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23 Pain in Burn Patients

23 Pain in Burn Patients
The Massachusetts General Hospital Handbook of Pain Management

23
Pain in Burn Patients

Salahadin Abdi and Bucknam J. McPeek

There is physical pain, there is mental pain and scarring. You can see the outside, but what a lot of people don’t see is that we are truly burned on the inside as well.
—Burn survivor

I. Types of burn injury
II. Types of burn pain
III. Acute treatment for burn pain

1. Acetaminophen

2. Nonsteroidal anti-inflammatory drugs

3. Opioids

4. Ketamine

5. Antihistamines

6. Regional anesthesia

7. General anesthesia
IV. Chronic treatment of burn pain
V. Nonpharmacologic treatments for burn pain
VI. Conclusion
Selected Readings

More than 2 million burn injuries occur annually in the United States: thermal burns are the most prevalent, and chemical and electrical burns occur less commonly. Approximately 1 in 20 burn patients requires extended hospitalization. Burn injury results in both physical and psychological distress, and pain is a major component of both. In fact, burns are among the most painful of all injuries. Pain evaluation and treatment is an important aspect of the care of patients inflicted with burn injuries.
The management of acute and chronic burn pain is challenging and may require input from an experienced pain specialist. A careful pain management plan helps circumvent potential hazards in these often critically ill and psychologically disturbed patients. It is important to be attentive to the specific type of pain the patient is experiencing, as well as to the risks of pain treatment in relation to the pathophysiology of the injured patient. The likelihood of the development of chronic pain and life-long suffering (e.g., chronic pain, post-traumatic stress disorder) can be reduced by appropriate and aggressive acute pain management, with meticulous attention to psychological and social factors. The purpose of this chapter is to outline the essential issues so that proper planning and care can be provided.
I. TYPES OF BURN INJURY
The extent of a burn injury is measured as the percentage of body surface area burned. Burns vary in depth from superficial to full thickness, with a possibility of massive destruction of muscle and bone in the latter.
In first-degree burns, the injury is superficial, characterized by erythema, and it involves only the epidermis. There is usually only mild to moderate discomfort, and healing occurs within a week.
Second-degree burns are deeper, partial-thickness injuries that destroy the epidermis and variable amounts of dermis as well as epidermal appendages. Second-degree burns are extremely painful. Most of the pain is the result of the damage of sensory nociceptive receptors that are preferentially sensitive to tissue damage. In addition to direct damage from the burn, second-degree burns leave the protective layer of skin damaged, and the normally protected nerve endings exposed. These lesions heal slowly with some tissue contraction, nerve regeneration, and the occasional need for skin grafting.
Third-degree burns destroy the skin completely. They are, by definition, full-thickness injuries. Regions of third-degree burns may be painless after the initial injury for a period because of the destruction of cutaneous nociceptors. Although the central part of the initial wound may be analgesic, painful areas of second-degree injury surround almost every third-degree burn. These areas heal by epidermal regeneration, since some of the epidermal appendages remain intact, and this healing process can be painful. With inadequate cleansing and debridement, a surface pseudomembrane composed of wound exudate and necrotic eschar accumulates. As long as the eschar and pseudomembrane exist, the center of a thirddegree burn is painless. The eschar is usually removed surgically since the unremoved eschar and membrane serve as a nidus for infection (the major life-threatening factor in burn injury). It is important to emphasize that patients with third degree burns suffer severe pain needing treatment despite some areas of the burn being analgesic.
II. TYPES OF BURN PAIN
There are two categories of pain:
First, procedural pain (incidental or evoked) is pain experienced during or after wound care, stent removal, dressing change, physical therapy, or other treatments. This type of pain is usually acute and short lasting but of great intensity. Debridement usually requires general anesthesia. It is helpful to administer an adequate and appropriately timed dose of narcotic and/or benzodiazepine before beginning any procedure.
Second, background pain (spontaneous or resting or constant) is pain experienced by the patient while at rest. This type of pain is usually dull, continuous, and of lower intensity. Nevertheless, this low-intensity pain should be controlled or it may prime patients to experience more pain, as well as increasing their anxiety, particularly about procedures. Background pain is best treated with regularly administered opioids (or alternative analgesics), not on an as-needed basis.
In addition, there are two temporal components of burn pain, acute and chronic. Immediately after the burn, the most severe pain results from therapeutic procedures such as dressing changes. Background pain may persist for weeks to months or even years. Pain related to burn injury might worsen with time as a result of several factors, including increased anxiety and depression, continuing sleep disturbance, and deconditioning and regeneration of nerves endings (possible neuroma formation, known as post-burn neuralgia). Chronic pain may result from contractures, nerve injury (neuropathic pain), or subsequent nerve and tissue damage following surgical procedures.
III. ACUTE TREATMENT FOR BURN PAIN
The main treatment goal for serious burns is to clean the burn area by debridement or surgical excision, thus removing necrotic tissue and other sources of infection. Microorganisms that release exotoxins and endotoxins exacerbate the inflammation already present in burns and quickly colonize retained necrotic tissue. After removal of necrotic tissue by cleaning or surgical excision, the next step is to promote coverage of the open wound wherever possible by a skin graft from unburned areas of the patient’s own body. In large burns, allografts, xenografts, or artificial skin can provide temporary coverage.
Patients suffer continual shifts, from mild to moderate background discomfort to excruciating pain associated with treatments such as burn dressing changes, manual debridement of open wounds, and physical therapy. In addition, there are frequent surgical operations, excisions of eschar, and harvesting of large areas of normal skin for grafting (also a source of pain). Burn dressing changes and debridements may occur twice a day, physical therapy once or twice a day, and surgical interventions several times a week. Because of the variation in the intensity of pain from hour to hour or even minute to minute, burn pain treatment for patients suffering from acute burns requires repeated assessments and titration of analgesic drugs for treatment. Patients typically require increasing amounts of opioid medication for the control of pain during these procedures as they become tolerant to the opioid (Chapter 30).
