4: Control of pain and anxiety

Control of pain and anxiety

Overview

This chapter deals with pain; it describes the types of pain and their significance and the methods available to the dentist for the control of pain and anxiety.

Systemic analgesic protocols are outlined and related to the types of procedure for which they are suitable. Considerations of dosing schedules and preoperative and postoperative regimens are discussed. Local anaesthetic drugs in common use are described together with their mechanisms of action. Drug dosages, including maximum safe doses are covered, as are the types of complication that can arise from the use of local anaesthetics. The use of vasoconstrictors with a local anaesthetic is also explained.

The role of conscious sedation is outlined with both the indications and contraindications. Nitrous oxide and the benzodiazepines are described. Various sedation techniques are outlined together with the methods for monitoring patients during and after sedation.

The assessment of patients for general anaesthetic is covered together with the possible investigations to establish suitability and the medical conditions that can complicate general anaesthesia. Preoperative preparation of patients for general anaesthesia is described.

4.1 Systemic analgesia

Nociception and pain

The pain system

Not all noxious stimuli that activate nociceptors are necessarily experienced as pain. While the sensations we call pain, pricking, burning, aching or stinging may have an urgent and primitive quality, they can be modulated. For example, in situations of crisis or emergency, or even when an individual’s attention is simply elsewhere, noxious inputs may trigger much less pain sensation than would otherwise be expected. It is observed that fear for survival in a war situation may suppress the pain of an inflicted injury until the individual is away from the immediate danger of the front line. Equally, anxiety about undergoing elective surgery may intensify the postoperative pain experience.

The variability of human pain suggests that there are neural mechanisms that modulate transmission in pain pathways and modify the individual’s emotional experience of pain. The transmission of pain is therefore, no longer viewed as a static process using exclusive pathways from peripheral tissues through the spinal cord to the brain, but rather as messages arising from the interplay between neuronal systems, both excitatory and inhibitory, at many levels of the central nervous system (CNS).

Dental pain and pain after surgery

Analgesics should be prescribed according to their effectiveness and appropriate to the pain intensity reported by the patient or the anticipated postoperative pain intensity and taking into account potential adverse effects and the general health of the patient (Table 4.1). There are many clinical trials comparing analgesic effectiveness and the most effective drugs have a low NNT, where the NNT is the number of patients who need to receive the active drug to achieve at least 50% relief of pain compared to placebo over a 4–6 hour treatment period.

Table 4.1

Systemic pain relief after dental and surgical procedures

Typical pain level Type of procedure Protocol
Mild pain Forceps extraction Paracetamol 1 g every 6 hours regularly (maximum 4 g/24 h)
Moderate pain Surgical removal of tooth Ibuprofen 400 mg every 6 hours regularly (maximum of 2.4 g/24 h) and paracetamol 1 g every 6 hours as necessary (maximum of 4 g/24 h)
Severe pain Surgical removal of tooth involving bone removal Ibuprofen 400 mg every 6 hours regularly (maximum of 2.4 g/24 h) and paracetamol 1 g/codeine 60 mg combination every 6 hours regularly (maximum of 4 g paracetamol/24 h)
When NSAIDs contraindicated: paracetamol 1 g/codeine 60 mg combination every 6 hours regularly (maximum of 4 g paracetamol/24 h)
Severe pain for inpatients More difficult surgical removal of teeth or major surgery Morphine by intravenous titration or intermittent intramuscular injection

These adult protocols are based on evidence from postoperative pain systematic reviews. The British National Formulary and other sources contain more extensive lists of analgesics.

Acetaminophen (paracetamol) possesses antipyretic activity and is an effective analgesic. It is considered safe because it does not have the side-effects such as gastrointestinal ulceration and haemorrhage, cardiorenal adverse effects or impair platelet aggregation. However, paracetamol is associated with liver toxicity, especially in patients who already have compromised liver function, cirrhosis or hepatitis. Patients should always be warned that many combination analgesics may contain paracetamol and they should only take the analgesics recommended or prescribed. Paracetamol may be administered intravenously, intraoperatively followed by oral administration after discharge home.

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclo-oxygenase (COX) enzyme which is crucial for the production of prostaglandins that mediate pain via COX-2 but also via COX-1, for gastrointestinal mucosal protection, platelet function and protection of the inadequately purfused kidney. Consequently, NSAIDs are effective analgesics but are also responsible for the loss of gastric protection and consequent ulceration and bleeding that can occur and other effects. They are contraindicated in:

A proton pump inhibitor such as lansoprazole or omeprazole may be prescribed to take alongside the NSAID to offer some gastrointestinal protection. COX-2-selective inhibitors such as celecoxib have been specifically developed to be effective analgesics without the adverse effects of the non-selective NSAIDs. These are useful although not completely selective.

