By I. Dawson. Fairfield University.
Clearance is the most important factor determining the maintenance dosage of drugs and can influence the response to drugs given by infusion or repeated bolus during anesthesia buy 100 mg zudena with mastercard. Drug clearance is influenced by four factors: metabolism 100mg zudena, protein binding, renal excretion, and novel excretion pathways (e. All of these factors are significantly altered in burns, often to the point that the dosage should be adjusted. The complexity of these changes make it difficult to describe specific guidelines for most drugs. The most impor- tant principle to remember is to monitor response and titrate the dosage of anes- thetic drugs. This is fortunate because, in terms of anesthetic management, the most profound and clinically significant changes in drug response occur with this group of drugs. Large burns cause sensitization to succinylcholine and exaggeration of the hyperkalemic response to succinylcholine. In patients soon after burn injury, the hyperkalemic response to succinylcholine can be sufficient to cause cardiac arrest. It is not known for certain when this risk develops, but most agree that succinylcholine should not be used in burn patients after 48 h following injury. Succinyl- choline probably should not be used until at least a year after wounds have healed. In contrast to succinylcholine, most nondepolarizing muscle relaxants re- quire larger and more frequent dosages to maintain muscle relaxation because of the marked resistance that occurs after burns. Stan- dard dosages of mivacurium retain their efficacy in burn patients. Mivacurium is metabolized by plasma cholinesterase and this enzyme is decreased after burns. This is thought to increase the concentration of mivacurium at its site of action and delay its elimination, so that dosing need not be altered for burn patients. MANAGEMENT OF ANESTHESIA Monitors The choice of hemodynamic monitors is a major concern in planning anesthetic management for burn patients. Since access may be limited and difficult in these patients, careful preoperative assessment is necessary for effective management. As with any critically ill patient, the choice of monitors in burned patients depends on the extent of the patient’s injury, physiological state, and planned surgery. An arterial catheter provides much information, including pulmonary and metabolic status as well as hemodynamic function. When blood loss is expected to be extensive and rapid, blood pressure may change more quickly than the interval between cycles of a noninvasive blood pressure monitor. In this case, an arterial catheter provides beat-to-beat monitoring capability. As explained below, direct arterial pressure monitoring also allows observation of wave form and respiratory variation in systolic blood pressure, which are very useful for titrating fluid admin- istration for volume replacement during periods of rapid blood loss. An arterial catheter also allows arterial blood sampling for blood gas analysis. This helps with the assessment of tissue perfusion as well as pulmonary function. In patients with large burn injuries, a central venous catheter serves several functions. Although central venous pressure has been found to be a poor indicator of preload, it can quickly show if the filling pressure is low or very high. If the pressure is low, volume administration will probably be an effective intervention for hypoten- Anesthesia 119 sion, if the pressure is already high, a vasoactive infusion is more likely to help. Elevated central venous pressure in the presence of pulmonary capillary leak from inhalation injury or systemic inflammation is likely to cause pulmonary edema.
Critical developments in understanding and managing pain in acute and chronic settings have also arisen from the application of the gate control theory (GCT) of pain (Melzack & Wall purchase 100mg zudena with mastercard, 1965 buy zudena 100mg overnight delivery, 1982) and the subsequent dem- onstration of the plasticity of the nervous system. These advances in clari- fying mechanisms and opening new avenues for pain relief are addressed extensively elsewhere (see chap. This perspective provides a foun- dation for understanding the role of the biopsychosocial model in the study of pain and pain treatments (see chap. This systems theory approach (Engelbart & Vranken, 1984) has been used by health psycholo- gists to develop comprehension and, from this perspective, psychological interventions suited to many different health problems and diseases. A so- cial model of pain based on research evidence can be developed within this framework, by organizing social elements that affect and are affected by pain and then using the model to direct how treatment is conducted. Once the model is established, it can be reused to provide guidance on how ther- apeutic elements can be systematically changed and tested, with the aim of improving outcomes. In short, there is nothing as practical as a good the- ory, as GCT illustrates. This way, micro-level processes, for example, changes in heart rate, are nested in those at a macro level—for example, stereotypic profes- sional views about people with chronic back pain. Consequently, changes at a micro level can have macro-level effects, and vice versa. Because bio- logical processes connected with pain are commonly at the micro level, and psychological and social processes are more likely to be macro-level phenomena, it requires commitment to multidisciplinary thinking to be able to select and use this diverse multivariate information appropriately and effectively in problem solving. Work to date on biopsychosocial mod- els already points to the urgent need to understand and address all three components in these models, if we are to create successful treatments (Taylor, 1999). We argue here that pain researchers have been very successful with the application of biological approaches to pain relief (McQuay & Moore, 1998), and to some extent with psychological approaches, such as cognitive be- havior therapy. But the contribution of social factors to the study of pain is poorly defined, weakly elaborated, and infrequently conducted, compared to other types of research on pain. It will be necessary to show which social factors directly and significantly affect and exacerbate pain if this approach is to gain acceptance as an important, independent, and equal contributor to the biopsychosocial triad. Important social factors will need to be prop- erly evaluated for their potential to generate new types of treatment or styles of management. On the basis of existing evidence about the effective- ness of the model, it is increasingly clear that an integration of sociocultural factors is essential to achieving positive outcomes, relieving suffering, and diffusing action from the narrow medicalization of pain, in ongoing pro- grams of care. A MODEL OF THE PSYCHOSOCIAL FACTORS IMPLICATED IN THE ETIOLOGY AND MAINTENANCE OF CHRONICALLY PAINFUL ILLNESS Although health professionals who work in pain research and practice have become pioneers in the design and running of smoothly functioning multi- disciplinary teams, it is arguable that when examining the key social influ- ences that affect pain and pain behavior, we have been slow to draw on contributions from the wider range of social science disciplines available, and to extend and apply them to improve our understanding of the pain re- sponse and its management. SOCIAL INFLUENCES ON PAIN RESPONSE 183 the social factors that affect pain, illness, and treatments, with the aim of il- luminating the inherently complex interaction between a pain sufferer and their psychosocial environment. Furthermore, it is not possible to do this properly without taking a multidisciplinary approach but within the per- spective of a different but overlapping set of disciplines. The model developed by Skevington (1995) proposes four levels of un- derstanding that provide a framework within which the social aspects of chronic pain may be better appreciated, and this is shown in Fig. Level 1 defines the individual processes affected by social influences, such as per- ceived bodily sensations. In contrast, Level 2 characterizes salient interper- sonal behaviors, in particular, that person’s relationship with significant others. Level 3 defines group and intergroup behaviors such as group be- liefs, experience, and influences, whereas Level 4 encompasses some of the higher order factors that affect sociopsychological processing, such as health ideology and health politics.
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