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Department of Anaesthesiology and Intensive Care Medicine
Campus Benjamin Franklin
Freie Universität Berlin
The number of patients with chronic pain has increased in the last decades. It is estimated that about 10% of the population in developed countries suffer from chronic pain. Awareness regarding this patient group is low. Practice guidelines for the management of acute(1) and chronic pain,(2) published by the American Society of Anaesthesiology, do not include specific considerations for the perioperative management of chronic pain. Therefore, although surgeons, anaesthesiologists and nurses working in hospitals are highly likely to be dealing with patients with a chronic pain problem scheduled for surgery, chances are low that these patients are receiving adequate treatment. Literature on this topic is scarce; thus, not all of the following recommendations are evidence-based.
To identify patients at risk, the characteristics of this particular patient group must be known (see Box). The International Association for the Study of Pain (IASP) defines chronic pain as “pain without apparent biological value that has persisted beyond the normal tissue healing time, which is usually taken to be three months”.(3) There is a tradition to distinguish between chronic pain associated with cancer – malignant pain – and nonmalignant pain. However, little evidence exists to suggest that different somatic or psychological mechanisms warrant such a distinction.(4)
Cancer patients tend to have more serious health restrictions and are prescribed more narcotics and other medications than patients with other chronic diseases.(5) Chronic pain patients have in common the complex experience of biological, psychological and social changes. Patients with nonmalignant pain have higher scores than those with malignant pain. It is possible that cancer patients do not expect as much pain relief as patients with nonmalignant pain. It is also possible that patients with nonmalignant pain believe that higher scores would result in medication increases.(6) A major problem in the treatment of cancer pain remains the lack of correlation between patients’ self-reporting and assessment by clinical staff:(5) pain is underestimated by nursing and physician staff, as well as family members, which often results in poor pain control.(5) Frequently, these patients also have reduced reserves of organ function and are therefore at increased risk from the deleterious physiological effects of the neuroendocrine response on pain.(7) Disease progression and psychosocial factors and/or tolerance may account for increased opioid requirements,(8,9) which should not go unnoticed in the perioperative period.
The chronic nonmalignant pain patient has no universal characteristics of a “pain personality”, but some unique features are apparent, such as tight musculature, limited mobility, lack of energy, changes in appetite, depression, anger, anxiety(10) and fear of reinjury.(4,11) Pain may disrupt sleep and cause irritability and social withdrawal.(11) The patient’s beliefs about their pain (or their perceived ability to control it) and the strategies they use to cope are associated with pain intensity ratings.(11) Preoperative intensity of pain alone – independently of the use of analgesics – correlates positively with postoperative pain.(12) In addition, certain psychiatric diseases, such as hypochondriasis, depression and occasionally psychosis, may coexist.(5) Treating only one aspect of this complex syndrome is insufficient(4) – presumably also during the perioperative period.
Chronic pain patients are often pretreated with opioids, cyclooxygenase (cox) inhibitors and/or co-analgesics (often including antidepressants and anticonvulsants). They have prolonged inactivity and/or suffer from neurological deficits that may be connected with complications and adverse events resulting from the perioperative treatment. Tolerance problems, as well as drug interactions and side-effects, may occur. In addition, inappropriate or excessive medication is commonly observed.(13) Furthermore, chronic pain patients tend to underestimate and underreport their medication use. This tendency is more pronounced for opioid analgesics than for other medications and is greater in women than in men.(14) Thus, undertreatment in the perioperative period may be unnoticed and may induce withdrawal.(15) This may result in serious cardiopulmonary strain, caused by the neuroexcitatory withdrawal syndrome. Furthermore, such patients may require higher opioid doses to treat postoperative pain effectively.(15) Physicians may overestimate tolerance, addiction and sedation induced by analgesics but underestimate dependence and the impact of co-analgesics and cox inhibitors on pain.(16)
