Anaesthetics for Junior Doctors and Allied Professionals

The Essential Guide

Daniel Cottle, Laha Shondipon

• Publisher: CRC Press
• Year: 2018
• eBook ISBN: 9780429017063
• Edition: 1
• Topic: Medicine
• Subtopic: Medical Theory, Practice & Reference

Arriving in the anaesthetic room for the first time can be a daunting experience. You will be closely supervised, but everything will seem very new. Surgery is a stressful life-event for the patient and your job as an anaesthetist is to make it as safe and as comfortable as you can whilst ensuring the best outcome possible. Anaesthesia is no longer the preserve of the medical anaesthetist. It increasingly features in undergraduate and postgraduate healthcare education, and many of the competencies required need to be attained quickly, in conjunction with new drugs and equipment. This guide provides practical and clinically relevant advice in easily understandable sections to give you confidence and prepare you for your days in theatre - without the complicated physiology, pharmacology and physics. It allows you to understand the most common drugs and provides a rationale for using them. It's the perfect quick, clinical reference for dealing with common problems and emergencies; ideal for everyday use. This book is invaluable for anaesthetists starting out in their career, but is also highly recommended for Foundation, ACCS, ICM trainees, medical students, operating department trainees and nurses. It also provides an excellent revision basis for Primary FRCA candidates. 'This book provides the basic background and ground rules for how anaesthetists work, how they approach a problem and how one can prepare for it. Some of the initial chapters could be usefully read by all surgeons, especially those in Foundation Training posts, and medical students considering an anaesthetic or intensive placement. The use of lists, key points and limited use of references help make the book easy to read, or dip into between cases, and keep it a manageable size whilst still providing a mine of information for the target audience.' From the Foreword by Peter Nightingale

CHAPTER 1

The fundamental principles of anaesthesia

Daniel Nethercott

Anaesthesia provides the vital interface between the surgeon and the patient. Implicit in a patient giving their consent to surgery is that they will be protected from the undesirable aspects of the experience by some form of anaesthesia, which can be:

• regional – where only a proportion of the body is rendered insensate
• general – in which consciousness is impaired
• or a combination of both.

Serious contemplation should be given when seeking to artificially diminish a person’s consciousness, even temporarily and with their agreement. Consciousness is perhaps what defines the experience of being alive and although anaesthesia has become so common as to seem mundane, patients still entrust us with something fundamental, even profound.

The Elements of Anaesthesia

It is not always the case that patients want to be completely removed from the experience of their surgery. Some fear the loss of control and autonomy from allowing themselves to be made unconscious and so elect to have a regional technique alone. Other patients take interest in being able to watch a part of the procedure, such as an arthroscopy. Caesarean section under spinal anaesthesia is the default technique in most circumstances to allow the patient to fully experience and remember the birth. However, all patients need to be spared from pain, and surgeons require the operative site to be still and accessible. Therefore, a standard general anaesthetic can be broken down into the provision of three separate but interrelated elements: (1) hypnosis, (2) analgesia and (3) akinesia.

Hypnosis

Hypnosis means that the patient has no conscious awareness of the surgery taking place, nor any memory of what has happened after he or she wakes up.

Anaesthesia is not, of course, a binary state. There exists a continuum from:

• fully awake
• lightly sedated
• nicely asleep
• acceptably unrousable
• worryingly comatose
• to, eventually, irredeemable death: ‘The undiscovere’d country, from whose bourn no traveller returns.’¹

These are referred to as planes of anaesthesia.

Processed electroencephalography such as the bispectral index monitor measures brain activity directly and can be interpreted as indicating depth of anaesthesia, but use of these monitors is not currently standard practice for most UK anaesthetists.

Analgesia

This means that the patient is not experiencing any pain or unpleasant sensations during the surgery. Pain is ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage’, and so it is subjective. Therefore, in reality it is not absolutely true to describe a patient who is unconscious as experiencing ‘pain’. However, physiological responses mediated by the autonomic nervous system are commonly interpreted as signs of increased nociception (the neural process of encoding and processing noxious stimuli).

