Burn Pain

Shelley A. Wiechman

Sam R. Sharar

If burn injuries in themselves are not the most painful type of trauma a person can sustain, then they likely reach this status once the nature of their treatment is considered. Contemporary treatment of burn injuries involves a multitude of invasive and rehabilitative procedures that continue—often on a daily basis—for days, weeks, or months. Each intervention is critical to achieving optimal wound healing and long-term physical/occupational function yet has the potential for inflicting more pain, on a repeated basis, than that of the initial trauma. Burn injuries are pervasive in both industrial nations and developing countries around the world and affect individuals across a wide demographic span. In the United States, it is estimated that burn injuries account for 40,000 hospitalizations annually (about half of these hospitalizations are children or adolescents) and 3,275 deaths.¹ This is down from 5,500 deaths just 15 years ago. As death rates for burn injuries decline, due primarily to burn prevention strategies and improved surgical care, more patients with large burns are surviving and pose unique physical and psychological rehabilitation challenges such as scarring, contractures, amputations, psychological adjustment, and pain.²

Despite this increased challenge to provide effective pain relief, there has long been substantial evidence that pain from burn injuries is undertreated, particularly in children and the elderly.³^,⁴ Furthermore, the magnitude of pain reported after burn injury and during burn care correlates strongly with long-term adverse psychological outcome in this patient population.⁵^,⁶ Thus, there are humane, medical, and economic reasons to better control burn pain in a practical and cost-effective fashion. Pain management is closely tied to a patient’s satisfaction with care, and uncontrolled pain is associated with poorer long-term outcomes in both adults and children.⁷^,⁸^,⁹^,¹⁰^,¹¹ Evidence-based pain management protocols have been shown to reduce pain.¹² Both the United States and New Zealand have developed clinical guidelines for the management of burn pain that were based on rigorous standards for evaluation and treatment,¹³^,¹⁴ and the American Burn Association has identified priority topics for research and additional clinical guidance.¹⁵

The Nature of Burn Pain

Treating the human suffering from burn pain is challenging from the perspectives of both the patient and clinician. It is well known that a burn injury results in one of the most intense types of sensory nociception imaginable, attributable to the unique tissue injury that results from a thermal insult to the dermal sensory organs and acute inflammatory response that, at least in the early postburn period, is related to the depth of tissue injury (Figs. 53.1 and 53.2).

First-degree burns (e.g., sunburn) are characterized by tissue injury that is limited to the epidermal skin layer and an inflammatory response in the superficial dermal layers and results in hyperemia (manifest as erythema), an intact epidermis (no skin blistering), and sensitization of dermal sensory organelles producing hyperalgesia and mild to moderate pain. Second-degree or partial-thickness burns involve tissue injury that extends to variable depths into the dermis; superficial second-degree burns involve only the upper, papillary dermis and are more likely to heal spontaneously, whereas deep second-degree burns involve the deeper, collagen-dense reticular dermis and are more likely to require surgical treatment. Because second-degree burns consistently injure and/or inflame sensory receptors in the dermis, these burns are associated with marked hyperalgesia and produce moderate to severe pain. Third-degree burns are characterized by complete destruction of the dermis, including its sensory and vascular structures, such that although pain may still be a presenting symptom, hypalgesia to cutaneous stimulation, a leathery skin texture, and lack of capillary refill are common. Complaints of acute pain with third-degree burns are typically minimal but can be variable and are universally present with respect to the transition zone between burned and unburned skin. All burn injuries involving the dermis (i.e., second- and third-degree) result in sensitized and reorganized states of both peripheral mechanoheat receptors and dorsal horn neurons. Models of these cellular alterations provide a conceptual framework for understanding how such peripheral neuronal injuries that are present after a burn can cause acute and subacute pain, hyperalgesia, and chronic pain and are described in detail elsewhere.¹⁶^,¹⁷

FIGURE 53.1 Anatomic layers of skin. Graphic representation of skin layers including the outer epidermis, the thin papillary dermis, the collagen-dense reticular dermis, and the deep subcutaneous fat. The dermal sensory neurons of mechanoheat receptors and dermal capillaries are shown, relative to a first-degree burn injury (confined to the outer epidermal skin layer). (Reprinted from Sharar SR, Patterson DR, Wiechman-Askay S. Burn pain. In: Waldman SD, ed. Pain Management. 1st ed. Philadelphia: Saunders-Elsevier; 2007:240-256. Copyright © 2007 Elsevier. With permission.)

