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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Serie: Lecture Notes
- Sprache: Englisch
Perfect for medical students, junior doctors, anaesthetic nurses and allied health professionals, Lecture Notes Clinical Anaesthesia provides a thorough introduction to the modern principles and practices of clinical anaesthesia.
Full-colour diagrams, photographs and key fact boxes support easy understanding of the theory of anaesthetics allowing confident transfer of information into clinical practice.
This fourth edition has been fully revised and updated to reflect recent developments within the anaesthetics specialty and is fully supported by a wide-range of self-assessments for study and revision purposes together with a range of 'tips for anaesthesia attachments' that start each chapter.
Whether you need to develop your knowledge for clinical practice, or refresh that knowledge in the run-up to examinations, Lecture Notes Clinical Anaesthesia will help foster a systematic approach to the clinical situation for all medical students and hospital doctors.
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Seitenzahl: 447
Veröffentlichungsjahr: 2012
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Contents
Cover
Title Page
Copyright
Dedication
List of Contributors
Preface
Acknowledgments
List of Abbreviations
Chapter 1: Anaesthetic Assessment and Preparation for Surgery
The Preoperative Assessment Clinic
The Anaesthetic Assessment
Investigations
Risk Associated with Anaesthesia and Surgery
Obtaining Informed Consent
Further Useful Information
Chapter 2: Anaesthetic Equipment and Monitoring
Airway Equipment
The Safe Delivery of Anaesthesia
Measurement and Monitoring
Further Useful Information
Chapter 3: Drugs and Fluids Used During Anaesthesia
Premedication
Intravenous Anaesthetic Drugs
Inhaled Anaesthetic Drugs
Total Intravenous Anaesthesia
Neuromuscular Blocking Drugs
Analgesic Drugs
The Regulation of Opioid Drugs
Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)
Anti-Emetics
Local Anaesthetic Drugs
Calculation of Doses
Intravenous Fluids
Risks of Blood and Blood-Product Transfusions
Further Useful Information
Chapter 4: The Practice of General Anaesthesia
Preoperative Checks
Preparation for Anaesthesia
Induction of Anaesthesia
Maintaining the Airway
Maintenance of Anaesthesia
Transfer Into the Operating Theatre
Emergence from Anaesthesia
Further Useful Information
Chapter 5: Local and Regional Anaesthesia
The Role of Local and Regional Anaesthesia
Local and Regional Anaesthetic Techniques
Monitoring During Local and Regional Anaesthesia
Complications of Central Neural Blockade
Local Anaesthetic Toxicity
Regional Anaesthesia: In Awake or Anaesthetised Patients?
Further Useful Information
Chapter 6: Special Circumstances
Anaesthesia for Emergency Surgery
Reducing the Risks of Aspiration
Anaesthesia for Obstetric Patients
Anaesthesia for Thoracotomy
Aspiration of Gastric Contents
Anaphylaxis
Malignant Hyperpyrexia (Hyperthermia) (MH)
Difficult Intubation
Failed Intubation
Needle Cricothyroidotomy
Further Useful Information
Chapter 7: Post-Anaesthesia Care
The Post-Anaesthesia Care Unit
Postoperative Complications and their Management
Postoperative Intravenous Fluid Therapy
Major Surgery
Postoperative Analgesia
Further Useful Information
Chapter 8: The Acutely Ill Adult Patient on the Ward
Section 1: Recognition and Assessment
Clinical Scoring Systems (Track and Trigger Systems)
Critical Care Outreach Teams
Receiving a Call
The Principles of Assessment
Initial Approach to the Patient
Primary Assessment and Resuscitation
What to Do Next?
Section 2: Management of Common Emergencies
Acute Shortness of Breath
Hypotension
Low Urine Output
Chest Pain
Cardiac Arrhythmias
Cardiac Arrest
Reduced Conscious Level
Further Useful Information
Answers to Short-Answer Questions
Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Answers to True/False Questions
Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Index
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Library of Congress Cataloging-in-Publication Data
Lecture notes. Clinical anaesthesia / Carl Gwinnutt, Matthew Gwinnutt. – 4th ed.
p. ; cm.
Clinical anaesthesia
Includes bibliographical references and index.
ISBN 978-0-470-65892-5 (pbk. : alk. paper)
I. Gwinnutt, Matthew. II. Title. III. Title: Clinical anaesthesia.
[DNLM: 1. Anesthesia. 2. Anesthetics. WO 200]
617.9′6–dc23
2012007478
A catalogue record for this book is available from the British Library.
Cover image: Juan Herrera, iStock Photo
Cover design: Grounded design
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.
Set in 8.5/11pt, Utopia-Regular by Thomson Digital, Noida, India.
1 2012
To a wonderful wife and marvellous, uncomplaining mother.
Contributor
Anthony McCluskey
Consultant in Anaesthesia and Critical Care
Stockport NHS Foundation Trust
Stepping Hill Hospital
Stockport, UK
Preface
It is now over 15 years since I embarked upon the first edition of this book, and with each subsequent edition I have tried to respond to the demands of the readers and the changes within the specialty of anaesthesia itself. In recent years the anaesthetist's role has expanded dramatically from simply ‘providing the conditions under which surgery can be performed safely’ and now involves contact with the majority of patients admitted to hospital. This includes playing a major role in preoperative assessment and postoperative care, acute and chronic pain management, as well as the recognition, resuscitation and management of the critically ill. This edition sees many changes to reflect this.
The first major change to this edition is the loss of the chapter giving an overview of critical care. During my career in anaesthesia I have been privileged to see this specialty grow from the efforts of groups of enthusiasts to its recent formal recognition and the formation of the Faculty of Intensive Care Medicine within the Royal College of Anaesthestists. Consequently, I would encourage students to turn to the many excellent texts available on this fascinating and evolving specialty.
The next change in this edition is a reorganization of the way anaesthesia is presented. Firstly, information on equipment, monitoring and the drugs and fluids you will see anaesthetists use in their everyday practice. This is followed by an overview of ‘giving an anaesthetic’, which describes the processes and procedures used to ensure the patient's safety. Also included is a small chapter covering some of the specialist branches of anaesthesia that students may encounter; it has not been possible to cover every one and I hope those whose specialties are not included will understand.
