Professor Peter JD Andrews Anesthetics, Intensive Care & Pain Medicine University of Edinbu rgh & Lothian University Hospitals Division Dr Dennis CJJ Bergmans Intensive Care Center Maastricht Maastricht University Medical Cente r+ The Netherlands Professor Djillali Annane General Intensive Care Unit, Department of Acute Medicine Raymond Poincar hospital (AP-HP) University of Versailles SQY (UniverSud Paris) 104 boulevard Ra ymond Poincar , 92380 Garches, France Professor Julian Bion Professor of Intensive Care Medicine University Department of Anesthe sia & Intensive Care Medicine, N5 Queen Elizabeth Hospital, Edgbaston, Birmingham Dr Andrew Bodenham Anesthetic Department Leeds General In \201 rmary Leeds Dr Tarek F Antonios Senior Lecturer & Consultant Physician Blood Pressure Unit, St. George \200\231s, University of London London Dr Jonathan Booth Consultant Gastroenterologist Royal Berkshire Hospital Reading Dr Elizabeth Ashley The Intensive Care Unit The Heart hospital, Westmoreland Street, London Mr Michael Booth FRCS Consultant Upper GI Surgeon, Royal Berkshire Hospital Reading Dr Jonathan Ball Consultant in Intensive Care General Intensive Care Unit St George \200 \231s Hospital London Mr Mark Borthwick, Consultant Pharmacist, Critical Care John Radcliffe Hospital Oxford Dr Nicholas Barrett Consultant in Intensive Care Medicine Guy \200\231s and St Thomas \200 \231 Hospital Westminster Bridge Road London Mr Richard Bourne, Lead Critical Care Pharmacist Shef \201 eld Teaching Hospital Shef \201 eld Ms Gillian Bradbury Matron, Intensive Care Unit The Royal London Hospital Whitechapel Road London Dr Anthony Bastin Specialist Registrar in Intensive Care Medicine Royal Brompton Hospital L ondon xx CONTRIBUTORS Dr Aimee Brame Specialist Registrar in Intensive Care Medicine Adult Intensive Care Unit, R oyal Brompton Hospital London Professor Christine Collin Neurorehabilitation Royal Berkshire Hospital Reading Ms Catherine Collins Dept of Nutrition and Dietetics St Georges Hospital London Dr Stephen Brett Consultant in Intensive Care Medicine Imperial College London Hammersmith Hospital Du Cane Road, London Mr P Conaghan Specialist Registrar John Radcliffe Hospital Oxford Dr Kate Brignall, Specialist Registrar in critical care Guy \200\231s and St Thomas \200 \231 Hospital Trust London Dr Daniel Conway Dept of Anesthesia Manchester Royal In \201 rmary Manchester Dr Matthew A Butkus The CRISMA (Clinical Research, Investigation, and Systems Modeling of A cute Illness) Laboratory, Department of Critical Care Medicine, University of Pittsburgh, P ittsburgh, PA, USA Dr Jeremy Cordingley Consultant in Intensive Care Medicine Royal Brompton Hospital London Dr Luigi Camporota Specialist Registrar in Intensive Care Medicine Department of Adult Inte nsive Care Guy \200\231s and St Thomas \200\231 NHS Foundation Trust London, UK Dr Matthew Cowan, Specialist Registrar & NIH Research Fellow St. George \200\231s, Universi ty of London, London Dr Jean Carlet Directeur m dical, Direction de l \200\231Am lioration et de la Qualit e t de la S curit des Soins (DAQSS) HAS, 2 avenue du Stade de France 93218 Saint-Denis La Plaine Cedex France Dr Agnieszka Crerar-Gilbert Consultant in Cardiothoracic Intensive Care & Anesthesia St Geo rge \200\231s Cardiothoracic Intensive Care Unit London Dr Chris Danbury Consultant Intensivist Royal Berkshire Hospital Reading Dr Susana Afonso de Carvalho Unidade de Cuidados Intensivos Polivalente Hospital de St. Ant nio dos Capuchos Centro Hospitalar de Lisboa Central, E.P.E. Lisboa Portugal Dr Craig Davidson Director Lane Fox Respiratory Unit Guys & St Thomas \200\231 Foundation T rust London Dr Maurizio Cecconi Consultant in Anesthesia and Intensive Care Medicine Dept. of Anesthesi a and Intensive Care, University of Udine Italy Dr Rebecca Davis Microbiology department Chelsea and Westminster Hospital Fulham Road Londo n Dr. Felix Chua Consultant in Respiratory Medicine St. George \200\231s Healthcare NHS Trust Blackshaw Road London Dr Jamil Darrouj Pulmonary/Critical Care Division Cooper University Hospital Robert Wood Jo hnson Medical School 393 Dorrance Camden USA Dr Jerome Cockings Consultant in Intensive Care Medicine and Anesthesia Royal Berkshire Hos pital Reading Dr Andrew Cohen Consultant, Anesthesia and Intensive Care Medicine St James \200\231s Unive rsity Hospital Leeds Dr Daniel De Backer Dpt of Intensive Care Erasme University Hospital Universit Libre de B ruxelles 808 Route de Lennik B-1070 Brussels (Belgium) xxi CONTRIBUTORS Dr Kayann Dell John Radcliffe Hospitals Oxford Dr Phil Gillen Specialist Registrar in Anesthesia and Intensive Care Royal Berkshire Hospit al Reading Prof. Giorgio Della Rocca Professor of Anesthesia and Intensive Care Chair of the Dept of A nesthesia and Intensive Care University of Udine. Udine, Italy Dr David Goldhill