The end point for the use of analgesic techniques during general anaesthesia is therefore autonomic stability. An anaesthetised patient who is tachycardic and hypertensive with dilated pupils and beads of sweat on his or her forehead might be nicely managed with a generous intravenous dose of fentanyl.

Akinesia

Only the most generous and forgiving of surgeons allows the patient to move around the operating table without passing comment. During some surgery – for example, on the middle ear or around the brainstem – unexpected movement could cause disaster. Muscle relaxation can be important for surgical access, and increased tone in the abdominal muscles during laparotomy provides unnecessary opportunity for satirical remarks that are rarely becoming of trainee general surgeons.

Balanced Anaesthesia

Modern techniques are built upon targeting these three elements with different drugs in different routes of administration to achieve a balanced anaesthetic. This refers to the use of specific agents for specific effects. To achieve akinesia and analgesia with a volatile agent alone (such as sevoflurane) would need such a high concentration that the side effects would start to cause trouble.

A judicious combination of anaesthetic agent, analgesic (or regional technique) and muscle relaxant will contribute all three required elements with minimal side effects. For example, a patient undergoing laparotomy could be successfully anaesthetised with an intravenous infusion of propofol and remifentanil, and intravenous bolus doses of atracurium. The patient could equally successfully be managed with inhaled sevoflurane, epidural infusion of bupivacaine and a continuous infusion of rocuronium.

It is a bit too simplistic to think of these three elements as being totally separate and solely achieved with different agents. Drugs delivered by various routes can interact in complex ways. For example, systemic opiates will contribute to overall depth of anaesthesia, and it is even postulated that muscle relaxants decrease afferent neural input associated with proprioception and might contribute to depth of anaesthesia too (although this would only be a small effect).²

The Art Of Anaesthesia

Creating the right balance is where the artistry comes into it all, and where the frustrations begin for the novice who strives for competent, independent practice. Observing an experienced anaesthetist can give an illusion of simplicity and economy of action, and yet there can be quite a degree of individual variety in the approach to each case. With only a limited range of drugs and equipment to choose from, any two anaesthetists can manage the same case in different ways.

Although the ‘recipe’ might seem simple, success is often dependent on the skill and experience of the ‘cook’. One element of this skill is being able to match the plane of anaesthesia to the degree of surgical stimulus. Some surgery only causes a little nociception and so a ‘light’ plane of anaesthesia is suitable. Some surgical events are enormously ‘painful’/stimulating and the patient needs to be ‘deepened’ to counter this. Such differing needs can occur within a few minutes of each other. With experience of the surgery (and the surgeon) the anaesthetist can predict and anticipate these changes and titrate the plane of anaesthesia accordingly.

The drug dose that gives the right plane of anaesthesia with least side effects differs between a frail, elderly patient with severe co-morbidities and a boisterous youth with intoxicating habits. A keen grasp of physiology and pharmacology is the basis on which to develop a clinical intuition that gets the balance right for each case.

Biplanes and Butlers

The work of the anaesthetist has attracted some common analogies. Comparison with aircraft pilots has been made,³ which seems acceptable in the similarity between the excitement of the take-off and the landing being interspersed by the sitting-down and interest in a monitor; expecting calm travel but being prepared to avert rapidly intruding disaster. However, this comparison fails when it is recognised that aeroplanes are designed to fly but patients are not designed to be anaesthetised; that an aeroplane with a misfiring engine and a rusty fuselage would not be chanced in the air; and that aeroplanes rarely have people hacking at the fuel lines midflight.

The anaesthetist has perhaps more satisfyingly been characterised as P. G. Wodehouse’s sage butler Jeeves to the surgeon’s Bertie Wooster, guiding his hapless master, encouraging him in his darker moments, restraining his excesses, holding unexpected calamities at bay (in Bertie’s case these always seem to come in the shape of menacing maiden aunts⁴) and deferring personal glory for the greater goal.