Trainees from many specialties now work as part of the ‘Hospital at Night’ team, and one of their roles is to respond to requests for help with acutely ill patients that they may not be familiar with. Following on from the success of the chapter in the previous edition on the recognition and management of the acutely ill patient on the ward, this has now been expanded into two sections; the first on recognition and assessment of these challenging patients, followed by advice on how initially to manage commonly encountered problems.
But perhaps the greatest change for this edition is that I now welcome my son, as he embarks on a career in anaesthesia, as co-author. He has provided a fresh insight into the specialty as seen by an anaesthetist in training, and is more aware of what medical students need to know, rather than what I think they ought to know. He has worked tirelessly on the manuscript and provided new photographic illustrations; for that I owe him enormously – thank you!
I close by reiterating what I said at the end of the preface of the previous edition, but this time the message comes from both of us; we hope you enjoy this book, but even more we hope it helps you care for your patients. If it has, tell your friends; if it hasn't, tell us why and we'll try to ensure that the next edition is even better!
Acknowledgments
I would like to thank Intersurgical for Figures 2.3 and 2.5, Aircraft Medical for Figure 2.7(d), and Tanya Lachlan, Deltex Medical for Figures 2.18 and 2.19.Figure 2.10 is from McGuire and Younger, 2010 (see useful information section in Chapter 2), with permission of Oxford University Press on behalf of the British Journal of Anaesthesia.
Figures 8.6, 8.7, 8.8 and 8.9 are reproduced with kind permission from Michael Scott and the Resuscitation Council (UK).
Figure 4.12 is reproduced with permission of Dr. P. Ross and I am grateful to Dr J. Corcoran for his help and advice with transversus abdominis plane blocks and Figure 5.2.
Thanks are due to the Difficult Airway Society for Figure 6.3 and the National Tracheostomy Safety Project for Figures 8.1 and 8.2.
I would also like to express my sincere gratitude to Dr Richard Morgan, Professor Gary Smith and Dr Jas Soar for their contributions to the previous edition, some of which by necessity have been included in this edition.
Abbreviations
AAGBIAssociation of Anaesthetists of Great Britain and IrelandABGarterial blood gasACE-Iangiotensin converting enzyme inhibitorsACSacute coronary syndromeADHantidiuretic hormoneAKIacute kidney injuryALSadvanced life supportAMIacute myocardial infarctionANTTantiseptic no-touch techniqueARDSacute respiratory distress syndromeASAAmerican Society of AnesthesiologistsATanaerobic thresholdATNacute tubular necrosisBISbispectral indexBMIbody mass indexBNFBritish National FormularyBiPAPbilevel positive airway pressureBPblood pressureBTSBritish Thoracic SocietyCAPcommunity-acquired pneumoniaCCUcoronary care unitCEPODConfidential Enquiry into Perioperative DeathCNScentral nervous systemCO2carbon dioxideCOPDchronic obstructive pulmonary diseaseCOXcyclo-oxygenase enzymeCPAPcontinuous positive airway pressureCPRcardiopulmonary resuscitationCPXcardiopulmonary exerciseCRPc-reactive proteinCRTcapillary refill timeCSFcerebrospinal fluidCTcomputerised tomographyCTPAcomputerised tomography pulmonary angiographyCVCcentral venous catheterCVPcentral venous pressureCVScardiovascular systemCXRchest X-rayDASDifficult Airway SocietyDBPdiastolic blood pressureDBSdouble-burst simulationDNARdo not attempt resuscitationDSdegrees of substitutionDVTdeep vein thrombosisECFextracellular fluidECGelectrocardiographEEGelectroencephalographEMLAeutectic mixture of local anaestheticENTear, nose, and throatETTexercise tolerance testEWSearly warning scoreFASTfocused assessment with sonography in traumaFBCfull blood countFEV1forced expiratory volume in 1 secondFFPfresh frozen plasmaFiO2fractional inspired oxygen concentrationFRCfunctional residual capacityFVCforced vital capacityGCSGlasgow Coma ScaleGFRglomerular filtration rateGIgastrointestinalGIFTASUPguidelines on IV fluid therapy for adult surgical patientsGTNglyceryl trinitrateHAFOEhigh airflow oxygen enrichmentHAPhospital acquited pneumoniaHbhaemoglobinHbA1cglycosylated haemoglobinHDUhigh dependency unitHIVhuman immunodeficiency virusHRheart rateHRThormone replacement therapy5-HT5-hydroxytryptamineHTLVhuman T-cell lymphotrophic virusICFintracellular fluidICPintracranial pressureI:E ratioinspiratory:expiratory ratioILMintubating LMAINRinternational normalized ratioIPPVintermittent positive pressure ventilationIRimmediate releaseIVintravenousIVCinferior vena cavaIVRAintravenous regional anaesthesiaJVPjugular venous pressureK+potassium ionskPakilopascalsLBBBleft bundle branch blockLEDlight-emitting diodeLFTliver function testLMAlaryngeal mask airwayLPlumbar punctureLSDlysergic acid diethylamideMACminimum alveolar concentrationMAPmean arterial pressureMETmetabolic equivalentMHmalignant hyperpyrexiaMImyocardial infarctionMRmodified releaseMRImagnetic resonance imagingNa+sodium ionsNCEPODNational Confidential Enquiry into Patient Outcome and DeathNIBPnon-invasive blood pressureNICENational Institute for Health and Clinical ExcellenceN2Onitrous oxideNSAIDnon-steroidal anti-inflammatory drugNSTEMInon-ST-segment elevation myocardial infarctionNYHANew York Heart AssociationOCPoral contraceptive pillOLVone lung ventilationOSAHSobstructive sleep apnoea and hypopnoea syndromeOTCover the counterPaCO2arterial partial pressure of carbon dioxidePACUpost-anaesthesia care unitPCApatient-controlled anaesthesiaPCIpercutaneous coronary interventionPCVpressure-controlled ventilationPEpulmonary embolismPEApulseless electrical activityPEEPpositive end expiratory pressurePEFRpeak expiratory flow ratePMGVpiped medical gas and vacuum systemPaO2arterial partial pressure of oxygenPOCTpoint of care testingPONVpostoperative nausea and vomitingpsipounds per square inchPTprothrombin timeROSCreturn of spontaneous circulationRRTrenal replacement therapyRSIrapid-sequence inductionSBPsystolic blood pressureSpO2peripheral oxygen saturationSTEMIST-segment elevation myocardial infarctionSVCsuperior vena cavaTAPtransversus abdominis planeTCItarget-controlled infusionTIVAtotal intravenous anaesthesiaTOFtrain-of-fourTTEtransthroacic echocardiographyU&Eurea and electrolytesVCO2carbon dioxide productionVFventricular fibrillationVIEvacuum-insulated evaporatorVO2oxygen consumptionV/Qventilation/perfusion ratioVTventricular tachycardiaVTEvenous thromboembolismWHOWorld Health OrganisationChapter 1