Consultant, Department of Anesthesia and Critical Care The Royal National Orthopedic Hospital Stanmore Middlesex Dr Phil Dellinger Critical Care Division Cooper University Hospital Robert Wood Johnson Med ical School 393 Dorrance Camden USA Dr Andrew Gratrix Consultant in Intensive Care and Anesthesia Hull Royal In \201 rmary Hul l Dr Mark Grif \201 ths Consultant in Intensive Care Medicine The Royal Brompton Hospital Lo ndon Dr James Down Consultant in Intensive care and Anesthesia University College Hospital Londo n Prof Richard D Grif \201 ths Professor of Medicine (Intensive Care), Unit of Pathophysiolo gy School of Clinical Science University of Liverpool Liverpool Dr Martin Dresner Consultant Obstetrics Leeds Royal In \201 rmary Leeds Dr Robert T Duncan Senior Trainee in Burns Wythenshawe Hospital Manchester Dr Mark Hamilton Consultant in Anesthesia & Intensive Care Medicine St. George \200\231s Ho spital, London, Miss N Dunne Specialist Registrar John Radcliffe Hospital, Oxford Dr Olfa Hamzaoui R animation m dicale CHU Bic tre Universit Paris-Sud, 11 France Dr Andy Eynon Director of Neurosciences Intensive Care Wessex Neurological Center Southampt on General Hospital Southampton Dr Jonathan M Handy Consultant in Intensive Care Medicine Chelsea & Westminster Hospital Ho norary Senior Lecturer Imperial College London Dr Paul Ferris Advanced Trainee in Intensive Care Wythenshawe Hospital Manchester Dr Derek Hausenloy Clinical Lecturer, The Hatter Cardiovascular Institute, University Colle ge London Hospital, London Dr Simon Finney Consultant in Intensive Care Medicine The Royal Brompton Hospital London Dr Robert Galland Royal Berkshire Hospital Reading Professor Ken Hillman Professor of Intensive Care, University of New South Wales Sydney Aus tralia Dr Magnus Garrioch Dept of Anesthesia and Critical Care, Manchester Royal In \201 rmary, M anchester Dr Steven Hollenberg Professor of Medicine Robert Wood Johnson Medical School/UMDNJ Directo r, Coronary Care Unit Cooper University Hospital Camden, NJ Anis el Ghorch D partement d \200\231Anesth sie et R animation H pital Lariboisi re Pa ris France xxii CONTRIBUTORS Dr Simon Hughes RAF Consultant in Intensive Care Medicine and Anesthesia John Radcliffe Hos pital, Oxford Dr Richard Keays Consultant in Intensive Care Medicine Chelsea & Westminster Hospital Londo n Dr John A Kellum The CRISMA (Clinical Research, Investigation, and Systems Modeling of Acut e Illness) Laboratory, Department of Critical Care Medicine, University of Pittsburgh, Pitt sburgh, PA, USA Professor Beverley J Hunt Consultant, Depts of Hematology, Pathology & Rheumatology Lead in Blood Sciences, Guy \200\231s & St Thomas \200\231 Trust London Dr Shabnam Iyer Dept Microbiology Royal Berkshire Hospital Dr Chris Kirwan Clinical Research Fellow, Intensive Care Medicine St George \200\231s NHS T rust Dr Ana Luisa Jardim Unidade de Cuidados Intensivos Polivalente Hospital de St. Ant nio dos Capuchos Centro Hospitalar de Lisboa Central, E.P.E. Lisboa Portugal Dr Roop Kishen, Consultant in Intensive Care Medicine & Anesthesia, Hon Lecturer, Salford R oyal NHS Foundation Trust, Salford, Manchester Dr. Michael Joannidis, Professor Director, Medical Intensive Care Unit Department of Intern al Medicine Medical University of Innsbruck Innsbruck, Austria Dr John Knighton Consultant in Critical Care & Anesthesia Portsmouth Hospitals NHS Trust Po rtsmouth Dr Martin Kuper Consultant in Anesthesia and Intensive Care. The Whittington Hospital NHS T rust, London Dr Max Jonas Consultant in Intensive Care Intensive Care Unit Southampton General Hospital Southampton Professor Richard Langford Professor of In \202 ammation Science William Harvey Research I nstitute Barts and The London, Queen Mary \200\231s School of Medicine and Dentistry London Dr Andrew Jones Consultant Critical Care and Respiratory Medicine Guy \200\231s and St Thom as \200\231s NHS Foundation Trust Department of Intensive Care St Thomas \200\231s Hospital London Dr Smaoui Lass ad D partement d \200\231Anesth sie et R animation H pital Lariboisi r e Paris France Dr Christina Jones Nurse Consultant Critical Care Follow-up Whiston Hospital Warrington Roa d Prescot Liverpool Dawn Lau Specialist Registrar in Respiratory Medicine Osler Chest Unit Churchill Hospital O xford Dr Jonathan Lightfoot Anesthetic Trainee Bristol Rotation Department of Anesthetics Weston- Super-Mare General Hospital Dr Rachael Jones Department of HIV/GU Medicine, St Stephens Center, Chelsea & Westminster H ealthcare NHS Trust, London Dr Thiago Lisboa, CIBER Respiratory Diseases. Tarragona, Spain Dr Atul Kapila Consultant Anesthetist Royal Berkshire Hospital Reading Professor Richard Langford Director, Anesthetic Laboratory Barts and the London NHS Trust L ondon Dr Juliane Kause Department of Critical Care Queen Alexandra Hospital Portsmouth xxiii CONTRIBUTORS