In addition to the significant pain caused by the burn injury itself, the major clinical analgesic challenge results from procedural and postoperative pain associated with contemporary burn care, which incorporates a series of aggressive procedures that stimulate nociceptive peripheral afferent fibers on a daily basis for days, weeks, or months after the initial injury. In the typical treatment paradigm, a burn injury will first be assessed as to its depth and then treated accordingly. Shallow burns will be left to heal on their own, and full-thickness thermal injuries will typically be excised and covered with a skin graft. Burns of indeterminate depth in many burn centers will
undergo a series of wound débridements and dressing changes, typically on a daily basis, until burn depth can be more accurately determined. Burn care-related pain can be anticipated and treated, to a large degree, based on the clinical setting in which the pain occurs. Wound débridement, limb/joint mobility exercises, therapeutic skin stretching, and other medical procedures result in procedural pain, which is of high intensity but limited duration. Patients who are between procedures and have minimal physical activity continue to experience resting pain that is relatively less intense but almost constant in duration. When pain control interventions fail to control resting pain, patients will experience breakthrough pain. Finally, because surgical interventions are a frequent treatment for severe burn injuries, postoperative pain is an additional type of pain to be considered. Each of these four types of burn pain has specific treatment strategies, as described later in this chapter.

FIGURE 53.2 Definitions and examples of partial- and full-thickness burn injuries. Superficial and deep skin burns are defined, including clinical characteristics (etiology, physical exam findings, tissue injury, and usual treatment), photographic examples, and graphic representations of tissue injury (including zones of hyperemia, stasis, and coagulation). (Reprinted from Sharar SR, Patterson DR, Wiechman-Askay S. Burn pain. In: Waldman SD, ed. Pain Management. 1st ed. Philadelphia: Saunders-Elsevier; 2007:240-256. Copyright © 2007 Elsevier. With permission.)

In addition to these four distinct yet overlapping clinical settings, burn pain varies somewhat temporally with the phase of treatment, most often divided into the resuscitative, healing, and remodeling phases.¹⁷ In the resuscitative phase immediately after the injury, the patient is stabilized hemodynamically and initial wound treatments are performed. This phase is usually of short duration (e.g., hours), but depending on the size of injury can last up to 72 hours, as in the case of large surface area burns. Initial wound care in this phase is often intensely painful and, in the rush of treating life-threatening events, analgesia may be unintentionally de-emphasized. Pain in the healing phase is characterized by repeated episodes of burn wound care and dressing changes, wound examinations, needle sticks for intravenous (IV) access or blood sampling, and surgical procedures including débridement and grafting. The healing phase can last from days to several weeks depending on the severity of the burn and progress of the systemic response to the injury. It has been reported that hyperalgesia is more severe during this phase, independent of the size and degree of the burn. In the remodeling phase, the systemic and local inflammatory responses decrease, wound healing is nearing completion, and rehabilitative activities gain emphasis. Depending on the characteristics of the wound scar, this phase is characterized by not only reductions in resting pain but also ongoing episodic procedural pain associated with physical and occupational therapy sessions. It is important to note that the duration and sequence of these phases can vary depending on the clinical progress of wound treatment. For example, a patient who has progressed to the remodeling phase can return to
the healing phase after a surgical procedure recreates an open wound (e.g., burn site or skin graft donor site).

Although the clinical and temporal settings of burn care can provide some prediction as to the pain a patient might experience, the magnitude and quality of a given individual’s pain experience have proven extremely difficult to anticipate. The sensory and affective qualities of burn pain have received scant attention in the literature, and few studies have addressed pain patterns over the course of hospitalization. For example, Choinière and colleagues¹⁸ observed the evolution of burn pain experienced over the course of hospitalization and found that it varied substantially both within and across patients over time. They also reported that burn pain was not accurately predicted by sociodemographic factors or burn size (the latter finding is contrary to the inaccurate assumptions of many clinicians inexperienced in treating burns). Similarly, patient pain reports do not correlate with the quantity of opioid analgesics received, a finding first published in 1981 and still reported over two decades later.³^,¹⁹ This unpredictable and often opioidresistant nature of burn pain has been hypothetically linked to underlying sensory nerve damage²⁰^,²¹ and contributes to the difficulty of effectively treating burn pain.