Anaesthetic Assessment and Preparation for Surgery
The nature of anaesthetists' training and experience makes them uniquely qualified to assess the inherent risks of anaesthetising each individual patient. Ideally, every patient should be seen by an anaesthetist prior to surgery to identify, manage, and minimize these risks. Traditionally, this occurred when the patient was admitted, usually the day before an elective surgical procedure. However, if at this time the patient was found to have any significant comorbidity, surgery was often postponed, but with insufficient time to admit a different patient, leading to wasted operating time. Increasingly, in attempts to improve efficiency, patients are admitted on the day of their planned surgical procedure. This further reduces the opportunity for an adequate anaesthetic assessment, limits the investigations that can be done and virtually prevents optimization of any comorbidities. This has led to significant changes in the preoperative management of patients undergoing elective surgery, including the introduction of clinics specifically for anaesthetic assessment. A variety of models of ‘preoperative’ or ‘anaesthetic assessment’ clinic exist; the following is intended to outline their principle functions. Those who require greater detail are advised to consult the document produced by the Association of Anaesthetists of Great Britain and Ireland (AAGBI), Pre-operative Assessment and Patient Preparation. The Role of the Anaesthetist (see useful information section).
The Preoperative Assessment Clinic
Stage 1
Although not all patients need to be seen by an anaesthetist in a preoperative assessment clinic, all patients do need to be assessed by an appropriately trained individual. This role is frequently undertaken by nurses who may take a history, examine the patient, and order investigations (see below) according to the local protocol. The primary aim is to identify those patients at low risk of complications during anaesthesia and surgery. This includes patients who:
have no coexisting medical problems;have a coexisting medical problem that is well controlled and does not impair daily activities, such as hypertension;do not require any, or require only baseline investigations (Table 1.1);have no history of, or predicted, anaesthetic difficulties;require surgery for which complications are minimal.Table 1.1 Baseline investigations in patients with no evidence of concurrent disease (ASA I)
Having fulfilled these criteria, patients can then be listed for surgery. At this stage the patient will usually be given preliminary information about anaesthesia, often in the form of an explanatory leaflet. On admission patients will be seen by a member of the surgical team to ensure that there have not been any significant changes since attending the clinic, reaffirm consent and mark the surgical site if appropriate. The anaesthetist will:
confirm the findings at the preoperative assessment;check the results of any baseline investigations;explain the options for anaesthesia appropriate for the procedure;obtain consent for anaesthesia;have the ultimate responsibility for deciding whether it is safe to proceed.Stage 2
Clearly not all patients are as described above. Common reasons are:
coexisting medical problems that impair activities of daily living;the discovery of previously undiagnosed medical problems, such as diabetes or hypertension;medical conditions that are less than optimally managed, such as angina, chronic obstructive pulmonary disease (COPD);abnormal baseline investigations.These patients will need to be sent for further investigations – for example, an ECG, pulmonary function tests, echocardiography, or will be referred to the appropriate specialist for advice or management before being re-assessed. The findings of further investigations dictate whether or not the patient needs to be seen by an anaesthetist.
Stage 3
Patients that will need to be seen by an anaesthetist in the preoperative clinic are those who:
have concurrent disease that impairs activities of daily living (ASA 3, see below);are known to have had previous anaesthetic difficulties, such as difficult intubation, allergies to drugs;are predicted to have the potential for difficulties, for example morbid obesity or a family history of prolonged apnoea after anaesthesia;are to undergo complex surgery with or without planned admission to the intensive care unit (ICU) postoperatively.The consultation will allow the anaesthetist to:
make a full assessment of the patient's medical condition;evaluate the results of any investigations or advice from other specialists;request any additional investigations;review any previous anaesthetics given;decide on the most appropriate anaesthetic technique, for example general or regional anaesthesia;begin the consent process, explaining and documenting:These patients will also be seen by their anaesthetist on admission, who will confirm that there have not been any significant changes since they were seen in the clinic, answer any further questions that the patient may have about anaesthesia, and obtain informed consent.
The ultimate aim of this process is to ensure that once patients are admitted for surgery, their intended procedures are not cancelled as a result of them being deemed ‘unfit’ or because their medical conditions have not been adequately investigated. Clearly the time between the patient being seen in the assessment clinic and the date of admission for surgery cannot be excessive; 4–6 weeks is usually acceptable.
The Anaesthetic Assessment
The anaesthetic assessment consists of taking a history from, and examining, each patient, followed by any appropriate investigations. When performed by non-anaesthetic staff, a protocol is often used to ensure all the relevant areas are covered. This section concentrates on features of particular relevance to the anaesthetist.
Present and Past Medical History
For the anaesthetist, the patient's medical history relating to the cardiovascular and respiratory systems are relatively more important.
