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Core Topics in Mechanical Ventilation
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Book description

Mechanical ventilation is a life-critical intervention provided to patients in a wide variety of clinical settings, involving the careful interplay of physiology, pathology, physics and technology. This unique text explains the underlying physiological and technical concepts of ventilation, aided by numerous full colour diagrams, and places these concepts into clinical context with practical examples. Core Topics in Mechanical Ventilation provides a broad and in-depth coverage of key topics encountered in clinical practice, from the initial assessment of the patient to transportation of the ventilated patient and weaning from ventilation. Issues such as sedation, analgesia and paralysis and the management of complications are reviewed, along with a discussion of various ventilation modes and practical advice on patients with pre-existing diseases. Appealing to doctors, nurses, physiotherapists and paramedics, this book is applicable to a wide range of settings including intensive care, anaesthesia, respiratory medicine, acute medicine and emergency medicine.

Reviews

'… the book is well laid-out, with frequent colour diagrams, tables and photographs. Chapters are concise and clinically relevant … comprehensive but less 'wordy' than many traditional reference books and can be recommended for its target audience.'

Source: Anaesthesia

'This text makes a commendable effort in the initiation of the theory and practice of mechanical ventilation, and is a worthy member of the growing number of works on this subject which is integral to intensive care medicine, as well as anaesthesia. It would be a worthwhile text for trainees and it certainly would make a welcome addition to a departmental library.'

Source: Anaesthesia and Intensive Care

'… practical but concise A major strength of this book is the extensive use of visual aid and thoughtfully constructed illustrations, which maximizes the reader's ability to rapidly assimilate the information being presented … recommended reading for any individual in training or clinical practice who needs more than a superficial overview on the subject of mechanical ventilation … concise, well-written, practical … an extremely valuable addition to the library of physicians involved in the practice of anaesthesia and critical care medicine. Editor Iain Mackenzie and his collaborators have laudably achieved their stated goal in organizing this unique new book.'

Source: www.anesthesia-analgesia.org

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Contents

  • 1 - Physiology of ventilation and gas exchange
    pp 1-20
  • View abstract

    Summary

    Among its many functions, the lung has two major ones: it must harvest oxygen to fuel aerobic respiration and it must vent acid-forming carbon dioxide. This chapter offers a brief overview of how the lung fulfills these functions. It also discusses some of the mechanisms through which adequate oxygenation can fail. A secure understanding of these principles allows an insight into the way in which mechanical ventilation strategies can be altered in order to enhance oxygenation and carbon dioxide clearance. Lung compliance represents the 'distensibility' of the lung and alters in disease. Homogeneous and matching ventilation and perfusion of all lung units would offer perfect gas exchange. There is a heterogeneity of ventilation/perfusion matching in normal lungs, and this may worsen in disease. The chapter also talks about diffusion and partial pressure, calculation of total dead space and estimation of total shunt.
  • 2 - Assessing the need for ventilatory support
    pp 21-31
  • View abstract

    Summary

    This chapter focuses on assessing the need for ventilatory support in seriously ill patients in acute wards, emergency departments and critical care units. The need for ventilatory support is probably the commonest reason for patients requiring admission to critical care units, and the provision of mechanical ventilation has major resource implications. Patients requiring ventilatory support fall into two broad categories. First, there are those with established or impending respiratory failure. Second, there are those who need support for reasons not directly related to the respiratory system. The chapter summarizes the aims of ventilatory support, and concentrates on those aspects of the clinical assessment which identify actual or impending respiratory muscle fatigue or weakness and which assess the adequacy of ventilation and gas exchange. In general, when assessing the need for ventilatory support, clinical symptoms and signs are more useful than arterial blood gases or other physiological measurements.
  • 3 - Oxygen therapy, continuous positive airway pressure and non-invasive ventilation
    pp 32-53
  • View abstract

