Background

There is no evidence that the experience of pain is any less intense in children than in adults. Despite this, children in hospital are given less analgesia than adults with the same conditions,1 and invasive procedures are too often carried out without adequate analgesia.4 Children recovering from major surgery have tended to receive fewer and smaller doses of parenteral opioids per kilogram body weight than adults and are switched to weaker oral analgesics sooner despite continuing severe pain.5 This is largely because of fear of respiratory depression, of cardiovascular effects, and because of exaggerated worry about addiction. Traditional regimens for postoperative analgesia at 4-6 hourly intervals 'as required' have usually resulted in nurses having to decide whether the child needs an intramuscular opioid or a weaker oral analgesic. Neither the 'as required' regimen nor the intramuscular route favours the smooth maintenance of analgesia. Assessment of pain has been haphazard and children themselves often hide pain rather than have an injection.5

General considerations

Successful management of pain depends on identifying its source and cause and assessing its character (intensity, site, temporal pattern) and what eases or aggravates it. It is important to consider not only the sensory component caused by noxious stimuli, but also the psychological, emotional and behavioural response, and the context in which pain is suffered. Relief of pain therefore requires more than the control of painful sensations by analgesic drugs, and management must be tailored to the individual child.

In children, the relief of fear and anxiety is particularly important. Careful explanation in terms that the child can understand (what is going to happen, what it might feel like, who will be there, and what will be done to prevent it hurting) can help the child to cope. Explanation will also relieve anxiety in the parent(s), helping them to reassure their child. A reassuring environment, the presence of a parent, and the comfort of a special teddy or a favourite video will often add to the relief achievable with analgesic drugs.

Pain assessment and monitoring

Accurate assessment of a child's pain is central to effective management.6^,7 Parents can often help but their contribution is frequently overlooked. They will know how the child normally copes with pain and what usually brings relief. They can help interpret symptoms by knowing if the child is naturally quiet and shy or noisy and extrovert.8 Often they can be involved in determining the child's need for analgesia.

Assessment depends heavily on the age and development of the child and on his or her capacity to communicate.6 In very young children and during anaesthesia, physiological measures such as heart rate, blood pressure, respiratory rate and palmar sweating may help indirectly to assess pain. However, these measures reflect stress rather than pain itself, so also change in response to factors other than pain. Absence of physiological changes does not exclude pain. Crying, irritability, grimacing, and loss of interest in play or eating can be behavioural clues to pain in children too young to describe their experience or who are suffering in silence.6 Formal observational scoring9^,10 is generally too laborious for use in routine practice, and the validity of such scores depends on the age of the child and the clinical situation.

Children over 4 are usually more able to report pain, and its intensity can be assessed using colour scales, graded pictures of facial expression or visual analogue scales.11 A simple 4-point scale of pain and sedation, based on observation by a nurse and self-reporting by the child, can be used to monitor the effectiveness and safety of postoperative opioid in children receiving patient-controlled analgesia.12

Assessments such as these should improve the medical team's awareness of the child's pain and provide a way of monitoring the effectiveness of treatment. Some sort of assessment should be used for each child, the type adopted depending on the child's age and on local experience.

Management

Both drug and non-drug approaches to pain relief should be considered. Their use in a complementary way can enhance pain relief, reduce the need for drugs, and so lessen the risk of unwanted effects. The choice of treatments should be governed by the severity of the pain and the individual needs and circumstances of the child.

Anticipating and preventing pain is better than trying to relieve established pain. Wherever possible all necessary blood tests should be performed from a single venepuncture, and where several invasive procedures are needed they should be carried out during a single anaesthetic. Plans for post-operative analgesia should be agreed before the operation.

