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Review

Flagging the pain: preventing the burden of chronic pain by identifying and treating risk factors in acute pain

Shipton, E. A.*; Tait, B.*

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European Journal of Anaesthesiology: June 2005 - Volume 22 - Issue 6 - p 405-412
doi: 10.1017/S0265021505000694

Abstract

Epidemiological studies have shown that chronic pain represents a major public health problem [1]. A recent 4 yr follow-up study concluded that pain is a common persistent problem in the community with relatively high incidence and low recovery rates [2]. The prevalence of chronic pain obtained ranges from 8% to 80% due in part to the differences and inconsistencies in the definitions of chronic pain used [1]. In a Gallup survey of ‘Pain in America’ more than 4 out of 10 adults (42%) said that they have experienced pain on a daily basis [3]. Females were more likely to report pain than males, and the prevalence of pain increased with age [4]. Chronic pain is more common in children than previously thought. Chronic pain impacts upon almost one in five of the adult Australian population (17.1% for males, 20% for females) [5]. Over 10% of Australians are significantly disabled by low back pain [6]. The most recent study shows the overall prevalence of chronic pain in Denmark to be 19% (16% for males, 21% for females) [1].

Apart from the suffering (to the affected individuals and their families) and the quality-of-life issues involved, an economic burden of this size impacts negatively on healthcare costs and on working age populations due to reduced functionality and work performance [1,4,7].

But how does this burden of chronic pain occur? Each year, between 0.05% and 1.5% of post-surgical patients have pain after 1 yr [8]. It is becoming clearer that unrelieved acute post-traumatic and postoperative pains are risk factors in the development of chronic pain, although psychological and environmental factors are at work as well.

Twenty-five percent of patients referred to chronic pain treatment centres have persistent post-surgical pain [9]. When considering the total number of patients undergoing surgery and trauma each year, these figures are staggering [8]. The risk factors for developing chronic post-surgical pain can be tagged by the use of flags (blue, yellow and red). Blue flags indicate the perioperative risk factors to note, yellow flags, the psychological and environmental factors at work and red flags, the postoperative physical disorders that need treatment.

Many studies suggest that postoperative and post-traumatic pain is often under-treated as a result of inadequate education of healthcare providers and fear of causing opioid addiction [10,11]. A recent survey shows that nearly 80% of patients still experience pain after surgery. Of these patients, 86% had moderate, severe or extreme pain [12].

However, there is increasing recognition that long-term neurobiological changes occur much more quickly than previously anticipated (within hours of acute injury) with the potential of progression from an acute persistent phase to a chronic phase [13]. In some patients, the hyperphenomena (primary and secondary hyperalgesia, mechanical allodynia) that are normal in the first days or weeks after surgery, do not regress but persist beyond the usual course of an acute injury (surgery) and is different from that suffered preoperatively [14].

Post-traumatic neuropathic pain is a major contributor to persistent pain affecting roots, nerves, the plexuses and central structures. Chronic pain after surgery is common following procedures such as thoracotomy (up to 67%), breast surgery (up to 57%), limb amputation (up to 83%), sternotomy (27%) and gallbladder surgery (up to 56%) [13]. Current evidence suggests that continued peripheral nociceptive input from the perioperative noxious injury barrage might maintain central sensitization, amplify postoperative pain, and contribute to chronic pain [8].

Preoperative blue flags (Table 1)

Table 1
Table 1:
Risk factors in acute perioperative pain for developing chronic pain.

Independent predictors of severe postoperative pain are younger age, female gender, level of preoperative pain, incision size and type of surgery [10].

Female gender, younger age

Female gender is a risk factor (odds ratio: 1.5; 95% confidence interval (CI): 1.2-2.0) for postoperative pain [15,16]. After major orthopaedic surgery, significant (P ≤ 0.01) multivariate correlates of both worse than expected pain experience and low satisfaction were found to be female gender and young age [17].

Pain before surgery

Another risk factor may be the presence of preoperative pain. The presence of preoperative pain significantly influences postoperative pain experience (odds ratio = 2.841, P < 0.001) [18]. Preoperative pain is one of the best predictors of severe pain in the early postoperative period and opioid consumption [10,19]. In cardiac surgery, patients with preoperative angina or who were overweight (body mass index ≥ 25) at the time of surgery were more likely to report chronic pain [20]. Preoperative pain intensity was the most important predictor for improved neck disability index in patients undergoing anterior cervical decompression and fusion [21]. Patients with previous episodes of male pelvic pain and more severe symptoms were found to be at higher risk for persistent pelvic pain following surgery [22]. In phantom-limb pain, a major role is assigned to pain occurring before the amputation and to the central and peripheral neural changes related to it [23].