Cardiovascular System
Enquire specifically about symptoms of:
ischaemic heart disease;heart failure;hypertension;valvular heart disease;conduction defects, arrhythmias;peripheral vascular disease, previous deep venous thrombosis (DVT) or pulmonary embolus (PE).Patients with a proven history of myocardial infarction (MI) are at a greater risk of further infarction perioperatively. The risk of reinfarction falls as the time elapsed since the original event increases. The time when the risk falls to an acceptable level, or to that of a patient with no previous history of MI, varies between patients. For a patient with an uncomplicated MI and a normal exercise tolerance test (ETT) elective surgery may only need to be delayed by 6–8 weeks. Patients should be asked about frequency, severity, and predictability of angina attacks. Frequently occurring or unpredictable attacks suggests unstable angina. This should prompt further investigation and optimization of anti-anginal therapy prior to proceeding with anaesthesia. The American Heart Association has produced guidance for perioperative cardiovascular evaluation (see useful information section).
Heart failure is one of the most important predictors of perioperative complications, mainly as an increased risk of perioperative cardiac morbidity and mortality. Its severity is best described using a recognized scale, such as the New York Heart Association classification (NYHA) (Table 1.2).
Table 1.2 New York Heart Association (NYHA) classification of cardiac function compared to Specific Activity Scale
NYHA functional classificationSpecific Activity Scale classificationClass I:Cardiac disease without limitation of physical activityNo fatigue, palpitations, dyspnoea or anginaCan perform activities requiring ≥7 METsJog/walk at 5 mph, ski, play squash or basketball, shovel soilClass II:Cardiac disease resulting in slight limitation of physical activityCan perform activities requiring ≥5 but < 7 METsAsymptomatic at rest, ordinary physical activity causes fatigue, palpitations, dyspnoea or anginaWalk at 4 mph on level ground, garden, rake, weed, have sexual intercourse without stoppingClass III:Cardiac disease causing marked limitation of physical activityCan perform activities requiring ≥2 but < 5 METsAsymptomatic at rest, less than ordinary activity causes fatigue, palpitations, dyspnoea or anginaPerform most household chores, play golf, push the lawnmower, showerClass IV:Cardiac disease limiting any physical activitySymptoms of heart failure or angina at rest, increased with any physical activityPatients cannot perform activities requiring ≥2 METsCannot dress without stopping because of symptoms; cannot perform any class III activitiesUntreated or poorly controlled hypertension may lead to exaggerated cardiovascular responses during anaesthesia. Both hypertension and hypotension can be precipitated, which increase the risk of myocardial and cerebral ischaemia. The severity of hypertension will determine the action required:
Mild (SBP 140–159 mmHg, DBP 90–99 mmHg): No evidence that delaying surgery for treatment affects outcome.Moderate (SBP 160–179 mmHg, DBP 100–109 mmHg): Consider review of treatment. If unchanged, requires close monitoring to avoid swings during anaesthesia and surgery.Severe (SBP > 180 mmHg, DBP > 109 mmHg): With a blood pressure this high, elective surgery should be postponed due to the significant risk of myocardial ischaemia, arrhythmias and intracerebral haemorrhage. In an emergency, it will require acute control in conjunction with invasive monitoring.Respiratory System
Enquire specifically about symptoms of:
COPD.asthma;infection;restrictive lung disease.Patients with pre-existing lung disease are at increased risk of postoperative chest infections, particularly if they are also obese, or undergoing upper abdominal or thoracic surgery. If an acute upper respiratory tract infection is present, anaesthesia and surgery should be postponed unless it is for a life-threatening condition.
Assessment of Exercise Tolerance
Exercise capacity has long been recognized as a good predictor of postoperative morbidity and mortality. This is because surgery provokes similar physiological responses to exercising, namely an increase in tissue oxygen demand necessitating an increase in cardiac output and oxygen delivery. An indication of cardiac and respiratory reserves can be obtained by asking the patient about their ability to perform everyday physical activities before having to stop because of symptoms of chest pain, shortness of breath, etc. For example:
Could you run for a bus?How far can you walk uphill?How far can you walk on the flat?Are you able to do the shopping?How many stairs can you climb before stopping?Are you able to do housework?Are you able to care for yourself?The problem with such questions is that they are very subjective, dependent on the patient's motivation and patients often tend to overestimate their abilities!
The assessment can be made more objective by reference to The Specific Activity Scale (Table 1.2). Common physical activities are graded in terms of their metabolic equivalents of activity or ‘METs’, with 1 MET being the energy (or more accurately oxygen) used at rest. The more strenuous the activity, the greater the number of METs used. This is not specific for each patient but serves as a useful guide, and once again relies on the patient's assessment of their activity.
Other Important Considerations
Indigestion, heartburn and reflux: possibility of a hiatus hernia. If exacerbated on bending forward or lying flat, this increases the risk of regurgitation and aspiration.Rheumatoid disease: limited movement of joints makes positioning for surgery difficult. Cervical spine and temporo-mandibular joint involvement may complicate airway management. There is often a chronic anaemia.Diabetes: an increased incidence of ischaemic heart disease, renal dysfunction, and autonomic and peripheral neuropathy. There is also an increased risk of perioperative complications, particularly disruption of glycaemic control, hypotension and infections.Neuromuscular disorders: poor respiratory function (forced vital capacity (FVC) < 1 L) predisposes to chest infection and increases the chance of needing ventilatory support postoperatively. Poor bulbar function predisposes to aspiration. Care is needed when using muscle relaxants. Consider regional anaesthesia.Chronic renal failure: anaemia and electrolyte abnormalities. Altered drug excretion restricts the choice of anaesthetic drugs. Surgery and dialysis treatments need to be coordinated.Jaundice (associated with liver dysfunction): coagulopathy. Altered drug metabolism and excretion. Care is needed especially with use of opioids.Previous Anaesthetics and Operations
These have usually occurred in hospitals or occasionally, in the past, dental surgeries. Enquire about any perioperative problems, such as nausea, vomiting, dreams, awareness, jaundice. Ask if any information was given postoperatively, for example difficulty with intubation or delayed recovery. Whenever possible, check the records of previous anaesthetics to rule out or clarify problems such as difficulties with intubation, allergy to drugs given, or adverse reactions (such as malignant hyperpyrexia, see below). Some patients may have been issued with a ‘Medic Alert’ type bracelet or similar device giving details or a contact number. Details of previous surgical procedures may reveal potential anaesthetic problems, for example cardiac, pulmonary or cervical spine surgery.
