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Control of acute pain in postoperative and post-traumatic situations and the role of the acute pain service
Pain
Control of acute pain in postoperative and posttraumatic situations and the role of the acute pain service
training for all staff involved in managing acute pain, introducing new drugs and techniques, and auditing the outcomes. Since 1990 there has been substantial investment in acute pain services, with acute pain teams now being part of normal prac tice. However, in spite of these changes subsequent publications have demonstrated a substantial number of patients continuing to experience severe pain after surgery.2 These finding have been substantiated by audits in individual departments. In an effort to tackle this continuing problem, some departments have introduced systems to identify those patients who have had previous unsatis factory pain experiences before they are admitted for further pro cedures. By identifying these patients and investigating possible reasons for poor pain control at the pre-assessment visit, their subsequent admissions can be better managed. Those patients who are taking strong opioid analgesia before admission can also be identified in advance and their management planned. There has been an enormous growth in the publication of guidelines for acute pain management, many of them evidencebased. The second edition of the book Acute pain management: scientific evidence3 provides a wealth of information with careful ranking of levels of evidence. The Royal College of Anaesthetists (RCA) published guidelines that drew on the experience of many specialists to guide the process of providing epidural analgesia as part of an acute pain service.4 In 2006, the RCA published a com pendium of audit recipes for continuous quality improvement in anaesthesia, which includes a chapter on acute pain services.5 Concerns about serious complications related to continuous epi dural analgesia have prompted the RCA to perform a national survey of such problems, and this is ongoing. A related project, National Confidential Acute Pain Critical Incident Audit (NCAP CIA), is currently seeking information regarding serious incidents involving any kind of acute pain management strategy. This pro ject is also attempting to define the denominators (i.e. how many of these procedures are performed annually in the UK) in order to better understand the frequency of these events. The Prospect group promote the concept of procedure-specific analgesia and have produced evidence-based guidance to managing pain after a number of common procedures (see Further Reading).
Andrew P Vickers
Abstract There has been considerable investment in services that promote the effective management of acute pain. Despite acute pain teams being normal practice in UK hospitals and an increasing volume of guidance, there are still a substantial number of patients who suffer moderate or severe acute pain. Acute pain teams improve analgesia, reduce side effects and improve safety on the basis of comparative studies. Simple scales for assessing pain are effective. Assessment may be more difficult in certain patient groups such as babies, infants and children, elderly patients and non-English speakers. Assessment for the symptoms and signs of neuro pathic pain is important when nerve injury is suspected. Effective pain management obtunds the adverse effects of the injury response and may reduce the risk of chronic postsurgical pain. Preventive analgesia in terms of reducing postoperative pain and/or analgesic use is associated with the use of local anaesthetics, opioids or N-methyl-d-aspartate antagonists. Paracetamol is an effective analgesic and lowers the number needed to treat of other analgesics. The use of non-steroidal anti-inflammatory drugs is limited by side effects. Tramadol has important non-opioid mechanisms that widen its scope. In the future there will be a greater focus on those areas where current pain control approaches are of limited benefit.
Keywords acute-on-chronic pain; chronic postsurgical pain; opioid tolerance; patient-controlled analgesia
The acute pain team The concept of the acute pain team (APT) was first described by Ready in Seattle, USA before being introduced into a number of units in the UK. APTs are now normal practice and usually com prise one or more specialist nurses and designated consultant anaesthetist sessions. The multidisciplinary approach as advo cated by the 1990 report is much less common. Staff and patient education, the development of guidelines and protocols, and audit of outcome and complications are all key functions of the APT. Activity may be limited to patients on surgical wards but a comprehensive service includes other departments, including medical wards and the accident and emergency department. The wide variability in APTs makes it difficult to analyse their benefits. Furthermore, the quality of studies into the effective ness of APTs is not suitable for meta-analysis. Evidence from comparative studies and case series supports the premise that APTs reduce pain scores and side effects. Expert opinion is that supervision by an anaesthesia-based pain service is necessary for the safe provision of epidural analgesia using local anaes thetic–opioid mixtures on general hospital wards.
A watershed for acute pain management occurred in 1990 with the publication of the joint collegiate report: report of the working party on pain after surgery.1 Prompted by numerous publications detailing unacceptable levels of severe pain after surgery, the report highlighted areas of concern and made recommendations as to how the situation could be improved. Inadequate education, poor organ ization and under-funding were regarded as major deficiencies. The report recommended the development of multidisciplinary teams with a designated leader. Acute pain teams would sup port and develop acute pain services by providing education and
Andrew P Vickers, FRCA, is Consultant in Anaesthetics and Pain Management at the Royal Lancaster Infirmary. A graduate of St Thomas’ Hospital, London, he trained in anaesthetics in Nottingham, the South West and Leicester. His interest in acute pain management began when he witnessed a close friend suffer uncontrolled pain after thoracotomy. Conflicts of interest: Andrew P Vickers has received honoraria from Pfizer and Bristol-Myers Squibb for speaking on acute pain issues.
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© 2007 Elsevier Ltd. All rights reserved.
Pain
side effects, has been championed by Kehlet6 as part of a process of accelerated recovery after surgery. Clinical studies in humans have not demonstrated a significant difference in effect from administering analgesics before surgical stimulus rather than after it (pre-emptive analgesia). Preventive analgesia is defined as a reduction in postoperative pain and/or analgesic consumption relative to another treatment (or a pla cebo or no other treatment) at a point in time that exceeds the expected duration of action of the target agent. The intervention may or may not be initiated before surgery. A systematic review has shown benefit from the use of preventive analgesia with local anaesthetics, opioids or NMDA antagonists.7
Pain assessment and measurement Regular assessment of pain leads to improved acute pain manage ment. In general, the use of one-dimensional pain scales is suf ficient. Where a significant neuropathic element is suspected, a multidimensional approach is needed that should include descrip tors specific for neuropathic pain; for example, the Leeds Assess ment of Neuropathic Symptoms and Signs (LANSS) and, possibly, simple sensory assessment looking in particular for allodynia and hyperalgesia. Verbal descriptor scales (VDS) (e.g. none, mild, mod erate and severe) correlate well with visual analogue scales (VAS) and, although they are less sensitive for measuring treatment out come, they are sufficient for use in the clinical setting. VAS avoid imprecise descriptive terms but require more concentration and coordination than VDS, and so are unsuitable for children aged less than 5 years and, possibly, for up to 25% of adults. Pain assessment may be difficult in certain situations. Valid ated tools are available for neonates, infants and young chil dren (Anaesthesia and intensive care medicine 8:5: 180). Elderly patients may have difficulties due to auditory and visual impair ment. Cognitive impairment, whether long term or an acute delirium, results in fewer complaints of pain. This may be due to diminished memory, a failure to report pain or, perhaps, that less pain is experienced. The VDS is more sensitive and reliable than VAS in elderly patients, including those with mild-to-moderate cognitive impairment who may also need more time to under stand and respond to questions regarding pain. The assessment of pain in non-English-speaking patients may be facilitated by the use of pain scales available in a number of languages from the British Pain Society’s website (see Further Reading).
