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Chronic Poststernotomy Pain: Incidence, Risk Factors, Treatment, Prevention, and the Anesthesiologist's Role

Kleiman, Amanda M. MD; Sanders, Daniel T. MD; Nemergut, Edward C. MD; Huffmyer, Julie L. MD

doi: 10.1097/AAP.0000000000000663
Regional Anesthesia and Acute Pain: Review Article

Abstract: Chronic pain following median sternotomy is common after cardiac surgery. If left untreated, chronic sternal pain can reduce quality of life, affecting sleep, mood, activity level, and overall satisfaction. This has a significant societal effect given the large number of cardiac surgeries annually. Although a number of pathophysiologic processes and risk factors are assumed to contribute, the exact cause and major risk factors remain unknown. Moreover, the treatment of chronic poststernotomy pain is often inadequate, relying on opioids and other medications that provide minimal benefit to the patient and have significant adverse effects. Indeed, little is known regarding the prevention of chronic pain development following sternotomy. This review aims to present the current, limited data regarding the incidence, risk factors, treatment, and prevention of chronic poststernotomy pain and to identify areas of future research to improve management of this common complaint following cardiac surgery.

From the Department of Anesthesiology, University of Virginia, Charlottesville, VA.

Accepted for publication May 17, 2017.

Address correspondence to: Amanda M. Kleiman, MD, University of Virginia Health System, PO Box 800710, Charlottesville, VA 22908 (e-mail: ak8zg@hscmail.mcc.virginia.edu).

The authors declare no conflict of interest.

Author Contributions: A.M.K. and D.T.S. helped design and conduct the review and write the manuscript. E.C.N. and J.L.H. helped write the manuscript.

Although the most serious complications following cardiac surgery are fairly well known, the most common complication may be underdiagnosed. Recent studies suggest that cardiac surgery through median sternotomy is associated with the development of chronic sternal pain with a reported incidence of 11% to 56% at 1 year after surgery.1–7 In the United States, more than 280,000 patients undergo cardiac surgery annually according to the Society of Thoracic Surgeons Database, with up to 156,800 patients suffering chronic poststernotomy pain at 1 year following cardiac surgery.8 The incidence of chronic poststernotomy pain, however, may be underestimated. Without proper diagnosis and treatment, chronic sternal pain can reduce quality of life affecting sleep, mood, activity level, and overall satisfaction.4,9 This review aims to discuss the current knowledge of risk factors, prevention, and treatment of chronic thoracic pain following cardiac surgery via median sternotomy.

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DISCUSSION

Diagnosis

Chronic postoperative pain following median sternotomy is defined as any nonanginal postoperative pain lasting more than 3 months. It may present as numbness, allodynia, palpation tenderness, or constant pain.4,10 Chronic poststernotomy pain has a variable presentation, impacting 1 or multiple sites. Although most frequently affecting the thorax, chronic pain associated with cardiac surgery may also involve the upper and lower extremities, neck, and back, potentially explaining the difficulty in properly diagnosing chronic pain resulting from median sternotomy.4,5,8 Thoracic pain following coronary artery bypass grafting (CABG) may be further divided into 3 different subcategories: (1) anterior chest wall pain on the left side, (2) midline scar pain, and (3) right-sided chest wall pain. Like the location of pain, descriptors are also varied, with some patients experiencing intermittent pain, whereas others describe constant pain. Factors that aggravate poststernotomy pain include pressure at the site, clothes rubbing against the scar, movement, deep breathing, coughing, weather/temperature change, and stress.2

Previous studies may have underestimated the incidence of chronic pain because of its variable presentation, accounting for some of the large variation in incidence between groups.8 In addition, the diagnosis of chronic pain after sternotomy can be made only when reported. Given the considerable anxiety and fear surrounding cardiac surgery, patients may underreport pain as they are simply happy to have survived surgery and do not wish to complain about what they may consider comparatively trivial.11 Patients may view chronic pain following cardiac surgery as “normal” or “expected” and be more concerned with their cardiac health. Thus, many patients may fail to report any symptoms to their surgeon or cardiologist, leading to delayed or improper diagnosis and treatment.5