In total knee replacements, patients with greater preoperative pain were found to have more postoperative pain [24]. Preoperative pain levels may predict the onset of complex regional pain [25]. The pain response to a preoperative heat injury with a contact thermode may be useful in predicting the intensity of postoperative pain [26,27].

Preoperative chronic pain

Opioid-dependent patients have special needs in the perioperative period [28]. To prevent undermedication, doses of opioid may have to be titrated that would clearly result in an overdose in opioid-naïve patients [28].

Site and extent of surgery (thoracic, major limb amputation, spinal surgeries)

The duration of anaesthesia and surgery as well as certain types of surgery are significant predictors of pain in the post-anaesthesia care unit [29]. After colectomies, a positive correlation has been found between postoperative opioid use and operative time (r = 0.14, P = 0.007) and a negative correlation with patient age (r = −0.37, P = 0.0001) [30]. Persistent postoperative pain is a well-recognized problem after various types of surgery such as major limb amputation, thoracotomy, major cancer surgery (mastectomy) [31], major orthopaedic surgeries and abdominal surgery (gallbladder, inguinal hernia) [32,33]. Sternotomy causes considerable postoperative pain. Patients with persistent post-sternotomy pain are often referred to pain clinics. A recent prospective study shows that the overall incidence of non-cardiac pain after sternotomy for cardiac surgery is high (28%) [34]. Major spinal surgery is associated with high postoperative pain scores and opioid requirements [35]. After Caesarean section, persistent pain is experienced in at least 5.9% of patients [32]. Even inguinal hernia repair is associated with a 5-30% incidence of persistent pain [36]. In acute musculoskeletal injury, there is limited evidence (level 3) that the location and extent of injury predicts reports of pain and poor functional activity outcomes [37].

Reoperations

Reoperations often lead to more pain experienced or pain that is difficult to control. The incidence of permanent pain or discomfort was unexpectedly high being 15% after recurrent hernia repairs [38]. Only 60% of shoulder revisions offered satisfactory pain relief [32].

The yellow flags

Psychological factors

Like acute low back pain, the importance of psychological (behavioural) and environmental factors is increasingly being realized as factors determining progression to chronicity. Pain is a multifactorial dynamic experience, not just a sensation. Emotion, perception and past experience all affect an individual's response to noxious stimuli. Patient attitudes and concerns about postoperative pain need to be understood. Those with pre-event distress or psychological factors may be at higher risk of developing persistent pain after surgery [39]. The main characteristics of a dissatisfied patient postoperatively were found to be a younger age and female sex [40]. Factors such as the worry or expectation of chronicity, may increase the risk of chronic symptom development [39]. Preoperative anxiety too has long been recognized as a significant predictor of postoperative pain [10]. Following total knee replacement, preoperative depression and anxiety were associated with heightened pain at 1 yr [24]. In children, predictors of postoperative pain include prior pain experiences, pain expectation, pain acceptance and pain tolerance [41]. In breast cancer, patients with higher anxiety and depression levels were found to have higher postoperative pain and analgesic requirements [42]. Pain-related beliefs, such as fear-avoidance, in the form of cognitive expectancies, may have as much influence on the duration of disability in patients with acute pain as they do in patients with chronic pain [43].

Environmental factors

Chronic pain has been independently related to low self-rated health in the general population [1,44]. Individual income is strongly associated with self-rated health [1,15].

Odds for chronic pain are 1.9 higher among those with an education of less than 10 yr compared with individuals with an education of 13 yr or more [1]. Compared with married persons, divorced or separated persons had 1.5 higher odds of chronic pain [1].

Postoperative blue flags

Unrelieved pain

Unrelieved acute postoperative pain is a risk factor in developing persistent pain [45]. Poorly controlled postoperative pain may result in the development of chronic pain after surgery [13]. Under-treatment of acute pain may also result in greater use of healthcare resources and ultimately lead to poor outcomes [46]. Following arthroplasty, unrelieved postoperative pain has been shown to delay patients' recovery and discharge from the hospital [46]. Most coronary artery bypass patients report unrelieved pain [47]. Postoperative gynaecological patients report moderate to severe pain that is often incompletely relieved with patient-controlled analgesia [48]. Of the many factors that may influence postoperative pain, chronic sleeping difficulties emerge as a determinant of pain at rest [49]. Interestingly, intra-peritoneal surgery and having a relative with a history of pain are determinants of pain during cough/mobilization [49].

Severe pain

The severity of postoperative and post-traumatic pain has been suggested as an important predictor for development of chronic pain [13]. Severe postoperative pain (typically recorded with visual analogue or numerical rating scales of 8 or higher) results in extreme patient discomfort and reduces patient satisfaction. It contributes to the development of chronic pain syndromes, such as post-thoracotomy pain [10]. In the elderly, high postoperative pain intensities have been associated with delayed ambulation, postoperative pulmonary complications, increased hospital length of stay, long-term functional impairment and chronic pain syndromes [50].

