European Respiratory Society

New Developments in Mechanical Ventilation

Edited by M. Ferrer and P. Pelosi
New Developments in Mechanical Ventilation

Mechanical ventilation is the life-support technique most frequently used in critically-ill patients admitted to intensive care units. This monograph is intended to update relevant aspects and novel developments in mechanical ventilation that has occurred in recent years. The topics discussed include conventional and innovative ventilator modalities, adjuvant therapies, modes of extracorporeal respiratory support, and weaning from mechanical ventilation and noninvasive ventilation.

  • European Respiratory Society Monographs
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  4. Page 1
    Abstract
    Correspondence: P.R.M. Rocco, Laboratory of Pulmonary Investigation, Carlos Chagas Filho Biophysics Institute, Federal University of Rio de Janeiro, Centro de Ciências da Saúde, Avenida Carlos Chagas Filho, s/n, Bloco G-014, Ilha do Fundão, 21941-902, Rio de Janeiro, Brazil. Email prmrocco@biof.ufrj.br

    Mechanical ventilation has become essential for the support of critically ill patients; however, it can cause ventilator-induced lung injury (VILI) or aggravate ventilator-associated lung injury (VALI), contributing to the high mortality rates observed in acute respiratory distress syndrome. This chapter discusses the mechanisms leading to VILI/VALI, the diagnostic procedures of early detection and how to prevent it.

    The clinical relevance of low lung volume injury and the application of high positive end-expiratory pressure levels remain debatable. Furthermore, researchers were not successful in transferring the measurement of inflammatory mediators during VILI/VALI from bench to bedside. Therefore, the following issues still require elucidation: 1) the best ventilator strategy to be adopted; 2) which ventilator parameters should be managed; 3) how to monitor VILI/VALI (arterial blood gases, lung mechanics, proinflammatory mediators); 4) the role of imaging (computed tomography scan, lung ultrasound and positron emission tomography; and 5) how to prevent VILI/VALI (new ventilatory and pharmacological strategies).

  5. Page 19
    Abstract
    Correspondence: A. Esan, Dept of Pulmonary and Critical Care, New York Methodist Hospital, 506 Sixth Street, Brooklyn, NY 11215, USA. Email bayoesan@yahoo.com

    Mechanical ventilation of patients with acute lung injury/acute respiratory distress syndrome (ARDS) should commence with low tidal volume (VT), low stretch and adequate positive end-expiratory pressure (PEEP), as proposed by the first ARDSnet trial. The majority of patients with ARDS will achieve their goals of oxygenation and plateau pressure, utilising the lung protective strategy. In the remaining minority of patients, these end-points may not be achieved. Such patients have a significantly high mortality and should be considered for rescue strategies relatively early on. If the patients respond positively to lung recruitment trials, using rescue strategies may open atelectactic alveoli and allow oxygenation or plateau pressure targets to be achieved. None of these rescue strategies have been shown to reduce mortality, although short-term objectives of improvement in oxygenation or reduction in plateau pressures may be achieved. Therefore, the selection of these strategies should be based on availability and level of comfort of the operators.

  6. Page 40
    Abstract
    Correspondence: E. Fan, Mount Sinai Hospital, 600 University Avenue, Room 18-232, Toronto, M5G 1X5, ON, Canada. Email efan@mtsinai.on.ca

    A pressure- and volume-limited ventilatory strategy has been shown to improve short-term mortality in patients with acute lung injury (ALI). However, such a strategy may lead to alveolar de-recruitment and atelectrauma. Recruitment manoeuvres (RMs) may be an important component of a lung protective strategy, leading to increased end-expiratory lung volume, with a subsequent improvement in oxygenation and respiratory mechanics. Furthermore, experimental data suggest that RMs may play an important role in preventing ventilator-associated lung injury. Clinical studies have yielded conflicting results, with some demonstrating a transient improvement in oxygenation following RMs, which has not translated into a significant survival advantage. Thus, despite a strong pathophysiological rationale, there is little evidence to support their routine use in unselected ALI populations. While serious complications may be uncommon, it is essential to monitor for barotrauma and hypotension. Further clinical trials are needed to confirm the safety and efficacy of RMs in ALI patients with recruitable disease, as well as to elucidate the optimal type, timing and frequency of RMs in these patients.