Paracetamol Paracetamol did not gain popularity until the late 1940s. It acts via the CNS but its mode of action is still unknown. Inhibition of a sub type of the cylooxygenase-1 (COX-1) enzyme, promoting serotoninrelated anti-nociception, and inhibition of substance P may all play a part in its analgesic effects. Oral paracetamol is rapidly absorbed with a time to maximum concentration in the plasma (Tmax) of 30–120 minutes and a high bioavailability. It is well tolerated with very few contraindications. The number needed to treat (NNT) for paracetamol, 1 g, is 3.8 in acute pain. It enhances the analgesic effect of codeine, reducing the NNT of codeine (60 mg, from 16.7 to 4.2) and tramadol (Table 1). Paracetamol suppositories or the intravenous prodrug propacetamol have been used when the oral route is not suitable. An intravenous preparation of paracetamol is now available. It has a shorter time to meaningful pain relief than the oral form (8 versus 37 minutes) and better early analgesia. There is a cost consideration in the use of the intravenous prepara tion; restricting its use to when the oral route is not suitable or to when rapid-onset analgesia is needed will minimize the cost.
The physiology of pain The process whereby an injury, whether chemical, thermal or mechanical, generates nociceptive traffic is well understood. The role of the ‘chemical soup’, including prostaglandins and brady kinin, in changing nociceptor sensitivity in the periphery is central to the generation of a pain message, but the involvement of the immune system, especially mast cells, is now known to be impor tant in modifying this role. Changes within the CNS can be shown within hours of a surgical insult in terms of gene induction, and produce profound modification in CNS organization (e.g. activation of the N-methyl-d-aspartate (NMDA) receptor). Recent functional MRI images have shown changes in the somato-sensory cortex in response to injury, demonstrating that the CNS is not ‘hard-wired’ but is capable of plasticity. An understanding of the interaction of the many nerve pathways and neurotransmitters provides an insight into how drugs may assist in the process of pain management.
Non-steroidal anti-inflammatory drugs and COX-2 inhibitors These drugs, which block the production of prostaglandins by cylooxygenase, are effective alone for managing mild or moder ate pain, and reduce opioid consumption in treating severe pain. Concerns about excessive bleeding have seen the introduction of
The Oxford league table of analgesics in acute pain: the benefits of combining paracetamol with other analgesics
The treatment of pain Pain control can be justified on humanitarian grounds alone, but pain is also one of the factors that triggers the injury response, resulting in metabolic, endocrine, and water and electrolyte flux changes that may have an adverse effect on recovery. Effective pain control is capable of modifying these responses, although improved outcome or reduction in mortality is difficult to con firm. Severe postoperative pain is one of the risk factors for the development of chronic postsurgical pain (discussed below), but the multifactorial nature of this problem means that it is difficult to determine whether effective pain control reduces the risk. The concept of using effective pain management, whilst minimizing
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:1
Analgesic
NNT
Morphine, 10 mg (intramuscularly) Paracetamol, 1000 mg Codeine, 60 mg Codeine, 60 mg + paracetamol 1000 mg Tramadol, 75 mg Tramadol, 75 mg + paracetamol 650 mg
2.9 3.8 16.7 4.2 5.3 2.6
NNT, the number of patients who need to receive the active drug for one patient to achieve at least 50% relief of pain compared with placebo over a 4–6-hour treatment period. www.jr2.ox.ac.uk/bandolier/booth/painpag/ Acutrev/Analgesics/Leagtab.html
Table 1
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Pain
a specific contraindication to the use of ketorolac in the pre- and intraoperative period. Furthermore, studies of some of the COX-2 inhibitors have shown an increased risk of myocardial ischaemia or stroke in ‘at risk’ groups. Subsequently, this has been shown to apply to many if not all non-steroidal anti-inflammatory drugs (NSAIDs). Recent surveys have shown that many anaesthetists have significantly reduced their use of these drugs, choosing paracetamol in preference.
The incidence of chronic pain after surgery
Tramadol Originally considered as an opioid analgesic, it is now recognized that tramadol is only a weak agonist at the μ-receptor, and owes much of its analgesic effect to the inhibition of the reuptake of norepinephrine and serotonin at descending inhibitory neurons. There is logic, therefore, in using tramadol in addition to opioids (discussed below). There is some evidence to show that trama dol is more effective for neuropathic pain than opioids.
Incidence of chronic pain (%)
Amputation Thoracotomy Mastectomy Chlolecystectomy Inguinal hernia Vasectomy Dental surgery
30–85 5–67 11–57 3–56 0–63 0–37 5–13
Table 2
Research with animal models demonstrated that a presurgical dose of gabapentin inhibited the development of hyperalgesia following a surgical incision. Several randomized controlled trials using different pain models have shown an effect on post operative pain in humans. Single doses of gabapentin between 600 and 1200 mg (in excess of the licensed starting dose) have been shown to reduce pain scores and/or morphine consump tion after, for example, abdominal and vaginal hysterectomy, lower limb arthroplasty and laparoscopic cholecystectomy. Metaanalyses have confirmed these effects, which persist for up to 24 hours after surgery.10 Common side effects are dizziness and drowsiness, which may limit the value of gabapentin in day sur gery. Gabapentin has minimal drug interactions. The growing awareness of chronic postsurgical pain has raised the question as to whether gabapentin should be continued into the postoperative period, especially in those cases with a high risk of neuropathic pain (e.g. amputation, peri pheral vascular disease and spinal surgery for neuropathic pain). Although gabapentin has a numbers needed to harm of 3.7 for minor side effects, significant major adverse effects are unusual. Furthermore, gabapentin is widely used long term for chronic neuropathic pain. Deciding when gabapentin should be used postoperatively, at what dose and for how long are questions yet to be answered. Pregabalin has the same mechanism of action as gabapentin. Unlike gabapentin it has linear pharmokinetics (i.e. the CNS drug concentration rises with increasing dose) which suggests that it may have higher efficacy. In addition, pregabalin appears to have a faster onset of action. For these reasons, pregabalin may prove superior to gabapentin, but clinical studies in acute pain models are awaited.