Dr. Lies Langouche Department of Intensive Care Medicine University Hospital Katholieke Uni versiteit Leuven Belgium Dr Rui Moreno Unidade de Cuidados Intensivos Polivalente Hospital de St. Ant nio dos Capuc hos Centro Hospitalar de Lisboa Central, E.P.E. Lisboa Portugal Dr Andrew Lawson Consultant in Pain Medicine & Anesthesia Royal Berkshire Hospital Reading Dr Giles Morgan Queen Alexandra Hospital Portsmouth Mr Satvinder Mudan Consultant Surgeon Royal Marsden Hospital Fulham Road London Dr Peter MacNaughten Clinical Director Critical Care Intensive Care Unit Derriford Hospital Plymouth Raghavan Murugan, The CRISMA (Clinical Research, Investigation, and Systems Modeling of Acu te Illness) Laboratory Department of Critical Care Medicine University of Pittsburgh Pittsb urgh PA, USA Professor Brendan Madden Professor of Cardiothoracic Medicine St George \200\231s Hospital, Cardiothoracic Unit Blackshaw Road London Dr Mark Nelson Director of HIV Services Chelsea and Westminster Hospital London Dr Hilary Madder Clinical Director, Neurosciences Intensive Care Unit John Radcliffe Hospit al Oxford Dr Peter Nightingale Consultant in Anesthesia Wythenshawe Hospital Manchester Dr Nicholas Madden The CRISMA (Clinical Research, Investigation, and Systems Modeling of Ac ute Illness) Laboratory, Department of Critical Care Medicine, University of Pittsburgh, Pi ttsburgh, PA, USA Dr Jerry Nolan Consultant in Anesthesia and Intensive Care Medicine Royal United Hospital B ath Dr. Michael MacMahon Anesthetic Trainee South East Scotland Rotation Intensive Care Unit We stern General Hospital Edinburgh Mrs Michelle Norrenberg Head of ICU physiotherapist Dept of Intensive Care Erasme Universit y Hospital Brussels Alexander R. Manara Consultant in Anesthesia and Intensive Care. The Intensive Care Unit, F renchay Hospital, Frenchay Park Road, Bristol Dr Pauline O \200\231Neil Aberdeen Royal In \201 rmary Foresterhill Aberdeen Dr Mark Palazzo Consultant Critical Care Medicine Imperial College Healthcare NHS Trust Cha ring Cross Hospital London Dr Luciana Mascia Department of Anesthesia and Intensive Care Medicine University of Turin, Italy Alexandre Mebazaa Universit Paris 7 Denis Diderot D partement d \200\231Anesth sie et R animation H pital Lariboisi re Paris France Dr Tim Palfreman Specialist Registrar in Intensive Care Medicine Adult Intensive Care Unit, Royal Brompton Hospital London Dr John Park Specialist Registrar in Intensive Care Medicine The Royal Brompton Hospital Lo ndon Mr S Middleton Royal Berkshire Hospital Reading xxiv CONTRIBUTORS Dr Tim Parke Consultant in Intensive Care Medicine and Anesthesia Royal Berkshire Hospital Reading Dr Paul Quinton Consultant in Cardiothoracic Intensive Care & Anesthesia St George \200\231 s Cardiothoracic Intensive Care Unit London Dr Hina Pattani Specialist Registrar in Critical Care Queens Medical Center Nottingham Dr Tony Rahman Consultant Gastroenterologist & ICU Physician Honorary Senior Lecturer, St. George \200\231s, University of London, London Dr Rupert Pearse Senior Lecturer and Honorary Consultant in Intensive Care Medicine Barts a nd The London School of Medicine and Dentistry Queen Mary \200\231s, University of London Professor Marco Ranieri President of ESICM Professor of Anesthesia and Intensive Care Unive rsity of Turin, Italy Dr Barbara Philips Senior Lecturer, Intensive Care Medicine Department of Cardiac and Vascu lar Sciences St Georges Hospital Medical School London Dr Ravishankar Rao Baikady Consultant in Anesthesia The Royal Marsden NHS Foundation Trust London Mr Giles Peek Consultant in Cardiothoracic Surgery & ECMO Glen \201 eld Hospital Groby Roa d Leicester Dr Charlotte FJ Rayner Consultant Physician Parkside Hospital, London Dr Ian Rechner Consultant in Intensive Care Medicine and Anesthesia Royal Berkshire Hospita l Reading Dr Amanda Pinder Consultant Obstetric Anesthetist, Leeds Teaching Hospitals Dr Jennie Rechner Specialist Registrar is Anesthesia John Radcliffe Hospital Oxford Dr Alison Pittard Consultant in Anesthesia and Intensive Care Leeds General In \201 rmary Leeds Dr A Reece-Smith Clinical Fellow in Surgery Addenbrookes Hospital Cambridge Professor Michael R Pinsky Professor of Critical Care Medicine, Bioengineering and Anesthes iology University of Pittburgh Pittsburgh USA Mr Howard Reece-Smith Consultant Surgeon Royal Berkshire Hospital Reading Dr Kees Polderman Associate Professor in Intensive Care Medicine, Department of Intensive C are University medical center Utrecht Heidelberglaan 100 Utrecht 3584 CX The Netherlands Prof. Dr. Konrad Reinhart Director of Clinic for Anaesthesiology and Intensive Care Univers ity of Jena Erlanger Allee 101 07747 Jena Germany Dr Susanna Price Consultant Cardiologist and Intensivist, Royal Brompton Hospital, London Jordi Rello, Critical Care Department. Joan XXIII University Hospital