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Pathophysiology

Whereas the exact mechanism for the development of chronic poststernotomy pain has not been determined, a number of different potential contributing processes have been hypothesized. After any surgical procedure, the up-regulation, activation, and neural sensitization during the acute pain phase are important contributors to the development of chronic pain.12 These factors are also likely involved in the development of chronic poststernotomy pain. Processes specific to cardiac surgery include neuropathy from anterior intercostal nerve entrapment or injury during internal mammary harvest, arthritis or hypersensitivity associated with sternal wire placement, musculoskeletal injury from surgical incision and manipulation, sternal fracture or incomplete bone healing, and the development of sternal wound infections.2,4,13–15 Although a myofascial component has been implicated in postthoracotomy pain syndromes, there is currently no evidence that this pathophysiology is involved in chronic poststernotomy pain.16,17

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Impact

Reported incidence of chronic pain following median sternotomy varies widely between 11% and 56% at 1 year following surgery, with the number of patients reporting chronic pain gradually decreasing over time. A number of factors likely contribute to the variable incidence, including differences in the definition and diagnosis of chronic poststernotomy pain, differences in surgical procedures and techniques, and patient-specific factors including additional medical and psychological issues that would affect ability to cope with the surgical stress both physically and emotionally. Heterogeneity in study design may also affect the reported incidence of chronic pain after cardiac surgery.

Most patients with chronic poststernotomy pain report their pain as mild or moderate; however, approximately 15% report severe pain (>7 on visual analog scale). Regardless of the severity, patients with chronic pain report lower scores on the 36-item Short-Form Health Survey, a generic, coherent, and easily administered survey of quality-of-life measures, suggesting that even mild pain may negatively impact patients. Likewise, 47% of patients reported interference with 1 or more daily activities, with sexual activity being the most commonly affected.2 Patients reporting pain at multiple locations are more likely to report an impact on quality of life and activities of daily living.2,4,7,9

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Risk Factors

Surgical Techniques

At 1 time, use of the internal mammary artery for revascularization was thought to be the primary cause of chronic pain following cardiac surgery.18,19 Internal mammary harvesting can be associated with an increase in acute pain following surgery, perhaps due to added tissue trauma, intercostal nerve injury, damage from retraction, and more extensive electrocautery use. Initial primarily retrospective studies showed an increase in the development of chronic pain after internal mammary artery (IMA) harvest.18,19 More recent studies including several prospective trials failed to show a higher incidence of chronic pain with IMA grafting.3,8,9,20–22 Improvements in methods of internal mammary harvest with less injury may be responsible for the changes seen in more recent studies. However, in 2014, another study showed a higher rate of chronic pain with IMA harvest. It should be noted that the percentage of patients reporting chronic pain in this study was considerably higher than that found in previous studies.23 It is likely that improvements in technique have diminished the effect of IMA harvest on chronic pain development, but better surveillance may account for the increased incidence reported in a few recent studies.

The use of bilateral IMA harvest might be expected to contribute to the development of chronic poststernotomy pain, although there are currently no supportive data. The Women's Recovery From Sternotomy-Extension (WREST-E) trial found those patients with bilateral IMA harvest to have more incisional pain compared with patients with only left-sided graft usage.24 The use of pedicled bilateral grafts, where the IMA is taken as a pedicle including fascia, muscle, connective tissue, and veins, is associated with an increased incidence of mediastinitis, especially in diabetic patients. The development of mediastinitis itself is associated with chronic pain development. Interestingly, the use of skeletonized bilateral mammary grafts, in which surrounding structures are removed, is not associated with mediastinitis.25

Although the impact of the type of surgical procedure may be unclear, urgent or emergent surgeries confer a higher risk of developing chronic thoracic pain.12,21 Emergent surgery is the strongest procedural predictor of the development of chronic thoracic pain.21 Emergent procedures may be associated with more local tissue trauma due to the need for quicker incision, sternotomy, and cannulation strategies, which may account for an increased likelihood of developing chronic pain. While the development of chronic pain following other emergent procedures is well studied, urgent and emergent surgeries were often excluded from early studies evaluating risk factors for chronic pain following sternotomy. Additional studies including the analysis of urgent and emergent cardiac surgery are needed to fully quantify this risk.12,21 Interestingly, neither cardiopulmonary bypass nor aortic cross-clamp times seem to have an association with chronic pain.7