Family History
All patients should be asked whether any family members have experienced problems with anaesthesia; for example, a history of prolonged apnoea suggests pseudocholinesterase deficiency (see Chapter 2), and an unexplained death suggests malignant hyperpyrexia (see Chapter 6). Elective surgery should be postponed if any conditions are identified while the patient is investigated appropriately. In the emergency situation, anaesthesia must be adjusted accordingly, for example by avoiding triggering drugs in a patient with a potential or actual family history of malignant hyperpyrexia.
Drug History and Allergies
Identify all medications, both prescribed and over the counter (OTC), including complementary and alternative medicines. Patients will often forget to mention the oral contraceptive pill (OCP) and hormone replacement therapy (HRT) unless specifically asked. On the whole, the numbers of medications patients take rises with age. Many commonly prescribed drugs such as angiotensin converting enzyme inhibitors (ACE-I) can have important effects during anaesthesia. These can be identified by consulting a current British National Formulary (BNF), or the BNF website. Allergies to drugs, latex, topical preparations (e.g. iodine), adhesive dressings and foodstuffs should be noted.
Social History
Smoking: ascertain the amount of tobacco smoked. This is usually calculated as the number of pack years; number of packs smoked each day multiplied by the number of years smoked. This gives an idea of the total amount smoked and allows comparison between individuals. In the long term smoking causes chronic lung disease and carcinoma but it also has a number of other important effects relevant to the perioperative period. It produces carbon monoxide, which combines with haemoglobin and reduces oxygen carriage and nicotine, which stimulates the sympathetic nervous system causing tachycardia, hypertension, and coronary artery narrowing. Cilliary function is impaired, increasing the risk of postoperative chest infections. Stopping smoking before anaesthesia reduces the risk of perioperative complications – the further in advance, the better. As a guide, stopping for eight weeks improves the airways; for two weeks reduces airway irritability and for as little as 24 hours before anaesthesia decreases carboxyhaemoglobin levels. Help and advice should be available at the preoperative assessment clinic.Alcohol: this is measured as units consumed per week; > 50 units/week causes induction of liver enzymes and tolerance to anaesthetic drugs. The risk of alcohol withdrawal syndrome postoperatively must be considered.Drugs: ask specifically about the use of drugs for recreational purposes, including type, frequency and route of administration. This group of patients is at risk of infection with hepatitis B and human immunodeficiency virus (HIV). There can be difficulty with venous access following intravenous drug abuse due to widespread thrombosis of veins. Withdrawal syndromes can occur postoperatively.Pregnancy: the date of the last menstrual period should be noted in all women of childbearing age. The anaesthetist may be the only person in theatre able to give this information if X-rays are required. Anaesthesia increases the risk of inducing a spontaneous abortion in early pregnancy. There is an increased risk of regurgitation and aspiration in late pregnancy. Elective surgery is best postponed until after delivery.The Examination
This concentrates on the cardiovascular and respiratory systems; the remaining systems are examined if problems relevant to anaesthesia have been identified in the history. At the end of the examination, the patient's airway is assessed to try and identify any potential problems. If a regional anaesthetic is planned, the appropriate anatomy (for example, lumbar spine for central neural block) is examined.
Cardiovascular System
Examine specifically for signs of:
arrhythmias;heart failure;hypertension;valvular heart disease;peripheral vascular disease.Don't forget to inspect the peripheral veins to identify any potential problems with IV access.
Respiratory System
Examine specifically for signs of:
respiratory failure;impaired ventilation;collapse, consolidation, pleural effusion;additional or absent breath sounds.Nervous System
Chronic disease of the peripheral and central nervous systems should be identified and any evidence of peripheral neuropathy, motor or sensory, recorded to ensure that any abnormalities postoperatively are not attributed to injury intraoperatively. It must be remembered that some disorders will affect the cardiovascular and respiratory systems, for example dystrophia myotonica and multiple sclerosis.
Musculoskeletal System
Note any restriction of movement and deformity if a patient has connective tissue disorders. Patients suffering from chronic rheumatoid disease frequently have a reduced muscle mass, peripheral neuropathies and pulmonary involvement. Particular attention should be paid to the patient's cervical spine and temporomandibular joints (see below).
The Airway
The airway of all patients must be assessed, in order to try to predict those patients who may be difficult to intubate.
Observe the patient's anatomy looking specifically for:
limitation of mouth opening;a receding mandible;position, number and health of teeth;size of the tongue;soft tissue swelling at the front of the neck;deviation of the larynx or trachea;limitations in flexion and extension of the cervical spine.Finding any of these suggests that intubation may be more difficult. However, it must be remembered that all of these are subjective.
Some simple bedside tests can also be performed:
Mallampati criteria: the patient, sitting upright, is asked to open their mouth and maximally protrude their tongue. The view of the pharyngeal structures is noted and graded I–IV (Fig. 1.1). Grades III and IV suggest difficult intubation.Thyromental distance: with the head fully extended on the neck, the distance between the bony point of the chin and the prominence of the thyroid cartilage is measured (Fig. 1.2). A distance of less than 7 cm suggests difficult intubation.Calder test: the patient is asked to protrude the mandible as far as possible. The lower incisors will either lie anterior to, aligned with, or posterior to the upper incisors. The latter two suggest reduced view at laryngoscopy.Wilson score: increasing weight, a reduction in head and neck movement, reduced mouth opening, and the presence of a receding mandible or buck-teeth all predispose to increased difficulty with intubation.Figure 1.1 The pharyngeal structures seen during the Mallampati assessment.
Figure 1.2 The thyromental distance.
