Practical Conscious Sedation

Quintessentials of Dental Practice – 15

Oral Surgery and Oral Medicine - 2

Practical Conscious Sedation

Second Edition

By

David C Craig

Carole A Boyle

Editor-in-Chief: Nairn H F Wilson

Editor Oral Surgery and Oral Medicine: John G Meechan

Quintessence Publishing Co. Ltd.

London, Berlin, Chicago, Copenhagen, Paris, Milan, Barcelona, Istanbul, São Paulo, Seoul, Singapore, Tokyo, New Dehli, Moscow, Prague, Warsaw

A CIP record for this book is available from the British Library.

ISBN
978-3-86867-369-2 epub
978-1-78698-005-2 print

Copyright © 2017 Quintessence Publishing Co. Ltd., London

All rights reserved. This book or any part thereof may not be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, or otherwise, without the written permission of the publisher.

Foreword

The ability to provide effective, safe conscious sedation is a tremendous attribute for a dental team. Patients with a real fear of dentistry and individuals with other conditions which make it extremely difficult, if not impossible, for them to be treated under normal conditions rightfully expect conscious sedation treatment to be available to assist them obtain the treatment they require. In addition, patients faced with the prospect of an unpleasant, possibly distressing dental procedure, such as a difficult surgical extraction, should have the option of conscious sedation to help them through the difficult phase of their treatment. As a consequence, conscious sedation is considered to be an integral element of the control of pain and anxiety in the delivery of dental care. In other words, conscious sedation is an important fundamental aspect of the modern practice of dentistry.

Practical Conscious Sedation, Volume 15 of the highly acclaimed Quintessentials of Dental Practice Series, is a succinct authoritative text on the provision of conscious sedation in the primary dental care setting. As with all the books in the Quintessentials of Dental Practice Series, Practical Conscious Sedation presents, in a generously illustrated text, a wealth of information for all members of the dental team. For the practitioner reluctant to make conscious sedation available, this book provides the necessary knowledge, guidance and encouragement to expand their range of methods for the control of pain and anxiety. For the dental team already providing conscious sedation, this book promotes and gives lots of practical advice on good practice and the safety of patients. Although not primarily intended for students, they too can learn a great deal from this easy-to-read book.

Nairn Wilson
Editor-in-Chief

Acknowledgements

We wish to thank Andrew Dyer, Ted Dawson and Nigel Pearson for their patient and meticulous preparation of the photographs for this book.

Preface to 2nd Edition (2017)

Since publication of the 1st edition in 2004 there have been a number of significant changes in the practice of conscious sedation. This 2^nd edition updates the original volume in line with current UK guidance on clinical practice and training.

Carole Boyle has replaced one of the original authors (Meg Skelly) who is now retired. In addition to reviewing the text and figures, Carole has contributed a valuable chapter on the role of general anaesthesia and conscious sedation in the management of patients requiring special care dentistry.

Notwithstanding the changes made by the current authors, Meg’s enthusiasm and clarity of expression continues to shine through.

We hope this new edition will continue to be useful to undergraduate and postgraduate dentists, dental nurses, hygienists and therapists interested in learning how to provide safe and effective pain and anxiety control for those under their care.

David Craig

Guy’s & St Thomas’ NHS Foundation Trust, London SE1 9RT

March 2017

Contents

Chapter 1

Historical Development of Conscious Sedation

Aim

The aim of this chapter is to describe the historical development of conscious sedation techniques for dentistry.

Outcome

After reading this chapter you should have an understanding of the way conscious sedation techniques have evolved. You will also understand the close historical links between conscious sedation and general anaesthesia.

Introduction

The ability of 21st century dentists to provide comfortable treatment for their patients has its origin in the discovery and development of general anaesthetic drugs in the 19th century. Before the advent of these drugs, the dental patient was expected to endure considerable pain and distress. The most commonly performed surgical procedure was the extraction of teeth. Grim stoicism and occasional self-medication with alcohol were the only ways of coping.

Dentists contributed in no small measure to the early development of general anaesthesia and, later, to the introduction of local anaesthesia and conscious sedation techniques. In the USA, Horace Wells used nitrous oxide for the first time in 1844 and William Morton administered ether for dental extractions in October 1846. Both these men were dental surgeons. In England, another dentist, James Robinson, was the first to administer ether to a patient in London only two months after Morton.

Carl Koller pioneered the use of topical and injected cocaine for local anaesthesia in ophthalmology in 1884. Twenty years later, procaine was available for use in dental patients. This was superseded by lidocaine (lignocaine) in the late 1940s. Reports of dentists using nitrous oxide to provide inhalational conscious sedation, rather than general anaesthesia, started to appear in the early 1900s. By the 1930s, an intravenous barbiturate, hexobarbitone, was in use in UK dental practices for sedation.