  7. Page 54
    Abstract
    Correspondence: J. Kesecioglu, Dept of Intensive Care, Room F06.149, University Medical Center Utrecht, Heidelberlaan 100, 3584 CX, Utrecht, The Netherlands. E-mail: J.Keseciolgu@umcutrecht.nl

    Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) occur after diverse pulmonary or systemic insults. Although necessary for keeping the patient alive, mechanical ventilation has been implicated in the associated high morbidity and mortality. New therapies have attempted to improve oxygenation and ventilation, while providing lung protection. A multitude of causes can lead to ALI/ARDS. However, the dysfunction of the endogenous surfactant system is a shared characteristic. It has been suggested to use surfactant replacement therapy in patients with ARDS in order to overcome the ongoing inactivation of endogenous surfactants by plasma proteins entering the alveolar spaces. The evidence regarding surfactant replacement therapy in ARDS patients is discussed in this chapter.

    Although some small studies have shown beneficial effects of surfactant replacement therapy, larger studies failed to establish this effect. Therefore, exogenous surfactants are not recommended for routine use in patients with ALI/ARDS.

  8. Page 65
    Abstract
    Correspondence: L. Brochard, Hopitaux Universitaires de Genève, Rue Gabrielle-Perret-Gentil 4, 1211 Geneva 14, Switzerland. Email Laurent.brochard@hcuge.ch

    Physiological studies have clearly established the effectiveness of noninvasive ventilation (NIV) in patients with hypoxaemic acute respiratory failure (ARF). Patient selection is nevertheless crucial and the risk–benefit ratio should be carefully evaluated for each potential patient. It is essential to consider the use of NIV separately, based on the different aetiologies of hypoxaemic ARF, because the results vary accordingly. Use of NIV in the post-operative period emerges as an important indication that requires further studies. It is critical that NIV does not delay a necessary endotracheal intubation as this has been linked to the worst clinical outcomes. A practical approach for using NIV in hypoxaemic ARF patients will be proposed in this chapter.

  9. Page 81
    Abstract
    Correspondence: M. Gama de Abreu, Dept of Anesthesiology and Intensive Care Therapy, University Hospital Carl Gustav Carus, Dresden University of Technology, Fetscherstr. 74, 01307 Dresden, Germany. Email mgabreu@uniklinikum-dresden.de

    Biphasic positive airway pressure (BIPAP)/airway pressure release ventilation (APRV) is a mechanical ventilation mode based on a high flow or demand-valve continuous positive airway pressure (CPAP) system, in which the level of CPAP is switched between a higher and a lower pressure in a time-dependent manner, generating time-cycled, pressure-limited ventilation. Supported and unsupported spontaneous breathing is possible at both levels of airway pressure, but the optimal level of spontaneous breathing has yet to be determined. BIPAP/APRV has proved efficient in increasing oxygenation compared with controlled mechanical ventilation in acute respiratory distress syndrome (ARDS). In addition, BIPAP/APRV with spontaneous breathing waives the need for muscle paralysis, and allows reduced sedation, as well as cardiovascular support with drugs. BIPAP/APRV with spontaneous breathing seems to be a useful ventilatory strategy for patients with less severe hypoxaemic respiratory failure, but caution is required in those patients with more severe lung injury, as reflected by an arterial oxygen tension(Pa,O2)/inspiratory oxygen fraction (FI,O2) of <120 mmHg.