Current techniques Intravenous patient-controlled analgesia with morphine is effec tive and offers greater patient satisfaction than ‘as required’ opioids analgesia. Continuous epidural analgesia can provide excellent analgesia, but whether it offers clear advantages in terms of reduced mortality and morbidity is uncertain. It does have a beneficial effect on some measures of cardiac and res piratory function. Level of insertion is important so that the catheter tip corresponds to the dermatomes of the surgical inci sion. Despite the benefits, epidural analgesia has not been shown to reduce hospital stay. Concerns about failure rates and seri ous complications have triggered audit projects to try to define the optimal use of this technique. Incisional infusions of local anaesthetics, taking advantage of the availability of elastomeric pumps, have been shown to be effective in a number of different procedures.8 They may reduce hospital stay and could be used after hospital discharge. If they fulfil their early promise, there may be a significant reduction in the use of epidurals. Chronic postsurgical pain There is a growing awareness that pain may persist for months or years after many surgical procedures (Table 2).9 The cause of this chronic pain is unclear but nerve injury is thought to play a role. This implies that surgical technique is important and surgical approaches that minimize the risk of nerve injury (e.g. minimally invasive surgery) should be used whenever possible. Patients who develop chronic postsurgical pain often describe severe pain immediately after surgery. Multimodal analgesia (including drugs such as clonidine and ketamine, and, to a lesser extent, paracetamol and NSAIDs) obtunds the CNS response to a surgical incision. These medications also counteract opioidinduced hyperalgesia, which is seen in association with the use of short-acting opioids and remifentanil in particular. Confirma tion as to whether this reduces the risk of chronic postsurgical pain is awaited.
Specific situations Severe pain in the recovery ward: good postoperative pain control begins in the operating theatre and progresses through recovery to the ward. Sometimes this process fails and patients complain of severe pain in the recovery ward. Rapid pain control is essential. Treatable causes of pain such as wound haematoma or a full bladder should be sought. If appropriate, intravenous paracetamol and NSAIDs should be administered. Recent publi cations have shown better efficacy after 2 g than 1 g paracetamol, so a second dose of paracetamol could be considered if one dose has already been administered intraoperatively. If these are unsuccessful, other strategies may be tried (Table 3).
Gabapentin and pregabalin These anticonvulsant drugs are licensed for the management of neuropathic pain. They bind to the α2δ1 subunit of the pre synaptic voltage-gated calcium channels of the primary afferent nociceptor, inhibiting the release of excitatory neurotransmitters.
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Type of operation
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Pain
three times more via patient-controlled analgesia than their opi oid-naïve counterparts). It is important to avoid withdrawal as well as provide appropriate pain relief. Intravenous patient-con trolled analgesia can be very effective, but bigger boluses and a background infusion may be necessary. Tolerance to side effects may also occur but cannot be relied on. Neuraxial blockade can offer excellent pain control but may not prevent withdrawal even if low-dose opioids are used (e.g. patient-controlled epidu ral analgesia). Multimodal analgesia will be of benefit. Ketamine may be very effective, but use of this drug on the general surgical ward must be carefully considered. Clear communication with the patient and their general prac titioner is essential before discharge to plan for the continued use of strong opioids or their withdrawal if no longer necessary.
Managing severe pain in the recovery ward • Exclude treatable conditions (e.g. haematoma, full bladder) • Intravenous paracetamol? – second dose • Intravenous NSAID/COX-2 inhibitor if appropriate • The Lancaster protocol for morphine/alfentanil titration in recovery8 Morphine, 15 mg Alfentanil, 1 mg Normal saline, to a total volume of 15 ml 3 ml of the mixture administered every 2 minutes to effect • Tramadol 50–100 mg (intravenously) • Ketamine 10 mg • Clonidine 1 μg/kg • Midazolam 1–2 mg
Substance abuse disorder (SAD) is defined as a state in which the extent and pattern of substance use interferes with the psy chological and sociocultural integrity of the individual affected. These patients can present many challenges to achieving effec tive pain control. They may exhibit behaviours relating to their chaotic use of substances and to fears about their treatment by healthcare workers (Table 4). Hospital staff may stereotype the patient, which inhibits appropriate attitudes to managing the patient’s pain. The patient may have recently used illicit sub stances and may continue to use them whilst in hospital. They may exhibit high levels of tolerance to opioid analgesics, whilst having a low pain tolerance. Patients may be registered with local community drugs teams and be on maintenance programmes, but they may or may not use non-prescribed drugs or may be unknown to these teams. Patients who have stopped using illicit substances may be fearful of relapse if they are given opioid analgesics. Some of the drugs used as maintenance therapy can cause major difficulties for pain control. The aims of pain management in patients with SAD should be to provide realistic pain control, avoid withdrawal, prevent harm from
Table 3
Ludbrook et al11 performed pharmacokinetic modelling of estim ated CNS concentrations to derive the optimum mixture of mor phine and alfentanil for the treatment of postoperative pain. The alfentanil provides rapid analgesia, whilst an equipotent dose of morphine for longer-term analgesia is administered simultaneously. This approach was adopted in Lancaster in 2002 and has been shown to achieve rapid pain control, with most patients improving from a pain score of 3 (severe) to 1 (mild) within 10 minutes. Tramadol does not rely on its effects at the μ-receptor to pro duce analgesia. It is less likely to cause respiratory depression and sedation than opioids, although other side effects, in particu lar nausea and vomiting, can be troublesome. NMDA-receptor antagonists may be used, and ketamine has been shown to improve analgesia in patients who are poorly responsive to opi oids. Clonidine, an α2-agonist, consistently improves periopera tive analgesia. Low-dose midazolam may be useful. Midazolam is known to augment analgesia when administered intrathecally, but why it may improve analgesia when administered intra venously is not clear. Reduction of anxiety may be a factor but an effect on muscle spasm may play a role. There are two important caveats when employing the above strategies. First, they are intended to control severe pain but are likely to be short-lived. It is essential, therefore, to plan for the long-term management of pain. Second, the use of these drugs may cause significant side effects, so it is important to ensure a high level of supervision before the patients are returned to the general ward. For this reason, caution should be exercised before employing these strategies outside the theatre setting (e.g. in the accident and emergency department).