Over the course of the second half of the 20th century, there were further developments in the drugs and techniques used for dental conscious sedation. These are shown in Table 1-1.

Relative Analgesia

Joseph Priestley discovered oxygen in 1771 and nitrous oxide in 1772. The analgesic properties of nitrous oxide were discovered by Humphry Davy in 1798. It appears that Davy inhaled nitrous oxide in order to determine its effects, while suffering pain from a partially erupted wisdom tooth. He noticed that his painful pericoronitis was relieved. In 1800, Davy published a treatise on nitrous oxide in which he suggested that the gas “may probably be used with advantage during surgical operations”.

No further progress was made until 1844, when Horace Wells had one of his own teeth extracted under nitrous oxide anaesthesia. Edmund Andrews, a Chicago surgeon, reasoned that the asphyxia often seen during nitrous oxide anaesthesia was due to the oxygen in nitrous oxide not being available to oxygenate the blood. In 1868 he demonstrated that a mixture of 20% oxygen and 80% nitrous oxide was satisfactory for safe and effective anaesthesia. In 1881, nitrous oxide was first used as an analgesic during childbirth in St Petersburg. In 1889 nitrous oxide was used to provide analgesia for a dental procedure in Liverpool. By current standards, the machines used to deliver nitrous oxide and oxygen were crude and the gases far from pure. Many dentists manufactured their own nitrous oxide.

During the first half of the 20th century interest in nitrous oxide sedation came and went. Success was variable, partly as a consequence of the use of inappropriate equipment, but also because of a misunderstanding about the properties of the gas and the best way to use it. Hitherto, the main emphasis had been placed on the analgesic properties of nitrous oxide, but attempts to achieve total analgesia in every patient often led to failure. Many patients experienced nausea, vomiting and excitement-stage symptoms. Appreciation of the excellent sedative properties of nitrous oxide came later following the work of Harry Langa (USA), Ulla Holst (Denmark) and Paul Vonow (Switzerland) during the 1940s and 1950s. The change in use of nitrous oxide from analgesia to sedation led to alterations in technique, dosage and in the approach to the patient.

Langa used the term “Relative Analgesia” to describe his sedation technique. The technique involved the administration of low to moderate concentrations of nitrous oxide in oxygen (using a specially designed machine) accompanied by a steady stream of reassuring and encouraging talk. The technique, with some minor modifications, has now been in use for over 50 years.

Barbiturate-based Techniques

The Jorgensen Technique

In 1945 Niels Jorgensen used a cocktail of intravenous agents as “premedication” for patients about to undergo dental procedures under local analgesia. The method, also known as the Loma Linda technique, took advantage of the hypnotic and tranquillising effects of pentobarbitone, the analgesic action of pethidine and the amnesic properties of hyoscine. It allowed prolonged treatment to be carried out, but the method was unsuitable for procedures lasting less than two hours. Recovery could be prolonged.

Methohexitone

Barbituric acid was first prepared in 1864 by Adolph von Baeyer – a research assistant to Kekule in Ghent. The first hypnotic barbiturate, diethylbarbituric acid (barbitone), was introduced into medicine by Fischer and von Mering in 1903. Barbitone had excellent hypnotic properties and was used for many years. Phenobarbitone (Luminal) was introduced in 1912. Hexobarbitone, thiopentone and methohexitone were classified as ultra-short-acting drugs and, therefore, the most likely to be of use for dental sedation.

In the 1930s, Stanley Drummond-Jackson, a Huddersfield dentist, used intravenous hexobarbitone (and later thiopentone) to produce “insensibility” in patients undergoing not only extractions, but also more lengthy conservative procedures. He used a single dose technique, which was calculated on the basis of the estimated length of the procedure. If the procedure took longer, the anaesthesia was maintained by the use of inhalational agents. The technique was satisfactory in the skilled hands of a fast worker, but there were few dentists who possessed sufficient knowledge and competence in the use of these drugs and, as a consequence, the technique did not gain popularity.

