- Section 1 ICU organization and management
- Section 2 Pharmacotherapeutics
- Section 3 Resuscitation
- Section 4 The respiratory system
- Part 4.1 Physiology
- Part 4.2 Respiratory monitoring
- Part 4.3 Upper airway obstruction
- Part 4.4 Airway access
- Part 4.5 Acute respiratory failure
- Part 4.6 Ventilatory support
- Chapter 88 Physiology of positive-pressure ventilation
- Chapter 89 Respiratory support with continuous positive airways pressure
- Chapter 90 Non-invasive positive-pressure ventilation
- Chapter 91 Indications for mechanical ventilation
- Chapter 92 Design and function of mechanical ventilators
- Chapter 93 Setting rate, volume, and time in ventilatory support
- Chapter 94 Respiratory support with positive end-expiratory pressure
- Chapter 95 Volume-controlled mechanical ventilation
- Chapter 96 Pressure-controlled mechanical ventilation
- Chapter 97 Pressure support ventilation
- Chapter 98 High-frequency ventilation and oscillation
- Chapter 99 Prone positioning in the ICU
- Chapter 100 Failure to ventilate in critical illness
- Chapter 101 Ventilator trauma in the critically ill
- Part 4.7 Weaning ventilatory support
- Part 4.8 Extracorporeal support
- Part 4.9 Aspiration and inhalation
- Part 4.10 Acute respiratory distress syndrome
- Part 4.11 Airflow limitation
- Part 4.12 Respiratory acidosis and alkalosis
- Part 4.13 Pneumonia
- Part 4.14 Atelectasis and sputum retention
- Part 4.15 Pleural cavity problems
- Part 4.16 Haemoptysis
- Section 5 The cardiovascular system
- Section 6 The gastrointestinal system
- Section 7 Nutrition
- Section 8 The renal system
- Section 9 The neurological system
- Section 10 The metabolic and endocrine systems
- Section 11 The haematological system
- Section 12 The skin and connective tissue
- Section 13 Infection
- Section 14 Inflammation
- Section 15 Poisoning
- Section 16 Trauma
- Section 17 Physical disorders
- Section 18 Pain and sedation
- Section 19 General surgical and obstetric intensive care
- Section 20 Specialized intensive care
- Section 21 Recovery from critical illness
- Section 22 End-of-life care
(p. 403) Ventilatory support
During positive pressure ventilation the lung volume is reduced because of loss of respiratory muscle tone. This promotes airway closure that occurs in dependent lung regions. Gas absorption behind the closed airway results sooner or later in atelectasis depending on the inspired oxygen concentration. The elevated airway and alveolar pressures squeeze blood flow down the lung so that a ventilation/perfusion mismatch ensues with more ventilation going to the upper lung regions and more perfusion going to the lower, dependent lung. Positive pressure ventilation may impede the return of venous blood to the thorax and right heart. This raises venous pressure, causing an increase in systemic capillary pressure with increased capillary leakage and possible oedema formation in peripheral organs. Steps that can be taken to counter the negative effects of mechanical ventilation include an increase in lung volume by recruitment of collapsed lung and an appropriate positive end-expiratory pressure, to keep aerated lung open and to prevent cyclic airway closure. Maintaining normo- or hypervolaemia to make the pulmonary circulation less vulnerable to increased airway and alveolar pressures, and preserving or mimicking spontaneous breaths, in addition to the mechanical breaths, since they may improve matching of ventilation and blood flow, may increase venous return and decrease systemic organ oedema formation (however, risk of respiratory muscle fatigue, and even overexpansion of lung if uncontrolled).
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- Section 1 ICU organization and management
- Section 2 Pharmacotherapeutics
- Section 3 Resuscitation
- Section 4 The respiratory system
- Part 4.1 Physiology
- Part 4.2 Respiratory monitoring
- Part 4.3 Upper airway obstruction
- Part 4.4 Airway access
- Part 4.5 Acute respiratory failure
- Part 4.6 Ventilatory support
- Chapter 88 Physiology of positive-pressure ventilation
- Chapter 89 Respiratory support with continuous positive airways pressure
- Chapter 90 Non-invasive positive-pressure ventilation
- Chapter 91 Indications for mechanical ventilation
- Chapter 92 Design and function of mechanical ventilators
- Chapter 93 Setting rate, volume, and time in ventilatory support
- Chapter 94 Respiratory support with positive end-expiratory pressure
- Chapter 95 Volume-controlled mechanical ventilation
- Chapter 96 Pressure-controlled mechanical ventilation
- Chapter 97 Pressure support ventilation
- Chapter 98 High-frequency ventilation and oscillation
- Chapter 99 Prone positioning in the ICU
- Chapter 100 Failure to ventilate in critical illness
- Chapter 101 Ventilator trauma in the critically ill
- Part 4.7 Weaning ventilatory support
- Part 4.8 Extracorporeal support
- Part 4.9 Aspiration and inhalation
- Part 4.10 Acute respiratory distress syndrome
- Part 4.11 Airflow limitation
- Part 4.12 Respiratory acidosis and alkalosis
- Part 4.13 Pneumonia
- Part 4.14 Atelectasis and sputum retention
- Part 4.15 Pleural cavity problems
- Part 4.16 Haemoptysis
- Section 5 The cardiovascular system
- Section 6 The gastrointestinal system
- Section 7 Nutrition
- Section 8 The renal system
- Section 9 The neurological system
- Section 10 The metabolic and endocrine systems
- Section 11 The haematological system
- Section 12 The skin and connective tissue
- Section 13 Infection
- Section 14 Inflammation
- Section 15 Poisoning
- Section 16 Trauma
- Section 17 Physical disorders
- Section 18 Pain and sedation
- Section 19 General surgical and obstetric intensive care
- Section 20 Specialized intensive care
- Section 21 Recovery from critical illness
- Section 22 End-of-life care