Basics and modern practice of nasal high-flow therapy

Nasal high-flow therapy (NHF) is an emerging respiratory therapy that has been gaining traction in acute care settings throughout the world. Critically eyed at the beginning, the benefit of NHF therapy has been demonstrated in clinical practice. The unbroken and burst enthusiasm for NHF has resulted in a rapid growing research activity. As with any emerging technology, what is currently known is dwarfed by what is unknown. Authors from the very start have provided their expertise and helped to develop this textbook, which for the first time summarizes the knowledge of the NHF technology, mechanisms and applications. This book aims to contribute to a faster understanding and acceptance of the NHF and to stimulate all colleagues, researchers and interested parties. It contains essential information on technical aspects and mechanisms of action as well as clinical applications like use in children, for hypoxemic respiratory failure, post extubation respiratory failure, hypercapnic respiratory failure and other specific conditions. This NHF volume should prove useful to pulmonary and critical care specialists as well as trainees, respiratory nurses and therapists, pharmacologists and physiotherapists.

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1. Introduction 15 1.1. Pathophysiology of respiratory insufficiency 15 1.2. High- and low-flow oxygenation devices 15 1.3. Principles of mechanical ventilation 16 1.4. Role and limits of non-invasive ventilation 16 1.5. Rationale for the use of a NHF device 17 2. Nasal High-flow Devices 19 3. Mechanisms of Action 21 3.1. Humidification of the respiratory tract and comfort during NHF therapy 21 3.1.1. Introduction 21 3.1.2. Comfort during NHF 22 3.1.3. Humidification during oxygen therapy 22 3.1.3.1. Humidification during low- and medium-flow oxygen therapy 22 3.1.3.2. Humidification during high-flow oxygen therapy 23 3.1.3.3. Optimal humidification level during NHF 23 3.1.3.4. Performances of NHF devices 24 3.1.4. Conclusion 24 3.2. Changes in Upper Airway and Thoracic Pressures 26 3.3. Changes in ventilation and respiratory gases 27 3.3.1. Introduction 27 3.3.2. Reduction of functional dead space 28 3.3.3. Peak inspiratory flow coverage 29 3.3.4. CO2 rebreathing 30 3.3.5. Airway wash-out 30 3.3.6. Effects on the blood gases 31 3.3.6.1. Decarboxylation 31 3.3.6.2. Oxygenation with NHF systems 32 3.3.7. Conclusion 34 3.4. Changes in breathing patterns 36 3.4.1. Healthy subjects 36 3.4.2. Acute hypoxemic respiratory failure 36 3.4.3. COPD 38 3.4.4. Interstitial lung disease 39 3.4.5. Conclusion 40 3.5. Respiratory effort during nasal high-flow therapy 41 3.5.1. Introduction 41 3.5.2. Indicators of respiratory effort during NHF 42 3.5.3. Clinical markers of respiratory effort 42 3.5.4. Physiological markers of respiratory effort 43 3.5.4.1. In paediatrics 43 3.5.4.2. In adult patients in the acute setting 43 3.5.5. In adult patients in the chronic setting 45 3.5.6. In adult patients during sleep 45 3.5.7. Conclusion 45 4. Nasal High-flow Therapy in Infants and Children 49 4.1. Neonatal nasal high-flow 49 4.1.1. Physiological evidence of high flow in neonates 50 4.1.2. Evidence based efficacy of high-flow in premature infants 50 4.2. Pediatric high-flow 50 4.2.1. Definition of nasal high-flow in pediatric respiratory disease 51 4.2.2. Physiological principles of NHF therapy in children 51 4.2.3. Clinical evidence in pediatric respiratory disease 52 4.2.4. Authors recommendation 52 4.3. Conclusions 53 5. Nasal High-flow Therapy in the Management of Acute Hypoxemic Respiratory Failure 55 5.1. Introduction 55 5.2. Pathophysiologic rationale NHF oxygen therapy in hypoxemic ARF 55 5.2.1. Oxygenation and PEEP effect 55 5.2.2. Ventilatory support 56 5.2.3. Comfort and humidification 57 5.3. Clinical impact of NHF oxygen therapy in hypoxemic ARF 57 5.3.1. Hypoxemic ARF 57 5.3.2. Immunocompromised patients 59 5.4. Conclusion 59 6. Nasal High-flow Therapy in Postextubation Respiratory Failure 63 6.1. Introduction 63 6.2. Risk factors and causes for postextubation respiratory failure 63 6.3. Pathophysiological mechanisms of postextubation respiratory failure 63 6.4. NHF role in postextubation respiratory failure 64 6.4.1. NHF after extubation in surgical patients in ICU 64 6.4.2. NHF after extubation in medical patients in ICU 67 6.5. Conclusions 71 7. Nasal High-flow Therapy in Specific Conditions and Diseases 75 7.1. Introduction 75 7.2. Emergency department 75 7.2.1. Important unknowns 77 7.2.2. Implication for future research 77 7.3. Apneic oxygenation/ intubation process 77 7.3.1. Important unknowns 78 7.4. Aerosol delivery 79 7.5. Fiberoptic bronchoscopy 81 7.5.1. Important unknowns 84 7.6. Palliative care 84 7.6.1. Important unknowns 84 7.7. Conclusion 85 8. Nasal High-flow Therapy in Hypercapnic Respiratory Failure 87 8.1. Introduction 87 8.2. Early physiological studies and retrospective evaluations 87 8.3. Prospective clinical trials 88 8.4. Effectiveness in decarboxylation and limitations 89 9. List of abbreviations 93 Index 95