Adverse attitudes and behaviours affecting the management of pain in patients with substance abuse disorder Patient factors • Patients may fail to disclose information because of fear of: Stigma Being given an antagonist or partial agonist Being denied analgesia • Pseudo-addiction – seeking more medication because of inadequate pain control • Drug-seeking Healthcare worker factors • Healthcare workers may believe that: Maintenance methadone is sufficient to manage postsurgical pain Methadone is suitable for managing postsurgical pain All requests for analgesia represent drug-seeking Withdrawal should be immediate
The opioid-tolerant patient: tolerance is defined as a decrease in the effect of a drug over time so that a progressive increase in dose is required to achieve the same effect. Tolerance devel ops to most side effects as well as to the desired therapeutic effect. Opioid tolerance is most commonly seen in patients being treated with opioids for chronic or cancer pain and in patients with substance abuse disorder (discussed below). Opioid-toler ant patients have been shown to be relatively intolerant of pain and so are likely to require increased opioid doses (approximately
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Table 4
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© 2007 Elsevier Ltd. All rights reserved.
Pain
the use of non-prescribed drugs and minimize the impact of their behaviour on other patients. Open, honest discussion can produce empathy and cooperation. This can be backed up with information from the community drugs team and/or general practitioner. Use urine testing (more than once if necessary) for qualitative informa tion. Avoid using long-acting analgesics, especially methadone, for acute pain. Morphine is effective, is familiar to all staff and will prevent withdrawal. Be mindful of tolerance to both the effects and side effects of morphine. Multimodal analgesia and neuraxial blockade may be helpful but do not prevent withdrawal. The recovering patient may be fearful of relapse. Multimodal analgesia, avoiding strong opioids, is desirable but patients should be reassured that opioids may be necessary. Plans for the subsequent withdrawal of opioids are necessary and involve ment of the community drugs team may be helpful. Methadone is used for maintenance therapy because its slow onset avoids the ‘high’ associated with heroin but prevents withdrawal. If the dose normally taken can be confirmed (by the community drugs team, prescribing general practitioner or community pharmacy) it can be administered orally. If there is any doubt about the dose, caution must be exercised, and small doses of methadone, 10 mg, given every 4–6 hours, with careful observation for signs of opioid overdose. If the patient is nil by mouth, intravenous patient-controlled analgesia with morphine will provide analgesia and prevent withdrawal. It is usually necessary to programme bigger boluses with shorter lockout than usual and, possibly, a background infusion. Naltrexone is a long-acting pure antagonist of opioid receptors. It is licensed for promoting abstinence in the UK, and also in the USA for the management of alcoholism. A single dose of naltrex one will produce a blockade of about 50% of opioid receptors after 72 hours. Naltrexone is also available as a subcutaneous implant, with effects lasting between 9 and 12 months. Naltrexone will render even large doses of opioids ineffectual.12 It is important that its use is recognized before elective procedures so that pain management can be planned. In the emergency situation, altern ative methods of analgesia will be necessary. Ketamine may be very useful. Close supervision of the patient will be necessary. Subutex (buprenorphine) is used to prevent withdrawal and is used as an alternative to methadone in about 25% of cases. Buprenorphine has a long half-life and a high affinity for opioid receptors. The effects of opioid analgesics will be unpredictable, and so reliance should be placed on alternative methods, as with naltrexone.
at minimizing these factors. About 20% of patients are more difficult to manage. The early identification of these patients and measures to control their pain and long-term outcome will become even more important in the future. Acute pain manage ment will be seen as part of a process to aid patient recovery rather than an issue in its own right. ◆
References 1 Working Party of the Commission of the Provision of Surgical Services. Pain after surgery. London: The Royal College of Surgeons of England and the College of Anaesthetists, 1990. 2 Dolin SJ, Cashman JN, Bland JM. Effectiveness of acute postoperative pain management: evidence from published data. Br J Anaesth 2002; 89: 409–23. 3 Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine. Acute pain management: scientific evidence, 2nd edn. Canberra: Australian Government National Health and Medical Research Council, 2005. Also available at: http://www.nhmrc.gov. au/publications/index.htm (assessed 5 September 2007). 4 Royal College of Anaesthetists. Good practice in the management of continuous epidural analgesia in the hospital setting. London: Royal College of Anaesthetists, 2004. Also available at: http://www.rcoa. ac.uk/docs/Epid-Analg.pdf (assessed 5 September 2007). 5 Royal College of Anaesthetists. Raising the standard: A compendium of audit recipes, 2nd edn. London: Royal College of Anaesthetists, 2006. Available at: http://www.rcoa.ac.uk/index.asp?PageID=125 (assessed 5 September 2007). 6 Kehlet H, Dahl JB. Anaesthesia, surgery and challenges for postoperative recovery. Lancet 2003; 362: 1921–8. 7 Katz J, McCartney CJ. Current status of pre-emptive analgesia. Curr Opin Anaesthesiol 2002; 15: 435–41. 8 Liu SS, Richman JM, Thirlby RC, Wu C. Efficacy of continuous wound catheters delivering local anesthetic for postoperative analgesia: a quantitative and qualitative systematic review of randomized controlled trials. J Am Coll Surg 2006; 203: 914–32. 9 Macrae WA. Chronic pain after surgery. Br J Anaesth 2001; 87: 88–98. 10 Seib RK, Paul JE. Preoperative gabapentin for postoperative analgesia: a meta-analysis. Can J Anaesth 2006; 53: 461–9. 11 Ludbrook GL, Macintrye PE, Douglas H, et al. A mixture of alfentanil and morphine for rapid postoperative loading with opioid: theoretical basis and initial clinical investigation. Anaesthesia 2001; 56: 739–44. 12 Vickers AP, Jolly A. Naltrexone and problems in pain management. Br Med J 2006; 332: 132–3. 13 Kendall NAS, Linton SJ, Main CJ. Guide to assessing psychosocial yellow flags in acute low back pain: risk factors for long-term disabilty and work loss. Accident rehabilitation and compensation insurance corporation of New Zealand and the National Health Committee 1997. Wellington, NZ. http://www.nhc.health.govt.nz/ (accessed 25 September 2007).
Acute-on-chronic pain: chronic, painful conditions such as low back pain, pancreatitis and ureteric colic may have acute exacer bations necessitating hospital admission and admissions may be recurrent. Careful assessment is necessary, with particular regard to psychosocial factors: the so-called yellow flags.13 Treatment must consider long-term management of persisting pain and, possibly, future acute exacerbations. Involvement of chronic pain specialists is advisable. Clear communication with primary care healthcare workers is essential.
Further Reading British pain society. http://www.britishpainsociety.org (accessed 5 September 2007). Power I. Recent advances in postoperative pain therapy. Br J Anaesth 2005; 95: 43–51. Procedure Specific Postoperative Pain Management (Prospect). www.postoppain.org (accessed 5 September 2007).