Rib fractures occur in up to 5% of patients following median sternotomy.26 Pain from rib fractures occurs most frequently in the upper thorax and may radiate down the arm or into the neck, mimicking angina and pain from other cardiac conditions. Fractures of the first rib account for approximately one-third of poststernotomy rib fractures and if displaced posteriorly may injure the brachial plexus.27 Brachial plexus injury following median sternotomy primarily affects the C8–T1 nerve roots and is associated with pain, dysesthesia, and hand weakness.28 In most patients, symptoms improve within 1 week; however, in approximately 1% of patients, permanent pain or sensory deficits may develop.29 Interestingly, only 15% of rib fractures associated with pain or sensory deficits are detected on standard chest imaging but are evident on radionuclide imaging.27,30 Brachial plexus injury may also occur in the absence of rib fractures if traction is placed on the brachial plexus or if there is compression of the nerve roots between the clavicle and the first rib.28

The use of sternal retraction may determine the characteristics of the dysesthesia, hypesthesia, and hyperalgesia seen following IMA harvest. The sternal retractors used for IMA harvest are associated with a statistically significant increase in sternal fractures compared with cardiac surgery without IMA harvest. Although most sternal fractures are well tolerated, some patients may develop significant pain associated with these fractures.31 The Favaloro retractor is the most commonly used retractor for IMA harvest and consists of 2 vertical bars with a suspended horizontal rod. Retraction is generated by screwing on 2 retractors from the free edge of the sternum to the horizontal piece. The use of the Favaloro retractor was associated with brachial plexus injuries, including compression of the radial nerve between the vertical bar and the humerus.32 Several modifications have been made to the Favaloro retractor including the addition of blunt teeth and a screw system, permitting less force of retraction and injury as well as a sternal-based system.33 The Chevalier retractor exposes both sides of the sternum to more pressure than standard sternal retractors.34 The Chaux retractor is associated with primarily right-sided symptoms. The Medtronic sternal retractor had the highest association with hypesthesia, which is thought to be due to bilateral pressure on intercostal nerves as a consequence of excessive retraction of the costovertebral joints.34

Not surprisingly, patients requiring resternotomy during the same hospitalization have a higher incidence of chronic pain.21 Repeated tissue trauma and inflammatory changes associated with resternotomy likely contribute to increases in chronic pain. Despite these observations, history of a prior sternotomy has not been well correlated with a higher risk of chronic pain after subsequent surgeries.

Finally, patients who suffer sternal wound infections seem to exhibit an increased incidence of chronic pain.7,35 Wound complications, including infection, mediastinitis, keloid formation, and wound dehiscence, have been linked to the development of chronic poststernotomy pain.35 Increased risk is conferred with minor superficial wound infections, as well as more severe, deeper infections including mediastinitis. Major sternal wound infection, including sternal dehiscence, occurs in approximately 2% of patients following median sternotomy.36 Deep wound infections involving sternal bone and mediastinum occur in approximately 0.6% of patients.37 The prolonged inflammatory changes associated with sternal wound infections may lead to chronic tissue damage, wound dehiscence, and scarring. These changes are likely the cause of the development of chronic pain in patients with wound complications.35

Likewise, poor sternal healing may contribute to the development of chronic pain. Sternal pseudoarthrosis and sternal nonunion occur in up to 1% of patients following median sternotomy and are characterized by cessation of both the periosteal and endosteal healing responses after 3 months. Patients with sternal nonunion suffer from sternal instability, as well as pain, and often do not have any signs of infection, although the wound may be reactive with hypertrophic features. Surgical and environmental factors associated with sternal nonunion include bilateral IMA harvest, prolonged cardiopulmonary bypass time, postoperative prolonged ventilator dependence, low cardiac output, and cardiac massage. Patient factors linked to sternal nonunion include diabetes, chronic obstructive pulmonary disease, use of steroids, history of radiation, and poor nutritional status. Surgical factors implicated in sternal nonunion include technical errors in sternotomy, off-midline sternotomy, osteoporotic bone, multiple fracture lines, fracture gap, decreased vascularity of the bony segments, and instability of the sternal closure.38

