A 28-year-old man in the hospital burn unit has been febrile for the past 48 hours. He was admitted to the hospital 4 days ago after sustaining inhalational injury and burns over 40% of the total body surface area in a methamphetamine laboratory explosion. There were no signs of wound infection 4 hours ago in the operating room, where the patient underwent dressing changes and a second stage of burn excision and skin grafting under general anesthesia. Temperature is 38.5 C (101.3 F), blood pressure is 146/92 mm Hg, and pulse is 118/min. The patient is sedated and intubated and on mechanical ventilation. He arouses to a loud voice and follows simple commands, moving the extremities symmetrically. Telemetry shows sinus tachycardia. Multiple wound and blood cultures taken since admission are negative. Which of the following is the most likely explanation for this patient's condition?
Hypermetabolic response in burn injury | |
Etiology |
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Clinical features |
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Treatment |
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TBSA = total body surface area. | |
This patient with severe burns now has persistent fever, tachycardia, and hypertension. In the absence of infection (eg, negative blood and wound cultures), the most likely cause is a hypermetabolic response to severe burn injury.
The severity of the hypermetabolic response increases proportionally with burn size. It typically arises within the first 5 days postinjury, after an initial 24-48 hours of shock (eg, increased capillary permeability, myocardial depression). It is likely triggered by the profound release of inflammatory mediators from damaged tissue, leading to increased levels of catecholamines and glucocorticoids, with the following clinical features:
Tachycardia and hypertension due to a hyperdynamic circulatory response
Hyperglycemia due to increased gluconeogenesis and insulin resistance
Elevated basal body temperature (often up to 38.5 C [101.3 F]) and lean muscle wasting due to an increased basal metabolic rate with increased protein and lipid catabolism
Strategies to attenuate the hypermetabolic response include decreasing the inflammatory source (eg, early burn excision and grafting), blunting the catecholamine effect (eg, beta blockers), reducing lean muscle mass loss (eg, nutritional support, anabolic steroid therapy), and controlling hyperglycemia (eg, insulin).
(Choice A) Severe physiologic stress (eg, severe burn injury) can lead to acute adrenal insufficiency (ie, adrenal crisis) with nonspecific symptoms, including fever; however, hypotension (vs hypertension) is a primary manifestation of adrenal crisis.
(Choice B) Cyanide poisoning impairs aerobic metabolism and may initially cause catecholamine-mediated compensatory hypertension and tachycardia to increase oxygen delivery; however, this typically lasts only minutes (vs 2 days) before degenerating into bradycardia and hypotension from cardiovascular toxicity.
(Choice C) The shock wave from a large explosion can cause traumatic brain injury, which may be complicated by elevated intracranial pressure (ICP); however, hypertension due to elevated ICP is classically accompanied by bradycardia and irregular respirations (ie, Cushing triad), as well as significantly depressed global consciousness (eg, patient would not follow commands).
(Choice E) Malignant hyperthermia can cause fever and tachycardia but also causes diffuse muscle rigidity (vs symmetric extremity movement). In addition, it typically occurs within minutes of anesthetic agent administration (vs fever lasting 48 hours).
(Choice F) Methamphetamine intoxication, rather than withdrawal, can cause fever, hypertension, and tachycardia due to its sympathomimetic effect. Methamphetamine withdrawal is typically characterized by depression, fatigue, and increased appetite, without significant vital sign disturbances.
Educational objective:
Severe burn injury often leads to a hypermetabolic response characterized by a hyperdynamic circulatory response, causing tachycardia and hypertension; increased gluconeogenesis and insulin resistance; and increased protein and lipid catabolism, causing elevated basal body temperature.