None of these tests, alone or in combination, will predict all difficult intubations. A Mallampati grade III or IV with a thyromental distance of < 7 cm will predict 80% of difficult intubations. If problems are anticipated, anaesthesia should be planned accordingly. If intubation proves to be difficult, it must be recorded in a prominent place in the patient's notes and the patient informed.
Investigations
There is little evidence to support ‘routine’ investigations, and so an investigation should only be ordered if the result would affect the patient's management. The National Institute for Health and Clinical Excellence (NICE) produces guidelines for preoperative investigation of patients. In general, the type and number of investigations depends on the patient's age, the nature and severity of their comorbidities and the surgery planned. A synopsis of the current guidelines for patients with no evidence of concurrent disease (ASA 1, see below) is shown in Table 1.1. For each age group and grade of surgery, the upper entry, shows ‘tests recommended’ and the lower entry ‘tests to be considered’ (depending on patient characteristics). Dipstick urinalysis need only be performed in symptomatic individuals.
Additional Investigations
The following is a guide for when to request some of the common preoperative investigations. Again the need for these will depend on the grade of surgery and the age of the patient. Further information can be found in Clinical Guideline 3, published by NICE (see useful information section).
Urea and electrolytes: patients taking digoxin, diuretics, steroids, and those with diabetes, renal disease, vomiting, diarrhoea.Liver function tests: known hepatic disease, a history of a high alcohol intake (>50 units/week), metastatic disease or evidence of malnutrition.Blood sugar: diabetics, severe peripheral arterial disease or taking long-term steroids.Electrocardiogram (ECG): hypertensive, with symptoms or signs of ischaemic heart disease, a cardiac arrhythmia or diabetics > 40 years of age.Chest X-ray: symptoms or signs of cardiac or respiratory disease, or suspected or known malignancy, where thoracic surgery is planned, or in those from areas of endemic tuberculosis who have not had a chest X-ray in the last year.Pulmonary function tests: dyspnoea on mild exertion, COPD or asthma. Measure peak expiratory flow rate (PEFR), forced expiratory volume in 1 s (FEV1) and FVC. Patients who are dyspnoeic or cyanosed at rest, found to have an FEV1 < 60% predicted, or are to have thoracic surgery, should also have arterial blood gas analysed while breathing air.Coagulation screen: anticoagulant therapy, a history of a bleeding diatheses, or a history of liver disease or jaundice.Sickle-cell screen (sickledex): a family history of sickle-cell disease or where ethnicity increases the risk of sickle-cell disease. If positive, electrophoresis will be required for definitive diagnosis.Cervical spine X-ray: rheumatoid arthritis, a history of major trauma or surgery to the neck, or when difficult intubation is predicted.Cardiopulmonary Exercise Testing
Cardiopulmonary exercise (CPX) testing objectively determines each patient's ability to increase oxygen delivery to the tissues under controlled conditions and thereby makes a preoperative assessment of their fitness. Consequently, high-risk patients can be identified allowing appropriate preparation to be made for their perioperative management.
To perform a CPX test, patients exercise using a bicycle ergometer, against an increasing resistance (like peddling uphill) while breathing through a mouthpiece. The volume and composition of inhaled and exhaled gases are monitored and analysed to determine oxygen consumption (VO2, ml/min/kg), carbon dioxide production (VCO2, ml/min/kg), respiratory rate, tidal volume and minute ventilation. The patient's peripheral oxygen saturation (SpO2) and ECG are also usually monitored. The principle of the test is that, during exercise, VO2 is the same as VCO2. As the intensity of exercise increases, a point is reached where oxygen delivery can no longer meet metabolic demand and anaerobic metabolism starts. At this point CO2 production exceeds oxygen consumption; this is termed the ‘anaerobic threshold’ (AT). If the intensity of exercise increases further, the oxygen consumption will eventually plateau (VO2 max). This equates to the peak aerobic capacity. Many assessments of fitness measure the AT as it occurs before VO2 max, is more easily achieved by the elderly and is less influenced by patient motivation. The lower the AT, the less cardiopulmonary reserve the patient has and the greater risk of postoperative morbidity and mortality. Table 1.3 shows values that have been used to predict risk and the need for an increased level of care postoperatively.
Table 1.3 Anaerobic threshold (AT) values used to predict risk and the need for an increased level of care postoperatively
AT >14 mL/min/kg;no specific risk, ward based careAT 11 – 14 mL/min/kg;low risk, requires HDU care postoperativelyAT <11 mL/min/kg;high risk, requires ITU care postoperativelyBasal oxygen consumption:3.5 mL/kg/minHDU: high dependency unit, ITU: intensive therapy unit.Unfortunately, not all patients can be assessed in this way; for example, those with severe musculoskeletal dysfunction may not be able to exercise to their anaerobic threshold. In such circumstances further investigations will be required. The most readily available method of non-invasive assessment of cardiac function in patients is some type of echocardiography (see below).
Echocardiography
This is a useful tool to assess many aspects of cardiac function in a number of diseases. In patients with heart failure or following a myocardial infarction, left ventricular function can be assessed by calculating the ejection fraction, observing the strength of contractility and looking for regional wall motion abnormalities caused by coronary artery disease. In patients with chronic pulmonary disease the right ventricular function and pulmonary artery pressures can be assessed. In patients with aortic stenosis the valve (aperture) area can be measured and the pressure gradient across the valve, which is a good indication of the severity of the disease, can be calculated. In patients with newly diagnosed atrial fibrillation, the presence of any intra-atrial blood clots can be identified. All of these things are assessed with the patient at rest and so do not give any indication of what happens when metabolic demand is increased. It is possible to simulate exercise, and hence the conditions a patient may encounter during anaesthesia or after surgery. This is often achieved by administering an inotrope, such as dobutamine, which increases heart rate and myocardial work while any changes in myocardial performance are monitored (dobutamine stress echocardiography). This is particularly useful for assessing cardiac function in patients whose exercise ability is limited, for instance by severe osteoarthritis.
Medical Referral
Patients with significant medical (or surgical) comorbidities should be identified in the preoperative assessment clinic, not on the day of admission, to allow time for adequate investigation and management. Clearly a wide spectrum of conditions exists; the following are examples of some of the more commonly encountered that may need specialist advice.