    Summary

    Non-invasive ventilation (NIV) is a standard of care for some patient groups with acute respiratory failure and a number of national and international bodies have produced guidelines. Novel uses of NIV continue to be explored, although not all trials have demonstrated successful outcomes when compared with traditional alternatives. Research in the field continues at a pace with recent reports including possible use in severe acute respiratory syndrome (SARS) and motor neuron disease. This chapter presents in three parts an overview of three related fields. The first part discusses the issues of oxygen therapy both alone and in conjunction with non-invasive support. The second part surveys the use and role of continuous positive airway pressure (CPAP), which remains a valuable alternative to ventilation. The final part focuses on NIV and includes a summary of the available evidence base, and covers some of the more practical issues of machine and patient interfaces.
  • 4 - Management of the artificial airway
    pp 54-87
  • View abstract

    Summary

    A supraglottic airway is an airway that does not pass across the vocal cords, such as an oropharyngeal airway or a laryngeal mask. Intubation of the trachea with a cuffed tube is the only way to simultaneously provide a secure airway, repeated access to the trachea and ventilatory support. Unfortunately, the placement of an artificial airway, be it a supraglottic airway or an endotracheal or tracheostomy tube, bypasses many of the patient's natural defences and thus increases the risk of upper and lower airway colonization, aspiration and infection. For anything other than immediate life support, however, the airway needs to be secured with a cuffed endotracheal tube, or in some circumstances, a tracheostomy endotracheal intubation in the critically ill patient carries challenges over and above those encountered during routine anaesthesia airway management because of a number of additional complicating factors. A primary goal of airway management is oxygenation.
  • 5 - Modes of mechanical ventilation
    pp 88-114
  • View abstract

    Summary

    Mechanical substitution of the natural act of breathing could never hope to match what nature has achieved, but within the intensive care ventilator we do have at our disposal a range of breath types that are characterized by properties that fall into two principle domains, those of cycling and inspiratory motive force. The cycling properties of a breath describe what makes the breath start, what makes the breath end and describes the relationship the breath has with other breaths. The inspiratory motive force simply refers to the mechanism the ventilator uses to drive gas into the lungs. Ventilator manufacturers bring together one or more breath types, programme the rules by which the constituent breaths interact and thereby define a particular mode of mechanical ventilation. Broadly speaking, modes fall into four categories: mandatory, triggered, spontaneous and hybrid modes.
  • 6 - Oxygenation
    pp 115-141
  • View abstract

    Summary

    Oxygenation is one of the primary gas exchange functions of the lung. This chapter reviews how to assess the adequacy of oxygen uptake and, in the context of the mechanisms of arterial hypoxaemia, examines how this can be improved in the mechanically ventilated patient. The oxygenation assessment has two facets, one pulmonary, and one extra-pulmonary. Oxygen moves from the alveolar gas to the pulmonary capillary blood by diffusion. Currently in the UK, as with high-frequency oscillatory ventilation (HFOV), airway pressure release ventilation (APRV) is typically used as a rescue technique for those failing to achieve adequate oxygenation with conventional ventilation. The diffusion coefficient for a gas is proportional to the gas's solubility in the medium through which the gas has to diffuse, and is inversely proportional to the square root of the gas's relative molecular mass. Imbalance between pulmonary ventilation and pulmonary perfusion is the most common cause of hypoxaemia.
  • 7 - Carbon dioxide balance
    pp 142-159
  • View abstract

    Summary

    Carbon dioxide is excreted by the lungs. Carbon dioxide production is based on metabolic rate and the substrates that are being utilized to drive the Kreb's cycle. Factors that influence pulmonary elimination of carbon dioxide include the volume of dead space, tidal volume, respiratory frequency and positive end-expiratory pressure (PEEP). The balance between arterial and venous carbon dioxide is based upon cardiac output. Hypocapnia can be controlled relatively through adjustment of ventilator settings to reduce minute ventilation in the sedated patient. The effects of hypercapnia and the associated acidaemia may be mitigated through the use of buffering agents. Traditionally, extracorporeal gas exchange (ECGE) has been utilized in patients only as a rescue therapy. In practice, clinicians adopt a technique somewhere between optimal carbon dioxide clearance and more liberal clearance targets, based on assessment of the severity of lung disease and the risks and benefits of ventilatory manipulations or associated interventions.
  • 8 - Sedation, paralysis and analgesia
    pp 160-183
  • View abstract

