Management of Pain and Other Discomforts in Burned Patients

Introduction

The words “burn injury” trigger, for almost anyone, immediate and vivid images of excruciating pain and suffering. Children are conditioned from early childhood that burn injuries are painful and can cause great harm. At the time of the first edition of this book there was still debate about the importance of pain management in the burn survivor. Many practitioners believed that the treatment of burn injury pain, especially in children, was more dangerous than leaving it untreated. The past 20 years has shown that children's pain can be effectively and safely managed with significant benefits in recovery and long-term outcomes. There are now data showing that even premature babies have significant pain that needs to be addressed.

A series of therapeutic approaches have been developed to approach both pain and its associated anxiety. There is justified concern about opiate and benzodiazepine dependence and abuse, but this is offset by the importance of treating pain aggressively. In addition to pain and anxiety, practitioners are now focused on pruritus as well. Scales have been developed to measure pain, anxiety, and itch separately.

Pathology of a Burn Injury Pain and Pain-Generating Mechanisms

Pain is the most frequent complaint of burn-injured patients. Injury-induced nociceptive responses can be described as hyperalgesia and allodynia. Hyperalgesia is increased nociceptive response to painful stimulus (e.g., pinprick). Allodynia is exaggerated pain to nonpainful stimuli (e.g., touch). All burn injuries are painful. Even first-degree burns can produce at least mild pain and discomfort, especially when something such as clothing rubs against the burned area (allodynia). Even the slightest change in air currents moving past the injured/exposed skin can cause a patient to experience excruciating pain. The loss of protective covering of the epidermis and the associated inflammation leads to sensitization of the nerve endings. Studies of humans and monkeys confirm that burn injuries not only make the injured area but also the surrounding tissue more painful. Second-degree, moderate to deep partial-thickness burns result in variable amounts of pain depending on the amount of destruction to the dermis. In addition, as the inflammatory response progresses, the release of cytokines and chemokines increases the pain not only in the burned area but also in the surrounding tissues by the activated peripheral circulating macrophages and the central nervous system microglia.

Areas of deeper partial-thickness and full-thickness burns may display a confusing pattern of pain over the first few days. These areas may show little or no response to sharp stimuli such as a pinprick initially, yet a patient may complain of deep, severe pain related to the inflammatory response. In a full-thickness burn, the dermis is completely destroyed along with its rich network of nerve endings. This leads to an initial response of a completely anesthetic wound when a sharp stimulus (e.g., pin prick) is present on the dead skin. Over time, patients begin to complain of a dull or intense pain during manipulation of these areas (e.g., dressing changes). Once the devitalized tissue (i.e., eschar) sloughs and is replaced by granulation tissue, the patient again experiences the sensation of sharp pain to noxious stimuli. Thus it appears that, in all types of burn injury pain, there is an inflammatory and neuropathic component both resulting from injury to tissues and to sensory nerves endings. As to which of these (inflammatory vs. neuropathic) components contributes more to the nociceptive responses is still not understood.

Additional Factors Contributing to Pain Generation

Ptacek et al. found that although there was a general trend for pain to decrease over time in patients with small or superficial burns, there was also considerable variability in the course of pain among adult survivors after major burns. Persons with large burns showed a higher affective (suffering) component to the pain, but there was no reliable correlation between the pain scores and burn size. Quite in contrast to that report, studies in children have shown that the intensity of pain increased as the burn size increased. Whether this is related to the increased anxiety of children is unclear. Other reports confirm that pain intensity at rest was correlated with psycho-affective responses such as anxiety, depression, anorexia, fatigue, and helplessness. Choinière et al. also noted that pain at rest was significantly and positively related to levels of anxiety or depression (i.e., with elevated anxiety or depression, pain scores at rest increased). Depression also plays a similar role in the enhancement of pain. Pain leads to depression, and depression increases the perception of pain. Confusion therefore can occur concerning the amount of pain expressed by burn patients on the role played by psychiatric disorders that are concomitantly present in any form of injury versus injury-induced biochemical changes at the local and central nervous system level. Treatment of anxiety with benzodiazepines may have either beneficial or paradoxical effects on anxiety and pain. Clinical observation and rodent studies indicate that although benzodiazepines acutely potentiate the analgesic effects of other opiates, the prolonged administration of benzodiazepines together with opiates can induce tolerance or even hyperalgesia.