Cardiovascular Disease
untreated or poorly controlled hypertension or heart failure;symptomatic ischaemic heart disease, despite treatment (unstable angina);arrhythmias: uncontrolled atrial fibrillation, paroxysmal supraventricular tachycardia, and second and third degree heart block;symptomatic or newly diagnosed valvular heart disease, or congenital heart disease.Respiratory Disease
COPD, particularly if dyspnoeic at rest;bronchiectasis;asthmatics who are unstable, taking oral steroids or have a FEV1 < 60% predicted.Endocrine Disorders
insulin-dependent and non-insulin-dependent diabetics who have ketonuria, glycosylated Hb (HbA1c) > 10% or a random blood sugar > 12 mmol/L. Local policy will dictate referral of stable diabetics for perioperative management;hypo- or hyperthyroidism symptomatic on current treatment;Cushing's or Addison's disease;hypopituitarism.Renal Disease
chronic renal failure;patients undergoing renal replacement therapy.Haematological Disorders
bleeding diatheses, for example haemophilia, thrombocytopenia;therapeutic anticoagulation;haemoglobinopathies;polycythaemia;haemolytic anaemias;leukaemias.The Obese Patient
The degree of obesity is defined by a patient's body mass index (BMI), the ratio of weight to height and expressed in kg/m2 (Table 1.4). An alternative definition uses waist circumference:
overweight: > 80 cm for women, > 94 cm for men;obese: > 88 cm for women, > 102 cm for men.Table 1.4 Classification of obesity by body mass index (BMI)
ClassificationBMI (kg/m2)Healthy20–25Overweight25–30Obese30–40Morbidly obese40–50 (or >35 if significant comorbidity)Super obese>50In 2008 approximately 37% of adults in UK were overweight and 24% were obese, with a government report predicting that over 50% of adults will be obese by 2050 (Tackling Obesities: The Foresight Report). Consequently, increasing numbers of obese patients are presenting for surgery either to treat their obesity (bariatric surgery) or for unrelated surgery. Most of the principles of assessment are common to both forms of surgery. Patients with mild degrees of obesity pose few additional problems for their perioperative management. Those whose weight is greatly increased require special consideration in terms of their anatomical and physiological abnormalities and associated comorbidities when planning anaesthesia and surgery.
All patients must have their height and weight measured and their BMI calculated and recorded. Do not rely on the patient's own estimate. Specific attention should be paid to comorbidities that place obese patients at higher risk.
Cardiovascular System
Hypertension, ischaemic heart disease, hyperlipidaemia and heart failure are more common in obese patients. Although the history and examination may reveal signs and symptoms of cardiac disease, immobility often limits the patient's exercise tolerance and symptoms are not evident. A lower threshold should be used for requesting a 12-lead ECG and a stress echocardiogram may be indicated for patients who are unable to exercise sufficiently.
Respiratory System
A careful history should be taken of dyspnoea, exercise tolerance and for obstructive sleep apnoea. Pulse oximetry can easily be carried out in the preoperative clinic and a supine SpO2 < 96% on room air suggest that further investigations (spirometry, arterial blood gases) or referral to a respiratory physician are appropriate. Morbidly obese patients with asthma or COPD are at even greater risk of perioperative respiratory complications. Wheeze in obese patients may be due to airway closure rather than asthma. Pulmonary function tests before and after bronchodilator therapy may be useful in differentiation between the two conditions. Obstructive sleep apnoea and hypopnoea syndrome (OSAHS) are common in this group of patients. Those who have symptoms of daytime sleepiness should complete an Epworth sleepiness assessment (Table 1.5). If positive (score > 10), they should be referred for further investigations and consideration of continuous positive airway pressure (CPAP) or bi-level positive airway pressure (BiPAP) therapy preoperatively. Intubation may be more difficult because of deposition of fat into the soft tissues of the neck – a full assessment of the airway is mandatory.
Table 1.5 Epworth sleepiness assessment. Each category is scored: 0 = would never doze or sleep, 1 = slight chance of dozing or sleeping, 2 = moderate chance of dozing or sleeping, 3 = high chance of dozing or sleeping. The total of the scores is summed, >10 is considered abnormal
• Sitting and reading• Watching TV• Sitting inactive in a public place• As a passenger in a car for an hour without a break• Lying down in the afternoon when circumstances permit• Sitting and talking to someone• Sitting quietly after lunch without alcohol• In a car stopped for a few minutes in trafficMetabolic and Gastrointestinal Systems
Morbidly obese patients have a high incidence of diabetes mellitus. All patients should be questioned about symptoms of diabetes and have appropriate investigations if symptomatic. Those known to be diabetic should be assessed for the adequacy of glucose control, for example HbA1c, and also for the presence of complications, especially coronary artery disease, diabetic nephropathy and autonomic dysfunction. Improved perioperative glucose control may help reduce complications such as wound infections or the development of keto- or lactic acidosis. Ask about symptoms of acid reflux, appropriate antacid prophylaxis may be indicated preoperatively.
Other Issues
Preoperative assessment several weeks prior to planned surgery will allow the opportunity to optimize the patient's medical comorbidities, plan for anaesthesia, and arrange the appropriate level of postoperative care. All of these may be more complicated than for patients of normal weight. Informed consent should be obtained with discussion of any specific increased risks related to anaesthesia. Following full assessment and an explanation of the potential risks, some patients may reconsider whether or not to proceed with surgery.