University Rovira & V irgili. Tarragona, Spain Dr Caroline Pritchard Clinical Research Fellow Department of Neuroanesthesia and Neurocriti cal Care The National Hospital for Neurology and Neurosurgery Queen Square London Dr Andrew Retter Specialist Registrar in Intensive Care and Hematology Department of Hemato logy Guy \200\231s & St Thomas \200\231 Trust London xxv CONTRIBUTORS Dr Andrew Rhodes Consultant in Intensive Care St George \200\231s Hospital London Dr Suveer Singh Consultant Intensive Care and Respiratory Medicine Chelsea and Westminster Hospital London Dr Zaccaria Ricci, Dept of Pediatric Cardiac Surgery, Bambino Ges Hospital, Rome, Italy Dr Andrew Smith Consultant in Anesthesia & Intensive Care The Heart Hospital Westmoreland S treet London Dr Angela Riga Specialist Registrar Upper GI/HPB Academic Surgery Department Royal Marsden Hospital London Dr Martin Smith Consultant in Neuroanaesthesia and Neurocritical Care Department of Neuroan aesthesia and Neurocritical Care The National Hospital for Neurology and Neurosurgery Unive rsity College London Hospitals Queen Square London Dr Claudio Ronco, Dept of Nephrology, Dialysis and Transplantation, S.Bortolo Hospital, Vic enza Italy Dr Neil Soni Honorary Clin Senior Lecturer Division of Surgery, Oncology, Reproductive Biol ogy and Anesthetics Imperial College London Dr Hendrick KF van Saene, Department of Clinical Microbiology and Infection Control Royal L iverpool Children \200\231s NHS Trust of Alder Hey Liverpool Professor Charles L. Sprung General Intensive Care Unit, Department of Anesthesiology and C ritical Care Medicine, Hadassah Hebrew University Medical Center, P.O. Box 12000, Jerusalem , Israel 91120 Dr Som Sarkar Specialist Registrar in Anesthesia Leicester Dr Karnan Satkunam Specialist Registrar in Respiratory Medicine Royal London Hospital Londo n Dr Paul Stevens Department of Renal Medicine Kent and Canterbury Hospital Ethelbert Road Ca nterbury Pallav Shah Consultant Physician Royal Brompton Hospital Chelsea & Westminster Hospital Lon don Dr Sarah Stirling Specialist Registrar Intensive Care Medicine and Anesthesia Barts and The London NHS Trust London Dr Manu Shankar Hari Specialist Registrar Anesthesia and Intensive Care Medicine. Guy \200 \231s and St Thomas Hospital NHS foundation trust, London Dr Stephanie Strachan Specialist Registrar in Anesthesia Chelsea and Westminster, London Dr Alasdair Short Director, Critical Care Broom \201 eld Hospital Chelmsford Essex Dr Gustav Strandvik Specialist Registrar in Intensive Care Medicine Adult Intensive Care Un it, Royal Brompton Hospital London Dr Jeroen Schouten, Internist/Intensivist Intensive Care Unit Canisius Wilhelmina Hospital Nijmegen, The Netherlands Dr Daniel Tarditi, Cardiovascular Associates of the Delaware Valley Camden, NJ Dr Bruce Taylor Dept of Critical Care Portsmouth Hospitals NHS Trust Queen Alexandra Hospit al Cosham Hants Dr Kevin Sim Aberdeen Royal In \201 rmary Foresterhill Aberdeen xxvi CONTRIBUTORS Miguel Tavares Departmento de Anestesia e Cuidados Intensivos Hospital Geral de Santo Ant nio Porto Portugal Dr Gorazd Voga Department of Intensive Internal Medicine, General Hospital, Celje, Slovenia Prof. Jean-Louis Teboul R animation m dicale CHU Bic tre Universit Paris-Sud, 11 Franc e Dr Sam Waddy Consultant in Intensive Care and Acute Medicine Derriford Hospital Plymouth Chris Theaker Royal Brompton Hospital Sydney Street London Dr Adrian Wagstaff Magill Department of Anesthesia Chelsea and Westminster London Dafydd Thomas Consultant in Intensive Care Morriston Hospital Abertawe Bro Morganwwg Univer sity NHS Trust Swansea Dr Andrew Walden Specialist Registrar in intensive care John Radcliffe hospital Oxford Dr Ian Thomas Advanced Trainee in Intensive Care Medicine The Intensive Care Unit, Frenchay Hospital, Frenchay Park Road, Bristol Dr Carl Waldmann Consultant in Anesthesia and Intensive Care Royal Berkshire Hospital Readi ng Dr Colin Webb Intensive care Registrar Royal Berkshire Hospital Reading Dr Sam Thomson, Specialist Registrar & Clinical Research Fellow St. George \200\231s, Unive rsity of London, London Professor Nigel R Webster Anesthesia and Intensive Care Institute of Medical Sciences Fores terhill Aberdeen Dr Louise Thwaites Specialist in Musculoskeletal Medicine Oxford University Clinical Resear ch Unit Oxford Dr Jan Wernerman Dept of Anesthesia University Hospital Stockholm S-141 86 HUDDINGE Dr David Treacher Department of Intensive Care St Thomas \200\231 Hospital Guy \200\231s & St Thomas \200\231 NHS Foundation Trust London Dr Bob Winter Adult Intensive Care Queens Medical Center Nottingham Dr W James N Uprichard Clinical Lecturer in Hematology Imperial College London Hammersmith Hospital Du Cane Road London Dr Duncan Wyncoll Dept of Intensive Care St Thomas \200\231 Hospital Lambeth Palace Road Lo ndon Prof. Dr. Greet