Although capturing the pain experience of an individual patient will likely continue to prove elusive for the reasons listed, it remains important to continue to treat burn pain aggressively. Not only can burn recovery (like that from any trauma) be hindered by the presence of acute pain,²²^,²³^,²⁴ burn pain has also been reported to influence posthospitalization emotional recovery more than the size of the burn, the duration of hospitalization, or even the patient’s preinjury mental health. Ptacek and colleagues⁵ reported that inpatient pain scores in adults correlated more strongly with distress and quality of life scores at 1 month after discharge than did any other independent variable studied, a finding that persisted at 1- and 2-year follow-up periods.⁶ Similarly, Saxe et al.²⁵ reported that the amount of morphine received by burn-injured children may impact their subsequent development of posttraumatic stress disorder (PTSD). Future studies will likely further substantiate the practical utility of adequately treating burn pain.

Psychological Factors

It is well known that pain processing may be largely subjective and that the degree to which pain is interpreted as a threat will influence how much patients will suffer. A burn injury is a form of trauma that has dire emotional consequences for many survivors, and the threat value of the injury will likely have an impact on the amount of pain they perceive. Moreover, the nature of a patient’s preinjury psychological makeup also has a great deal to do with how much pain he or she will perceive. In considering psychological factors, it is then important to consider the preinjury status of patients as well as their emotional adjustment during and after hospitalization.

Burn injuries often occur when people are at risk because of low social resources or because of personality and/or psychiatric factors. The estimates of preinjury psychological problems in some studies of burn patients are so high that injuries of this type should be considered to be, in part, a symptom of social ills.²⁶ Estimated rates of psychiatric diagnoses in patients admitted for burn care have ranged from 25% to 75%, with the most prevalent diagnoses including depression, personality disorders, and substance abuse.²⁶ Psychopathology and psychological problems are common in patients with burn scars that impact body function and image.²⁷ In addition, the nature in which the burn injury occurred is often cause for concern: suicide attempts, child and elder abuse (or neglect), domestic violence, illicit drug manufacturing (methamphetamine production, hash oil production), and juvenile fire setting are all common sources of the injury. Psychological disturbances that predate the burn injury have the potential to increase complications, lengthen hospital stays, and lead to more serious long-term adjustment problems.²⁸^,²⁹ A number of these preinjury complications have direct relevance to pain control. Patients with drug and alcohol histories may show lower pain tolerance, more delirium, and higher drug-seeking behaviors. Particularly, those with a prior opioid addiction will be more sensitive to pain and greater have a greater tolerance to opioids. Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) Axis II character disorders can present a particular challenge to clinicians. Patients with such personality predispositions may show not only drug-seeking but also dramatic acting out behaviors, manipulation, staff splitting, and low frustration tolerance. Patients with borderline personality disorders, in particular, engage in parasuicide behavior and self-mutilation. All of these factors might complicate pain control, in addition to making the patient’s overall management a challenge.

Both the burn care environment and psychological reactions to burn injuries contribute to pain and complications in its management. Patients with large unhealed burn areas or other significant medical complications are usually placed in intensive care units (ICUs). In the critical care setting, delirium and other psychotic reactions are common.³⁰^,³¹ There has been recent emphasis on managing delirium more aggressively in the ICU as it leads to complications such as more infections, respiratory problems, and longer lengths of hospitalization. Unfortunately, there is a dilemma in achieving optimal management as opioids and anxiolytics are needed for pain control but are the primary contributors to delirium. Furthermore, uncontrolled pain can also increase delirium. Finding appropriate doses requires constant vigilance and adjustment. Poor communication from altered mental status or endotracheal intubation may further impede pain assessment. Anxiety is commonly reported by burn-injured patients, both at greater levels than reported to be tolerable and for prolonged periods throughout hospitalization.³² As a result, anxiety assessment tools specific for burn-injured patients have been reported and validated and may predict burn pain and postdischarge functional capacity better than other anxiety assessment tools.³³ As hospitalization persists and patients show greater mental capacity, depression becomes increasingly common and is well known to interact with pain.³⁴ Depressive symptoms have a prevalence as high as 54% during postburn hospitalization³⁵ and are a significant predictor of physical health at 2 months postdischarge.³⁶ PTSD is another complication that can negatively impact pain control as PTSD can cause agitation and hypervigilance.²⁷^,³⁷