Despite thoracic surgery via a thoracotomy approach having a higher incidence of chronic pain (61% at 1 year), cardiac surgery via anterolateral minithoracotomy could be associated with less psychological impact when compared with cardiac surgery via sternotomy. Sternotomy seems to be associated with a higher psychological stress response prior to the procedure, as well as on postoperative day 4; however, this psychological stress is similar in thoracotomy and sternotomy at 1 month.39 Pain behavior rating scale and physical activity are also improved on day 4 and similar at 1 month.39

Although cardiopulmonary bypass time does not seem to impact the development of chronic pain, procedures performed with cardiopulmonary bypass may also be associated with increased pain compared with procedures performed without cardiopulmonary bypass. Compared with minimally invasive direct coronary artery bypass (MIDCAB) using an anterolateral minithoracotomy and off-pump technique, conventional CABG with cardiopulmonary bypass was associated with increased pain beginning on postoperative day 4 along with reduced quality of life.40 In addition, at 3 months, standard CABG utilizing cardiopulmonary bypass was associated with increased pain, lower physical activity, and poor sleep compared with MIDCAB.40 Unfortunately, the effect of cardiopulmonary bypass is not completely clear as a thoracotomy incision was used for the MIDCAB operation.

Table 1 summarizes the impact of surgical factors on the risk of developing poststernotomy chronic pain.

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Acute Pain Severity and Treatment

The presence of persistent acute and severe pain requiring the use of opioids and other analgesics in the initial perioperative period is one of the largest risk factors associated with the development of chronic pain.41 Prospective observational studies show that the intensity of acute postoperative pain is a significant predictor for both the presence and severity of chronic poststernotomy pain.7 Those receiving greater cumulative opioid pain medications are at greater risk.19 A numeric rating scale score of greater than 4 on the third postoperative day is associated with an increase in the risk of chronic pain at 1 year following surgery.21 One possible explanation for this finding is that greater acute pain may indicate greater musculoskeletal injury or tissue trauma.13,19 Inadequate treatment of even less severe acute pain could also play a role in the development of chronic poststernotomy pain.19

Persistent and/or severe pain activates pathways in the peripheral and central nervous systems with activation and central sensitization of neurons and neural processes that leads to chronic pain, allodynia, hyperpathia, and hyperalgesia.42 Release of procytokines, chemokines, and neurotrophins due to pain and inflammation accounts for both peripheral and central sensitization. Peripheral and central sensitizations are ultimately responsible for the conversion of acute pain into chronic pain.42 Both modulation and, more importantly, modification of the nervous system occur in response to pain stimuli with modification representing irreversible changes that are more likely to contribute to chronic pain development. Remodeling of the dorsal horn and central nervous system also occurs in response to pain with death of inhibitory neurons, remodeling of neural synapses by glial cells, and increased intensity of responses to noxious stimuli with continued pain.

Secondary hyperalgesia, which precedes central sensitization, is thought to play a major role in the development of postsurgical pain. Unfortunately, the medications used to treat postoperative pain, including opioids, have little effect on secondary hyperalgesia once it occurs. Finding treatments for secondary hyperalgesia may hold the key to improvements in chronic pain prevention. Blocking the effects of one particular neurotransmitter is unlikely to prevent peripheral or central sensitization.43 Moreover, better control of acute pain after cardiac surgery has been shown to reduce cardiovascular morbidity, pneumonia, and hypercoagulability due to reductions in the stress response.44–46

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Patient Factors

Certain patient demographics are associated with a higher risk of chronic pain (Table 1). Like other chronic pain pathologies, sex may play a role. Following sternotomy, women are more likely to experience chronic thoracic pain for the first year. This difference is not seen beyond 1 year following surgery.4,21,47 The WREST-E trial studied the incidence of chronic poststernotomy pain in women specifically and reported an incidence of 47% 1 year after surgery, higher than what had been previously reported in studies that included both men and women.24 Much like other risk factors for chronic pain, the evidence for sex as a predictor is mixed as other studies have not shown consistent association between patient sex and chronic pain.5,7,19 The lower percentage of women undergoing cardiac surgery and included in these studies may account for the variable impact of sex on pain.7