Van den Berghe Department of Intensive Care Medicine University Hospital Ka tholieke Universiteit Leuven Belgium Dr Gary Yap Intensive care Registrar Royal Berkshire Hospital Reading Dr. Ilse Vanhorebeek Department of Intensive Care Medicine University Hospital Katholieke U niversiteit Leuven Belgium Professor Dr DF Zandstra Professor of Intensive Care Faculty of Medicine Universiteit van A msterdam Amsterdam Netherlands Dr Nilangi Virgincar Royal Berkshire Hospital Reading Dr Andrew Zurek Consultant Respiratory Physician Royal Berkshire Hospital Reading 1 Chapter 1 Respiratory therapy techniques Chapter contents Oxygen therapy 2 Ventilatory support: indications 6 IPPV \200\224description of ventilators 8 IPPV \200\224modes of ventilation 10 IPPV \200\224adjusting the ventilator 12 IPPV \200 \224barotrauma 14 IPPV \200\224weaning techniques 16 High-frequency ventilation 18 Positive end-respiratory pressure 22 Continuous positive airway pressure ventilation (CPAP) 24 Recr uitment maneuvers 26 Prone position ventilation 28 Non-invasive positive pressure ventilati on (NIPPV) 30 Extracorporeal membrane oxygenation (ECMO) for adults in respiratory failure 32 Tracheostomy 34 Aftercare of the patient with a tracheostomy 36 Chest drain insertion 38 Pleural aspiration 40 Flexible bronchoscopy 42 Chest physiotherapy 44 Humidi \201 cation 46 Heart \200\223lung interactions 48 2 A WAGSTAFF Oxygen therapy Clinical signs such as heart rate, blood pressure and urine output can be misleading, espec ially in the young. This therefore requires the concept of an effective cardiac out- put (E CO). This couples the clinical signs with evidence of normal DO2 and VO2 balance. The asses sment includes peripheral temperature, oxygen hemoglobin saturation and arterial partial pr essure, the presence of acidosis with a base excess greater than \200\2232, lactataemia an d abnormal SvO2 or ScvO2. These more technical measures of adequacy of oxygen delivery and uptake must always be taken in the clinical context. For example, in cyanide poisoning, bot h circulatory and ventilatory indices appear normal, yet the severe acidosis and lactataemi a seen in this condition dem- onstrates tissue hypoxia. Manipulating DO2 by increasing the environmental oxygen fraction (FiO2) or cardiac output in this setting is unlikely to be he lpful, and, even in sepsis and other more common types of shock, achieving supranormal valu es for DO2 is not thought to be bene \201 cial. Strategies for increasing DO2 By assessing the type of hypoxia and its likely cause, the correct choice of DO2-improving strategy can be chosen. In the critically ill, the commonly seen combination of mechanisms leading to h ypoxia may require several tech- niques to be instigated in parallel. The methods for impro v- ing oxygen delivery to the tissues are based on reversing problems seen at each of the s ix stages of oxygen delivery. Improving the transportation of oxygen once in the body will be covered later in this book. This chapter is concerned with improving oxygen delivery fro m the environment to the bloodstream. Oxygen delivery at this stage should be considered a support mechanism, and treatment of the underlying cause is most important to reverse hypox ia. Aerobic respiration is the most ef \201 cient method of energy production in the mammalian cell. It utilizes oxygen to produce adenosine triphosphate (ATP). The absence of oxygen or low oxygen levels result in more inef \201 cient anaerobic respiration. Cellular energy l evels become inad- equate, and this can lead to loss of cellular homeostasis, which in turn can lead to cellular death and very possibly organism death. A substantial part of critica l care is targeted at treating and/or preventing hypoxia. Pathophysiology of oxygen delivery In critical illness the delivery (DO2) and uptake (VO2) of oxygen are often abnormal. Curre ntly there are few thera- peutic strategies for improvement of VO2. Most methods of oxygen therapy target improvement in DO2. Delivery of oxygen from the environment is necessary to provide for cellular metabolism. In single-celled organisms (e.g. amoeba), simple diffusion suf \201 ces. However, in the multi-cellular, multi-organ human, more sophisticated mecha nisms have evolved, each with their problems in illness. Transportation of oxygen to the ce lls follows six stages reliant only on the laws of physics. 1 Convection from the environme nt (ventilation). 2 Diffusion into the blood. 3 Reversible chemical bonding with hemoglobin . 4 Convective transportation to the tissues (cardiac output). 5 Diffusion into the cells a nd organelles. 