV may be done by a standardized protocol driven approach of the unit. (2B)

How to cite this article: Chawla R, Dixit SB, Zirpe KG, Chaudhry D, Khilnani GC, Mehta Y, et al. ISCCM Guidelines for the Use of Non-invasive Ventilation in Acute Respiratory Failure in Adult ICUs. Indian J Crit Care Med 2020;24(Suppl 1):S61–S81.

Comparison of Inspiratory Effort, Workload and Cycling Synchronization Between Non-Invasive Proportional-Assist Ventilation and Pressure-Support Ventilation Using Different Models of Respiratory Mechanics

Background

This study assessed lung models for the influence of respiratory mechanics and inspiratory effort on breathing pattern and simulator-ventilator cycling synchronization in non-invasive ventilation.

Material/Methods

A Respironics V60 ventilator was connected to an active lung simulator modeling mildly restrictive, severely restrictive, obstructive and mixed obstructive/restrictive profiles. Pressure-support ventilation (PSV) and proportional-assist ventilation (PAV) were set to obtain similar tidal volume (V_T). PAV was applied at flow assist (FA) 40–90% of resistance (Rrs) and volume assist (VA) 40–90% of elastance (Ers). Measurements were performed with system air leak of 25–28 L/minute. Ventilator performance and simulator-ventilator asynchrony were evaluated.

Results

At comparable V_T, PAV had slightly lower peak inspiratory flow and higher driving pressure compared with PSV. Premature cycling occurred in the obstructive, severely restrictive and mildly restrictive models. During PAV, time for airway pressure to achieve 90% of maximum during inspiration (T90) in the severely restrictive model was shorter than those of the obstructive and mixed obstructive/restrictive models and close to that measured in the PSV mode. Increasing FA level reduced inspiratory trigger workload (PTP₃₀₀) in obstructive and mixed obstructive/restrictive models. Increasing FA level decreased inspiratory time (T_I) and tended to aggravate premature cycling, whereas increasing VA level attenuated this effect.

Conclusions

PAV with an appropriate combination of FA and VA decreases work of breathing during the inspiratory phase and improves simulator-ventilator cycling synchrony. FA has greater impact than VA in the adaptation to inspiratory effort demand. High VA level might help improve cycling synchrony.

Information conveyed by electrical diaphragmatic activity during unstressed, stressed and assisted spontaneous breathing: a physiological study

Background

The electrical activity of the crural diaphragm (Eadi), a surrogate of respiratory drive, can now be measured at the bedside in mechanically ventilated patients with a specific catheter. The expected range of Eadi values under stressed or assisted spontaneous breathing is unknown. This study explored Eadi values in healthy subjects during unstressed (baseline), stressed (with a resistance) and assisted spontaneous breathing. The relation between Eadi and inspiratory effort was analyzed.

Methods

Thirteen healthy male volunteers were included in this randomized crossover study. Eadi and esophageal pressure (Peso) were recorded during unstressed and stressed spontaneous breathing and under assisted ventilation delivered in pressure support (PS) at low and high assist levels and in neurally adjusted ventilatory assist (NAVA). Overall eight different situations were assessed in each participant (randomized order). Peak, mean and integral of Eadi, breathing pattern, esophageal pressure–time product (PTPeso) and work of breathing (WOB) were calculated offline.

Results

Median [interquartile range] peak Eadi at baseline was 17 [13–22] μV and was above 10 μV in 92% of the cases. Eadi_max defined as Eadi measured at maximal inspiratory capacity reached 90 [63 to 99] μV. Median peak Eadi/Eadi_max ratio was 16.8 [15.6–27.9]%. Compared to baseline, respiratory rate and minute ventilation were decreased during stressed non-assisted breathing, whereas peak Eadi and PTPeso were increased. During unstressed assisted breathing, peak Eadi decreased during high-level PS compared to unstressed non-assisted breathing and to NAVA (p = 0.047). During stressed breathing, peak Eadi was lower during all assisted ventilation modalities compared to stressed non-assisted breathing. During assisted ventilation, across the different conditions, peak Eadi changed significantly, whereas PTPeso and WOB/min were not significantly modified. Finally, Eadi signal was still present even when Peso signal was suppressed due to high assist levels.