The manner in which the burn environment and patients’ personality factors can amplify pain is particularly notable in children, for whom the burn unit environment can be extremely strange and frightening. There is little opportunity for the burn staff to prepare children psychologically for the repeated medical procedures they must endure, and conditioned anxiety to the stimuli associated with burn care can be expected. Children will also often demonstrate regression and behavioral acting out in response to hospitalization, making pain control during procedures a particular challenge. It should be noted that although many burn centers have pediatric-specific pain protocols, their emphasis is appropriately on safety; hence, they are often not aggressive enough to adequately address pain or prevent procedural anxiety in every child. As previously mentioned, aggressive treatment of pain may serve to reduce the subsequent development of PTSD in children.²⁵ A comprehensive review of issues specific to pediatric burn pain can be found elsewhere.³⁸^,³⁹

There is growing evidence that although pain was once thought to be a problem only during the early phases (e.g., resuscitative and healing phases) of burn care, a significant
number of patients experience ongoing pain long after hospital discharge. For example, a long-term, neuropathic pain syndrome has been recently described in burned patients, presenting approximately 4 months after the initial injury⁴⁰ and persisting for an average of 13 months. Similarly, in a survey of 358 respondents of a burn survivor support group,⁴¹ 52% reported ongoing pain, 66% said that it interfered with their rehabilitation, and 55% said the pain interfered with their daily lives. Respondents in this study also reported that thoughts of the accident and depression made their pain worse. Although much research has been done to address acute pain control after a burn injury, little is known about ongoing opioid needs once patients are discharged. Wibbenmeyer et al.⁴² tracked opioid use from discharge to the outpatient setting and found that 85% of patients were on opioids at discharge with a morphine equivalent (ME) of 114. Although 90% had weaned off by 14 days postdischarge, these high doses are within the range (50 to 100 ME) associated with harmful drug effects reported in nonburn populations.⁴³ Furthermore, patients may show persistent depression, anxiety, or PTSD that can interfere with pain control, with both depression and anxiety predicting worse outcomes in pain, fatigue, and physical functioning assessments up to 2 years postdischarge.⁴⁴ Sleep problems are prevalent, yet frequently overlooked in postdischarge phase, and may reflect inadequate pain treatment.⁴⁵ When psychological or pain problems persist long after hospital discharge, the possibility of social or financial disincentives should be entertained. Although some patients will certainly have internally generated psychological problems, for others, the issues will persist because of such factors as litigation or the desire to avoid returning to an undesirable job.

Generalized Treatment Paradigm for Burn Pain

Because burn pain is highly variable and cannot be reliably predicted by either clinical assessment of the patient or his or her burn wound, we recommend a structured approach to burn analgesia that incorporates both pharmacologic and nonpharmacologic therapies, targets specific pain issues unique to the burn patient, and can be tailored to anticipated variations in patient need and institutional capability. One clear goal of such a paradigm is to avoid the undertreatment of burn pain.