Analgesic drugs should be tried in logical sequence, based on an accepted scale of efficacy such as the World Health Organization 'analgesic ladder'.13 A milder analgesic such as paracetamol should be tried before a stronger one unless pain is immediately severe, as in major trauma. Drugs of similar efficacy should not be substituted: if one drug on a rung of the ladder has proved ineffective, a drug from the next rung should be tried. Alternatively, a drug of similar efficacy but with a different, complementary action may be added (e.g. a non-steroidal anti-inflammatory drug plus paracetamol): this can sometimes offer better pain relief with less severe unwanted effects than substitution of a stronger drug.

Adequate and regular dosing - For each child the dose, dosage interval and route of administration must be reviewed regularly in the light of the clinical response. The optimal regimen is the one that provides a pain-free and comfortable child with minimal unwanted effects. 'As required' regimens are best avoided: controlling renewed pain when analgesia wears off is harder than maintaining a stable level of analgesia and often requires larger doses of analgesia. Peak and trough effects are more likely and unwanted effects may be more troublesome.

Route of administration will depend on the drug, on the nature and severity of the pain and on the unwanted effects encountered. Drugs are best given by mouth when pain is not severe. Rectal administration may be better tolerated if nausea or vomiting is a problem. Parenteral administration is used if the drug selected can be given only by injection or when enteral administration has failed. A continuous infusion by means of a pump is one way of maintaining a stable level of analgesia; the drug can be given through an indwelling intravenous catheter or subcutaneously. Intramuscular injections should be avoided because they are often painful, absorption may be unpredictable and bleeding can occur in children with thrombocytopenia.

The drugs

Paracetamol

Paracetamol is effective for the relief of mild or moderate pain. Given as an oral suspension, the dose needed to relieve pain (as opposed to fever) is usually 15mg/kg, which may be repeated every 4-6 hours to a maximum total dose of 60mg/kg daily. Oral doses above 20mg/kg offer no greater analgesia. The drug may be given rectally if a child is vomiting but absorption is less reliable; 20mg/kg is needed.

Non-steroidal anti-inflammatory drugs (NSAIDs)

Aspirin should not be given to children under 12 years old because of an association with Reye's syndrome.14 Few data sheets for NSAIDs list general analgesia in children as an indication. Experience is probably greatest with ibuprofen (20mg/kg/day in divided doses as paediatric suspension). Diclofenac is available as a paediatric suppository; the suppositories are used widely for postoperative analgesia (an unlicensed indication).

The main uses of NSAIDs in children are the control of pain from mild musculoskeletal trauma, from inflammation in soft tissues and joints, and from prostaglandin-releasing metastases. NSAIDs are also useful for the relief of post-operative pain in children: they do not depress respiration or impair gastrointestinal motility - an advantage especially in day-case surgery - and they may reduce the need for opioids after major surgery. Very few studies have compared NSAIDs with paracetamol in children; one found ibuprofen superior to paracetamol or codeine plus paracetamol after dental extraction.15 In another study, diclofenac suppositories controlled pain better than paracetamol after adenoidectomy.16

NSAIDs should be avoided in children with a history of gastrointestinal bleeding and used only with careful monitoring in children with renal impairment.17 NSAIDs may interfere with platelet function, which may make them unsuitable in children with thrombocytopenia and in those at risk of haemorrhage from other causes.

Opioids

Opioid analgesics are used to relieve moderate or severe pain.

Codeine (0.5-1 mg/kg every 4-6 hours) or dihydrocodeine (0.5-1 mg/kg every 4-6 hours) may be useful, alone or with paracetamol, when pain relief is inadequate with paracetamol. However, constipation (especially with codeine) and dysphoria may offset the benefit of the additional pain relief. Codeine may be given by mouth, rectally or subcutaneously. It should never be given intravenously because of the particular risk of severe hypotension or apnoea.18

Morphine is the standard opioid for the relief of severe pain in children. It can be given by mouth in a variety of standard or modified-release formulations. The usual oral dose for acute pain using the standard formulation is 200-500µg/kg every 4 hours.