Conclusion

Eadi analysis provides complementary information compared to respiratory pattern and to Peso monitoring, particularly in the presence of high assist levels.

Trial registration The study was registered as NCT01818219 in clinicaltrial.gov. Registered 28 February 2013

Electronic supplementary material

The online version of this article (10.1186/s13613-019-0564-1) contains supplementary material, which is available to authorized users.

Patient-Ventilator Dyssynchrony

In mechanically ventilated patients, assisted mechanical ventilation (MV) is employed early, following the acute phase of critical illness, in order to eliminate the detrimental effects of controlled MV, most notably the development of ventilator-induced diaphragmatic dysfunction. Nevertheless, the benefits of assisted MV are often counteracted by the development of patient-ventilator dyssynchrony. Patient-ventilator dyssynchrony occurs when either the initiation and/or termination of mechanical breath is not in time agreement with the initiation and termination of neural inspiration, respectively, or if the magnitude of mechanical assist does not respond to the patient's respiratory demand. As patient-ventilator dyssynchrony has been associated with several adverse effects and can adversely influence patient outcome, every effort should be made to recognize and correct this occurrence at bedside. To detect patient-ventilator dyssynchronies, the physician should assess patient comfort and carefully inspect the pressure- and flow-time waveforms, available on the ventilator screen of all modern ventilators. Modern ventilators offer several modifiable settings to improve patient-ventilator interaction. New proportional modes of ventilation are also very helpful in improving patient-ventilator interaction.

Improvement of the trigger of a ventilator for non-invasive ventilation in children: bench and clinical study

BACKGROUND AND AIMS

Even though numerous ventilators are licensed for a use in children, very few have been specifically developed for this age range. Therefore, home ventilators may not be able to adequately synchronize with the child's respiratory effort, and the inspiratory triggers (ITs) of assist modes are not always appropriate for children. The aim of the study was to test the improvement of the IT of a ventilator on a pediatric bench and in pediatric patients.

METHODS

A classical IT (ITc) and an improved IT [non-invasive ventilation (NIV) + IT] were tested on a bench with six pediatric profiles and in six young patients (mean age 14.1 ± 2.7 years old) requiring long-term NIV.

RESULTS

On the bench, trigger time delays (ΔT) and trigger pressures (ΔP) were reduced with the NIV + IT as compared with the ITc (ΔT: 0.481 ± 0.332 vs 0.079 ± 0.022 s for ITc and NIV + IT, respectively, P = 0.027; ΔP: -1.40 ± 0.70 vs -0.42 ± 0.28 cmH2 O for ITc and NIV + IT, respectively, P = 0.046). The clinical study confirmed the decrease in ΔT (0.267 ± 0.061 vs 0.178 ± 0.074 s for ITc and NIV + IT, respectively, P = 0.024) and ΔP (-0.68 ± 0.26 vs -0.39 ± 0.11 cmH2 O for ITc and NIV + IT, respectively, P = 0.030).

CONCLUSIONS

The sensitivity of the IT of a ventilator can be improved for pediatric use. The improvements observed on the bench study were confirmed in pediatric patients.

Work of breathing using different interfaces in spontaneous positive pressure ventilation: helmet, face-mask, and endotracheal tube

PURPOSE

Noninvasive positive pressure ventilation (NPPV) using a helmet is expected to cause inspiratory trigger delay due to the large collapsible and compliant chamber. We compared the work of breathing (WOB) of NPPV using a helmet or a full face-mask with that of invasive ventilation by tracheal intubation.

METHODS

We used a lung model capable of simulating spontaneous breathing (LUNGOO; Air Water Inc., Japan). LUNGOO was set at compliance (C) = 50 mL/cmH2O and resistance (R) = 5 cmH2O/L/s for normal lung simulation, C = 20 mL/cmH2O and R = 5 cmH2O/L/s for restrictive lung, and C = 50 mL/cmH2O and R = 20 cmH2O/L/s for obstructive lung. Muscle pressure was fixed at 25 cmH2O and respiratory rate at 20 bpm. Pressure support ventilation and continuous positive airway pressure were performed with each interface placed on a dummy head made of reinforced plastic that was connected to LUNGOO. We tested the inspiratory WOB difference between the interfaces with various combinations of ventilator settings (positive end-expiratory pressure 5 cmH2O; pressure support 0, 5, and 10 cmH2O).