The future Current methods for managing acute pain are satisfactory for most patients. Side effects and complications limit their benefits; new developments in drugs and techniques are likely to be aimed
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:1
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© 2007 Elsevier Ltd. All rights reserved.
Control of acute pain in postoperative and posttraumatic situations and the role of the acute pain service
training for all staff involved in managing acute pain, introducing new drugs and techniques, and auditing the outcomes. Since 1990 there has been substantial investment in acute pain services, with acute pain teams now being part of normal prac tice. However, in spite of these changes subsequent publications have demonstrated a substantial number of patients continuing to experience severe pain after surgery.2 These finding have been substantiated by audits in individual departments. In an effort to tackle this continuing problem, some departments have introduced systems to identify those patients who have had previous unsatis factory pain experiences before they are admitted for further pro cedures. By identifying these patients and investigating possible reasons for poor pain control at the pre-assessment visit, their subsequent admissions can be better managed. Those patients who are taking strong opioid analgesia before admission can also be identified in advance and their management planned. There has been an enormous growth in the publication of guidelines for acute pain management, many of them evidencebased. The second edition of the book Acute pain management: scientific evidence3 provides a wealth of information with careful ranking of levels of evidence. The Royal College of Anaesthetists (RCA) published guidelines that drew on the experience of many specialists to guide the process of providing epidural analgesia as part of an acute pain service.4 In 2006, the RCA published a com pendium of audit recipes for continuous quality improvement in anaesthesia, which includes a chapter on acute pain services.5 Concerns about serious complications related to continuous epi dural analgesia have prompted the RCA to perform a national survey of such problems, and this is ongoing. A related project, National Confidential Acute Pain Critical Incident Audit (NCAP CIA), is currently seeking information regarding serious incidents involving any kind of acute pain management strategy. This pro ject is also attempting to define the denominators (i.e. how many of these procedures are performed annually in the UK) in order to better understand the frequency of these events. The Prospect group promote the concept of procedure-specific analgesia and have produced evidence-based guidance to managing pain after a number of common procedures (see Further Reading).
Andrew P Vickers
Abstract There has been considerable investment in services that promote the effective management of acute pain. Despite acute pain teams being normal practice in UK hospitals and an increasing volume of guidance, there are still a substantial number of patients who suffer moderate or severe acute pain. Acute pain teams improve analgesia, reduce side effects and improve safety on the basis of comparative studies. Simple scales for assessing pain are effective. Assessment may be more difficult in certain patient groups such as babies, infants and children, elderly patients and non-English speakers. Assessment for the symptoms and signs of neuro pathic pain is important when nerve injury is suspected. Effective pain management obtunds the adverse effects of the injury response and may reduce the risk of chronic postsurgical pain. Preventive analgesia in terms of reducing postoperative pain and/or analgesic use is associated with the use of local anaesthetics, opioids or N-methyl-d-aspartate antagonists. Paracetamol is an effective analgesic and lowers the number needed to treat of other analgesics. The use of non-steroidal anti-inflammatory drugs is limited by side effects. Tramadol has important non-opioid mechanisms that widen its scope. In the future there will be a greater focus on those areas where current pain control approaches are of limited benefit.
Keywords acute-on-chronic pain; chronic postsurgical pain; opioid tolerance; patient-controlled analgesia
The acute pain team The concept of the acute pain team (APT) was first described by Ready in Seattle, USA before being introduced into a number of units in the UK. APTs are now normal practice and usually com prise one or more specialist nurses and designated consultant anaesthetist sessions. The multidisciplinary approach as advo cated by the 1990 report is much less common. Staff and patient education, the development of guidelines and protocols, and audit of outcome and complications are all key functions of the APT. Activity may be limited to patients on surgical wards but a comprehensive service includes other departments, including medical wards and the accident and emergency department. The wide variability in APTs makes it difficult to analyse their benefits. Furthermore, the quality of studies into the effective ness of APTs is not suitable for meta-analysis. Evidence from comparative studies and case series supports the premise that APTs reduce pain scores and side effects. Expert opinion is that supervision by an anaesthesia-based pain service is necessary for the safe provision of epidural analgesia using local anaes thetic–opioid mixtures on general hospital wards.
A watershed for acute pain management occurred in 1990 with the publication of the joint collegiate report: report of the working party on pain after surgery.1 Prompted by numerous publications detailing unacceptable levels of severe pain after surgery, the report highlighted areas of concern and made recommendations as to how the situation could be improved. Inadequate education, poor organ ization and under-funding were regarded as major deficiencies. The report recommended the development of multidisciplinary teams with a designated leader. Acute pain teams would sup port and develop acute pain services by providing education and
Andrew P Vickers, FRCA, is Consultant in Anaesthetics and Pain Management at the Royal Lancaster Infirmary. A graduate of St Thomas’ Hospital, London, he trained in anaesthetics in Nottingham, the South West and Leicester. His interest in acute pain management began when he witnessed a close friend suffer uncontrolled pain after thoracotomy. Conflicts of interest: Andrew P Vickers has received honoraria from Pfizer and Bristol-Myers Squibb for speaking on acute pain issues.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:1
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© 2007 Elsevier Ltd. All rights reserved.
Pain
side effects, has been championed by Kehlet6 as part of a process of accelerated recovery after surgery. Clinical studies in humans have not demonstrated a significant difference in effect from administering analgesics before surgical stimulus rather than after it (pre-emptive analgesia). Preventive analgesia is defined as a reduction in postoperative pain and/or analgesic consumption relative to another treatment (or a pla cebo or no other treatment) at a point in time that exceeds the expected duration of action of the target agent. The intervention may or may not be initiated before surgery. A systematic review has shown benefit from the use of preventive analgesia with local anaesthetics, opioids or NMDA antagonists.7
Pain assessment and measurement Regular assessment of pain leads to improved acute pain manage ment. In general, the use of one-dimensional pain scales is suf ficient. Where a significant neuropathic element is suspected, a multidimensional approach is needed that should include descrip tors specific for neuropathic pain; for example, the Leeds Assess ment of Neuropathic Symptoms and Signs (LANSS) and, possibly, simple sensory assessment looking in particular for allodynia and hyperalgesia. Verbal descriptor scales (VDS) (e.g. none, mild, mod erate and severe) correlate well with visual analogue scales (VAS) and, although they are less sensitive for measuring treatment out come, they are sufficient for use in the clinical setting. VAS avoid imprecise descriptive terms but require more concentration and coordination than VDS, and so are unsuitable for children aged less than 5 years and, possibly, for up to 25% of adults. Pain assessment may be difficult in certain situations. Valid ated tools are available for neonates, infants and young chil dren (Anaesthesia and intensive care medicine 8:5: 180). Elderly patients may have difficulties due to auditory and visual impair ment. Cognitive impairment, whether long term or an acute delirium, results in fewer complaints of pain. This may be due to diminished memory, a failure to report pain or, perhaps, that less pain is experienced. The VDS is more sensitive and reliable than VAS in elderly patients, including those with mild-to-moderate cognitive impairment who may also need more time to under stand and respond to questions regarding pain. The assessment of pain in non-English-speaking patients may be facilitated by the use of pain scales available in a number of languages from the British Pain Society’s website (see Further Reading).