Factors that determine the intensity of postoperative pain include surgical approach, anaesthetic technique and analgesics administered [51]. After thoracotomy, persistent pain can be prevented by continuous thoracic epidural analgesia started before surgery [52,53]. In abdominal pain, moderate to intense acute postoperative pain has been associated with ASA III (odds ratio = 1.99), preoperative moderate to intense pain (odds ratio = 2.96), chronic pain (odds ratio = 1.75), high trait-anxiety (odds ratio = 1.74) and moderate to intense depressive mood (odds ratio = 2.00) [54].

Most analgesics consumed (7 days)

The presence of persistent pain following cardiac surgery is related to the higher (P = 0.03) analgesic needs during the hospitalization [55].

Postoperative ‘red flags’

Post-surgical ‘red flags’ of physical disorders such as infection, bleeding, organ rupture or a compartment syndrome must be first excluded [56].

Management of risk factors (Table 2)

Table 2
Table 2:
Management of risk factors.

The single best approach to persistent acute postoperative pain is to prevent it. But how can these risk factors be managed?

Address patient attitudes and concerns

Social factors may be important determinants of outcome in patients with traumatic fractures. After surgery, inactivity and time off work appear to increase the risk of chronic symptoms [39]. Satisfaction with one's job may protect against development of chronic pain and disability after acute onset back pain [57]. After orthopaedic surgery, optimal care may involve attention to modifiable risk factors, including smoking and alcohol consumption [58].

Provide education (patient, physician)

Information influences the pain experience after surgery [59]. Research has shown the benefits of giving preoperative information to patients that include decreased length of stay, less demand for analgesia postoperatively and increased patient satisfaction [60]. More reassuring and proper information from the Anaesthetist has been found to result in better recovery from surgery [47,61]. In one study, coping instruction led to less postoperative anxiety and pain for adolescents aged 13 and younger [62]. In another study, the provision of preoperative information resulted in postoperative pain declining more rapidly, lower preoperative state anxiety, and more satisfaction with postoperative pain management [59]. Patient education decreases preoperative anxiety and pain [63]. Patients who learnt pain management report lower pain intensity and pain distress and less sleep disturbance than waiting list controls [64]. A period of peaceful rest before and after surgery has been found to reduce patient anxiety [65]. More support, more information and more suitable analgesic protocols are needed to manage patients' pain effectively, whilst in hospital and also following discharge, at home.

Physician education is important as well. Inappropriate and inadequate physicians' orders have been cited as two of the most common obstacles to managing pain and comfort [66]. Adequate training in preoperative education and communication skills should be given to all preoperative assessment teams.

Choose least painful surgical approach with acceptable exposure

The least painful surgical approach with acceptable exposure should be chosen and tissue trauma during surgery minimized. Advances in surgical technique such as key-hole surgery and the microsurgical approach using operating microscopes has led to ‘fast track’ surgery with minimal hospital stay and reduced convalescence [67]. In spinal surgery, microdiscectomy patients, for example, have greater reduction in pain and disability than patients undergoing fusions. Following inguinal hernia repair, chronic pain is reported less often after laparoscopic and mesh repairs. In thoracic surgery, intracostal sutures seem less painful than pericostal sutures [68].

Identify operative procedures that cause severe pain

Operative procedures associated with the development of pain must be identified so that preventive measures can be implemented. The expected severity and duration for each specific type of surgery needs to be reviewed. Nurses should encourage patients to report unrelieved pain [48].

Measure pain - the fifth vital sign

One of the obstacles to effective pain management is the lack of systematic and comprehensive methods for assessing and treating postoperative pain [69]. In 1995, the American Pain Society declared pain to be: ‘the fifth vital sign’, that needs to be measured alongside temperature, blood pressure, heart rate and respiratory rate [70]. For the assessment of pain by subjective self-report, verbal descriptors (adjective scale), a four-category verbal rating scale, 11-point-numeric rating scale or a 100-mm visual analogue scale (VAS) can all be used [10,69]. In general, there is good agreement between the VAS and the 11-point-numeric rating scale, although patients and nurses have expressed a preference for verbal ratings [10]. In one study, the mere fact that pain was measured on a 10-point VAS (0 no pain, 10 most severe pain) led to considerable improvement in postoperative pain scores [71]. In coronary artery bypass graft surgery, a modified Brief Pain Inventory has been found to be stable and valid to assess postoperative pain during the subacute postoperative period [33].