The situation did not change until the introduction of methohexitone (Brietal). In the mid-1960s Drummond-Jackson pioneered a method to produce a controlled level of unconsciousness by administering increments of the drug via an indwelling intravenous needle. Drummond-Jackson’s technique became known as “ultra-light anaesthesia” or “minimal increment methohexitone”. The technique was widely adopted, especially in the UK and in the USA. It was, however, a subject of controversy, and over the next two decades an increasing amount of evidence was produced in an attempt to undermine the confidence of both the dental profession and patients. There was much discussion about whether the technique produced anaesthesia or sedation and whether protective laryngeal reflexes were dangerously compromised. There were discussions about the meaning of sedation and the definition of anaesthesia. There was polarisation of views, hostility between medical and dental anaesthetists and, finally, a lengthy and hugely expensive libel action in the UK. The outcome was a rapid decline in the use of ultra-light methohexitone in dentistry.

Benzodiazepine-based Techniques

Diazepam

Benzodiazepine compounds were first synthesised in 1933. Early animal tests indicated that chlordiazepoxide had interesting muscle-relaxant properties. In 1960 Randall reported that it produced “taming” of a number of species of animals in doses much lower than those producing measurable hypnosis. It was this taming effect (later observed in monkeys) that led to the clinical trials of the drug in humans for the determination of its antianxiety potential. Chlordiazepoxide (Librium®) was the first compound introduced for clinical use.

Diazepam (Valium®) was first used to provide dental sedation by Davidau in France in 1966. It rapidly became the most commonly used intravenous sedation agent for dental procedures. A single titrated dose of 10–20 mg produced approximately 30 minutes of good-quality sedation, without loss of consciousness.

Although diazepam is an easy-to-use, safe and effective intravenous sedative, it has two important disadvantages. First, Valium preparations for intravenous injection contain propylene glycol as a vehicle. This proved to be an irritant to tissues and caused some degree of discomfort during injection in 75% of cases. Thrombophlebitis was also a problem. Second, diazepam has a long half-life and an active metabolite, which means that recovery may not be complete for up to 72 hours.

Diazemuls®

Diazemuls was introduced in the 1970s. This preparation used soya bean oil as a vehicle, which was much less of an irritant to veins than propylene glycol, but the problems associated with a relatively slow recovery remained.

Many dentists supplemented diazepam sedation with an opioid drug. The most commonly used agent was pentazocine (Fortral®). The indications for a multidrug technique were poorly defined. Some practitioners claimed that diazepam alone did not produce sufficiently deep sedation for treatment to be carried out comfortably. In some cases this was true, but it may also have been the result of the desire of both the patient and the dentist to produce the same level of sedation as had previously been achieved with general anaesthesia.

Midazolam

Midazolam (Hypnovel®) became available in 1983. Although it has properties very similar to diazepam, there are four principal differences that make midazolam a better agent for dental sedation:

•Non-irritant solution.

•A much shorter half-life.

•No clinically significant active metabolites.

•Increased potency (approximately two to three times that of diazepam).

Despite its excellent properties, midazolam is not always the ideal intravenous drug for dental sedation. Its relatively long period of action makes it inefficient for isolated procedures of short duration, e.g. removal of a single tooth. Sometimes there are indications for the use of midazolam in combination with other drugs, e.g. opioids, ketamine or propofol (see Chapter 6).

Flumazenil

Flumazenil (Anexate®) was introduced in 1988. It is a specific benzodiazepine antagonist, which reverses most of the agonistic effects of benzodiazepines. It is used electively and to manage severe benzodiazepine-induced respiratory depression.

Propofol-based Techniques

Di-isopropyl phenol (Diprivan®) was introduced in 1977. It is insoluble in water and was originally solubilised in Cremophor-EL. Following a number of anaphylactic reactions to Cremophor-EL, the vehicle was changed to soya bean oil. Owing to its very short half-life, propofol soon became the intravenous induction agent of choice for day-case general anaesthesia. It has become a very popular sedative agent that produces safe, controllable anxiolysis/sedation with rapid and clear-headed recovery.

Equipment

No account of the historical development of sedation would be complete without a mention of some of the changes in technology that have also taken place. In some cases, the availability of new or modified hardware has improved the ease of administration and the safety of conscious sedation. On other occasions, the introduction of a novel sedation agent has led to the design and manufacture of a new item of equipment. The following developments are representative:

Fig 1-1 Examples of modern Relative Analgesia machines.

Fig 1-2 Active scavenging system.

Fig 1-3 Active scavenging mask assembly.

•Failsafe Relative Analgesia machines (Fig 1-1).

•Active waste gas scavenging (Figs 1-2 and 1-3).

Fig 1-4 Venflon® safety cannula.

Fig 1-5 BD Nexiva® safety cannula.

•Disposable indwelling safety cannulae (Figs 1-4 and 1-5).

•Combined pulse oximeter and blood pressure monitor (Fig 1-6).

•Inexpensive blood pressure monitor (Fig 1-7).