The WREST-E group also found larger chest circumference to be associated with an increased risk of having chronic sternal or breast pain.24 Other studies have observed this finding in both men and women.48 Perhaps related to chest circumference, patients who were overweight or obese reported a higher incidence of chronic poststernotomy pain.9

Age may also play a role in the development of chronic poststernotomy pain. A higher incidence of chronic postoperative pain, as well as greater intensity of pain, has been shown in younger patients compared with those older than 70 years.9 A recent multicenter retrospective trial showed a significantly higher incidence of chronic pain in patients older than 75 years at 3 years after surgery despite showing no difference in the incidence of chronic pain at 3 months and 1 year following surgery.4 A higher New York Heart Association class and the presence of angina are also associated with a higher risk of chronic pain.19

Patients with hypothyroidism seem to be at greater risk of chronic pain following sternotomy. Hypothyroidism is thought to contribute to neuropathic pain, although the exact mechanism remains unclear.35 Demyelination, aminoglycan deposition, and regional hypoxia leading to muscle spasms have all been postulated as reasons for the association between hypothyroidism and chronic pain development.49,50

Like other forms of chronic pain, concomitant mood disorders including depression and anxiety increase the risk of chronic pain following sternotomy. Serotonin and norepinephrine are altered in depression and anxiety and are also responsible for the modulation of pain. Patients with mood disorders may express negative emotions as physical complaints, including pain. Lower socioeconomic status is also associated with an increased risk of developing poststernotomy pain. In addition, patients receiving disability or other secondary gain may be more likely to experience chronic pain, or at least report it.35 Patients with preoperative pain states, especially those prescribed opioids, as well as patients with angina also seem more likely to develop chronic pain.9

Undoubtedly, genetic predisposition toward the development of neuropathic injury and chronic pain exists and plays a role in poststernotomy pain. Differences in genetic control of the response to noxious stimuli, as well as modulation of the pain response, may make some patients more likely to experience chronic pain following surgery. The specific genes related to chronic pain development are unknown but may include variants of catechol-O-methyltransferase, voltage-gated Na+ channels, GTP cyclohydrolase, tetrahydrobiopterin-related genes, and the μ-opioid receptor, which are all involved in response to pain and development of chronic pain.51–53 Some patients may, in fact, be predisposed to chronic pain development even prior to surgical intervention.54

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Preexisting Chronic Pain

Preoperative nonanginal chronic pain, especially pain requiring treatment, is associated with an increased risk of chronic poststernotomy pain.7 Although seemingly linked, it is unclear whether preexisting pain syndromes confer a higher risk of pain due to genetic predispositions or additional risk factors or if the presence of chronic pain prior to surgery has a causal relationship to postsurgical pain by central sensitization and other mechanisms.12 Further study regarding the link between chronic pain syndromes is needed to better elucidate this relationship.

Figure 1 graphically depicts risk factors associated with the development of chronic poststernotomy pain.

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Natural Progression

Chronic pain after sternotomy seems to improve over time. There is lower incidence of chronic pain in patients surveyed after 1 year following surgery as compared with those who reported pain prior to the 1-year anniversary of their surgery.5 Likewise, some patients with chronic pain at 3 months often reported no chronic pain 6 months or 1 year after surgery.5 The lower prevalence at longer time intervals following surgery suggests that chronic pain may at least subjectively improve over time regardless of the effectiveness of treatment. Whether this improvement is attributed to a prolonged healing time required in elderly patients has not been well studied but is a possible explanation for the gradual improvement in pain.

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Treatment of Chronic Pain

The treatment of chronic pain often requires the utilization of multiple treatment modalities regardless of the etiology. Commonly prescribed medications include nonsteroidal anti-inflammatory drugs (NSAIDs), opioids, tricyclic antidepressants, serotonin and norepinephrine reuptake inhibitors, anticonvulsants such as carbamazepine and γ-aminobutyric acid (GABA) analogs, cannabinoids, muscle relaxants, benzodiazepines, and topical agents including lidocaine, NSAIDs, and capsaicin.13,20,55 The best evidence exists for the use of diclofenac and gabapentin showing benefit even after discontinuation.13,20,55