RESULTS

In the normal lung and restrictive lung models, WOB decreased more with the face-mask than the helmet, especially when accompanied by the level of pressure support. In the obstructive lung model, WOB with the helmet decreased compared with the other two interfaces. In the mixed lung model, there were no significant differences in WOB between the three interfaces.

CONCLUSION

NPPV using a helmet is more effective than the other interfaces for WOB in obstructive lung disease.

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.

Validation of the accuracy of a transport ventilator utilizing a pediatric animal model

OBJECTIVE

The objective of this study was to evaluate 2 transport ventilators utilizing both a test lung and a pediatric animal model.

METHODS

Two transport ventilators were utilized for evaluations. A test lung or intubated, sedated pigs (n = 9) with healthy and injured lungs were ventilated using control and support modes. A test lung was used to evaluate alarm responsiveness, FIO2 accuracy, oxygen consumption, and duration of battery power. Pigs were utilized to evaluate the exhalation valve, ventilator response, volume accuracy, and noninvasive functionality. Respiratory mechanics were determined using a forced oscillation technique, and airway flow and pressure waveforms were acquired utilizing a pneumotachograph.

RESULTS

For both ventilators, FIO2 accuracy was within 10% error. On an E cylinder of oxygen, the EMV+ operated for 3 hours 48 minutes and the LTV 1200 for 1 hour 4 minutes. On battery power, the LTV 1200 ventilated for 6 hours 51 minutes and the EMV+ for 12 hours 8 minutes. Ventilator response time was less (36%), and delta pressure was greater (38%) for the EMV+ utilizing noninvasive ventilation. The percent error for displayed volume was less than 10% for the EMV+.

CONCLUSIONS

In this study, we demonstrate that there are differences between the 2 ventilators in regard to oxygen consumption, duration of battery power, and volume accuracy. Clinicians should be aware of these differences to optimize the choice and use of both ventilators depending on clinical need/setting.

[Ventilator modes and settings during non-invasive ventilation: effects on respiratory events and implications for their identification. 2011]

Compared with invasive ventilation, non-invasive ventilation (NIV) has two unique characteristics: its non-hermetic nature and the fact that the ventilator-lung assembly cannot be considered as a single-compartment model because of the presence of variable resistance represented by the upper airways. When NIV is initiated, the ventilator settings are determined empirically based on clinical evaluation and blood gas variations. However, NIV is predominantly applied during sleep. Consequently, to assess overnight patient-machine "agreement" and efficacy of ventilation, more specific and sophisticated monitoring is needed. The effectiveness of NIV might therefore be more correctly assessed by sleep studies than by daytime assessment. The simplest monitoring can be done from flow and pressure curves from the mask or the ventilator circuit. Examination of these tracings can give useful information to evaluate if the settings chosen by the operator were the right ones for that patient. However, as NIV allows a large range of ventilatory parameters and settings, it is mandatory to have information about this to better understand patient-ventilator interaction. Ventilatory modality, mode of triggering, pressurization slope, use or not of positive end expiratory pressure and type of exhalation as well as ventilator performances may all have physiological consequences. Leaks and upper airway resistance variations may, in turn, modify these patterns. This article discusses the equipment available for NIV, analyses the effect of different ventilator modes and settings and of exhalation and connecting circuits on ventilatory traces and gives the background necessary to understand their impact on nocturnal monitoring of NIV.