After major surgery, continuous intravenous or subcutaneous morphine infusion provides stable, effective analgesia. Intravenous administration should be via a dedicated, indwelling catheter or using a one-way valve to prevent the drug tracking up another line (which risks a large dose being delivered suddenly if that line is flushed). A loading dose of 50-100µg/kg is infused over 30 minutes. To maintain analgesia, an infusion rate of 5-40µg/kg/hour is usual, titrated against the child's pain and unwanted effects;18 the rate is the same for subcutaneous infusion but the morphine solution is more concentrated. Careful monitoring is essential but treatment need not be on an intensive care unit provided that training and supervision of nurses, ward staffing, and procedures for immediate resuscitation at the bedside are adequate.

Sedation is an important early sign of respiratory depression. Respiratory rate and depth should be monitored hourly. A respiratory rate of <0/minute (or <0/minute in a child under 5) warrants concern; continuous pulse oximetry may be a more sensitive indicator of respiratory depression.12 If excessive sedation or respiratory depression occurs the infusion should be stopped, a clear airway ensured and oxygen given. Naloxone (4µg/kg by slow intravenous injection repeated every 3-5 minutes if necessary) reverses both respiratory depression and analgesia. Its action is brief compared with morphine, so monitoring for respiratory depression must continue.

Patient-controlled analgesia (PCA) - A patient-triggered, computer-controlled, parenteral morphine infusion pump can give good pain control after operations12^,19^,20 and has been used successfully in other situations such as sickle-cell crisis.21 PCA may be suitable for children over 5.20 Before the operation a doctor or specialist nurse should explain the machine and make sure that the child understands the protocol and can work the trigger to deliver a bolus dose. Most children waking after surgery will not remember the instructions straightaway so a background infusion (optimal rate 4µg/kg/hour) is needed to maintain the pain relief provided by the loading dose. Later, the child can trigger additional doses (10-20µg/kg). A 'lock-out' interval of 5-15 minutes, a 4-hour dose limit and a protocol that ensures that only the child (not the parents) can trigger the device will minimise the risk of accidental overdose.19 Respiratory depression is rare with PCA but strict monitoring is essential. Nausea and vomiting often occur and may warrant an antiemetic.19

Extradural opioid - Morphine may also be given continuously or intermittently through a catheter placed in the extradural space, usually via the caudal route. Analgesia is often excellent, but pruritus, nausea and vomiting and urinary retention are common. Respiratory depression can occur up to 20 hours after extradural opioid.

Local anaesthetics

EMLA cream is a mixture of lignocaine plus prilocaine (both 2.5%). The cream enables painfree venepuncture but to be effective it must be applied under an occlusive dressing for at least 60 minutes beforehand. EMLA can also be used before infiltration of local anaesthetic, split skin grafting or division of preputial 'adhesions'. It should not be applied directly onto wounds or mucous membranes, nor used rectally. Vasoconstriction may impede venepuncture but usually resolves within 15 minutes of removal of the cream, whilst analgesia persists for up to an hour.22

Infiltration of local anaesthetic works rapidly and is recommended before invasive ward procedures such as lumbar puncture. Lignocaine is effective for up to 2 hours, bupivacaine for up to 8. Local infiltration of the wound at the end of the operation reduces postoperative pain.23

Regional analgesia, undertaken whilst the child is under general anaesthetic, can give prolonged control of severe pain during or, after operations or following trauma.23 Regional analgesia avoids the unwanted effects of opioid and is particularly useful in children with chronic respiratory disease. It is often suitable for day-case surgery whilst use of parenteral opioid entails overnight monitoring in hospital. Extradural block using bupivacaine as a 'single shot' or infused through a paediatric extradural catheter gives profound analgesia to both surface and deep structures. Caudal block is suitable, for example, for herniorrhaphy, orchidopexy and circumcision. Children and their parents should be warned of the possibility of urinary retention and of transient weakness and numbness. Hypotension appears less of a problem in children under 6 years old than in older children and adults.18 Peripheral nerve block (e.g. brachial plexus or ilioinguinal block) is suitable for many day-case operations and after trauma (such as limb fractures). Use of an electrical nerve stimulator during the general anaesthetic can ensure effective blockade.