Multimodal pharmacological analgesia

Multimodal analgesia is the technique of combining multiple modalities of pain relief to provide more effective analgesia and a lower incidence of adverse effects. Commonly, acetaminophen (paracetamol) and non-steroidal anti-inflammatory drugs are in routine use as components of multimodal analgesia, in combination with opioids or local anaesthetic techniques to modulate this [72]. Alpha 2 antagonists (e.g. clonidine) and N-methyl-D-aspartate antagonists (e.g. ketamine to reduce wound secondary mechanical hyperalgesia) can be added either intravenously (i.v.) (in patient-controlled analgesia) or epidurally (single shot, constant infusion or by patient-controlled epidural analgesia) [73].

An integrated approach to perioperative care (comprising minimally invasive surgical access, optimal pain relief provided by epidural analgesia, early oral nutrition, avoidance of nasogastric tubes and aggressive active mobilization) decreases time to discharge, readmission rate and postoperative morbidity with increased patient satisfaction and safety after discharge [74]. By identifying the type of pain (nociceptive, neuropathic, visceral), the provider can more efficiently treat pain by selecting the most appropriate intervention. Multidisciplinary accelerated postoperative rehabilitation and recovery programmes may reduce stress induced organ dysfunction and morbidity. Epidural analgesia in a multimodal analgesic regimen results in significantly less deterioration in postoperative functional status (lower pain and fatigue scores, earlier mobilization and return of gastro-intestinal function) and improved health-related quality-of-life at 6-week follow-up [75].

Use of secondary analgesics

The use of secondary analgesics in acute postoperative pain is still in its infancy. For example, gabapentin reduces pain on movement after breast surgery for cancer [31]. Whether or not N-methyl D-aspartate receptor antagonists can be reliably used to prevent persistent pain syndromes (after thoracotomy, mastectomy, amputation) is still unknown.

Individualized discharge analgesic packages and home follow-up

Severe postoperative pain continues to be a problem in ambulatory patients once they are discharged to the home environment [76]. Pain on the second postoperative day has been found to be a predictor of delayed recovery [30]. A multimodal post-discharge analgesic regimen tailored to the patient's expected postoperative pain levels should be prescribed. This is particularly important for parents of infants and children undergoing operative procedures on a day surgery basis. Patient follow-up by telephone questionnaire will confirm those surgical procedures that result in mild or moderate-to-severe postoperative pain and provide feedback of the effectiveness of treatment plans [77].

Conclusion

Progress in understanding the processes involved in post-surgical recovery and the risk factors for chronic post-surgical pain would be aided by baseline and post-surgical measures of relevant psychological, emotional and physical variables [78]. A hospital-wide, comprehensive, postoperative pain management program has been found to provide an overall positive result for the healthcare system by improving postoperative pain and morbidity [79]. A recent systematic review has been negative as to the potential beneficial effect of pre-emptive analgesia on postoperative pain due to poor trial designs and confusion over terminology and definition [80]. The most effective pre-emptive analgesic regimens should be those that are capable of limiting sensitization of the nervous system throughout the entire perioperative period, thus providing protective analgesia. Analgesia needs to be started before surgery and continued well into the postoperative period. For example, continuous perioperative neuraxial blockade (up to 5-7 days following major abdominal or thoracic surgery) to reduce persistent postoperative pain. Developments and improvements of multimodal interventions within the context of ‘fast track’ surgery programmes represent the major change to achieve a pain (and risk) free perioperative course. A more specific task is the need to optimize perioperative pain management with improvement of multimodal pharmacological analgesic regimes and integration of acute pain services into perioperative rehabilitation [13]. Genomic variation may influence analgesic responses [81]. There is evidence of potential genetic predisposition in pain behavioural responses to nociceptive and neuropathic stimuli [82]. In the animal model, transfer at the spinal level of some genes, in particular those of opioid precursors, leads to the overproduction of products that they encode and attenuate persistent pains of both inflammatory and neuropathic origin [83]. Targeting some molecules involved in pain induction and perpetuation, such as pro-inflammatory cytokines, raises an interesting possibility to block the development of pain. Thus genetic, psychological and social factors may all contribute to the perception and expression of persistent pain [84].

Flagging pain (blue, yellow and red flags) helps to identify risk factors in acute pain that need attention to avoid the transition from acute postoperative pain to acute persistent and then on to chronic pain [85]. This offers a unique opportunity for preventative medicine. It highlights the importance of timely interventions to prevent this progression from acute to chronic pain. Prospective studies are required to define the precise role and weighting of risk factors identified in this review [86].

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Keywords:

PAIN; chronic; acute; postoperative; post-traumatic; neuropathic; RISK FACTORS; EPIDEMIOLOGY

© 2005 European Society of Anaesthesiology