Some patients have a sensitivity to aspirin such that they develop cutaneous reactions. Asthmatic patients are at risk of experiencing bronchospasm when exposed to aspirin and other NSAIDs. These reactions are described as aspirin sensitivity rather than allergy as they are not mediated via an immune reaction. It is difficult to predict sensitivity and there is no test available. If a patient reports asthma, chronic rhinitis or urticaria and NSAIDs have previously been a trigger of acute bronchospasm, then they should be avoided and paracetamol and codeine used.

Opioids offer effective management of severe acute pain but are associated with nausea and vomiting and respiratory depression. The strong opioids such as morphine are therefore used in hospital but are not suitable for use in outpatients. Weak opioids such as codeine are used in all settings. Morphine may be administered intramuscularly, intravenously or orally and is also used in electronic or disposable devices to allow the patient to self-administer, that is, patient-controlled analgesia (PCA). Dihydrocodeine has been shown to be poorly effective for dental pain. Codeine, 60 mg, in combination with 1 g paracetamol is much more effective (with an NNT of 2.2) than either 60 mg codeine (NNT of 16.5) or 1 g paracetamol (NNT of 3.8) alone.

Pain and the mind

It is well established that pain and depression are related, although the reasons for the association remain unclear. This has led to the unfortunate situation in the past when the dentist or other clinician, who could not find an obvious cause of the patient’s pain, believed that the reported pain was imaginary. It is now understood that if a patient reports pain then that pain is real. It is also now understood that any emotional disturbance in a patient with pain is more likely to be a consequence than a cause of the pain and it is dangerous to ascribe pain routinely to psychological causation. Traditional concepts focused either on medical or psychological explanations for pain, but the boundaries between these are being eroded as psychogenic cause is found to have a biochemical ‘physical’ basis.

4.2 Local anaesthesia

The correct selection of pain control technique for patients requiring dental treatment is important for safe and successful practice. As with other aspects of clinical dentistry, this clinical decision making is based on knowledge and experience. Generally patients for treatment under local anaesthesia will be managed by the dentist in a primary care setting, whereas those requiring a GA will be referred to hospital. However, there may be a few patients requiring local anaesthesia whose medical history dictates that they are treated in hospital. Patients requiring conscious sedation techniques are treated in both the primary care and hospital setting.

By common usage, the localised loss of pain sensation is referred to as ‘local anaesthesia’, rather than local analgesia, which would be more accurate. The word ‘anaesthesia’ implies loss of all sensation including touch, pressure, temperature and pain.

Mechanism of action

LA agents reversibly block nerve conduction and belong to the chemical groups of amino-esters or amino-amides.

Amino-amides

Lidocaine (lignocaine) was produced in 1943 and superseded procaine because of its pharmacological advantages. It is the gold standard historic reference LA in dentistry. It has topical anaesthetic properties and is available as a gel or spray.

Mepivacaine is similar to lidocaine but produced less vasodilation and is used less in dentistry. It is useful for short procedures and where a vasoconstrictor-free anaesthetic is required.

Prilocaine is similar to lidocaine. It has low systemic toxicity.

Bupivacaine and levobupivacaine are used where long duration of action is important.

Articaine has been available and commonly used in Europe and especially in Germany where first synthesised in 1969, but more recently introduced to the UK and USA. It is classified as an amide although it has both an amide and an ester link.

Failure of anaesthesia

Failure of anaesthesia can occur for a number of reasons:

• Inadequate dose administered: the full contents of a dental cartridge (1.8–2.2 ml) are required to obtain a reliable mandibular block according to minimum-dose calculations (Fig. 4.1).

• Inaccurate injection technique: inadvertent injection of solution into a vein or muscle will result in inadequate anaesthesia.

• Biological variation: duration of anaesthesia may vary widely between individuals.

• Anatomical variation: can lead to ineffective anaesthesia (e.g. of an inferior dental block when an aberrant mandibular foramen occurs).

Complications

General complications

There are three typical types of complication:

Types of local anaesthetic drugs

Topical local anaesthetics

Topical LAs may be used on intraoral mucous membranes prior to intraoral injections of LA or to reduce discomfort of minor procedures. They may also be applied to the skin prior to venepuncture.

Vasoconstrictors

Most LAs (except cocaine) cause blood vessel dilatation and, therefore, a vasoconstrictor is added to diminish local blood flow and slow absorption of the LA. In practice, LAs still enter the systemic circulation quite rapidly but vasoconstrictors are useful to accelerate the onset, lengthen the duration and increase the depth of anaesthesia. They also reduce the local haemorrhage, which can be very helpful during surgical procedures. However, vasoconstrictors should never be used for infiltration of the ears, fingers, toes or penis as ischaemic necrosis may result. The concentration used is higher in dentistry than in medicine, particularly in the UK.

Common drugs in dentistry

Drug dose for safety

Estimation of a safe dose must take into account:

The maximum recommended doses are given in Table 4.2. Articaine has not been recommended by the manufacturer for use in children under 4 years of age, although dentists have been known to use it and find it effective in children between 2–3 years.