Toxicity can occur with high plasma concentrations of local anaesthetic which can occur when large amounts of the drug are given, or if the drug is inadvertently introduced directly into blood or is injected into inflamed or infected tissues. In any 4-hour period, a safe maximum for bupivacaine in children is 3mg/kg, for lignocaine (without adrenaline) 6mg/kg.18 Toxicity causes numbness of the tongue and mouth, lightheadedness, twitching, convulsions, coma and respiratory and cardiac arrest.

Pain following trauma

The pain of accidental trauma is already established by the time the child reaches the GP surgery or hospital. Pain from minor trauma can often be controlled with paracetamol, ibuprofen or codeine. An oral dose of analgesic does not affect the safety of a general anaesthetic later, but gastric stasis accompanying trauma may impair absorption.

After major trauma the child must first be resuscitated and stabilised and adequate analgesia should be given as soon as possible. Immobilisation of the injured part greatly relieves pain. An opioid should be given only by slow intravenous injection because skin and muscle blood flow are unpredictable. Intravenous pethidine has no advantages over morphine and is best avoided; risk of respiratory depression is no less than with morphine at equianalgesic dose, and convulsions may occur with large doses of pethidine. Inhalation of Entonox (a 50:50 mixture of nitrous oxide and oxygen) acts and wears off rapidly and can be controlled by the patient. Entonox is useful in the management of burns as well as pain from procedures. It should not be used with air-containing injuries to the head or chest (e.g.pneumothorax) because diffusion of the gas into the space increases pressure.24

Non-drug approaches

Rocking, cuddling and 'rubbing it better' often help children in pain. Many non-drug approaches utilise similar principles. We can mention them only briefly, but their role in enhancing pain relief in children is increasingly recognised. They may work by partially blocking the 'spinal gate' for pain stimuli, by distracting the child from pain and by providing reassurance. To be effective, they need to be integrated into the overall approach to pain management on the ward.

Familiar activities such as play, reading stories, listening to music or watching a video, chosen by and suited to the child, can be structured to interest him or her during painful procedures on the ward.25 More formal behavioural approaches include relaxation (e.g. deep, rhythmic breathing to reduce muscle tension), massage and biofeedback. Transcutaneous electrical nerve stimulation, heat, ultrasound, and acupuncture are physical methods that can reduce pain. All can be effective adjuncts to drug treatment but carers need to remember that some compliant children may co-operate adeptly while suffering in silence.25

An acute pain service

An acute pain service can improve the management of pain in children in hospital by ensuring that effective analgesia is given safely and that children receiving it are properly monitored for pain relief and unwanted effects according to an agreed protocol.2^,19 Teams should include an anaesthetist and specialist nurses, and often a pharmacist, physiotherapist and psychologist. They provide training and support for staff, set practical standards for management on routine wards, assess and educate children before surgery (e.g. in use of patient-controlled analgesia) and see them regularly afterwards. Additionally the pain service team can audit the effectiveness of treatment, complications and patient satisfaction and can assess new treatments.

Conclusion

Children in acute pain are often undertreated. Use of 'as required' regimens are not an effective way of managing pain. Pain should be anticipated where possible. Children with established pain may need regular or continuous treatment, which should be given by an appropriate route, titrating the dose against pain relief and unwanted effects. Fear of unwanted effects should not deter use of an opioid for severe pain, but strict monitoring is essential. In hospital, an acute pain service optimises the use of modern approaches to analgesia and provides for training, supervision and audit.

Assessing pain in children is difficult. Parents should be closely involved, and the use of scales can often help when children are unable to describe their symptoms. Easing fear and anxiety, contact with parents, reassuring surroundings and careful explanation are central to management. The role of non-drug approaches in complementing drug therapy is increasingly recognised.