In the second of our series on anaesthesia Jo Fitz-Henry and Nina Ruth Lewis explain the management of perioperative pain and analgesia

Pain is a big problem, yet it is often poorly understood and badly managed. Everyone is taught the dangerous side effects of pain killers, but few are taught the equally dangerous side effects of pain.

Common misconceptions about pain and its control

• Pain is to be expected with illness or after an operation. Anyone who asks for more analgesia is regarded as "weak" or a drug seeker. Patients often collude with this belief and "don't want to make a fuss" to obtain adequate analgesia
• Opioids are dangerous and cause addiction. There is no evidence to support this when opioids are used to treat acute pain
• Analgesia will mask symptoms and delay diagnosis

What is pain?

Pain is primarily a protective mechanism meant to bring to conscious awareness the fact that tissue damage is occurring or about to occur. Pain is accompanied by motivated behavioural responses, such as withdrawal or defence, as well as emotional reactions, such as crying or fear. Past experiences, the patient's attitudes, beliefs, and personality can also shape the subjective perception of pain.

Why is pain a problem?

Pain hurts. But it has several important complications in addition to being unpleasant. Some of the morbidity and mortality related to surgery and trauma may be the result of the pathological disturbances initiated by severe or poorly controlled acute pain.

For example, patients with chest wall or abdominal incisions who do not receive adequate acute pain control have limited ability to take a deep breath, cough, and tolerate chest physiotherapy. This causes sputum retention and atelectasis, increasing the risk of pneumonia, hypoxaemiaand death. Pain limits mobilisation. This restricts participation in physiotherapy and rehabilitation, leading to longer hospital stay. It can also lead to complications of immobility, such as deep vein thrombosis and pressure sores.

The haemodynamic responses to acute pain are tachycardia and hypertension, which increase myocardial oxygen consumption. The coronary ischaemia that often follows is implicated in the development of myocardial infarction.

Non-pharmacological interventions

Surgery or trauma not only damages tissues but also elicits psychological responses, such as anxiety and fear - something that the torturer knows only too well. Optimum control of pain therefore reduces psychological injury after an operation or trauma. Similarly, psychological resilience and preparedness make it easier to control pain.¹ Cognitive and behavourial interventions, such as education, goal setting, being nice to the patient, and offering support may influence a patient's experience of pain and improve his or her psychological state. Even a hand to hold and a chat can make an important difference.

Other interventions that can give the patient some control over the painful situation are listed in box 2. These are not just in the domain of the nursing staff.

Pharmacological treatments

The analgesic ladder

The analgesic ladder is a common framework used to prescribe analgesia in a logical stepwise approach (see table 1). You start at the level most appropriate to the patient's level of pain and make sure that you have prescribed something from each "rung" below. Progress to the next rung if the pain is not controlled after an adequate trial period (the length of time in which you would have expected the drug to have some effect). All medication should be given regularly to maintain analgesic levels in the body. There should be rescue analgesia prescribed for break-through pain. Remember also to prescribe antidotes for the common side effects - nausea, constipation, etc.

Paracetamol

Paracetamol is an effective first line analgesic drug. It has analgesic and antipyretic effects through its action on central prostaglandin inhibition. It has a low incidence of side effects. Paracetamol is most effective when given regularly (1 g every six hours in an adult) rather than when the patient or the nurse thinks it is suitable.

There are several combined paracetamol and weak opioid preparations, for example, co-proxamol and co-codamol. However these combination preparations do not allow for variation in the strength or timing of the opioid component if required. Co-proxamol also does not allow for the full dose of paracetamol to be given. These drugs are probably best avoided.

Non-steroidal anti-inflammatory drugs (NSAIDs) When tissues are injured they release inflammatory mediators, which sensitise and stimulate the nociceptors. NSAIDs inhibit the enzyme cyclo-oxygenase, which is involved in the production of many of these inflammatory mediators - for example, prostaglandin through the arachidonic acid pathway and are therefore valuable analgesics.

NSAIDs are effective in treating pain and should be prescribed in every patient where contraindications to their use do not exist (see table 3). They do, however, have several predictable prostaglandin mediated side effects (see box 3) Since their mode of action is different from opioids, NSAIDs are safe to use in combination with opioids and as such reduce the opioid requirement and opioid induced side effects.

Opioids ("narcotics")

Opioids are highly effective in managing acute and chronic pain. Opioids do not make the pain go away, but make the patient feel better about having it. If the source of the pain is palpated the examiner will still elicit a response, especially if that response is a reflex, such as abdominal guarding in peritonism.

Opioids share several common properties since they all act through the same receptors (see table 4).