Studies suggest that of those with chronic poststernotomy pain only a small portion of patients received World Health Organization level III medications including opioids for more refractory pain.55 Regardless of treatment, approximately 50% of patients with chronic pain describe inadequate relief of symptoms using medical therapy with more severe pain associated with less satisfaction with their analgesic regimen.55

In addition to conventional vehicles for medication delivery, interventional pain procedures may be beneficial for the treatment of severe poststernotomy pain.55 Invasive procedures include neuraxial injections of steroids, opioids, or other relaxants; the placement of spinal cord stimulators; and direct nerve blocks in which local anesthetic, chemical neurolysis, or radiofrequency ablation is used.56–62 While each of these treatments has been used to treat chronic pain, the evidence to support their use following sternotomy is largely anecdotal.

Intercostal nerve blocks have been successful in the treatment of postoperative intercostal neuralgia in patients in whom alternative therapies including pharmacotherapy with opiates and other interventional treatments failed.57 A retrospective analysis of pulsed radiofrequency of the dorsal root ganglia showed superior pain control at 3 months in chronic postsurgical thoracic pain compared with both pharmacotherapy and pulsed radiofrequency of the intercostal nerves.58 Spinal cord stimulation has been used effectively to treat angina but may also be used for intractable postoperative neuropathic pain including chronic thoracic pain by placement of 2 leads, midline and lateral, between T1 and T4.60 Because these are invasive procedures with potential risks of complications and insufficient data exist to strongly support their use, interventional procedures for the treatment of poststernotomy pain should likely be limited to cases of intractable pain with appropriate risk stratification.

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Prevention Modalities

A meta-analysis by Chaparro et al63 of 40 randomized controlled trials evaluated various treatment modalities including N-methyl-D-aspartate (NMDA) antagonists, NSAIDs, GABA analogs, local anesthetics, steroids, and serotonin-norepinephrine reuptake inhibitors. Only ketamine demonstrated a modest preventive benefit, although the authors noted problems with the study size. Furthermore, in a recent review article, Reddi64 noted that although there is evidence for the efficacy of ketamine, gabapentin, and pregabalin in the prevention of chronic pain development, as well as potential benefit from regional anesthetic and nerve-sparing surgical techniques, these options cannot be fully recommended. Additional studies are needed to define the role that these medications and interventions play in postsurgical pain prophylaxis.

While evidence regarding the prevention of chronic pain is generally lacking, considerably more research exists regarding the treatment of acute pain following sternotomy. Given that the severity of acute pain is a significant predictor for both the presence and intensity of chronic pain, improved treatment of acute pain would be expected to improve not only the incidence but also the severity of chronic poststernotomy pain. Unfortunately, data to support the prevention of chronic pain with improved acute pain treatment are scant, and the data that do exist are inconclusive. Thus, treatment of acute pain is not a guaranteed prevention strategy.

Common treatment modalities for both acute and chronic pain control and current data on their use specifically for the prevention and/or treatment of chronic poststernotomy pain are included below and summarized in Tables 2 and 3.

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Acetaminophen

Acetaminophen is an inhibitor of prostaglandin synthesis that resembles the actions of selective cyclooxygenase 2 inhibitors with applications for the treatment of acute and chronic pain.65 Although acetaminophen has demonstrated an ability to reduce opioid consumption in the first 24 hours following cardiac surgery, few studies have assessed its effectiveness in the treatment of poststernotomy pain.66–68

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Gabapentinoids

Gabapentin and pregabalin are structural analogs of GABA that bind to the α2-δ site of voltage-dependent calcium channels and are a first-line treatment for chronic neuropathic pain.69 In addition, they have been used as adjuncts for postoperative pain management with an opioid-sparing effect and reduction in acute postoperative pain scores.70–74 Specifically as a means to prevent chronic postsurgical pain, 50% of patients showed a decreased incidence of chronic pain more than 2 months after surgery.69 In cardiac surgery, gabapentin may reduce opioid consumption and pain scores immediately following cardiac surgery both after a single preoperative dose and when continued in the postoperative period, although this has not been universally demonstrated.75–77 Gabapentin is also effective in the treatment of rib fractures caused during sternotomy.78 Similarly, pregabalin reduced postoperative opioid consumption, the incidence of confusion on the first postoperative day, and decreased pain with movement 3 months postoperatively.59–78

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Ketamine

Ketamine interacts with opioid receptors, monoaminergic receptors, muscarinic receptors, voltage-sensitive calcium channels, and most importantly as a noncompetitive antagonist of NMDA receptors. Ketamine has documented efficacy in the treatment of acute postoperative pain, as well as prevention and treatment of chronic pain syndromes.79–81 The use of ketamine in cardiac surgery was associated with decreased inflammation, opioid sparing, and improved patient satisfaction postoperatively.82–90 Its use in the prevention of chronic poststernotomy pain has not been studied.