The Magic Trick

To take a person who is conversant, breathing spontaneously with a stable heart and blood flow, to render that person unconscious, apnoeic with depressed cardiac function by the use of powerful and dangerous drugs, to rescue that person immediately from this iatrogenic state with instruments, oxygen and other powerful drugs, to hold that person in limbo for as long as necessary, then to put that same person back as they were – talking, breathing, comfortable, unaware of anything having happened at all – can feel like a rather brilliant and magical trick. Preparation, vigilance and anticipation are vital to pull off the trick of anaesthesia without harming the patient or allowing him or her to come to harm.

Summary

Divinum sedare dolorem (it is divine to alleviate pain) reads the motto of the Royal College of Anaesthetists, in somno securitas (safe in sleep) reads that of the Association of Anaesthetists of Great Britain and Ireland. Alleviating pain, horror and distress is indeed worthy, and striving to do it safely is imperative.

Key points

• Balanced anaesthesia requires hypnosis, analgesia and akinesia.
• The balance of the different elements depends upon the patient, the surgery and the anaesthetist’s personal experience.
• The planes of anaesthesia describe the depth of anaesthesia, from awake to deeply comatose.
• Your anaesthetic must alleviate pain, facilitate surgery and ensure the patient’s safety.

References

¹ Shakespeare W. Hamlet. Act 3, scene 1.

² Bonhomme V., Hans P. Muscle relaxation and depth of anaesthesia: where is the missing link? Br J Anaesth. 2007; 99(4): 456–460.

³ Hutchinson G., Biggles F.R.C.A. Today’s Anaesthetist. 1998; 13: 83–84.

⁴ Wodehouse P.G. Aunts Aren’t Gentlemen. London: Barrie & Jenkins; 1974.

Table of contents

• Cover
• Title Page
• Copyright Page
• Contents
• Foreword
• Preface
• List of Contributors
• Acknowledgement
• 1 The fundamental principles of anaesthesia
• 2 A very brief history of anaesthesia
• 3 The anaesthetic day
• 4 Preoperative assessment and investigations
• 5 Intra-operative patient monitoring
• 6 The anaesthetic machine
• 7 Anaesthetic breathing systems
• 8 Ventilation
• 9 Airway assessment
• 10 Airway management
• 11 Basic patient positioning
• 12 Recovery, handover and protocols
• 13 Post-operative analgesia
• 14 Drugs that put you to sleep
• 15 Drugs to keep you asleep: the inhalational agents
• 16 Muscle relaxants
• 17 Drugs that stop you vomiting
• 18 Emergency drugs
• 19 NCEPOD categories and anaesthetic implications
• 20 The pregnant patient
• 21 The obese patient
• 22 The cardiac patient presenting for non-cardiac surgery
• 23 The patient with respiratory disease
• 24 Paediatric anaesthesia
• 25 Day case surgery and anaesthesia
• 26 Transferring the anaesthetised patient
• 27 Regional anaesthesia
• 28 Stridor
• 29 Anaphylaxis
• 30 Major haemorrhage
• 31 Rapid sequence induction at a remote site
• 32 Asthma and anaesthesia
• Appendix 1: Management of a patient with suspected anaphylaxis during anaesthesia – safety drill
• Appendix 2: Checklist for anaesthetic equipment 2012 – AAGBI safety guideline
• Appendix 3: AAGBI safety guideline – management of severe local anaesthetic toxicity
• Appendix 4: Guidelines for the management of a malignant hyperthermia crisis
• Appendix 5: DAS guideline – unanticipated difficult tracheal intubation during rapid sequence induction of anaesthesia in a non–obstetric adult patient
• Appendix 6: DAS guideline – can’t intubate, can’t ventilate
• Index