6 The redox state of the cell. This chain of events is DO2. Failure of DO2 to match VO2 leads to shock. This occurs when D O2 declines to below approximately 300ml/min. Shock is de \201 ned loosely as fail- ure of delivery of oxygen to match tissue demand. Commonly this refers to circulatory failure, bu t low DO2 can result from several pathological mechanisms which can occur as a single probl em or in combination (Table 1.1.1). The impact of low DO2 can be made worse by an increase in VO2. Metabolic rate increases with exercise, in \202 amma- tion, sepsis, pyrexia, thryo toxicosis, shivering, seizures, agitation, anxiety and pain. This mismatch leads to the nee d for early detection of shock and prompt treatment. This has been shown to be bene \201 c ial in surviving sepsis. Oxygen therapy apparatus Principles In the hypoxic self-ventilating patient, delivery of ox ygen to the alveoli is usually achieved by increasing the FiO2. Commonly this involves the application of one of the many varieties of oxygen masks to the face, such that it covers t he mouth and/or nose. Each type of delivery system con- sists of broadly the same six compo nents: 1 Oxygen supply. Delivery of oxygen can be from pres- surized cylinders, hospital su pply from cylinder banks or Table 1.1.1 Types of hypoxia Type of hypoxia Pathophysiology Examples Hypoxic hypoxia Reduced supply of oxygen to the body leading to a low arterial oxygen tension 1. Low environmental oxygen (e.g altitude) 2. Ventilatory failure (respiratory arrest, drug overdose, neuromuscular disease) 3. Pulmonary shunt a. Anatomical \200\224ventricular septal defect with right to left \202 ow b. Physiologic al \200\224pneumonia, pneumothorax, pulmonary oedema, asthma Anemic hypoxia Normal arterial oxygen tension, but circulating hemoglobin is reduced or functionally impai red Failure of oxygen transportation due to inadequate circulation. Impaired cellular metab olism of oxygen despite adequate delivery. Massive hemorrhage, severe anemia, carbon monoxide poisoning, methaemoglobinaemia Left vent ricular failure, pulmonary embolism, hypovolaemia, hypothermia Cyanide poisoning, arsenic p oisoning, alcohol intoxication Stagnant hypoxia Histotoxic hypoxia 3 CHAPTER 1.1 Oxygen therapy a vacuum-insulated evaporator (VIE), or an oxygen con- centrator. 100 2 Oxygen \202 ow control. For example an OHE ball valve \202 ow meter. 3 Connecting tubing. Both from supply to control, and from control to patient. The bore of the tubing is impor- tant as it has effects on the oxygen \202 ow rate. In some systems i t can also act as a reservoir. 80 4 Reservoir. All have reservoirs. In the simple oxygen mask it is the mask itself. Nasal ca nnulae use the nasopharynx as the reservoir. An oxygen tent is a large- volume reservoir. T he reservoir serves to store oxygen, but must not allow signi \201 cant storage of exhaled gasses leading to rebreathing of carbon dioxide. 60 ) % ( C O E I 5 Patient attachment. This permits delivery of oxygen to the airway. This is achieved eithe r by directly covering the upper airway, e.g. plastic mask/head box, or by increasing the o xygen concentration in the wider envi- ronment, e.g. oxygen tent. 40 6 Expired gas facility. Expired gas needs to dissipate to the environment. This can be achi eved by having a small reser- voir with holes, one-way valves as in the non-rebreather mask s, or high oxygen \202 ows as seen in some of the con- tinuous positive airway pressure ( CPAP) systems. 20 0 Additional features of oxygen breathing systems are the presence of humidi \201 cation suc h as a water bath, to prevent drying of the mucosal membranes. Some devices have an oxygen monitor incorporated into the apparatus to permit more accurate de \201 ning of the FiO2. Factors that affect the performance of oxygen delivery systems Most of the simpler oxygen d elivery devices, e.g. plastic masks, nasal cannulae, etc., deliver oxygen at relatively low oxygen \202 ow rates. The patient inspiratory \202 ow rate varies throughout inspirati on (25 \200\223100+L.min-1) and exceeds the oxygen \202 ow rate. This drains the small re servoir and causes entrainment of environmental air. The effect is to dilute the oxygen con centration to the \201 nal FiO2. The actual FiO2 that reaches the alveolus is therefore u npredictable and is dependent on the interaction of patent factors and device factors (Tabl e 1.1.2). In the hypoxic patient it is common to \201 nd signi \201 cant increases in in spiratory \202 ow rates as well as the loss of the respiratory pause. This causes signi \201 cant entrainment of air, lowering the alveolar FiO2. This is par- ticularly true of th e variable performance masks, but is also seen in Venturi-type masks, particularly when hig her FiO2 inserts are used. The presence of a valve-controlled reser- voir bag on a non-rebr eather mask should compensate for high inspiratory \202 ows, hence the belief that such d evices can deliver an FiO2 of 1.0 which does not actually happen. This is not seen in model s of human ventilation (Fig. 1.1.1) 0 5 10 15 20 25 30 35 Respiratory