  10. Page 97
    Abstract
    Correspondence: D. Georgopoulos, Intensive Care Unit, University Hospital of Heraklion, Heraklion, 71110, Greece. Email georgop@med.uoc.gr

    Proportional assist ventilation (PAV) is a new mode of partially assisted mechanical ventilation, born from the growing demand for improvements in existing modes with respect to patient–ventilator interaction and physician facility. It differs radically in comparison with conventional modes (pressure support ventilation or assisted-controlled ventilation) in the way that, after triggering, mechanical support follows patient effort both in terms of timing and magnitude. Patient effort is represented by muscle pressure estimated by the equation of motion after measurement of elastance and resistance. Recently, with PAV+ (an updated version of PAV), these measurements are performed noninvasively and semi-continuously from the ventilator, eliminating errors and liberating the physician from extra workload. Studies performed with PAV+ have revealed that, compared with conventional modes, its application is simple and time saving, while it may more effectively reduce patient–ventilator dyssynchrony, facilitate weaning and improve sleep quality in critically ill adults. It can also be used as an alternative mode of noninvasive mechanical ventilation. However, further improvements are still needed in the field of triggering, especially in patients with flow limitation, since the presence of dynamic hyperinflation may counterbalance the advantages of PAV+. Meanwhile, following well-designed algorithms and bearing in mind specific limitations, PAV+ could be a valuable tool in the hands of experienced physicians.

  11. Page 116
    Abstract
    Correspondence: P. Navalesi, Dipartimento di Medicina Traslazionale, Università del Piemonte Orientale “A. Avogadro”, Via Solaroli 17, 28100 Novara, Italy. Email paolo.navalesi@med.unipmn.it

    Neurally adjusted ventilatory assist (NAVA) is a form of ventilator support in which the electrical activity of the diaphragm (EAdi) drives the ventilator. The signal, obtained from the crural portion of the diaphragm via a nasogastric or orogastric feeding tube, is transformed into a waveform that is utilised to regulate the inspiratory assistance. The ventilator applies pressure to the airway throughout inspiration in proportion to EAdi, which is multiplied by an adjustable gain constant (NAVA level). With NAVA, both the timing and the magnitude of ventilator delivered assistance are controlled by the EAdi. In contrast with the conventional pneumatically-driven modes, NAVA has been shown to improve patient–ventilator interaction and yield a remarkable reduction in any asynchronies. Furthermore, with NAVA the patient retains control of her/his breathing pattern, which is more variable in nature; this variability might determine improved oxygenation in patients with acute lung–volume reduction. Because tidal volume is not remarkably increased when augmenting the NAVA level, this novel mode has the potential to maintain protective ventilation in spontaneously breathing patients.

  12. Page 124
    Abstract
    Correspondence: S. Jaber, Intensive Care Unit, Anaesthesia and Critical Care Department B, University Montpellier 1; 80 avenue Augustin Fliche, 34295 Montpellier, Cedex 5, France. Email s-jaber@chu-montpellier.fr

    First described in the 1930s', there is a good theoretical rationale for using helium as an adjuvant treatment in the respiratory care of patients with severe airway obstruction. Pure helium has been replaced in clinical practice by “helium–oxygen” mixtures that are safer to use. Helium has no pharmacological effect. The physical properties of this light, single-element gas allow mechanical and physiological effects on the respiratory system that can be used in asthma and chronic obstructive pulmonary disease patients. Helium–oxygen can be used in different conditions (e.g. spontaneous ventilation, noninvasive ventilation (NIV) or mechanical ventilation) and with different aims (to increase drug delivery in bronchodilator aerosols, to decrease work of breathing, and to decrease ventilation pressures and air trapping during mechanical ventilation). The clinical success of helium treatment probably depends on technical conditions and devices. In the absence of adapted medical devices it is often used only as a last resort in critical patients. With more information, adapted equipment and experienced intensive care unit teams, more patients could potentially benefit from this very old therapeutic gas.

  13. Page 133
    Abstract
    Correspondence: A. Pesenti, University of Milan-Bicocca, Via Cadore 48, Monza, Italy. Email antonio.pesenti@unimib.it

    For the last three decades, extracorporeal lung assist (ECLA) has been employed as a life-saving therapy in few highly-specialised centres. A deeper understanding of acute respiratory distress syndrome (ARDS) pathophysiology, improved technology and the positive results of recent trials have led to a reassessment of ECLA in the clinical setting. The referral and transfer of sicker patients to specialised extracorporeal membrane oxygenation (ECMO) centres has been shown to improve clinical outcome. The CESAR (conventional ventilator support versus extracorporeal membrane oxygenation for severe adult respiratory failure) trial was the first positive randomised controlled trial to investigate ECMO use in adult patients with ARDS. In 2009, many healthcare systems worldwide successfully faced the influenza A (H1N1) pandemic, instituting networks of specialised intensive care units (ICUs), for transfer of the sickest patients and management with ECMO. There is also an increasing interest in new and less invasive extracorporeal techniques, primarily aimed at carbon dioxide removal, which may be more widely applied in combination with a strictly protective ventilatory strategy.