Another factor that contributes to pain is procedures. Baseline pain (pain at rest) is invariably present in most burn patients. This baseline increased nociception can be aggravated by procedural pain (hyperalgesia) induced by dressings changes, physical therapy, and other procedures. Procedural pain is the most intense burn injury pain that is undertreated. Thus the anticipation of pain related to procedures (e.g., wound care) that occurs at least once daily can increase a patient's perception of pain, which in turn can lead to greater anxiety. This reaction may explain some findings that suggest that pain increases over time in burned patients. There could also be another component—namely, tolerance to analgesics and/or opiate-induced hyperalgesia (see later discussion)—that explains the increase in pain over time. Finally, exaggerated adrenergic stimulation with release of catecholamines is part of the pain and stress response. Stress of any form has paradoxical effects on pain, initially causing stress-induced analgesia and then later exacerbation of pain, a feature known as “stress-induced hyperalgesia. Thus the stress of burn injury, with its concomitant release of catecholamines and adrenoceptor stimulation, leads to exaggeration of pain.

Pain as a Function of the Healing Process

As deep dermal or full-thickness burn wounds heal, either by primary intention from excision and grafting or by secondary intention through granulation tissue and scar formation, the injured neural tissue is reorganized. Reflex neural function returns to grafted burn skin approximately 5–6 weeks after the burn has been covered by autografted skin. Active vasodilatation, vasoconstriction, and pain sensation all return at this time. These functions also return to the burn wound that heals through scar formation but may take up to 6 months for complete neural reorganization. This could be an additional basis of neuropathic pain at the burn wound site and in surrounding tissue. Despite the healing of tissues, the memory of any form of trauma-induced pain lasts for a prolonged period. In other words, subsequent (e.g., reconstructive) surgery on this area leads to exaggerated nociceptive responses sooner and longer lasting than that seen at initial injury. This memory seems to be maintained by innate immune cells (macrophages and microglia), which seem to be already primed because of previous injury and become activated sooner with release of inflammatory cytokines and chemokines.

Although rare, causalgia, dysesthesia, and phantom pain syndrome can sometimes develop in healing skin. Phantom limb sensation and pain are more common following amputation, which is often associated with large burn injury or electrical injury. The incidence of these chronic pain syndromes seems to be related to the healing process. Burns that have been excised and grafted on a clean and uniform vascular bed rarely develop one of these chronic pain syndromes. Wounds that heal by granulation and scar formation seem to be more apt to develop a chronic pain problem because of the continued stimulation of nerve fibers in the area with enhancement of the hyperalgesia. Skin biopsies of granulation tissue have clearly shown neuronal tissue entrapment. Pain in scar tissue subsides over time as the scar tissue matures.

Tolerance to Opiates and Opiate-Induced Hyperalgesia

Opioids are highly effective analgesics and are the mainstay for treatment of moderate to severe burn pain. Continued use of opiates can lead to burned patients developing tolerance to their analgesic effects. There is a pharmacokinetic component to the tolerance to opiates: the clearance and the volume of distribution of many drugs are increased over time, resulting in lower therapeutic concentrations. The protein binding of opiates is also increased in burned patients, resulting in a lower free fraction available to act on target µ-opioid receptor. The most important reason for the tolerance is indeed related to µ-opioid receptor changes induced by the opiates.