Ventilatory failure, ventilator support, and ventilator weaning

The development of acute ventilatory failure represents an inability of the respiratory control system to maintain a level of respiratory motor output to cope with the metabolic demands of the body. The level of respiratory motor output is also the main determinant of the degree of respiratory distress experienced by such patients. As ventilatory failure progresses and patient distress increases, mechanical ventilation is instituted to help the respiratory muscles cope with the heightened workload. While a patient is connected to a ventilator, a physician's ability to align the rhythm of the machine with the rhythm of the patient's respiratory centers becomes the primary determinant of the level of rest accorded to the respiratory muscles. Problems of alignment are manifested as failure to trigger, double triggering, an inflationary gas-flow that fails to match inspiratory demands, and an inflation phase that persists after a patient's respiratory centers have switched to expiration. With recovery from disorders that precipitated the initial bout of acute ventilatory failure, attempts are made to discontinue the ventilator (weaning). About 20% of weaning attempts fail, ultimately, because the respiratory controller is unable to sustain ventilation and this failure is signaled by development of rapid shallow breathing. Substantial advances in the medical management of acute ventilatory failure that requires ventilator assistance are most likely to result from research yielding novel insights into the operation of the respiratory control system.

Ventilator auto-cycling from cardiogenic oscillations: case report and review of literature

BACKGROUND

Brain death is the total loss of all brain and brain stem functions, and its diagnosis is often confirmed by an apnoea test, which relies on disconnecting the patient from the ventilator. Auto-triggering or auto-cycling is defined as a ventilator being triggered in the absence of patient effort, intrinsic respiratory drive or inspiratory muscle activity. Ventilator auto-triggering could delay the diagnosis of brain death leading to unnecessary admission for the patient and false hopes of recovery for the family.

METHODS

We report a case of ventilator auto-triggering associated with cardiogenic oscillations in a female patient.

RESULTS

We confirmed the finding of ventilator auto-triggering by changing the patient's position and reassessing the triggering thresholds. Brain death was then confirmed by apnoea test.

CONCLUSION

This case is presented to arouse the awareness of the medical staff and nurses to this phenomenon, which can mimic an intrinsic respiratory effort in patients allegedly diagnosed with brain death. Along with this case report, we review the English language publications for similar cases.

Neurally triggered breaths have reduced response time, work of breathing, and asynchrony compared with pneumatically triggered breaths in a recovering animal model of lung injury

OBJECTIVE

Our objective was to compare response time, pressure time product as a reflection of work of breathing, and incidence and type of asynchrony in neurally vs. pneumatically triggered breaths in a spontaneously breathing animal model with resolving lung injury.

DESIGN

Prospective animal study.

SETTING

Experimental laboratory.

SUBJECTS

Male Yorkshire pigs.

INTERVENTIONS

Intubated, sedated pigs were ventilated using neurally adjusted ventilatory assist and pressure support ventilation with healthy and sick/recruited lungs. After injury, the lung was recruited using a computer-driven protocol. Respiratory mechanics were determined using a forced oscillation technique, and airway flow and pressure waveforms were acquired using a pneumotachograph.

MEASUREMENTS AND MAIN RESULTS

Waveforms were analyzed for trigger delay, pressure time product, and asynchrony. Trigger delay was defined as the time interval (ms) from initiation of a breath to the beginning of ventilator pressurization. Pressure time product was measured as the area of the pressure curve for animal effort (area A) and ventilator response (area B). Asynchrony was classified according to triggering problems, adequacy of flow delivery, and adequate breath termination. Mean values were compared using the Wilcoxon signed-ranks test (p < .05). Trigger delay (ms) was less in neurally triggered breaths (pressure support ventilation healthy 104 ± 27 vs. neurally adjusted ventilatory assist healthy 72 ± 30, pressure support ventilation sick/recruited 77 ± 18 vs. neurally adjusted ventilatory assist sick/recruited 38 ± 18, p < .01). Pressure time product areas A and B were decreased for neurally triggered breaths compared with pressure support ventilation in both healthy and recruited animals (p ≤ .02). Overall, the percentage of asynchrony was less for neurally adjusted ventilatory assist breaths in the recruited animals (pressure support ventilation 27% and neurally adjusted ventilatory assist 6%).

CONCLUSIONS

Neurally triggered breaths have reduced asynchrony, trigger delay, and pressure time product, which may indicate reduced work of breathing associated with less effort to trigger the ventilator and faster response to effort. Further study is required to demonstrate if these differences will lead to decreased days of ventilation and less use of sedation in patients.

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.