The interpretation and assessment of pain behavior in these patients can be very difficult. The pain is often superimposed by anxiety. Giving the patient a role in the pain management helps to alleviate the anxiety. An honest explanation about procedurerelated pain and how it can be relieved is a necessary prerequisite to being able to develop a plan with the patient. The following are treatment options for burn-related pain.
1. Acetaminophen
Acetaminophen is a weak analgesic and antipyretic. It is a useful first-line treatment for minor burns, but it can also be used as an adjunct to opioids for major burns. Because this drug acts mainly centrally, it is not associated with the typical nonsteroidal anti-inflammatory (NSAID) side effects that are produced by prostaglandin inhibition in the periphery. Acetaminophen is not useful for long-term pain management because of its toxic and cumulative effects on the liver (see Chapter 8).
2. Nonsteroidal anti-inflammatory drugs
NSAIDs reduce inflammation and pain. They may be used as sole analgesics for mild to moderate pain or as adjuncts to more potent analgesics. Side effects, specifically gastrointestinal (GI) bleeding, may limit their use in seriously burned patients, who are particularly susceptible to GI bleeding. If used, prophylaxis should be given with a prostaglandin analog (e.g., misoprostol) or H2 blockers (e.g., ranitidine). (Cave: DO NOT give a high dose of an NSAID as a substitution for opioids in the management of procedural pain.) A full description of the NSAIDs and their uses is provided in Chapter 8.
3. Opioids
Opioids (see Chapter 9) are the mainstay of treatment for severe acute pain, and various routes of administration have been described and tested for burn patients. Morphine is the most widely used drug in burn centers. Hydromorphone (Dilaudid) is useful in patients who have intolerable side effects to morphine, or who are morphine sensitive. Meperidine is not recommended because of the toxicity of its metabolite normeperidine. Continuous fentanyl infusion tends to cause the rapid development of tolerance with a resultant need for high dosage, but bolus fentanyl administration is sometimes useful for procedures such as burn dressing changes. High-dose fentanyl, however, can produce chest wall rigidity and should not be used in self-ventilating patients in whom muscle relaxants cannot be used to overcome the rigidity. Methadone can also be used, and it has the advantage of having N-methyl-D-aspartate (NMDA) receptor antagonist activity, which, theoretically at least, could be important in the prevention of neuropathic pain. In patients who are fed by mouth, a bowel regimen should be initiated with the initiation of opioids.
For most burn patients, probably the best mode of administration of opioids is intravenous patient-controlled analgesia (PCA) (see Chapter 21). This technique allows patients to self-administer the drug, usually morphine or hydromorphone. This eliminates the dependency of patients on nurses, and it provides a means of receiving immediate relief when needed. Most patients, even children as young as 6 or 7 years, can learn to control pain using PCA. Younger children, or adults who cannot push a button, may require a continuous infusion of opioid, at least during the acute phase. The onset of analgesia after an intravenous morphine bolus is approximately 6 to 10 minutes, so patients can pretreat themselves or be pretreated by a physician or nurse before painful therapeutic procedures. When patients have significant background pain, they may require a basal infusion in addition to demand doses.
4. Ketamine
Ketamine is an atypical anesthetic and a potent analgesic that is an NMDA receptor antagonist. It induces a dissociative anesthetic state. It can be used for both anesthesia and analgesia in burn patients. The main advantages of ketamine over the opioids are that spontaneous ventilation and airway reflexes are preserved, and the cardiovascular system is stimulated secondary to induced catecholamine release. Ketamine anesthesia is commonly associated with unpleasant postanesthesia phenomena such as vivid nightmares and hallucinations, which can be minimized by the concomitant use of a benzodiazepine. These effects are rarely associated with the subanesthetic doses that are used for analgesia. Ketamine should be used with an antisialagogue such as atropine or glycopyrrolate.
5. Antihistamines
Antihistamines are used in the burn center for the management of anxiety, itch, and pain (adjunctive effect). These drugs potentiate opioid analgesia and have a useful antipruritic effect, as the pruritus in burn patients is sometimes worse than the pain, especially in the healing phase of the injury. They are also useful to promote sleep and relieve anxiety.
6. Regional anesthesia
Regional anesthesia can be used for analgesia or even anesthesia if the burn wound is limited and accessible for a regional anesthesia technique. Epidural and spinal anesthesia and analgesia are relatively contraindicated in seriously ill patients with hypotension or sepsis.
7. General anesthesia
General anesthesia is sometimes needed for minor procedures if pain is severe and cannot be adequately and safely controlled in the awake patient.
IV. CHRONIC TREATMENT OF BURN PAIN
Unfortunately, the pain experience for burn patients often does not end after the acute phase, and many patients continue to have chronic pain even after complete wound healing. It is sometimes necessary to use chronic opioid therapy to maintain a reasonable level of comfort for these unfortunate patients, and it may be necessary to add adjuvant pain medications for the specific treatment of neuropathic pain. As already stated, the NSAIDs and acetaminophen are less suitable for long-term pain therapy. Issues of opioid therapy in chronic nonmalignant pain (CNMP) are discussed in Chapter 30. A description of neuropathic pain and its treatment can be found in Chapter 25. The most intractable cases should be referred to a pain clinic. Many of these patients need nonpharmacologic as well as pharmacologic treatment, and a multidisciplinary approach (including behavioral therapy, physical therapy, and occupational therapy) is optimal.
V. NONPHARMACOLOGIC TREATMENTS FOR BURN PAIN
Burn patients need psychological support in both the acute and chronic phases of burn treatment. Burn survivors frequently suffer fear, depression, nightmares, and hallucinations. Psychosocial support is as necessary as pharmacologic intervention (e.g., anxiolytic and antidepressants). Burn injury results not only in short-term changes and severe acute pain but also in chronic pain, long-term changes in health status, and often distressing permanent disfigurement. There are many psychological interventions that can be helpful to burn patients, including hypnosis, relaxation, and biofeedback. These techniques are described in Chapter 15.
VI. CONCLUSION
In summary, the pain experienced by burn patients is often excruciating and unrelenting, an unwelcome accompaniment to an already devastating injury. The management of these patients’ pain can be extremely challenging and demands expertise and experience. It is important to choose the right modality (or combination of modalities) with the aim of adequately controlling background as well as procedural pain. It is equally important to consider the psychological aspects of the pain, and to provide psychosocial as well as pharmacologic support. An interdisciplinary team approach is the key to successful pain management.
SELECTED READINGS