Paracetamol Paracetamol did not gain popularity until the late 1940s. It acts via the CNS but its mode of action is still unknown. Inhibition of a sub type of the cylooxygenase-1 (COX-1) enzyme, promoting serotoninrelated anti-nociception, and inhibition of substance P may all play a part in its analgesic effects. Oral paracetamol is rapidly absorbed with a time to maximum concentration in the plasma (Tmax) of 30–120 minutes and a high bioavailability. It is well tolerated with very few contraindications. The number needed to treat (NNT) for paracetamol, 1 g, is 3.8 in acute pain. It enhances the analgesic effect of codeine, reducing the NNT of codeine (60 mg, from 16.7 to 4.2) and tramadol (Table 1). Paracetamol suppositories or the intravenous prodrug propacetamol have been used when the oral route is not suitable. An intravenous preparation of paracetamol is now available. It has a shorter time to meaningful pain relief than the oral form (8 versus 37 minutes) and better early analgesia. There is a cost consideration in the use of the intravenous prepara tion; restricting its use to when the oral route is not suitable or to when rapid-onset analgesia is needed will minimize the cost.
The physiology of pain The process whereby an injury, whether chemical, thermal or mechanical, generates nociceptive traffic is well understood. The role of the ‘chemical soup’, including prostaglandins and brady kinin, in changing nociceptor sensitivity in the periphery is central to the generation of a pain message, but the involvement of the immune system, especially mast cells, is now known to be impor tant in modifying this role. Changes within the CNS can be shown within hours of a surgical insult in terms of gene induction, and produce profound modification in CNS organization (e.g. activation of the N-methyl-d-aspartate (NMDA) receptor). Recent functional MRI images have shown changes in the somato-sensory cortex in response to injury, demonstrating that the CNS is not ‘hard-wired’ but is capable of plasticity. An understanding of the interaction of the many nerve pathways and neurotransmitters provides an insight into how drugs may assist in the process of pain management.
Non-steroidal anti-inflammatory drugs and COX-2 inhibitors These drugs, which block the production of prostaglandins by cylooxygenase, are effective alone for managing mild or moder ate pain, and reduce opioid consumption in treating severe pain. Concerns about excessive bleeding have seen the introduction of
The Oxford league table of analgesics in acute pain: the benefits of combining paracetamol with other analgesics
The treatment of pain Pain control can be justified on humanitarian grounds alone, but pain is also one of the factors that triggers the injury response, resulting in metabolic, endocrine, and water and electrolyte flux changes that may have an adverse effect on recovery. Effective pain control is capable of modifying these responses, although improved outcome or reduction in mortality is difficult to con firm. Severe postoperative pain is one of the risk factors for the development of chronic postsurgical pain (discussed below), but the multifactorial nature of this problem means that it is difficult to determine whether effective pain control reduces the risk. The concept of using effective pain management, whilst minimizing
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Analgesic
NNT
Morphine, 10 mg (intramuscularly) Paracetamol, 1000 mg Codeine, 60 mg Codeine, 60 mg + paracetamol 1000 mg Tramadol, 75 mg Tramadol, 75 mg + paracetamol 650 mg
2.9 3.8 16.7 4.2 5.3 2.6
NNT, the number of patients who need to receive the active drug for one patient to achieve at least 50% relief of pain compared with placebo over a 4–6-hour treatment period. www.jr2.ox.ac.uk/bandolier/booth/painpag/ Acutrev/Analgesics/Leagtab.html
Table 1
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a specific contraindication to the use of ketorolac in the pre- and intraoperative period. Furthermore, studies of some of the COX-2 inhibitors have shown an increased risk of myocardial ischaemia or stroke in ‘at risk’ groups. Subsequently, this has been shown to apply to many if not all non-steroidal anti-inflammatory drugs (NSAIDs). Recent surveys have shown that many anaesthetists have significantly reduced their use of these drugs, choosing paracetamol in preference.
The incidence of chronic pain after surgery
Tramadol Originally considered as an opioid analgesic, it is now recognized that tramadol is only a weak agonist at the μ-receptor, and owes much of its analgesic effect to the inhibition of the reuptake of norepinephrine and serotonin at descending inhibitory neurons. There is logic, therefore, in using tramadol in addition to opioids (discussed below). There is some evidence to show that trama dol is more effective for neuropathic pain than opioids.
Incidence of chronic pain (%)
Amputation Thoracotomy Mastectomy Chlolecystectomy Inguinal hernia Vasectomy Dental surgery
30–85 5–67 11–57 3–56 0–63 0–37 5–13
Table 2
Research with animal models demonstrated that a presurgical dose of gabapentin inhibited the development of hyperalgesia following a surgical incision. Several randomized controlled trials using different pain models have shown an effect on post operative pain in humans. Single doses of gabapentin between 600 and 1200 mg (in excess of the licensed starting dose) have been shown to reduce pain scores and/or morphine consump tion after, for example, abdominal and vaginal hysterectomy, lower limb arthroplasty and laparoscopic cholecystectomy. Metaanalyses have confirmed these effects, which persist for up to 24 hours after surgery.10 Common side effects are dizziness and drowsiness, which may limit the value of gabapentin in day sur gery. Gabapentin has minimal drug interactions. The growing awareness of chronic postsurgical pain has raised the question as to whether gabapentin should be continued into the postoperative period, especially in those cases with a high risk of neuropathic pain (e.g. amputation, peri pheral vascular disease and spinal surgery for neuropathic pain). Although gabapentin has a numbers needed to harm of 3.7 for minor side effects, significant major adverse effects are unusual. Furthermore, gabapentin is widely used long term for chronic neuropathic pain. Deciding when gabapentin should be used postoperatively, at what dose and for how long are questions yet to be answered. Pregabalin has the same mechanism of action as gabapentin. Unlike gabapentin it has linear pharmokinetics (i.e. the CNS drug concentration rises with increasing dose) which suggests that it may have higher efficacy. In addition, pregabalin appears to have a faster onset of action. For these reasons, pregabalin may prove superior to gabapentin, but clinical studies in acute pain models are awaited.