Chronic pain patients with prior opioid consumption have been observed to have higher pain readings postoperatively, both with intravenous (IV) patient-controlled analgesia (PCA) and with epidural analgesia.(6) PCA use is significantly increased beyond mere replacement of preoperative doses.(6) Understanding the altered opioid demand to manage perioperative pain in patients chronically consuming opioids is a challenge.(17) In the perioperative period, chronic opioid treatment can result in increased (two to four times) requirement for systemic analgesics, compared with opioid-naive patients.(6,18) Systemic and epidural opioid requirements increase in the same range in patients with prior opioid exposure.(19) In some patients with high preoperative opioid doses, the postoperative opioid demand may reach extreme ranges.(20) Increased consumption may be due to a lower pain threshold or a need for larger opioid plasma levels.(6) Opioid-related side-effects such as nausea and pruritus may be less dominant.(6,19) Changes in the opioid receptors may also lead to an increase in opioid demand in chronic pain patients during the perioperative period. This could be due to pharmacodynamic tolerance.(21) Proposed mechanisms involved in tolerance and resensitisation of opioid receptors include G-protein receptor uncoupling, receptor internalisation and increased sensitivity of the N-methyl-d- aspartate (NMDA) receptor.(21–25)There is also evidence that opioids paradoxically induce pronociceptive processes, which can result in abnormal pain sensitivity (allodynia) and increased sensitivity to pain (hyperalgesia).(26,27) Based on clinical experience, patients with continuous opioid intake of a morphine equivalent exceeding 30mg (IV daily) for more than two to four weeks(28,29) should be considered at risk for withdrawal syndrome if adequate substitution of opioids in the perioperative period is withheld. Opioid and benzodiazepine withdrawal syndromes, especially tachycardia and hypertension, may be detrimental in high-risk cardiac patients.
Other frequent analgesic medications used in chronic pain include cox inhibitors, which have to be stopped 24 to 48 hours before regional anaesthesia(30) as they may impair renal function (especially if there is coexisting hypovolaemia and renal disease(31)) but may reduce cumulative opioid doses by up to 40%, and “co-analgesic drugs”. Co-analgesic drugs are drugs with analgesic potency that were not originally developed for the treatment of pain. Neuropathic pain is the main indication for these drugs. Anticonvulsants, tricyclics, NMDA antagonists and other drugs have been studied for the treatment of neuropathic pain.(32) Possible interactions with certain drugs used in anaesthesia and with organ systems with impaired function have to be considered, as well as difficulties in switching from an oral to an IV route.
The perioperative management of chronic pain starts with the preanaesthesia evaluation. In addition to risk stratification, the preanaesthesia visit should be used to educate patients about perioperative procedures and inform the anaesthesiologist and the surgeon about the diagnosis of the “chronic pain patient”. It has to be established whether there is addiction, pseudoaddiction and/or physical dependence in patients with long-term opioid medication, and perioperative opioid medication should be calculated accordingly. Benzodiazepines and anticonvulsants should be continued, all other nonopioid analgesics and co-analgesics stopped. Referral to the pain unit for additional evaluation is recommended. Selecting the anaesthesia technique has to be done on an individual basis since there are no data available favouring general, regional or combined anaesthesia for this specific patient population.
It can be concluded that all “individually adapted” perioperative schemes are superior to “conventional” analgesia,(18) regardless of the technique used. Integration of the patient in an acute pain service scheme is recommended wherever available. This might be of special importance when it comes to switching opioids and other analgesics with, for example, regional anaesthesia and analgesia, as well as IV patient-controlled and transdermal analgesia. Postoperatively, re-evaluation of the indication for opioid medication (“efficacy vs addiction”) should be carried out when acute pain has resolved.(33) Attempts to solve a chronic pain problem in the immediate postoperative period are not recommended. Instead, the patient should be given emotional support and, if necessary, offered counselling in the pain unit after postoperative recovery. In addition to the choice of analgesia technique and exploitation of opioids, optimisation of organisational structures can be a key factor to improving perioperative analgesia in chronic pain patients.(34) Dissemination and implementation of best-evidence data – as in perioperative medicine in general – also needs to be improved further.(35) The implications of chronic pain should be taught more effectively in postgraduate training programmes; currently, only half of anaesthesiologists and surgeons are considered competent to carry out a clinical pain assessment.(36,37)
The management of postoperative pain in chronic pain patients (with chronic opioid therapy) should include the following general and specific strategies:
Note to the reader: an extended version of this article was published previously (Kopf A, Banzhaf A, Stein C. Best Pract Res Clin Anaesthesiol 2005;19:59-76)