    Summary

    The benefits of therapeutic interventions among critically ill, mechanically ventilated, intensive care unit (ICU) patients must outweigh the risk of adverse consequences. New agents to ensure adequate sedation, paralysis and analgesia of ICU patients are being investigated. Unfortunately, the additive or synergistic effect of multiple sedatives applies not only to therapeutic benefit but also to adverse effects. Occasionally, though perhaps less frequently than necessary, attention has been paid to adequate sedation, analgesia and paralysis. This chapter includes a discussion of sedation, analgesia and paralysis for mechanically ventilated, adult ICU patients, and highlights the central role of analgesia. Each of these three topics is formatted as follows: overview and general discussion, monitoring and medications used (including mechanism of action, adverse effects and common adverse effects for each). Also, due to the likely aetiologic connection, the related topic of delirium is included.
  • 9 - Nutrition in the mechanically ventilated patient
    pp 184-195
  • View abstract

    Summary

    Respiratory failure and the need for mechanical ventilation brought about by a variety of medical, surgical and traumatic events makes the optimum nutritional requirements of this group of patients difficult to determine. Nonetheless, support is an important adjunct to the management of patients in the intensive care unit, and mechanically ventilated patients being especially vulnerable to complications of under- or over-feeding. This chapter considers the nutritional requirements, route and timing of nutritional support, and complications associated with feeding mechanically ventilated, critically ill patients. Compared with conventional insulin therapy, intensive insulin therapy was associated with improvements in renal function, duration of mechanical ventilation and discharge from intensive care unit (ICU) and from the hospital. Despite the lack of definitive trials demonstrating clinically meaningful benefit from nutritional support, there is strong evidence that malnutrition is associated with a worse outcome. In addition, under-feeding and over-feeding have had undesirable consequences.
  • 10 - Mechanical ventilation in asthma and chronic obstructive pulmonary disease
    pp 196-209
  • View abstract

    Summary

    Mechanical ventilation of the patient with severe asthma or chronic obstructive pulmonary disease (COPD) has unique problems not routinely encountered in the more common critically ill patient without significant airflow obstruction. These problems can lead to ventilator induced morbidity and mortality if not recognized or managed appropriately. In both asthma and COPD, full active management with bronchodilators and adjunctive therapies should be undertaken to avoid or minimize the need for ventilatory assistance. Non-invasive ventilation (NIV) has a well-established role in COPD and is now used more frequently than invasive mechanical ventilation. Regular follow-up should include regular spirometry, a plan for the management of deterioration and the institution of prevention strategies. Prevention, early active medical therapy and NIV remain the best ways to manage severe airflow obstruction. If mechanical ventilation is required, care should be taken to assess and minimize excessive dynamic hyperinflation, its complications, myopathy and lactic acidosis.
  • 11 - Mechanical ventilation in patients with blast, burn and chest trauma injuries
    pp 210-221
  • View abstract

    Summary

    The recent increase in terrorist bomb attacks on urban civilian targets in Europe and the USA has emphasized the need for all relevant health provision team members to become familiar with the pathophysiology and treatment of the resulting injuries. This chapter focuses on blast injuries, considers recent advances in ventilation strategies for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), and describes how this has been applied in the treatment of the severe blast injuries patient. Smoke, hot gas, or chemical inhalation injury are the most common cause of acute deterioration in lung function in burn injury patients and should always be suspected. Pulmonary contusion is a common lesion occurring in patients sustaining severe blunt chest trauma. The diagnosis of traumatic lung injury is usually made clinically with confirmation by chest radiography. Blunt thoracic trauma can result in significant morbidity in injured patients.
  • 12 - Ventilatory support: extreme solutions
    pp 222-229
  • View abstract