Sedation

Opioids have differing potencies, meaning that to get the same end analgesic effect different quantities of different drugs have to be given. Diamorphine is a potent analgesic and codeine a less potent one. However when enough of either drug is given to get a good analgesic effect, the type and severity of the side effects will be much the same. This is why the weaker or less potent opioids should not be thought of as "milder." Table 5 lists some common opioids and their doses.

Doses may need to be decreased in frail or elderly patients, and increased where there is severe pain or tolerance to opioids.

Opioid receptors are present in the nausea centre of the brain ("chemoreceptor trigger zone") and all opioids exert an emetic effect. They also cause delayed gastric emptying and make patients more prone to motion sickness.

An antiemetic must be prescribed with all opioids - for example, cyclizine, 50 mg, or ondansetron, 4 mg. Opioids also cause constipation - the one side effect that patients do not become tolerant to. Prescribe a regular laxative, such as lactulose 20 ml twice a day, especially if there are other reasons for constipation such as immobility.

Opioids reduce the respiratory rate and may cause hypoxia if the dose given is greater than that needed to control the pain.

Counting the respiratory rate is the simplest bedside test to assess respiratory depression. Give the patient face mask oxygen and have your intravenous naloxone, a competitive opioid antagonist, (200 µg) ready should the respiratory rate drop below eight breaths a minute.

A word of warning about pethidine. This is often wrongly regarded as more suitable for use in frail or elderly patients. Pethidine is a synthetic molecule with an anticholinergic effect like atropine. When pethidine crosses the blood brain barrier it causes confusion, especially in elderly patients. It also causes dysphoria rather than the euphoria seen with the other opioids and leads to agitation. Morphine is a much better alternative.

Local anaesthetic techniques

Although these do not appear on the analgesia ladder, do not forget that whole chunks of the body can be rendered comfortably numb with effective local anaesthetic techniques. Local anaesthetics can provide better analgesia than opioids and NSAIDs without exposing the patient to their inherent adverse effects. On the down side, local anaesthetic techniques, such as epidurals and nerve blocks, will need the skills of the anaesthetist and local anaesthetics have their own side effects. Ask your pain team if you think that a local anaesthetic technique would be suitable for your patient.

Which route of administration?

The oral route of administration is safe and convenient and is the preferred method of drug delivery whenever possible. It does require a functioning gut, which may be a problem after operations. If a patient has normal gut function there is no benefit in giving drugs, including opioids, intramuscularly. If you give opioids orally the lower bioavailability means that you will have to give three times as much as the parental dose - for example, 10 mg morphine by subcutaneous injection becomes 30 mg oral morphine.

Intramuscular injections hurt and will lead to the patient being reluctant to ask for analgesia, therefore adding to the total pain load. Furthermore, absorption of drugs from the muscle is affected by perfusion - for example, reduced in shock and hypovolaemia - and mobility - stored in inactive muscles of the bedbound. Another alternative to intramuscular administration is subcutaneous injection, which is less painful. Bolus administration of intravenous opioids titrated to the patient's reported pain levels is the way of rapidly controlling pain. This effective way of letting patients decide how much analgesia they need can be continued by setting up a patient controlled analgesia system.

Changing analgesia requirements

An unexpected increase in pain in a previously settled patient means that something is wrong. Look for underlying cause and initiate treatment, but do not forget to increase the analgesia as well. The patient will have steady state blood levels of analgesics which will need to be rapidly stepped up to keep pace with the higher levels of pain. Intravenous opioids are the method of choice.

Each patient is different when it comes to weaning down postoperative analgesia. Do not cross off their opioids or take away their patient controlled analgesia system on day four after the operation just because you do that for everyone. They are comfortable because of the drugs they are currently taking. Let them keep their access to these analgesics until they feel that they no longer want them. Remember that pain has a big psychological component, and for patients to feel in control they need this comfort blanket. Ask the advice of someone who knows (see below).

Who else can I ask?

If you need advice you have several sources of help apart from your own team. Most hospitals now have a multidisciplinary acute pain team. This is there to provide help with pain control problems and to train and support the staff who prescribe and administer the analgesia in its many forms. Your ward pharmacist will be able to provide you with drug information. Pick the brains of the anaesthetists about practical management and the use of regional techniques, such as nerve blocks or epidurals.

The important bits

• Pain is dangerous and has several significant complications including death
• Opioids are safe and do not cause addiction in managing acute pain
• Give paracetamol and NSAIDs to everyone in pain in whom they are not contraindicated
• Use as many different types of analgesia as possible
• If the patient is comfortable do not remove their analgesia

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Further reading

1 McQuay H, Moore A, Justins D. Treating acute pain in hospital. BMJ 1997;314:1531.
2 Gotzshe PC. Non-steroidal anti-inflammatory drugs. BMJ 2000;320:1058-61.