Comparison of 3 different methods used to measure the rapid shallow breathing index

PURPOSE

Rapid shallow breathing index (RSBI) is conveniently measured through the ventilator. If continuous positive airway pressure (CPAP) is used, it may change the RSBI value. We measured the RSBI with a handheld spirometer and through the ventilator, with and without CPAP, to assess differences.

MATERIALS AND METHODS

Rapid shallow breathing index was measured in 3 ways: (1) CPAP 0 cm H(2)O and fraction of inspired oxygen (Fio(2)) 0.4, (2) CPAP 5 cm H(2)O and Fio(2) 0.4, and (3) ventilator disconnected and Fio(2) 0.21. Tidal volume and respiratory frequency were recorded from ventilator monitor values in methods 1 and 2, and from a handheld spirometer and observed respiratory frequency, in method 3.

RESULTS

A total of 170 measurements, each using all 3 methods, were obtained from 80 patients admitted to a medical intensive care unit. The mean RSBI values for methods 1, 2, and 3 were 98.1 ± 58.7, 87.6 ± 51.2, and 108.3 ± 65.3, respectively (P < .001). The RSBI decreased by 9.4% when using CPAP 0 cm H(2)O and by 19.1% when using CPAP 5 cm H(2)O.

CONCLUSIONS

The RSBI values measured through the ventilator with CPAP 5 cm H(2)O are much lower than the values measured with a handheld spirometer. Even the RSBI values measured with CPAP 0 cm H(2)O are significantly lower. This is attributable to the base flow delivered by some ventilators. The difference must be taken into account during weaning assessment.

Ventilator autocycling and delayed recognition of brain death

BACKGROUND

Improvements in technology play an important role in caring for critically ill patients. One example is the advance in ventilator design to facilitate triggering of mechanical breaths. Minimal changes in circuit flow unrelated to respiratory effort can trigger a ventilator breath and may mislead caregivers in recognizing brain death.

METHODS

We observed patients with devastating brain injuries in a mixed medical/surgical intensive care unit (ICU) with a high clinical suspicion for brain death including the absence of cranial nerve function with apparent spontaneous breathing during patient-triggered modes of mechanical ventilation. Further clinical observation for spontaneous respirations was assessed upon removal of ventilatory support.

RESULTS

Nine patients with brain injury due to multiple etiologies were identified and demonstrated no spontaneous respirations when formally assessed for apnea. Length of time between brain death and its recognition could not be determined.

CONCLUSION

When brain-dead patients who are suitable organ donors are mistakenly identified as having cerebral activity, the diagnosis of brain death is delayed. This delay impacts resource utilization, impedes recovery and function of organs for donation, and adversely affects donor families, potential recipients of organs, and patient donors who may have testing and treatment that cannot be beneficial. Patients with catastrophic brain injury and absent cranial nerve function should undergo immediate formal apnea testing.

Control of breathing during mechanical ventilation: who is the boss?

Over the past decade, concepts of control of breathing have increasingly moved from being theoretical concepts to "real world" applied science. The purpose of this review is to examine the basics of control of breathing, discuss the bidirectional relationship between control of breathing and mechanical ventilation, and critically assess the application of this knowledge at the patient's bedside. The principles of control of breathing remain under-represented in the training curriculum of respiratory therapists and pulmonologists, whereas the day-to-day bedside application of the principles of control of breathing continues to suffer from a lack of outcomes-based research in the intensive care unit. In contrast, the bedside application of the principles of control of breathing to ambulatory subjects with sleep-disordered breathing has out-stripped that in critically ill patients. The evolution of newer technologies, faster real-time computing abilities, and miniaturization of ventilator technology can bring the concepts of control of breathing to the bedside and benefit the critically ill patient. However, market forces, lack of scientific data, lack of research funding, and regulatory obstacles need to be surmounted.