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Remifentanil

Remifentanil is an ideal agent for fast-track cardiac surgery but is associated with tachyphylaxis, opioid-induced hyperalgesia, and increased incidence of chronic pain 1 year after sternotomy.91–93

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Dexmedetomidine

Dexmedetomidine is a selective α2-agonist primarily used for sedation.94,95 Despite its ability to decrease acute postoperative pain and improve long-term outcomes including a decreased incidence of postoperative complications including major adverse cardiac events, delirium, and overall mortality up to 1 year postoperatively, no evidence exists to support a decrease in chronic pain.96,97

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Glucocorticoids

Glucocorticoids have an extensive history of use in cardiac surgery but the Steroids In Cardiac Surgery trial showed no difference in pain at 30 days or in chronic incisional pain at 6 months.98,99 Based on this alone, steroids cannot be recommended for the prevention of chronic pain after cardiac surgery.

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Transdermal Lidocaine

Despite evidence to support the use of systemic lidocaine as an adjuvant for pain control in the perioperative period, there is no evidence to support transdermal or intravenous lidocaine following cardiac surgery.100–102

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Thoracic Epidural Anesthesia

Thoracic epidural anesthesia is associated with a lower incidence of cardiopulmonary complications and provides excellent postoperative pain control75,103–105 Despite studies showing decreased pain scores and opioid consumption in the acute postoperative period, no reduction in chronic pain incidence or severity has been shown.106,107

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Intrathecal Opioids

Intrathecal opioids are often used in fast-track cardiac anesthesia to improve acute postoperative pain scores. However, there is no evidence that they improve chronic postoperative pain.108–118

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Parasternal Intercostal and Paravertebral Blocks

Parasternal intercostal and paravertebral blocks reduce acute postoperative pain.119–122 Despite this, there is no evidence that either has an effect on chronic poststernotomy pain.121,123

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Intrapleural Injection

Intrapleural local anesthetic injections have been utilized for pain control following thoracotomy with mixed results. There are only limited data for their use following median sternotomy.124,125 Their utility for prevention of chronic pain has not been studied.

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Continuous Wound Catheter

The use of catheters placed directly to continuously deliver local anesthetic has been shown to decrease acute postoperative pain likely due to the concomitant presence of an anterior intercostal block; unfortunately, there is concern for their safety and the actual efficacy of the intervention.126–133 No evidence regarding their effect on the development of chronic pain exists.126

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Transcutaneous Electrical Nerve Stimulation

Transcutaneous electrical nerve stimulation utilizes the “gate control theory.” Evidence regarding its use in chronic pain is mixed.134–137

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Wire Removal

Sternal wires may be a source of chronic pain. Their removal after healing has been associated with a significant improvement in reported chest pain; however, other causes of persistent chest pain must be excluded.133–139

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Psychological Interventions

Preoperative anxiety and catastrophizing have been shown to predict severity of acute postoperative pain and the probability of chronic postsurgical pain.140,141 However, psychological treatments prior to surgery have shown no beneficial effect on acute pain intensity or mobility.142

Depression remains a compelling psychological area for research and treatment after cardiac surgery. Patients with depressive symptoms after cardiac surgery are more likely to require readmission and rehospitalization, report a lower quality of life, increased mortality, and higher pain scores compared with patients without depressive symptoms.143,144 Depressed patients reported worse pain scores at baseline and up to 1 year after CABG, but those who received telephone-delivered collaborative care for depression reported improved pain scores.145