Rate (breath.min-1) Fig. 1.1.1 The performance of a Hudson non-rebreather mask on a model of human ventilation. Tidal volume of 500ml and four oxygen \202 ow rates (2l/min ((cid:1)), 6l/min ((cid:2)), 10l/min ((cid:3)) and 15l/min ((cid:4))). As the respiratory rate increases, so the effect ive inspired oxygen concentration (EIOC) deteriorates. Classi \201 cation of oxygen delivery devices Methods of delivering oxygen to the consciou s patient with no airway instrumentation can be broadly divided into the following categori es. \200 \200 \200 \200 Variable performance systems Fixed performance systems High \202 ow systems Others Variable performance systems are so called because their FiO2 can vary as described above. Fixed performance sys- tems cannot. High \202 ow systems use high oxygen \202 ows to ma intain a \201 xed performance. The common types and their properties are summarized in Ta ble 1.1.3. Hazards of oxygen therapy Oxygen is a drug and, like most drugs, its use is not without ris k. It is also a gas and commonly delivered from com- pressed sources. Supply Medical oxygen is supplied at 137bar from a cylinder, and 4bar from hospital pipelin es. Direct administration at deliv- ery pressures is highly dangerous and requires properly functioning pressure-limiting valves. Oxygen supports combustion. Patients must not smoke cigarettes when receiving oxygen therapy, and oxygen should be removed from the environment when sparking may occur, e.g. during de \201 brillation. Table 1.1.2 Factors that in \202 uence the FiO2 delivered to a patient by oxygen delivery devices5 Patient factors Device factors Inspiratory \202 ow rate Presence of a respiratory pause Tidal volume Oxygen \202 ow rate Volume of mask Air vent size Tightness of \201 t 4 A WAGSTAFF Table 1.1.3 Classi \201 cation of oxygen delivery systems Oxygen delivery system Types used Properties Non-sealed masks or nasal cannulae. Oxygen at low \202 ow (2 \200\22315l.min-1). Small re servoir. Signi \201 cant entrainment of environmental air. Accurate FiO2 not possible. Com fortable and simple to use. Venturi-type masks rely on the Venturi principle to dilute oxyg en predictably to FiO2. Need to change valve to alter FiO2. Higher FiO2 valves have larger ori \201 ces, so behave more like a variable performance system. Comfortable. Simple to us e, but needs attention to detail Variable performance Nasal cannulae, semi-rigid masks (Hudson, MC), non-rebreathing masks, tracheostomy mask, T- piece systems Venturi-type masks, anesthetic breathing circuits (waters circuit, Ambu-bag) Fixed performance Anesthetic breathing systems require sealing mask to prevent entrainment. Valves prevent re breathing. Large reservoir. Accurate FiO2. Sealed mask can be uncomfortable. Knowledge of b reathing systems required. Rely on high oxygen \202 ows to match patient \200\231s inspir atory \202 ow rate. Small reservoirs and sealed mask or naso-pharynx. Requires humidi \201 cation. Accurate FiO2. Sealed mask uncomfortable with risk of mucosal dryness. More co mplicated to set up. Unusual in the self-ventilating patient. Oxygenation achieved across s ynthetic membrane. CO2 removal can be an issue. FiO2 can be dif \201 cult to measure. Comp licated and limited to specialist centers. T-piece systems, Vapotherm (humidi \201 ed high \202 ow nasal cannulae) High \202 ow systems Others Intravascular oxygenation (cardiopulmonary bypass, interventional lung assist devices (Novo lung ), ECMO) Oxygen toxicity CNS toxicity (Paul Bert effect) Seen in diving, oxygen delivered at high pr essures (>3atm) can lead to acute central nervous system (CNS) signs and seizures. Table 1.1.4 Suggested indications for hyperbaric oxygen therapy Primary therapy Adjunctive therapy Carbon monoxide poisoning Air or gas embolism Decompression sickness (the \200\230bends \200\231) Osteoreadionecrosis Clostridial myositis and myonecrosis Radiation tissue damage Crush injuries Acute blood loss Lung toxicity (Lorraine Smith effect) Prolonged exposure to a high FiO2 results in pulmonar y injury. Possibly mediated by free oxygen radicals, there is a progressive reduction in lu ng compliance, associated with interstitial oedema and \201 brosis. Avoidance of long per iods of high oxygen concentrations reduces this effect. Clinically it can be dif \201 cult to prevent long exposure times; however, in general, patients should remain below an FiO2 of 0.5 where possible and not remain above this value for much longer than 30h. Compromised skin \202 aps or grafts Refractory osteomyelitis Intracranial abscess Enhance ment of healing of problem wounds pressure therapy also has important side effects. Whilst clearly of value in these situatio ns, the availability of a hyperbaric chamber often reduces its use, particularly in carbon monoxide poisoning. Broncho-pulmonary dysplasia (BPD) A condition