Risk Associated with Anaesthesia and Surgery
One of the most commonly asked questions of anaesthetists is ‘What are the risks of having an anaesthetic?’ The Royal College of Anaesthetists and the AAGBI have issued a guide for patients titled You and Your Anaesthetic. This divides the risks associated with anaesthesia and their frequency:
Common (1 in 10 to 1 in 100)
These are not life threatening and can occur even when anaesthesia has apparently been uneventful. They include:
bruising and soreness from attempts at IV access;sore throat;headache;dizziness;postoperative nausea and vomiting;itching;retention of urine.Uncommon (1 in 1000)
dental damage;chest infection;muscle pains;an existing condition worsening, such as myocardial infarction;awareness during general anaesthesia.Rare (<1 in 10000)
allergy to the anaesthetic drugs;eye injury, particularly if prone;nerve damage;hypoxic brain injury;death.In the United Kingdom, the Confidential Enquiry into Perioperative Deaths (CEPOD 1987) revealed an overall perioperative mortality of 0.7% in approximately 500 000 operations. Anaesthesia was considered to have been a contributing factor in 410 deaths (0.08%), but was judged completely responsible in only three cases–a primary mortality rate of 1:185 000 operations. Upon analysis of the deaths where anaesthesia contributed, the predominant factor was human error.
Clearly, anaesthesia itself is very safe, particularly in those patients who are otherwise well. Apart from human error, the most likely major risk is from an adverse drug reaction or drug interaction. However, anaesthesia rarely occurs in isolation and when the risks of the surgical procedure and those due to pre-existing disease are combined, the risks of morbidity and mortality are increased. Not surprisingly a number of methods have been described to try to quantify these risks.
Risk Indicators
The most widely used scale for estimating risk is the ASA classification of the patient's physical status. The patient is assigned to a category from one to five depending on any physical disturbance caused by either the disease process for which surgery is being performed, or any other pre-existing disease. It is relatively subjective, which leads to a degree of variability between scorers. Different studies have reported different mortalities for each grade. This is a result of differences in; populations of patients, sample sizes, types of surgery being performed and the duration of monitoring patients postoperatively, for example deaths at 48 hours or at one week. However, patients placed in higher categories are at increased overall risk of perioperative mortality (Table 1.6).
Table 1.6 ASA physical status scale
ClassPhysical statusAbsolute mortality (%)IA healthy patient with no organic or psychological disease process. The pathological process for which the operation is being performed is localized and causes no systemic upset0–0.3IIA patient with a mild to moderate systemic disease process, caused by the condition to be treated surgically or another pathological process, that does not limit the patient's activities in any way e.g. treated hypertensive, stable diabetic. Patients aged >80 years are automatically placed in class II0.3–1.4IIIA patient with severe systemic disease from any cause that imposes a definite functional limitation on activity e.g. ischaemic heart disease, COPD1.5–5.4IVA patient with a severe systemic disease that is a constant threat to life, e.g. unstable angina7.8–25.9VA moribund patient unlikely to survive 24 hours with or without surgery9.4–57.8VIA patient declared brain dead whose organs are being removed for transplantationNote: ‘E’ may be added to signify an emergency operation.The leading cause of death after surgery is myocardial infarction, and significant morbidity results from non-fatal infarction, particularly in patients with pre-existing heart disease. As well as the risks from pre-existing cardiac disease, different operations also carry their own varying levels of inherent risks; for example carpal tunnel decompression carries less risk than a hip replacement, which in turn carries less risk than aortic aneurysm surgery. Basically this can be summarized as ‘the sicker the patient and the bigger the operation, the greater the risk.’
Assessing patients as ‘low risk’ is no more of a guarantee that complications will not occur than ‘high risk’ means they will occur; it is only a guideline and indicator of probability. For patients who suffer a complication the rate is 100%! Ultimately the risk/benefit ratio must be considered for each individual patient. If a patient has a certain predicted risk of complications, an operation with the potential to offer only a small benefit may be deemed not worth the risk, whereas one with the potential to offer a large benefit may in fact be undertaken. Clearly this is a decision that can only be reached after careful and thorough discussion with a patient who has been given all the relevant information.
Improving preoperative preparation by optimizing the patient's physical status, adequately resuscitating those who require emergency surgery, appropriate intraoperative monitoring, and by providing suitable postoperative care in an appropriate level of critical care, has been shown to further reduce patients perioperative mortality.
Classification of Operation
Traditionally, surgery was classified as being either elective or emergency. Recognizing that this was too imprecise, the National Confidential Enquiry into Perioperative Outcome and Death (NCEPOD) has identified four categories:
All elective and the majority of expedited cases can be assessed as previously described. In urgent and emergency cases this will not always be possible, but as much information as possible should be obtained about allergies, the patient's medical history, drugs taken regularly and previous anaesthetics. In the trauma patient, enquire about the mechanism of injury. This may give clues to unsuspected injuries. Details may only be available from relatives and/or the ambulance crew. The cardiovascular and respiratory systems should be examined and an assessment made of any potential difficulty with intubation. Investigations should only be ordered if they would directly affect the conduct of anaesthesia. When life or limb is at stake, there will be even less or no time for assessment. All emergency patients should be assumed to have a full stomach.
Prevention of Venous Thromboembolism
Up to 25 000 patients die each year in the UK as a result of a hospital-acquired venous thromboembolism (VTE). It is now a requirement that all patients admitted to hospital are assessed for their risk of developing a VTE and appropriate preventative measures applied. Surgical patients and patients with trauma are at increased risk of VTE with:
a total anaesthetic and surgical time > 90 min;surgery to the pelvis or lower limb and the total anaesthetic and surgical time > 60 min;an acute surgical admission with inflammatory or intra-abdominal condition;an expected reduction in mobility.Further non-surgical factors increase the risk of VTE:
active cancer or treatment for cancer;age > 60 years;critical care admission;dehydration;known thrombophilia;BMI > 30 kg m−2;one or more significant medical comorbidities (for example, heart disease, respiratory disease, endocrine or metabolic disorders);personal or first-degree relative with a history of VTE;use of HRT;use of oestrogen containing contraceptive;varicose veins with phlebitis.Patients must also be assessed for their risk of bleeding:
active bleeding;acquired coagulopathy (for example, liver failure);concurrent anticoagulation;epidural, spinal anaesthesia (or lumbar puncture) within the last 4 hours or expected within 12 hours;acute stroke;thrombocytopaenia;uncontrolled hypertension (>230/120 mmHg);untreated bleeding disorders (for example, haemophilia).