Table 4.2

Maximum recommended doses of local anaesthetics

Preparation Maximum dose in healthy adult Child (20 kg)
2% Lidocaine 4.4 mg/kg up to 300  mg (7 cartridges) 2 cartridges
3% Prilocaine 6.0 mg/kg up to 400 mg (6 cartridges) 1.8 cartridges
4% Prilocaine 6.0 mg/kg up to 400 mg (4.5 cartridges) 1.4 cartridges
4% Articaine 7.0 mg/kg up to 440 mg (5 cartridges) 1.5 cartridges

1cartridge contains 2.2 ml.

4.3 Conscious sedation

Some patients are overly anxious about routine dental treatment, while others, who may be able to cope with uncomplicated treatment, may be distressed by more unpleasant procedures such as minor oral surgery with local anaesthesia alone. Management approaches vary according to the severity of the anxiety, the age of the patient, the degree of cooperation and the medical history. Psychological approaches have been widely used and range from informal and common-sense methods to formal relaxation training, hypnosis and cognitive behavioral therapy (CBT). These techniques are safe, free from side-effects and give the patient a sense of control.

An increasing number of patients are managed with conscious sedation techniques in combination with a LA but the more severely anxious and uncooperative may require treatment under a GA. As patient awareness of the risks of anaesthesia and the availability of sedation has increased, so the demand and popularity of conscious sedation for dentistry has increased. The control of pain and anxiety is fundamental to the practice of dentistry.

The aim of a sedation technique is to keep the patient conscious and cooperative but in a state of complete tranquillity. Ideally, the patient should have the sensations of warmth, confidence and a pleasant degree of dissociation from the realities of the situation. Sedation with drugs is not a replacement for, but rather an adjunct to, a caring and sympathetic attitude towards the patient. Conscious sedation may be defined as a state of depression of the central nervous system produced by a drug or drugs, enabling treatment to be carried out, and during which communication is maintained, such that a patient will respond to command throughout the period of sedation. The techniques used should carry a margin of safety wide enough to render unintended loss of consciousness unlikely.

Risk avoidance: When using sedation techniques, it is important to avoid risks and the dentist should only proceed with methods with which he or she feels competent, in an environment that is adequately equipped and with staff that are appropriately trained. There should always be a second person present who is trained in the care of sedated patients. While UK dental schools provide undergraduate students with the necessary knowledge and skills to enable them to provide conscious sedation to patients, the British General Dental Council currently recommends additional postgraduate training. It is essential that dentists and their staff working in these fields are familiar with the appropriate regulations according to their country of practice.

All dental treatment facilities must have appropriate equipment and drugs for resuscitation at hand, the dentist and his or her team must have the skills to use them in an emergency whether providing conscious sedation techniques or treatment under local anaesthesia alone.

Assessment for conscious sedation

Indications

Medical and behavioural indications: Systemic disorders such as mild angina, controlled hypertension or controlled anxiety-induced asthma, may be an indication for the use of sedation as this minimises the psychological response to stress and so will reduce the activity of the sympathetic nervous system. This may avoid, or at least reduce, the likelihood of an angina or asthma attack or of raising the systemic blood pressure. Those with cardiorespiratory compromise should receive supplemental oxygen.

In disorders such as spasticity, multiple sclerosis or parkinsonism, where a patient may be eager to cooperate but physically unable to do so, benzodiazepine sedation may be of use because of its muscle relaxant properties. Similarly, patients with controlled epilepsy may benefit from the anticonvulsant property of benzodiazepines. Anxiety-induced gagging is often very successfully managed with sedation.

Contraindications

Medical contraindications:

Pregnancy: Women who are, or may be pregnant, should preferably not be sedated or given a GA. Nitrous oxide inactivates vitamin B12, inhibits DNA formation and may be teratogenic. Its use in elective situations is therefore, contraindicated, particularly during the first trimester when cell differentiation is occurring. Nitrous oxide may be used safely, however, during late pregnancy and indeed is frequently used for pain relief during childbirth. Animal experiments have not indicated any teratogenic risk with midazolam, but evaluation in human pregnancy has not been undertaken and it would, therefore, be unwise to use it unless considered essential. High doses of benzodiazepines in the last trimester of pregnancy have been reported to produce irregularities of the fetal heart rate, hypotonia, poor sucking and hypothermia in the neonate. Midazolam should not, therefore, be used during the last trimester. Caution must be exercised when using intravenous sedation for breastfeeding mothers. If using midazolam, it is reasonable to ask the mother not to breastfeed for 8 hours after the sedation and use synthetic or pre-expressed milk during this time.

Jan 9, 2015 | Posted by in Oral and Maxillofacial Pathology | Comments Off on 4: Control of pain and anxiety
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