    Summary

    One of the extreme solutions for the management of ventilatory failure is to replace the lungs altogether, either by transplantation or by the use of machines. Once the transplant has been completed, the means used to support the new lungs are little different from those used for any other patient. In the context of severe respiratory failure, other solutions are therefore necessary to provide ventilatory support, either as a bridge to recovery or transplantation, or as long-term support in an increasingly elderly Western population. These solutions are based on various mechanical means that take over some of the lung functions. This chapter reviews some of the key clinical questions concerning the ventilation of the lung transplant recipient and mechanical support of the failing lung. Starting at the time of transplantation, pharmacological immunosuppression has to be continuously adjusted to balance the risks of infection or rejection.
  • 13 - Heliox in airway obstruction and mechanical ventilation
    pp 230-238
  • View abstract

    Summary

    Heliox, a mixture of helium and oxygen, was used by Barach in New York for the first time in the treatment of asthma and upper airway obstruction after its introduction to deep sea diving. Since then it has been used not only as a rescue medication in emergency situations for spontaneously breathing patients with airway obstruction but also as the driving gas for mechanical ventilators. The increasing interest in heliox is indicated by the rising number of publications in recent years. This chapter outlines the theoretical considerations, the application of heliox in non-intubated (e.g. with upper and lower airway obstruction) as well as in ventilated patients followed by a brief overview of potential risks and cost considerations. Future developments focus on ways to routinely apply heliox during mechanical ventilation, for example, as a commercially available add-on feature to conventional ventilators.
  • 14 - Adverse effects and complications of mechanical ventilation
    pp 239-283
  • View abstract

    Summary

    The adverse effects and complications of mechanical ventilation may arise from the artificial airway or from positive pressure ventilation and the drugs required to facilitate this. The occurrence of complications cannot be completely eliminated, but an appropriately managed intensive care unit will monitor the occurrence of complications and use this information to look for trends, to learn from the lessons that each complication can teach and as a quality assessment and quality assurance tool. Airway management and intubation in the operating department are performed under ideal circumstances with anaesthetists working in familiar, well-equipped surroundings supported by competent assistants on patients who, in the vast majority of cases, have been assessed and prepared for the procedure. Ventilator-induced diaphragmatic damage (VIDD) may contribute to the many factors causing failure to wean in patients undergoing mechanical ventilation. This chapter also talks about neurological function.
  • 15 - Mechanical ventilation for transport
    pp 284-295
  • View abstract

    Summary

    The number of transfers of critically ill patients within and between hospitals has been continuously increasing throughout the entire evolution of intensive care medicine. Even the transport of patients between two departments in one hospital can be hazardous. Arguably, the highest risk is that of ensuring a patent airway and adequate ventilation. This chapter discusses the process of transferring ventilated patients, and examines portable ventilators in some detail. The standard of patient monitoring during the transfer is essentially the same as that prior to transfer, although in some cases it may actually require increasing the monitoring. In essence, transport ventilators can be divided into two basic groups. The first group is pneumatically driven ventilators that require high-pressure oxygen to drive the ventilator. The second group of ventilators generates tidal volume with electrically powered internal compressors. The chapter also presents a discussion on difficult transfer and transport scenarios.
  • 16 - Special considerations in infants and children
    pp 296-309
  • View abstract

    Summary

    This chapter outlines the major differences that need to be considered when faced with neonates and children who require mechanical ventilation. It provides the anatomy, physiology and some particular examples of paediatric care. High frequency oscillatory ventilation (HFOV) is well established in neonatal practice having been in use for over two decades. Following a head injury, children may require intubation or ventilation for several different reasons. Humidification is the most important technical aspect of ventilation in children that may vary from adult practice. Staff involved in the ventilation of children needs to be aware of child protection issues. Recognition of features that may be seen in non-accidental injury such as a torn frenulum or other mouth trauma, and unusual bruises should give rise to discussion about possible causes. Equally, any injuries caused during line insertion or intubation should be carefully documented so that an appropriate explanation is clearly stated.
  • 17 - Tracheostomy
    pp 310-330
  • View abstract