•Infusion pump (Fig 1-8).

Conclusions

•Conscious sedation techniques have been used in dentistry for over 50 years.

•Many techniques have evolved from general anaesthetic practice.

•The development of new drugs and equipment continues.

Fig 1-6 Dinamap® pulse oximeter and BP monitor.

Fig 1-7 Inexpensive sphygmomanometer.

Fig 1-8 Fresenius® infusion pump.

Further Reading

Langa H. Relative Analgesia in Dental Practice: Inhalation Analgesia and Sedation with Nitrous Oxide. Philadelphia: Saunders, 1976.

Sykes P (Ed.). Drummond-Jackson’s Dental Sedation and Anaesthesia. London: Society for the Advancement of Anaesthesia in Dentistry, 1979.

Chapter 2

Basic Physiology and Anatomy: A Whistle-stop Tour

Aim

The aim of this chapter is to outline the basic principles of physiology and anatomy that are relevant to conscious sedation.

Outcomes

After reading this chapter you should have an understanding of:

•relevant respiratory and cardiovascular physiology;

•airway obstruction;

•anatomy of commonly used venepuncture sites;

•differences between adult and paediatric patients.

Introduction

To understand fully the principles of safe sedation practice, it is necessary to review certain aspects of physiology, in particular those relating to the respiratory and cardiovascular systems. A knowledge of the anatomy of the upper airway assists in airway management. Familiarity with the pattern of veins in the antecubital fossa and on the dorsum of the hand is essential for the administration of intravenous sedation.

Respiratory Physiology

The major function of the respiratory system is to ensure continuous effective gas exchange so that oxygen enters the bloodstream and carbon dioxide is removed.

Mechanics, volumes, capacities and flow rates

Quiet breathing is characterised by the rhythmic expansion and relaxation of the lungs and thorax. The diaphragm is the most important muscle of respiration, but the intercostal muscles contribute to the increase in the volume of the thorax during inspiration. The accessory muscles of inspiration are not used during quiet breathing. Expiration is normally a passive process resulting from the elastic recoil of the lungs. Active expiration, primarily involving the muscles of the anterior abdominal wall and the intercostal muscles, is seen during exercise and hyperventilation.

Fig 2-1 Lung volumes and capacities.VC, vital capacity; IC, inspiratory capacity; EC expiratory capacity; FRC, functional residual capacity; IRV, inspiratory reserve volume; ERV, expiratory reserve volume, RV, residual volume; Vt, tidal volume.

The size of the thorax and lungs determines the lung capacities while lung volumes are determined by inspiratory and expiratory effort (Fig 2-1). Tidal volume (Vt) is the volume of gas inhaled during a normal inspiration. A fit adult patient at rest normally has a tidal volume of approximately 500 ml. The residual volume (RV) is the volume of air remaining in the lungs at the end of a maximal expiratory effort. RV increases with age and with any decrease in elastic recoil of the lungs. Vital capacity (VC) is the volume of gas entering the lungs following a maximal inspiratory effort. Functional residual capacity (FRC) is the volume of the gas remaining in the lungs at the end of a normal expiration. Functional residual capacity is important because it is a measure of oxygen reserve.

Minute volume is the product of the tidal volume and the respiratory rate. A normal adult at rest breathes approximately 12 times per minute. Thus, the minute volume for an adult is usually about 6 litres. These figures provide the sedationist with a physiological basis for estimating the initial fresh gas flow required when using inhalational sedation techniques.

The dead space volume refers to the portion of the airways that is not available for the exchange of gases. Dead space increases with age and reduction in cardiac output. The term alveolar ventilation is used to describe the volume of gas entering the alveoli each minute and taking part in gas exchange. It is important to recognise that a patient who has very shallow breathing (where the tidal volume is less than the dead space volume) is effectively not breathing at all. Hypoventilation is common following the administration of central nervous system (CNS) depressant drugs such as benzodiazepines and opioids.

Pulmonary gas exchange

Gas exchange occurs at the alveolar-capillary membrane, where only two or three cells separate alveolar gas from the bloodstream. Oxygen and carbon dioxide cross the alveolar membrane by diffusion. The rate of diffusion depends upon the:

•concentration gradient of each gas across the alveolar membrane;

•area available for diffusion;

•rate of removal of oxygen and carbon dioxide.

Oxygen is removed by capillary blood and its rate of transfer is also dependent upon the rate of its chemical combination with haemoglobin. The rate of diffusion of carbon dioxide from capillary blood into the alveolus is 20 times more rapid than that of oxygen in the reverse direction.