In the generalized burn pain management paradigm, selection of an analgesic regimen is individualized and based on two broad categories: (1) the clinical need for analgesia (i.e., treatment of background vs. procedural vs. postoperative pain) and (2) limitations imposed by the patient (e.g., presence of IV access, endotracheal tube, or opioid tolerance) or by clinical facilities (available monitoring capabilities and personnel). The presence or absence of IV access directly influences analgesic drug choice, particularly in children in whom IV access may be problematic. Patients who are endotracheally intubated and ventilated are “protected” from the risk of opioid-induced respiratory depression; thus, opioids may be more generously administered in these individuals, as is often indicated for complex burn débridement procedures in patients with more extensive or severe burn injuries. Individual differences in opioid efficacy should be considered in all patients, including opioid tolerance in patients requiring prolonged opioid analgesic therapy or in those with preexisting substance abuse histories. Due to the development of drug tolerance with prolonged medical use or recreational abuse of opioids (both commonly seen in burn patients), opioid analgesic doses needed for burn analgesia may significantly exceed those recommended in standard dosing guidelines. One clinically relevant consequence of drug tolerance is the potential for opioid withdrawal to occur during inpatient burn treatment. Thus, the period of inpatient burn care is not an appropriate time to institute deliberate opioid withdrawal or detoxification measures in the substance-abusing patient because such treatment ignores the very real analgesic needs of these patients. Similarly, when reductions in analgesic therapy are considered as burn wounds heal, reductions should occur by careful taper, in order to prevent acute opioid withdrawal syndrome.

Institutional capability to provide adequate monitoring as required for “moderate sedation” (as defined by the American Society of Anesthesiologists; Table 53.1)⁴⁶ may also dictate which agents are used for procedural analgesia, as some of the more potent opioids (e.g., fentanyl) and anesthetic agents (e.g., ketamine, propofol) may unpredictably result in potentially dangerous levels of sedation (“deep sedation” or “general anesthesia”). The use of potent opioids and anxiolytics should only occur in settings with adequate monitoring, personnel, and resuscitation equipment appropriate for the degree of sedation anticipated. For many burn wound débridement procedures and most rehabilitative therapy sessions in the hospital ward or outpatient clinic setting, opioid analgesia with “minimal sedation” is sufficient and no special monitoring is required. Larger or more potent doses of opioids, or the concurrent use of anxiolytic sedatives (e.g., benzodiazepines), may not only produce more pronounced sedation (“moderate sedation”) but could also progress to “deep sedation” where patient-staff communication and/or patient consciousness are lost. Current guidelines of The Joint Commission,⁴⁷ as well as adult⁴⁶ and pediatric⁴⁸ physician specialty professional organizations, dictate both general and specific levels of monitoring (e.g., continuous pulse oximetry, presence of an independent observer specifically responsible for monitoring ventilation and vital signs) for patients requiring each of these levels of procedural analgesia and sedation.

TABLE 53.1 American Society of Anesthesiologists Continuum of Depth of Sedation

	Minimal Sedation (Anxiolysis)	Moderate Sedation/Analgesia (Conscious Sedation)	Deep Sedation/Analgesia	General Anesthesia
Responsiveness	Normal response to verbal stimulation	Purposeful* response to verbal or tactile stimulation	Purposeful^* response following repeated or painful stimulation	Unrousable even with painful stimulus
Airway	Unaffected	No intervention required	Intervention may be required	Intervention often required
Spontaneous ventilation	Unaffected	Adequate	May be inadequate	Frequently inadequate
Cardiovascular function	Unaffected	Usually maintained	Usually maintained	May be impaired
^*Reflex painful withdrawal from a painful stimulus is NOT considered a purposeful response.
Approved by the American Society of Anesthesiologists House of Delegates on October 13, 1999, and amended on October 27, 2004. Reprinted with permission from American Society of Anesthesiologists Task Force on Sedation and Analgesia by Non-Anesthesiologists. Practice guidelines for sedation and analgesia by non-anesthesiologists. Anesthesiology 2002;96(4):1004-1017.

TABLE 53.2 Harborview Medical Center/University of Washington Burn Center Burn Analgesia and Sedation Guidelines for Adults