  14. Page 142
    Abstract
    Correspondence: V.M. Ranieri, Dept of Anesthesia and Intensive Care Medicine, University of Turin, S. Giovanni Battista Molinette Hospital, Corso Dogliotti 14, 10126 Turin, Italy. Email marco.ranieri@unito.it

    Acute respiratory distress syndrome with 30–50% mortality affects approximately 150,000 patients per year and together with chronic obstructive pulmonary disease causes one in every seven deaths in the USA. Conventional mechanical ventilatory assistance, although a life-saving procedure, is itself injurious causing ventilator-induced lung injury.

    The use of lung protective strategies poses challenges for patient management, motivating research for improved lung support approaches. A possible valuable strategy consists of letting the lungs rest by means of apnoeic oxygenation diffusion and extracorporeal carbon dioxide elimination.

    Starting from the first approaches with oxygenators or haemodialysis to the current new and improved technologies and experiences, the use of extracorporeal gas exchange has become the key management strategy for respiratory failure, making clinicians rethink the treatment algorithm of all severe respiratory failure.

  15. Page 153
    Abstract
    Correspondence: A. Torres, Servei de Pneumologia i Al·lèrgia Respiratòria, Hospital Clínic, Calle Villarroel 170, Esc 6/8 Planta 2, 08036 Barcelona, Spain. Email atorres@clinic.ub.es

    Ventilator associated pneumonia (VAP) is associated with increased morbidity, mortality and burden for the healthcare system. Oropharyngeal secretions, pooled above the endotracheal tube (ETT) cuff, are the primary source of pathogens in this iatrogenic infection. Improvements in the ETT cuff design to achieve tracheal sealing and maintaining the internal cuff pressure within the recommended range (25–30 cmH2O) have a pivotal role in the prevention of pulmonary aspiration of colonised oropharyngeal secretions and VAP. Additionally, ETTs coated with antimicrobial agents prevent colonisation of their internal lumen and biofilm formation; however, further evidence is necessary to assess the role of biofilm in the pathogenesis of VAP. The semirecumbent position is universally recommended; yet, laboratory studies challenge the benefits of such a position. Finally, during positive pressure ventilation, the ventilatory parameters that influence the inspiratory flow, i.e. the duty cycle, have a significant effect on retention of mucus and, potentially, on risks of lung infections. Further clinical evidence is necessary to assess benefits and limitations of ventilatory settings on VAP prevention.

  16. Page 169
    Abstract
    Correspondence: F. Laghi, Loyola University of Chicago Stritch School of Medicine, Division of Pulmonary and Critical Care Medicine, Edward Hines, Jr. VA Hospital, 111N, 5th Avenue and Roosevelt Road, Hines, 60141, IL, USA. Email flaghi@lumc.edu

    The dangers of mechanical ventilation make it critical to wean patients at the earliest time possible. However, premature weaning trials trigger significant respiratory distress, which can cause setbacks in a patient's clinical course. Premature extubation is also a known risk. To reduce delayed weaning and premature extubation, a three-step diagnostic strategy has been suggested: 1) measurement of weaning predictors; 2) a trial of unassisted breathing (T-tube trial); and 3) a trial of extubation.

    It is imperative not to defer this first step by waiting for a more difficult diagnostic test, such as a T-tube trial. To increase the likelihood that a patient will tolerate extubation, a positive result on a screening test (weaning predictor test) is followed by a confirmatory test (weaning trial).

    Many difficult aspects of pulmonary pathophysiology encroach on weaning management. Accordingly, weaning commands sophisticated individualised care. Few other responsibilities of an intensivist require a more analytical effort and carry more promise for improving a patient’s outcome than the application of physiological principles in the weaning of patients.

