Dr Ed Charlton,
Consultant in Anaesthesia and Pain Management, Royal Victoria Infirmary, Newcastle-Upon-Tyne, UK.

Introduction		Non-opioid analgesics
Clinical factors		Weak opioids
Patient-related factors		Strong opioids
Local factors		Narcotics
Assessment of pain severity		Pain relief in children
Pharmacology		Pain relief in the elderly
Local anaesthetics

The purpose of this review is to suggest methods of relieving acute postoperative pain. It will discuss how the use of peripherally-acting drugs (such as the non-steroidal anti-inflammatory drugs, centrally-acting agents (such as opioids) and local anaesthetics can achieve this. Guidelines are offered for pain relief in children and the elderly. Further suggestions are made about the route of administration of analgesic drugs and factors which may alter the complaint of pain following surgery. This review is not comprehensive but is intended to summarise current thought about the practical management of postoperative pain in an understandable and accessible fashion.

The effective relief of pain is of paramount importance to anyone treating patients undergoing surgery. This should be achieved for humanitarian reasons, but there is now evidence that pain relief has significant physiological benefit. Not only does effective pain relief mean a smoother postoperative course with earlier discharge from hospital, but it may also reduce the onset of chronic pain syndromes.

Pain serves a biological function. It signals the presence of damage or disease within the body. In the case of postoperative pain it is the result of the surgery, but the principles outlined in this article apply also to the management of other acute pains such as those following burns or injury. The goal for postoperative pain management is to reduce or eliminate pain and discomfort with a minimum of side effects as cheaply as possible. Postoperative pain relief must reflect the needs of each patient and this can be achieved only if many factors are taken into account. These may be summarised as clinical factors, patient-related factors and local factors. In the final analysis the ultimate determinant of the adequacy of pain relief will be the patient's own perception of pain.

 
Clinical factors

The site of the surgery has a profound effect upon the degree of postoperative pain a patient may suffer. Operations on the thorax and upper abdomen are more painful than operations on the lower abdomen which, in turn, are more painful than peripheral operations on the limbs. However, any operation involving a body cavity, large joint surfaces or deep tissues should be regarded as painful. In particular, operations on the thorax or upper abdomen may produce widespread changes in pulmonary function, an increase in abdominal muscle tone and an associated decrease in diaphragmatic function. The result will be an inability to cough and clear secretions which may lead to lung atelectasis (collapse of lung tissue) and pneumonia. Matters are made worse by postoperative bowel distension or tight dressings.

Pain causes an increase in the sympathetic response of the body with subsequent rises in heart rate, cardiac work and oxygen consumption. Prolonged pain can reduce physical activity and lead to venous stasis and an increased risk of deep vein thrombosis and consequent pulmonary embolism. In addition, there can be widespread effects on gut and urinary tract motility which may lead, in turn, to postoperative ileus, nausea, vomiting and urinary retention. These problems are unpleasant for the patient and may prolong hospital stay.

The choice of pain-relieving techniques may be influenced by the site of surgery. Equally, it may be influenced by drug availability and familiarity with different methods of analgesia. For example, although patient-controlled analgesia (PCA), has often been shown to be better than the intermittent delivery of intramuscular opioids it does not produce as much pain relief as epidural opioid analgesia. Equally, a local anaesthetic block can effectively relieve pain, but only for the duration of the particular agent used. Choice of technique will also be influenced by the degree of training and expertise of the staff.

For many years, the standard method of treating postoperative pain in the developed world has been intramuscular opioid (usually morphine). The effects of opioid drugs vary greatly among patients and thus individual responses cannot be predicted. Many studies have shown that under-treatment of acute postoperative pain occurs because doctors and nurses overestimate the length of action and the strength of the drugs and that they have fears about respiratory depression, vomiting, sedation and dependency.

Improvement can be achieved by better education for all staff concerned with the delivery of postoperative pain relief and by making the assessment and recording of pain levels part of the routine management of each patient. Ideally, a named individual should be responsible in each hospital for the delivery and teaching of acute pain management.

 
Patient-related factors

Although it may be possible to predict, to a degree, the amount of postoperative pain knowing the site and nature of the surgery, other factors may alter the amount of pain suffered by the individual patient. The nature and intended purpose of the surgery may be important. If the proposed operation will lead to a restoration of normal function, for example, a hernia repair or fixation of a fracture, it is likely to be seen in a positive way by the patient. Where the outcome is not clear, for example, an operation for cancer or to investigate an unknown pain, the patients' fear and anxiety may lead to high levels of postoperative pain being reported. Patients who are afraid of anaesthesia or surgery may report more pain and this can be very difficult to treat.

Adequate time must be allowed to explain the intended operation and the steps that will be taken to ensure pain relief afterwards. It is important to establish the expectations of the patient before surgery. Some may fear the unknown and others may have previous experience of surgery or have heard stories from friends and relatives that present the postoperative period in an unfavourable way. An adequate and friendly explanation in simple terms will often reduce anxiety and minimise misunderstandings about the nature and purpose of the proposed surgery.

(Continued...)

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