[Invasive mechanical ventilation in COPD and asthma]

COPD and asthmatic patients use a substantial proportion of mechanical ventilation in the ICU, and their overall mortality with ventilatory support can be significant. From the pathophysiological standpoint, they have increased airway resistance, pulmonary hyperinflation, and high pulmonary dead space, leading to increased work of breathing. If ventilatory demand exceeds work output of the respiratory muscles, acute respiratory failure follows. The main goal of mechanical ventilation in this kind of patients is to improve pulmonary gas exchange and to allow for sufficient rest of compromised respiratory muscles to recover from the fatigued state. The current evidence supports the use of noninvasive positive-pressure ventilation for these patients (especially in COPD), but invasive ventilation also is required frequently in patients who have more severe disease. The physician must be cautious to avoid complications related to mechanical ventilation during ventilatory support. One major cause of the morbidity and mortality arising during mechanical ventilation in these patients is excessive dynamic pulmonary hyperinflation (DH) with intrinsic positive end-expiratory pressure (intrinsic PEEP or auto-PEEP). The purpose of this article is to provide a concise update of the most relevant aspects for the optimal ventilatory management in these patients.

Mechanical ventilation and the total artificial heart: optimal ventilator trigger to avoid post-operative autocycling - a case series and literature review

Many patients with end-stage cardiomyopathy are now being implanted with Total Artificial Hearts (TAHs). We have observed individual cases of post-operative mechanical ventilator autocycling with a flow trigger, and subsequent loss of autocycling after switching to a pressure trigger. These observations prompted us to do a retrospective review of all TAH devices placed at our institution between August 2007 and May 2009. We found that in the immediate post-operative period following TAH placement, autocycling was present in 50% (5/10) of cases. There was immediate cessation of autocycling in all patients after being changed from a flow trigger of 2 L/minute to a pressure trigger of 2 cm H₂O. The autocycling group was found to have significantly higher CVP values than the non-autocycling group (P = 0.012). Our data suggest that mechanical ventilator autocycling may be resolved or prevented by the use of a pressure trigger rather than a flow trigger setting in patients with TAHs who require mechanical ventilation.

Advanced closed loops during mechanical ventilation (PAV, NAVA, ASV, SmartCare)

New modes of mechanical ventilation with advanced closed loops are now available, and in the future these could assume a greater role in supporting critically ill patients in intensive care units (ICUs) for several reasons. Two modes of ventilation--proportional assist ventilation and neurally adjusted ventilatory assist--deliver assisted ventilation proportional to the patient's effort, improving patient-ventilator synchrony. Also, a few systems that automate the medical reasoning with advanced closed-loops, such as SmartCare and adaptive support ventilation, have the potential to improve knowledge transfer by continuously implementing automated protocols. Moreover, they may improve patient-ventilator interactions and outcomes, and provide a partial solution to the forecast clinician shortages by reducing ICU-related costs, time spent on mechanical ventilation, and staff workload. Preliminary studies are promising, and initial systems are currently being refined with increasing clinical experience. A new era of mechanical ventilation should emerge with these systems.

Respiratory muscle unloading during auto-adaptive non-invasive ventilation

RATIONALE

Non-invasive ventilation (NIV) has been shown to improve clinical outcomes in acute and chronic hypercapnic respiratory failure. A new timed, automated, auto-adaptive non-invasive ventilatory mode (TA-mode) has been recently introduced.

OBJECTIVE

To investigate the degree of respiratory muscle unloading with this new mode in comparison to assisted (S-mode) NIV in healthy individuals.

METHODS

Work of breathing, pressure time product and transdiaphragmatic pressure time product were measured during unassisted breathing, assisted and TA-mode-NIV in eight healthy, awake volunteers at inspiratory pressures of 20 and expiratory pressures of 4hPa.

RESULTS

Assisted and TA-mode-NIV reduced the work of breathing by 50 and 89.1%, pressure time product by 61.5 and 72.6% and transdiaphragmatic pressure time product by 77 and 88.7%, respectively when compared to unassisted breathing. The degree of respiratory muscle unloading was higher during TA-mode-NIV when compared to assisted non-invasive ventilation (work of breathing p<0.001, pressure time product p=0.04 and transdiaphragmatic pressure time product p=0,01).

CONCLUSION

TA-mode-NIV achieved significant higher levels of respiratory muscle unloading in healthy individuals when compared to assisted non-invasive ventilation.

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.