Current techniques Intravenous patient-controlled analgesia with morphine is effec tive and offers greater patient satisfaction than ‘as required’ opioids analgesia. Continuous epidural analgesia can provide excellent analgesia, but whether it offers clear advantages in terms of reduced mortality and morbidity is uncertain. It does have a beneficial effect on some measures of cardiac and res piratory function. Level of insertion is important so that the catheter tip corresponds to the dermatomes of the surgical inci sion. Despite the benefits, epidural analgesia has not been shown to reduce hospital stay. Concerns about failure rates and seri ous complications have triggered audit projects to try to define the optimal use of this technique. Incisional infusions of local anaesthetics, taking advantage of the availability of elastomeric pumps, have been shown to be effective in a number of different procedures.8 They may reduce hospital stay and could be used after hospital discharge. If they fulfil their early promise, there may be a significant reduction in the use of epidurals. Chronic postsurgical pain There is a growing awareness that pain may persist for months or years after many surgical procedures (Table 2).9 The cause of this chronic pain is unclear but nerve injury is thought to play a role. This implies that surgical technique is important and surgical approaches that minimize the risk of nerve injury (e.g. minimally invasive surgery) should be used whenever possible. Patients who develop chronic postsurgical pain often describe severe pain immediately after surgery. Multimodal analgesia (including drugs such as clonidine and ketamine, and, to a lesser extent, paracetamol and NSAIDs) obtunds the CNS response to a surgical incision. These medications also counteract opioidinduced hyperalgesia, which is seen in association with the use of short-acting opioids and remifentanil in particular. Confirma tion as to whether this reduces the risk of chronic postsurgical pain is awaited.
Specific situations Severe pain in the recovery ward: good postoperative pain control begins in the operating theatre and progresses through recovery to the ward. Sometimes this process fails and patients complain of severe pain in the recovery ward. Rapid pain control is essential. Treatable causes of pain such as wound haematoma or a full bladder should be sought. If appropriate, intravenous paracetamol and NSAIDs should be administered. Recent publi cations have shown better efficacy after 2 g than 1 g paracetamol, so a second dose of paracetamol could be considered if one dose has already been administered intraoperatively. If these are unsuccessful, other strategies may be tried (Table 3).
Gabapentin and pregabalin These anticonvulsant drugs are licensed for the management of neuropathic pain. They bind to the α2δ1 subunit of the pre synaptic voltage-gated calcium channels of the primary afferent nociceptor, inhibiting the release of excitatory neurotransmitters.
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Type of operation
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three times more via patient-controlled analgesia than their opi oid-naïve counterparts). It is important to avoid withdrawal as well as provide appropriate pain relief. Intravenous patient-con trolled analgesia can be very effective, but bigger boluses and a background infusion may be necessary. Tolerance to side effects may also occur but cannot be relied on. Neuraxial blockade can offer excellent pain control but may not prevent withdrawal even if low-dose opioids are used (e.g. patient-controlled epidu ral analgesia). Multimodal analgesia will be of benefit. Ketamine may be very effective, but use of this drug on the general surgical ward must be carefully considered. Clear communication with the patient and their general prac titioner is essential before discharge to plan for the continued use of strong opioids or their withdrawal if no longer necessary.
Managing severe pain in the recovery ward • Exclude treatable conditions (e.g. haematoma, full bladder) • Intravenous paracetamol? – second dose • Intravenous NSAID/COX-2 inhibitor if appropriate • The Lancaster protocol for morphine/alfentanil titration in recovery8 Morphine, 15 mg Alfentanil, 1 mg Normal saline, to a total volume of 15 ml 3 ml of the mixture administered every 2 minutes to effect • Tramadol 50–100 mg (intravenously) • Ketamine 10 mg • Clonidine 1 μg/kg • Midazolam 1–2 mg
Substance abuse disorder (SAD) is defined as a state in which the extent and pattern of substance use interferes with the psy chological and sociocultural integrity of the individual affected. These patients can present many challenges to achieving effec tive pain control. They may exhibit behaviours relating to their chaotic use of substances and to fears about their treatment by healthcare workers (Table 4). Hospital staff may stereotype the patient, which inhibits appropriate attitudes to managing the patient’s pain. The patient may have recently used illicit sub stances and may continue to use them whilst in hospital. They may exhibit high levels of tolerance to opioid analgesics, whilst having a low pain tolerance. Patients may be registered with local community drugs teams and be on maintenance programmes, but they may or may not use non-prescribed drugs or may be unknown to these teams. Patients who have stopped using illicit substances may be fearful of relapse if they are given opioid analgesics. Some of the drugs used as maintenance therapy can cause major difficulties for pain control. The aims of pain management in patients with SAD should be to provide realistic pain control, avoid withdrawal, prevent harm from
Table 3
Ludbrook et al11 performed pharmacokinetic modelling of estim ated CNS concentrations to derive the optimum mixture of mor phine and alfentanil for the treatment of postoperative pain. The alfentanil provides rapid analgesia, whilst an equipotent dose of morphine for longer-term analgesia is administered simultaneously. This approach was adopted in Lancaster in 2002 and has been shown to achieve rapid pain control, with most patients improving from a pain score of 3 (severe) to 1 (mild) within 10 minutes. Tramadol does not rely on its effects at the μ-receptor to pro duce analgesia. It is less likely to cause respiratory depression and sedation than opioids, although other side effects, in particu lar nausea and vomiting, can be troublesome. NMDA-receptor antagonists may be used, and ketamine has been shown to improve analgesia in patients who are poorly responsive to opi oids. Clonidine, an α2-agonist, consistently improves periopera tive analgesia. Low-dose midazolam may be useful. Midazolam is known to augment analgesia when administered intrathecally, but why it may improve analgesia when administered intra venously is not clear. Reduction of anxiety may be a factor but an effect on muscle spasm may play a role. There are two important caveats when employing the above strategies. First, they are intended to control severe pain but are likely to be short-lived. It is essential, therefore, to plan for the long-term management of pain. Second, the use of these drugs may cause significant side effects, so it is important to ensure a high level of supervision before the patients are returned to the general ward. For this reason, caution should be exercised before employing these strategies outside the theatre setting (e.g. in the accident and emergency department).