Opiates signal their beneficial analgesic effects by intercellular coupling to G-proteins. Just like any other G-protein coupled receptor (e.g., adrenoceptor), the repetitive administration of an agonist (e.g., epinephrine or opiate to adrenoceptor or opiate, respectively) leads to desensitization of the receptor in which the receptor responses are attenuated with each subsequent administration. The attenuated response is related to phosphorylation and not to down-regulation of receptor. The continued administration of opiates will, with time, result in down-regulation of the opiate receptor number.

Both the desensitization (phosphorylation) and down-regulation of opiate receptors lead to tolerance to opiates. Recent studies indicate that continued administration of opiates also induces increased nociceptive behaviors (hyperalgesia and allodynia: a.k.a. opiate-induced hyperalgesia [OIH]). Tolerance can be overcome by increasing the doses of the opiates, but OIH is made worse by increasing opioid administration. Studies in burn patients confirm OIH when pre- and intraoperative use of opiates resulted in worse postoperative pain. Opiates, similar to bacterial peptides, lead to activation of innate immune responses (activation of macrophages and microglia) with release of inflammatory cytokines and chemokines. Attenuation of microglial activation has been shown to decrease OIH, with improved control of pain.

Measurement of Pain in Burned Patients

Although pain cannot be measured directly, it can be quantified by using one of the standardized tools described here. Using reliable and valid tools allows us to gauge the effectiveness of our treatment for any one patient. Assessing pain on a scheduled basis and using the same tool for each assessment gives us information about how pain is experienced by a single patient throughout burn treatment; we can note patterns that emerge and schedule medications accordingly. Furthermore standardized tools allow us to compare the pain management of one patient with another, as well as of one burn unit pain management regime with that of other burn units in order to determine the effectiveness of protocols for pain management. Another important reason for assessing pain regularly and in a standardized way is that it communicates to the patient that we believe he or she has pain and that we are trying to do something about it. This communication reassures the patient, thereby reducing the likelihood that the patient will escalate pain, anxiety, and other related behaviors.

Gracely reviewed a number of objective modalities for the measurement of experimental pain. He notes that “pain arises from and is modulated by, a number of mechanisms. These mechanisms are not static but change over time and involve all levels of the central nervous system. In an attempt to understand these mechanisms, several experimental tools have been employed to further elucidate the exact pathways involved in pain transmission and to better understand the therapies used to relieve pain.”

Some of these tools are cortical evoked potentials, functional brain imaging (positive emission tomography [PET]), functional magnetic resonance imaging (fMRI), source analysis of evoked activity, and electrophysiological recording from the human brain. As noted by Gracely, comparing these measures with verbal judgments of pain magnitude validates these physiologic measures: “This implicitly elevates subjective judgment to the level of a validation standard.” Clinical measurements of pain must continue to rely on standard subjective measures. A tool to use in the clinical setting must be quick and easy to use and useful for frequently repeated assessments.

A major concern in the clinical setting is the use of a consistent pain measurement tool before and 1–2 hours after the administration of a pain-relieving medication. For procedural pain management, the same tool should be used to measure pain at the beginning of a procedure, during the procedure, and post-procedure in order to measure the effectiveness of the pain management regimen used for procedural pain.

Pain Measurement Techniques for Adult Burned Patients

A variety of pain measurement techniques have been used with adult burned patients. The more common measures include adjective scales ( Table 64.1 ), numeric scales (i.e., rating pain on a scale of 0–5, 0–10, or 0–100), and visual analog scales ( Fig. 64.1 ). Each of these scales measures the sensory component of a patient's pain. Adjective scales and numeric scales are quick and easy to administer because they do not require a visual representation of the scale. The visual analog scale requires a visual representation of the scale to be presented to a patient. Patients must mark or point to the place on the scale that represents their level of pain. This presents a problem for a patient whose hands are burned, so some investigators have used a technique of sliding a line or color strip along the scale with instructions to a patient to direct the movement of the slide, stopping at the point representative of the patient's pain. The visual analog scale has been used in a number of studies with a variety of patient samples and has been shown to be a valid method of measuring the sensory component of a patient's pain. The demonstrated validity of the scale allows for comparisons of visual analog pain assessments between studies with different patient samples. However the visual analog scale is not interchangeable with the graphic numeric rating scale.