    Summary

    Nowadays, most patients tolerate short-term trans-laryngeal tracheal intubation with few, if any, complications. For those who require more prolonged intubation, a tracheostomy may provide a number of advantages. This chapter outlines indications, timing, complications and techniques of tracheostomy. Complications of tracheostomy can be classified into perioperative, early and late, with both the type and incidence of specific complications differing between surgical and percutaneous techniques. In some centres routine tracheostomy for ventilator-dependent patients is viewed as an ideal training opportunity, increasing both the duration of the procedure and the risk of surgical misadventure. Ultrasound imaging of the neck prior to tracheostomy allows the anatomy of the anterior neck structures to be identified, particularly the location of blood vessels and the depth and angulation of the trachea. This information may contribute to the risk to benefit analysis between surgical and percutaneous tracheostomy. The chapter also discusses the role of cricothyroidotomy or mini-tracheostomy.
  • 18 - Weaning, extubation and de-cannulation
    pp 331-371
  • View abstract

    Summary

    The process of withdrawing mechanical ventilation is commonly referred to as 'weaning', but in the literature the term has acquired two distinct meanings, having been described as either (1) the process of gradually decreasing ventilatory support to return the work of breathing back to the patient or (2) a means of determining when patients have the ability to be safely liberated from the ventilator. In this chapter the term 'weaning' refers to the process of returning the work of breathing back to the patient. Determining readiness for extubation or de-cannulation is dealt with as a separate issue. Un-assisted spontaneous ventilation has two indispensable requisites: firstly, the ability to initiate rhythmic inspiratory effort, and secondly the muscular strength and stamina to maintain tidal ventilation. The establishment of a spontaneous respiratory rhythm is challenged in three ways: primary post-ventilation apnoea, failure to sustain an acceptable minute ventilation, and repeated periods of apnoea.
  • 19 - Long-term ventilatory support
    pp 372-387
  • View abstract

    Summary

    The polio outbreaks that affected the developed world in the early and mid-twentieth century are of particular historical importance. They acted as an impetus to the development of intensive care as a place where 'life support' could be provided while awaiting recovery from critical illness. Second, as survival in those who developed respiratory failure occurred, particularly following the introduction of positive pressure ventilation, significant numbers then required long-term respiratory support. The evidence for the effectiveness of non-invasive positive pressure ventilation (NIV) has been better investigated in the progressive neuromuscular (NM) diseases and in complicating chronic obstructive pulmonary disease (COPD). It was quickly appreciated that the home mechanical ventilation (HMV) patient using physical or negative pressure devices could benefit from the new technology. There are numerous advantages of NIV compared with invasive ventilation. The initial reason for introducing NIV is symptom control.
  • 20 - The history of mechanical ventilation
    pp 388-403
  • View abstract

    Summary

    The early attempts at mechanical ventilation were brought to an end in the 1830s by Leroy's studies in France in which he showed in animals and cadavers that overenthusiastic inflation, especially if exhalation was neglected in favour of inflation, resulted in serious lung damage or death. Until the introduction of the intravenous anaesthetic agent thiopentone in 1934, both anaesthesia and survival depended on spontaneous ventilation and a clear airway. During an epidemic of poliomyelitis in Stockholm in 1949 and 1950, Carl-Gunnar Engstrӧm, observed a series of patients with respiratory failure treated with tracheostomy and negative-pressure ventilation (NPV). The first major evolutionary step of the purely pneumatic and mechanical ventilators of the 1950s and 1960s came with release of Puritan-Bennet's MA1 in 1967, which controlled the mechanical gas delivery using electronics.

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