Adverse attitudes and behaviours affecting the management of pain in patients with substance abuse disorder Patient factors • Patients may fail to disclose information because of fear of: Stigma Being given an antagonist or partial agonist Being denied analgesia • Pseudo-addiction – seeking more medication because of inadequate pain control • Drug-seeking Healthcare worker factors • Healthcare workers may believe that: Maintenance methadone is sufficient to manage postsurgical pain Methadone is suitable for managing postsurgical pain All requests for analgesia represent drug-seeking Withdrawal should be immediate
The opioid-tolerant patient: tolerance is defined as a decrease in the effect of a drug over time so that a progressive increase in dose is required to achieve the same effect. Tolerance devel ops to most side effects as well as to the desired therapeutic effect. Opioid tolerance is most commonly seen in patients being treated with opioids for chronic or cancer pain and in patients with substance abuse disorder (discussed below). Opioid-toler ant patients have been shown to be relatively intolerant of pain and so are likely to require increased opioid doses (approximately
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Table 4
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the use of non-prescribed drugs and minimize the impact of their behaviour on other patients. Open, honest discussion can produce empathy and cooperation. This can be backed up with information from the community drugs team and/or general practitioner. Use urine testing (more than once if necessary) for qualitative informa tion. Avoid using long-acting analgesics, especially methadone, for acute pain. Morphine is effective, is familiar to all staff and will prevent withdrawal. Be mindful of tolerance to both the effects and side effects of morphine. Multimodal analgesia and neuraxial blockade may be helpful but do not prevent withdrawal. The recovering patient may be fearful of relapse. Multimodal analgesia, avoiding strong opioids, is desirable but patients should be reassured that opioids may be necessary. Plans for the subsequent withdrawal of opioids are necessary and involve ment of the community drugs team may be helpful. Methadone is used for maintenance therapy because its slow onset avoids the ‘high’ associated with heroin but prevents withdrawal. If the dose normally taken can be confirmed (by the community drugs team, prescribing general practitioner or community pharmacy) it can be administered orally. If there is any doubt about the dose, caution must be exercised, and small doses of methadone, 10 mg, given every 4–6 hours, with careful observation for signs of opioid overdose. If the patient is nil by mouth, intravenous patient-controlled analgesia with morphine will provide analgesia and prevent withdrawal. It is usually necessary to programme bigger boluses with shorter lockout than usual and, possibly, a background infusion. Naltrexone is a long-acting pure antagonist of opioid receptors. It is licensed for promoting abstinence in the UK, and also in the USA for the management of alcoholism. A single dose of naltrex one will produce a blockade of about 50% of opioid receptors after 72 hours. Naltrexone is also available as a subcutaneous implant, with effects lasting between 9 and 12 months. Naltrexone will render even large doses of opioids ineffectual.12 It is important that its use is recognized before elective procedures so that pain management can be planned. In the emergency situation, altern ative methods of analgesia will be necessary. Ketamine may be very useful. Close supervision of the patient will be necessary. Subutex (buprenorphine) is used to prevent withdrawal and is used as an alternative to methadone in about 25% of cases. Buprenorphine has a long half-life and a high affinity for opioid receptors. The effects of opioid analgesics will be unpredictable, and so reliance should be placed on alternative methods, as with naltrexone.
at minimizing these factors. About 20% of patients are more difficult to manage. The early identification of these patients and measures to control their pain and long-term outcome will become even more important in the future. Acute pain manage ment will be seen as part of a process to aid patient recovery rather than an issue in its own right. ◆
References 1 Working Party of the Commission of the Provision of Surgical Services. Pain after surgery. London: The Royal College of Surgeons of England and the College of Anaesthetists, 1990. 2 Dolin SJ, Cashman JN, Bland JM. Effectiveness of acute postoperative pain management: evidence from published data. Br J Anaesth 2002; 89: 409–23. 3 Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine. Acute pain management: scientific evidence, 2nd edn. Canberra: Australian Government National Health and Medical Research Council, 2005. Also available at: http://www.nhmrc.gov. au/publications/index.htm (assessed 5 September 2007). 4 Royal College of Anaesthetists. Good practice in the management of continuous epidural analgesia in the hospital setting. London: Royal College of Anaesthetists, 2004. Also available at: http://www.rcoa. ac.uk/docs/Epid-Analg.pdf (assessed 5 September 2007). 5 Royal College of Anaesthetists. Raising the standard: A compendium of audit recipes, 2nd edn. London: Royal College of Anaesthetists, 2006. Available at: http://www.rcoa.ac.uk/index.asp?PageID=125 (assessed 5 September 2007). 6 Kehlet H, Dahl JB. Anaesthesia, surgery and challenges for postoperative recovery. Lancet 2003; 362: 1921–8. 7 Katz J, McCartney CJ. Current status of pre-emptive analgesia. Curr Opin Anaesthesiol 2002; 15: 435–41. 8 Liu SS, Richman JM, Thirlby RC, Wu C. Efficacy of continuous wound catheters delivering local anesthetic for postoperative analgesia: a quantitative and qualitative systematic review of randomized controlled trials. J Am Coll Surg 2006; 203: 914–32. 9 Macrae WA. Chronic pain after surgery. Br J Anaesth 2001; 87: 88–98. 10 Seib RK, Paul JE. Preoperative gabapentin for postoperative analgesia: a meta-analysis. Can J Anaesth 2006; 53: 461–9. 11 Ludbrook GL, Macintrye PE, Douglas H, et al. A mixture of alfentanil and morphine for rapid postoperative loading with opioid: theoretical basis and initial clinical investigation. Anaesthesia 2001; 56: 739–44. 12 Vickers AP, Jolly A. Naltrexone and problems in pain management. Br Med J 2006; 332: 132–3. 13 Kendall NAS, Linton SJ, Main CJ. Guide to assessing psychosocial yellow flags in acute low back pain: risk factors for long-term disabilty and work loss. Accident rehabilitation and compensation insurance corporation of New Zealand and the National Health Committee 1997. Wellington, NZ. http://www.nhc.health.govt.nz/ (accessed 25 September 2007).
Acute-on-chronic pain: chronic, painful conditions such as low back pain, pancreatitis and ureteric colic may have acute exacer bations necessitating hospital admission and admissions may be recurrent. Careful assessment is necessary, with particular regard to psychosocial factors: the so-called yellow flags.13 Treatment must consider long-term management of persisting pain and, possibly, future acute exacerbations. Involvement of chronic pain specialists is advisable. Clear communication with primary care healthcare workers is essential.
Further Reading British pain society. http://www.britishpainsociety.org (accessed 5 September 2007). Power I. Recent advances in postoperative pain therapy. Br J Anaesth 2005; 95: 43–51. Procedure Specific Postoperative Pain Management (Prospect). www.postoppain.org (accessed 5 September 2007).
The future Current methods for managing acute pain are satisfactory for most patients. Side effects and complications limit their benefits; new developments in drugs and techniques are likely to be aimed
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