[Field 5. Safety practices procedures for mechanical ventilation. French-speaking Society of Intensive Care. French Society of Anesthesia and Resuscitation]

Invasive or endotracheal mechanical ventilation can lead to numerous complications likely to burden morbidity and mortality of patients in the intensive care unit. Various safety practices for mechanical ventilation may involve intubation, the mechanical ventilation period, weaning and extubation, the use of tracheostomy as well as non-invasive ventilation. The main objective of safety practices described in this chapter is to prevent or avoid the main risks due to invasive mechanical ventilation.

Subject-ventilator synchrony during neural versus pneumatically triggered non-invasive helmet ventilation

Objective

Patient–ventilator synchrony during non-invasive pressure support ventilation with the helmet device is often compromised when conventional pneumatic triggering and cycling-off were used. A possible solution to this shortcoming is to replace the pneumatic triggering with neural triggering and cycling-off—using the diaphragm electrical activity (EA_di). This signal is insensitive to leaks and to the compliance of the ventilator circuit.

Design

Randomized, single-blinded, experimental study.

Setting

University Hospital.

Participants and subjects

Seven healthy human volunteers.

Interventions

Pneumatic triggering and cycling-off were compared to neural triggering and cycling-off during NIV delivered with the helmet.

Measurements and results

Triggering and cycling-off delays, wasted efforts, and breathing comfort were determined during restricted breathing efforts (<20% of voluntary maximum EA_di) with various combinations of pressure support (PSV) (5, 10, 20 cm H₂O) and respiratory rates (10, 20, 30 breath/min). During pneumatic triggering and cycling-off, the subject–ventilator synchrony was progressively more impaired with increasing respiratory rate and levels of PSV (p < 0.001). During neural triggering and cycling-off, effect of increasing respiratory rate and levels of PSV on subject–ventilator synchrony was minimal. Breathing comfort was higher during neural triggering than during pneumatic triggering (p < 0.001).

Conclusions

The present study demonstrates in healthy subjects that subject–ventilator synchrony, trigger effort, and breathing comfort with a helmet interface are considerably less impaired during increasing levels of PSV and respiratory rates with neural triggering and cycling-off, compared to conventional pneumatic triggering and cycling-off.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-008-1163-z) contains supplementary material, which is available to authorized users.

Performance of noninvasive ventilation modes on ICU ventilators during pressure support: a bench model study

OBJECTIVE

Noninvasive ventilation (NIV) is often applied with ICU ventilators. However, leaks at the patient-ventilator interface interfere with several key ventilator functions. Many ICU ventilators feature an NIV-specific mode dedicated to preventing these problems. The present bench model study aimed to evaluate the performance of these modes.

DESIGN AND SETTING

Bench model study in an intensive care research laboratory of a university hospital.

METHODS

Eight ICU ventilators, widely available in Europe and featuring an NIV mode, were connected by an NIV mask to a lung model featuring a plastic head to mimic NIV conditions, driven by an ICU ventilator imitating patient effort. Tests were conducted in the absence and presence of leaks, the latter condition with and without activation of the NIV mode. Trigger delay, trigger-associated inspiratory workload, and pressurization were tested in conditions of normal respiratory mechanics, and cycling was also assessed in obstructive and restrictive conditions.

RESULTS

On most ventilators leaks led to an increase in trigger delay and workload, a decrease in pressurization, and delayed cycling. On most ventilators the NIV mode partly or totally corrected these problems, but with large variations between machines. Furthermore, on some ventilators the NIV mode worsened the leak-induced dysfunction.

CONCLUSIONS

The results of this bench-model NIV study confirm that leaks interfere with several key functions of ICU ventilators. Overall, NIV modes can correct part or all of this interference, but with wide variations between machines in terms of efficiency. Clinicians should be aware of these differences when applying NIV with an ICU ventilator.

Tracheal pressure regulated volume assist ventilation in acute respiratory failure

PURPOSE

Proportional assist ventilation (PAV) uses volume assist (VAV) and flow assist ventilation (FAV) to reduce elastic and resistive effort, respectively. Proportional assist ventilation may be difficult to apply clinically, particularly due to FAV related considerations. It was hypothesized that regulating tracheal (Ptr) rather than airway opening pressure (Pao), to overcome endotracheal tube related resistive effort, during VAV would provide an effective alternative method of ventilation. We therefore compared the effects of Pao and Ptr regulated VAV on breathing pattern and inspiratory effort.