	ICU No PO Intake	ICU Taking PO	Ward Large Open Areas	Ward Small Open Areas/Predischarge
Background pain	Continuous morphine sulfate (IV) drip	Scheduled methadone or MS Contin	Scheduled methadone or MS Contin	Scheduled NSAIDs/acetaminophen or scheduled oxycodone or none
Procedural pain	Morphine sulfate (IV) or fentanyl (IV)	Oxycodone, fentanyl IV, or fentanyl ACTIQ	Oxycodone, fentanyl IV, Nitrox (IH) or fentanyl ACTIQ	Oxycodone
Breakthrough pain (PRN dosing)	Morphine sulfate (IV) or fentanyl (IV)	Oxycodone	Oxycodone	NSAIDs/acetaminophen or oxycodone
Background anxiolysis	Scheduled lorazepam (IV) or continuous lorazepam (IV)	Scheduled lorazepam	None or scheduled lorazepam	None
Procedural anxiolysis	Lorazepam or midazolam	Lorazepam	None or lorazepam	None
Discharge or transfer pain medications	NA	For transfer to ward: wean drips, establish PO pain meds early, anticipate dose tapering as needs decrease	Oxycodone for procedural pain; methadone taper or MS Contin taper if applicable	Oxycodone or NSAIDs for procedural pain
NOTE: Medications are to be given orally unless otherwise specified. Exception: fentanyl ACTIQ is given transmucosal. Analgesic and anxiolytic choices are simplified to a minimum number of agents to encourage staff familiarity and are targeted to specific pain and anxiety needs. Therapy can be individualized to include agents not in this guideline when clinically indicated. This chart is laminated and prominently displayed in all patient care areas. ICU, intensive care unit; IH, inhalation; NA, not applicable; Nitrox, 50% nitrous oxide/50% oxygen inhaled; NSAIDs, nonsteroidal anti-inflammatory drugs; PRN, as needed.

Because nociception at the burn site is the predominant mechanism of pain and suffering in these patients during the resuscitative and healing phases, pharmacologic treatment with potent opioids, anxiolytics, and other agents (e.g., ketamine) is the first line of therapy. However, nonpharmacologic methods of treating burn pain are also extremely useful. Some pain control techniques should be second nature to the staff and integrated into standard care (e.g., minimizing the number and intrusiveness of dressing changes, limb elevation, brief educational approaches). Other, more novel nonpharmacologic analgesic techniques are more practically implemented after a stable pharmacologic regimen is established or may require special expertise (e.g., hypnosis). To reinforce a consistent approach to analgesic management, particularly in centers where house staff physicians or nursing staff may rotate or change frequently, the establishment of succinct yet detailed institutional guidelines may help physicians and nurses with choosing and administering analgesics that target specific analgesic needs,¹²^,⁴⁹^,⁵⁰ as shown in Table 53.2. To maximize simplicity and utility, it is recommended that such guidelines be safe and effective over a broad range of ages, be explicit in their dosing recommendations, have a limited formulary to maximize staff familiarity, and allow the bedside nurse to continuously evaluate efficacy and safety.⁵⁰ In addition, the regular use of a weight-based pediatric medication worksheet (placed at the bedside and in the patient record), containing all analgesic and resuscitation drugs likely to be administered, provides a supplemental safeguard against accidental overdose, particularly in the young pediatric age group.⁵¹

In recent years, a number of comprehensive reviews of burn pain management that emphasize such a systematic and multidisciplinary approach to burn pain management have been published,¹⁷^,⁵²^,⁵³^,⁵⁴^,⁵⁵ including practice guidelines from the American Burn Association.¹⁴ The reader is referred to these sources for additional perspective and detail.

Pharmacologic Approaches

In describing pharmacologic approaches for burn analgesia, three consistent observations can be made. First, for patients with injuries extensive enough to require hospitalization, pain from the burn itself is severe. Thus, potent opioids form the cornerstones of pharmacologic pain control in these patients, leaving few indications for the sole use of nonsteroidal antiinflammatory drugs (NSAIDs) or acetaminophen, with notable exceptions of minor burns and outpatient treatment. Second, because burn pain has well-defined components described previously—notably background, procedural, breakthrough, and postoperative pain—pharmacologic choices for analgesia should target each pain pattern individually. Final, because burn pain will vary somewhat unpredictably throughout hospitalization due to surgical intervention and activity levels, analgesic regimens should be continuously evaluated and reassessed to avoid problems of under- or overmedication.⁶ Pain assessment is facilitated by the regular use of standardized, self-report scales for adults and older children and observational scoring systems for the very young, as described in Chapter 20. A reliance on nurse assessment of patients’ burn pain can be problematic, however, as it is well documented that nurses’ and patients’ assessment of burn pain and analgesia are not always comparable¹⁸^,⁵⁶^,⁵⁷ with nursing staff typically underestimating the need for analgesic therapy.

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