concerning neonates, it is a chronic \201 b rotic lung disease associated with ventilation at high FiO2. Pathologically it is similar t o the adult condition above, but with the additional effect of immaturity. Surfactant and m aternal steroid therapies have lowered the incidence and severity. Further reading Dellinger RP, Carlet JM, Masur H, et al. Surviving Sepsis Campaign guidelin es for management of severe sepsis and septic shock. Crit Care Med 2004; 32: 858 \200\22373 . Retinopathy of prematurity This is a vasoproliferative disorder of the eye affecting pre- m ature neonates. Initially thought to be solely due to the use of high FiO2, its continued i ncidence despite tighter oxygen control suggests that other factors associated with prematu rity are involved. Gattinoni L, Brazzi L, Pelosi P, et al. A trial of goal-oriented hemo- dynamic therapy in c ritically ill patients. SvO2 Collaborative Group. N Engl J Med 1995; 333: 1025 \200\22332. Grocott M, Montgomery H, Vercueil A. High-altitude physiology and pathophysiology: implicat ions and relevance for intensive care medicine. Crit Care 2007; 11: 203. Hayes MA, Timmins AC, Yau EH, et al. Elevation of systemic oxygen delivery in the treatment of critically ill patients. N Engl J Med 1994; 330: 1717 \200\22322. Hyperbaric oxygen therapy Oxygen can be delivered to patients at higher than atmos- pheric pressures (2 \200\2233atm). This serves to increase the amount of oxygen dissolved in the p lasma, rather than that bound to hemoglobin. At rest, the metabolic demands of an average p erson can be met by dissolved oxygen alone when breathing an FiO2 of 1.0 at 3atm. Hyperbari c oxygen is delivered in a sealed chamber. The gas is warmed and humidi \201 ed. The commo n indications for hyperbaric oxygen therapy are listed in Table 1.1.4. High Leigh J. Variation in performance of oxygen therapy devices. Anesthesia 1970; 25: 210 \200\22322. Stoller KP. Hyperbaric oxygen and carbon monoxide poisoning: a critical review. Neurol Res 2007; 29: 146 \200\22355. Tibbles PM, Edelsberg JS. Hyperbaric-oxygen therapy. N Engl J Med 1996; 334: 1642 \200\2238. Wagstaff TAJ, Soni N. Performance of six types of oxygen delivery devices at varying respir atory rates. Anesthesia 2007; 62, 492 \200\223503. This page intentionally left blank 6 P MACNAUGHTON Ventilatory support: indications not ventilated (e.g. atelectasis, air spaces full of \202 uid, blood or in \202 ammatory exudate). The hypoxaemia associated with shunt is not reversed by increasing the inspired oxygen tension, and treatment needs to be directed towards opening up the non-ventilated pa rts of the lung by the application of positive pressure ventilatory support. Intracardiac s hunt: results in profound hypoxaemia that is not reversed by 100% oxygen or positive pressu re ventila- tion. Although usually associated with congenital heart disease, intracardiac s hunt may develop through a patent foramen ovale (present in 25% of the population). The for amen ovale remains closed as long as left atrial pressure is higher than right atrial press ure. In right ventricular failure (e.g. pulmonary hypertension secondary to pulmo- nary emb olus, ARDS, etc.), right atrial pressure is elevated above left atrial pressure which may o pen the foramen ovale causing a right to left shunt and severe hypoxaemia. Echocardiography can be invaluable in con \201 rming right to left intracardiac shunts as a cause for prof ound hypoxae- mia that is not corrected by conventional ventilatory management. The requirement for ventilatory support is the most common reason that patients are admitte d to an Intensive Care Unit (ICU). The aims of ventilatory support are to: \200 Improve gas exchange by correcting hypoxaemia and reversing acute respiratory acidosis. Rel ieve respiratory distress by reducing the work of breathing and reducing the oxygen cost of breathing. Change the pressure \200\223volume relationships of lungs including improving c ompliance and reversing or pre- venting atelectasis. Ensure patient comfort. Avoid complica tions and permit lung healing. \200 Use of ventilatory support In addition to the treatment of acute respiratory failure, venti latory support is also used in circulatory shock (e.g. cardiogenic shock, septic shock) and in the management of cerebral injury. In a study of 1638 patients from eight coun- tries, the indications for ventilatory support were as fol- lows: \200 Ventilatory support and cardiac failure Positive pressure ventilation may have adverse and bene \201 - cial effects on cardiac function. \200 Acute respiratory failure (66%) (including acute respira- tory distress syndrome) ARDS, sep sis, cardiac failure, pneumonia, post-operative respiratory failure, trauma) Coma (15%) Acu te exacerbation of chronic obstructive pulmonary disease (COPD) (13%) Neuromuscular disease (5%) \200 