  17. Page 191
    Abstract
    Correspondence: M. Ferrer, Servei de Pneumologia, Hospital Clinic, Villarroel 170, 08036 Barcelona, Spain. Email miferrer@clinic.ub.es

    Patients with chronic airflow obstruction and difficult or prolonged weaning are at increased risk for prolonged invasive mechanical ventilation. Several randomised controlled trials, mainly conducted in patients who had pre-existing lung disease, have shown that the use of noninvasive ventilation (NIV) in order to advance extubation in patients with difficult and prolonged weaning can result in reduced periods of endotracheal intubation, complication rates and improved survival. Patients in these studies were haemodynamically stable, with a normal level of consciousness, no fever and a preserved cough reflex. The use of NIV in the management of mixed populations with respiratory failure after extubation, including small proportions of chronic respiratory patients, did not show clinical benefits. By contrast, NIV immediately after extubation is effective in avoiding respiratory failure following extubation and improving survival in patients at risk for this complication, particularly those with chronic respiratory disorders, cardiac co-morbidity and hypercapnic respiratory failure. Finally, both continuous positive airway pressure and NIV can improve clinical outcomes in patients with post-operative acute respiratory failure, particularly abdominal and thoracic surgery.

  18. Page 206
    Abstract
    Correspondence: P. Terragni, Dept of Anesthesia and Intensive Care Medicine, University of Turin, S. Giovanni Battista Molinette Hospital, Corso Dogliotti 14, 10126 Turin, Italy. Email pierpaolo.terragni@unito.it

    Endotracheal intubation is commonly used for airway control, while tracheostomy is a procedure indicated for patients who suffer from respiratory failure and need prolonged mechanical ventilation. Between 6% and 11% of mechanically ventilated patients receive a tracheostomy that allows for a lower sedation and shorter weaning time leading to a reduction in intensive care unit (ICU) and hospital stay. The technique and timing of tracheostomy are still controversial in the literature. Percutaneous dilational tracheostomy techniques, performed at the bedside in the ICU, are widely used, but there are still patients (with severe coagulation disorders or cervical spine injury) who can benefit from the surgical “minimally invasive” techniques. The correct timing is also under debate but, excluding patients with severe brain or cervical spine injury, we can reasonably affirm that tracheostomy should not be performed earlier than 2 weeks following respiratory failure.

  19. Page 217
    Abstract
    Correspondence: F. Lellouche, Centre de Recherche de l'Institut Universitaire de Cardiologie et de Pneumologie de Québec, 2725, chemin Sainte-Foy, G1V4G5, Québec, QC, Canada. Email francois.lellouche@criucpq.ulaval.ca

    Automated mechanical ventilation using advanced closed loops is anticipated to assume a larger role in supporting critically ill patients in intensive care units (ICU) in the future, for several reasons. They have the potential to improve knowledge transfer by continuously implementing automated protocols while improving patient outcomes. Additionally, closed-loop systems may provide a partial solution to address forecasted clinician shortages by reducing ICU-related costs, time spent on mechanical ventilation, and staff workload. At present, few systems that automate medical reasoning with advanced closed loops are commercially available. Preliminary studies evaluating first generation automated weaning systems and fully automated ventilation are promising. These closed-loop programmes will be refined as the technology improves and clinical experience with these products increases.

  20. Page 229
    Abstract
    Correspondence: T. Strøm, Dept of Anaesthesia and Intensive Care Medicine, Odense University Hospital, Sdr Boulevard 29, 5000 Odense, Denmark. Email t.s@dadlnet.dk

    Routine use of sedation of critically ill patients is not without adverse effects. Evidence shows that the use of protocols and scoring systems for sedatives and daily interruption of sedatives can reduce the duration of mechanical ventilation. A strategy of no sedation is also possible and reduces both time spent on mechanical ventilation and in the intensive care unit, as well as the total length of hospital stay. Less sedation seems not to increase the risk of post-traumatic stress after intensive care. Also evidence shows that less sedation lowers the risk of complications during the intensive care stay. In addition, some evidence shows that organ failure might be less pronounced with the use of no sedation.