Table 64.1

Adjective Scales in English and Spanish.

0	No pain	0	Nada de color
1	Slight pain	1	Dolor leve (ligero)
2	Moderate pain	2	Dolor moderado
3	Severe pain	3	Dolor severo

Motivational-affective and cognitive-evaluative components of pain are most frequently measured using the McGill Pain Questionnaire (MPQ). The MPQ consists of 20 sets of adjectives that describe all three components of pain: sensory, affective, and evaluative. Qualitative profiles and quantitative scores for each dimension as well as a total pain score can be derived from the selected adjectives. The MPQ has been translated into several languages and has been shown to be a reliable and valid measurement tool. Since it takes 10–20 minutes to administer, it may not be as useful for frequent, repeated measurements. Many studies have employed this measurement on a daily basis to measure either overall or resting pain. Gordon et al. in a prospective multicenter study, asked 40 adult burned patients to rate their pain on four scales. These scales were a visual analog scale, an analog chromatic scale, an adjective scale, and a faces scale. At the end of the study patients were asked to choose their preferred scale. Patients preferred the faces and analog chromatic scales. Although further research is needed to validate these findings, the preference of patients is another variable to be considered.

Measurement of Anxiety

Anxiety is measured in a variety of ways. In 2000, Robert et al. surveyed 64 burn treatment centers to determine how they evaluated and treated anxiety, especially in children. They found that most centers did not use standardized measures of anxiety. Based on that survey and other information, the Shriners Hospital for Children in Galveston has been using the Fear Thermometer adapted by Silverman and Kurtines from the Walk's Fear Thermometer ( Fig. 64.2 ).

Taal and Faber introduced a tool to measure burn-specific pain anxiety (BSPAS). It uses a five-item scale used to measure anxiety associated with anticipated procedural pain in adult patients. Initial reliability, validity, and utility studies have been completed. A similar tool is needed for children.

Measurement of Itching

Itching is very common in burn survivors. Even in small burns, the prevalence is 35% with moderate pruritus and 14% with severe, and, in many cases, the pruritus impacts daily living. Another series of 510 burns reported a prevalence of 87%. The severe itching of burn scars and wounds has not been discussed much in the literature, but clinicians can testify that this phenomenon is a very serious problem. Patients who experience such itching often excoriate new grafts or recently healed skin, thus enhancing their susceptibility to infections. The measurement of itching has been part of a number of scales that focus on all the problems that the patient has, such as the Patient and Observer Scar Assessment Scale (POSAS) and the Assessment of Health Outcomes in Children with Burn Injury. When pruritus is severe, patients can focus on nothing else. Until very recently there have not been any tools focused on measuring itch. Now, Field et al. reported using a visual analog scale of 1–10 to assess itching. Pat Blakeney and Janet Marvin at the Shriners Hospital for Children in Galveston developed an instrument to measure itch called “itch man” ( Fig. 64.3 ). This instrument was based on a patient's drawing of his experience in the hospital. Children seem to be able to relate to “itch man,” and validation has been completed. Several scales have been developed for adults to use. One from Belgium has been translated and validated in English and seeks to measure all the aspects of itching and how it relates to other types of variables. Another coming from the dermatologic literature measuring itching in five dimensions is named the 5-D itch Scale.

In summary, symptom assessment and management are very important in burn care. The experience of pain may affect the perceptions of other symptoms, including anxiety, fear, or itch. Each symptom should be assessed within the context of other symptom assessments. There are many measurement tools for pain, anxiety, and itch assessment across the life span that can be useful to the clinician and the researcher. Further studies need to be completed in all these areas.

Treatment Considerations

Once pain has been assessed and quantified, treatment can be considered. Three modalities of treatment are effective with pain secondary to burn injury: surgical, pharmacological, and behavioral.