METHODS

In seven intubated patients, flow, volume, Pao, Ptr, esophageal and transdiaphragmatic pressure were measured during VAV (0-80% respiratory system elastance) using Pao vs Ptr to regulate ventilator applied pressure. Breathing pattern and the pressure-time integral of the inspiratory muscles (integralP(mus) . dt) and diaphragm (integralP(di) . dt) were determined.

RESULTS

Compared to spontaneous breathing, the respiratory rate to tidal volume ratio, or rapid shallow breathing index (RSBI), improved progressively with increasing VAV (130 +/- 64 vs 70 +/- 35, VAV 0 vs 80%; P < 0.05) while inspiratory effort fell (integralP(mus) . dt = 39.6 +/- 7.5 vs 28.5 +/- 7.2 cm H(2)O.sec.L(-1), integralP(di) . dt, = 35.4 +/- 7.8 vs 24.2 +/- 5.9 cm H(2)O.sec.L(-1), VAV 0 vs 80%; P < 0.05) due to a decrease in elastic related effort. At any given level of support, there was further reduction in RSBI, integralP(mus) . dt, and integralP(di) . dt (which averaged 23.6 +/- 2.7, 33.7 +/- 4.4, and 38.5 +/- 5.1%, respectively; P < 0.05) for Ptr compared to Pao regulated VAV due to a decrease in resistive effort.

CONCLUSIONS

Tracheal pressure regulated VAV can be a simple and effective method of partial ventilatory support in acute respiratory failure. Further work will be needed to determine its efficacy and potential benefit relative to PAV and other modes of ventilation in routine clinical practice.

Clinical review: patient-ventilator interaction in chronic obstructive pulmonary disease

Mechanically ventilated patients with chronic obstructive pulmonary disease often prove challenging to the clinician due to the complex pathophysiology of the disease and the high risk of patient-ventilator asynchrony. These problems are encountered in both intubated patients and those ventilated with noninvasive ventilation. Much knowledge has been gained over the years in our understanding of the mechanisms underlying the difficult interaction between these patients and the machines used to provide them with the ventilatory support they often require for prolonged periods. This paper attempts to summarize the various key issues of patient-ventilator interaction during pressure support ventilation, the most often used partial ventilatory support mode, and to draw clinicians' attention to the need for sufficient knowledge when setting the ventilator at the bedside, given the often conflicting goals that must be met.

[Non-invasive ventilation]

Non-invasive ventilation is a technique to ventilate patients without endotracheal intubation and analgosedation. Pressure tight masks allow the ventilation of patients with severe respiratory or ventilatory insufficiency. Non-invasive ventilation may be used as short-term treatment for patients with acute ventilatory decompensation, as well as for long-term therapy at home for patients with chronic respiratory diseases. The typical indications are hypoxaemic respiratory failure in pneumonia or cardiogenic pulmonary edema, and hypercapnic ventilatory insufficiency in severe chronic obstructive pulmonary disease, neuromuscular disorders, or advanced kyphoscoliosis. The physiological background, technical aspects of performing non-invasive ventilation, and typical indications are discussed.

Lung mechanics at the bedside: make it simple

PURPOSE OF REVIEW

The aim of this review is to describe ventilator-patient interaction, employing the equation of motion and the curves obtained by the ventilator. Practitioners confronted with mechanically ventilated patients every day in intensive care units should be able to sort out from all data available from modern ventilators those relevant for choosing a correct ventilatory strategy for each patient.

RECENT FINDINGS

Early determination of patient-ventilator asynchrony, air-leaks and variation in respiratory parameters is important during mechanical ventilation. A correct evaluation of data, for patient safety and tailored ventilatory strategy becomes mandatory when non-invasive ventilation by helmet or mask is applied.

SUMMARY

The equation of motion is described and dynamic and static respiratory mechanics are analysed to highlight all those data that can influence decision-making in setting mechanical or assisted ventilation in invasively and non-invasively ventilated patients.