1.
Atchison NE, Osgood PF, Carr DB, Szyfelbein SK. Pain during burn dressing change in children: Relationship to burn area, depth, and analgesic regimens. Pain 1991;47;41–45.

2.
Carr DB, Osgood PF, Szyfelbein SK. Treatment of pain in acutely burned children. In: Schechter NL, Berde CB, Yaster M, eds. Pain in infants, children, and adolescents. Baltimore: Williams & Wilkins, 1993.

3.
Choiniere M, Auger FA, Latarjet J. Visual analogue thermometer: A valid and useful instrument for measuring pain in burned patients. Burns 1994;20:229–235.

4.
Choiniere M, Grenier R, Paquette C. Patient-controlled analgesia: A double-blind study in burn patients. Anesthesia 1992;47;467–472.

5.
Dauber A, Carr DB, Breslau A. Burn survivors’ pain experiences: A questionnaire-based survey. Presented at the 7th World Congress on Pain, International Association for the Study of Pain, Paris, 1993.

6.
Herman RA, Veng-Pederson P, Miotto J, Komorowski J. Pharmacokinetics of morphine sulfate in patients with burns. Burn Care Rehabil 1994;15:95–103.

7.
Osgood PF, Szyfelbein SK. Management of pain. In: Martyn JAJ. ed. Acute management of the burned patient. Philadelphia: WB Saunders, 1990.

8.
Perry S, Heidrich G. Management of pain during debridement: A survey of U.S. burn units. Pain1982;13;267–280.

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