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Surgical Prevention

Compared with pedicled grafts, skeletonized internal mammary grafts are associated with reduced postoperative pain and dysesthesia at 3 months following surgery, as well as a reduction in major sensory deficits. This reduction in pain likely results from increased sternal perfusion.146 In addition, the use of bilateral skeletonized mammary grafts is preferable in high-risk patients, including diabetics, when bilateral mammary grafts are preferred because of a reduction in mediastinitis.25

The use and choice of sternal retractors likely contribute to chronic pain via sternal and rib fractures, as well as direct nerve injury. Careful placement of retractors to minimize injury and limitation of the duration and force of retraction may decrease injury and therefore prevent the development of chronic pain. Rib fractures and injury to the brachial plexus may be lowered by opening the sternal retractor as little as possible and by placing the retractor as caudally as possible.30,147

Avoidance of sternal nonunion begins with identifying at-risk patients and modifying risk factors, when possible. Prophylactic sternal plating has been suggested for high-risk patients, although this does not reliably eliminate sternal dehiscence and nonunion. There is currently no consensus as to the best treatment for sternal nonunion, although latching bone graft and wires, plate fixation, tension-band sternal plating, crimped cable grip system, metal plates, and autogenous bone graft have all been used.38

Prevention of sternal wound infections and wound dehiscence begins in the preoperative setting with identification of potential colonization, preoperative glucose control, and removal of any potential sources of bacteria including removal of hair and dental extractions if necessary. Intraoperatively, appropriate sterile precautions, glucose control, and timely, tailored antibiotic dosing should be used. In the postoperative period, discontinuing prophylactic antibiotics after 24 hours, regular dressing changes beginning on postoperative day 1, and monitoring and treatment of elevated blood glucose are helpful in preventing sternal wound infections and promoting wound healing.148

Continued innovation in surgical procedures and techniques contributes to a reduction in complications, including chronic pain. The use of minimally invasive techniques, as well as avoidance of cardiopulmonary bypass, may be associated with reduced pain, although controlled trials to support this hypothesis have not yet been performed. Future studies regarding the use of minimally invasive techniques are needed to determine the impact on chronic pain.

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CONCLUSIONS

Chronic poststernotomy pain is an increasingly recognized condition with major implications on daily function and quality of life. The presentation is varied and complex, and thus, the diagnosis may frequently be missed. Much of the data regarding risk factors for chronic pain are conflicting and unclear, which makes the identification of patients who are at risk to develop chronic poststernotomy pain daunting. A greater understanding of how best to prevent and treat this condition is needed. Of the perioperative modalities available, most lack sufficient evidence to fully support their use.

Despite best efforts, up to 80% of postoperative pain, including pain following sternotomy, is not adequately managed.149 Some interventions clearly improve acute postoperative pain and overall outcomes in cardiac surgery, as is the case in neuraxial techniques; however, the impact on chronic pain is unknown, largely because it is unstudied. Indeed, much of the data presented in this review show improved acute postoperative pain. Given that acute pain is a risk factor for chronic pain, the use of these agents warrants further investigation regarding their effect on the development of chronic pain. Gabapentin and pregabalin seem to reduce the incidence of chronic pain, but the quality and quantity of supporting evidence are limited. Ketamine is a known prophylactic agent and treatment for chronic pain, but there are no studies that looked at its effects on the development of chronic poststernotomy pain. Psychological interventions offer an additional nonpharmacological target for prevention and treatment of chronic poststernotomy pain.

Opioids are the most common treatment for postsurgical pain.150 Despite their prolific use, they are associated with a myriad of negative adverse effects, addiction, and risk of overdose. Indeed, opioid prescribing in the United States continues to increase, with approximately 50% of prescriptions given by pain management physicians and 37% of those from surgeons being for opioids in 2012.151 Moreover, whereas opioids are useful in the treatment of short-term pain, there is little evidence to support continued pain relief or improvements in quality of life associated with the use of opioids for chronic pain.128

Specifically regarding the treatment and prevention of chronic poststernotomy pain, most studies investigating chronic poststernotomy pain are retrospective and involve survey data. In many instances, the time between surgery and the administration of the survey is prolonged, leading to the possibility of significant recall bias. Randomized controlled trials that aim specifically to elucidate effective prevention and treatment strategies for chronic poststernotomy pain are needed.

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