A 13-year-old girl with cystic fibrosis is evaluated in the emergency department after developing lightheadedness and nausea during an outdoor soccer game. The patient bumped heads with another player 10 minutes into the game but did not lose consciousness and continued playing. Near the end of the second half, she developed profound generalized weakness, felt she was going to pass out, and had to be carried off the field. Her parents say that she has been well except for runny nose and congestion the past 4 days. Temperature is 39 C (102F), pulse is 136/min, and respirations are 26/min. The patient is alert and oriented but is sweating profusely. While being assessed, she develops abdominal cramps and nausea and then vomits. Which of the following is the most likely diagnosis in this patient?

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11ec25c8_d5f0_d5e9_bc81_fd8135c48ada_MD0003_00 This patient with cystic fibrosis developed nausea and presyncope associated with hyperthermia, tachycardia, and tachypnea while playing soccer, suggesting an exertional heat illness. Although exertional heat stroke (EHS) may present in a similar manner, the absence of CNS dysfunction in this patient suggests she has heat exhaustion. Heat exhaustion typically occurs after prolonged exercise (eg, soccer) in high ambient temperatures, particularly in the setting of high humidity, which limits evaporative cooling from sweat. Like other heat-related illnesses, heat exhaustion risk factors include older age, obesity, poor physical fitness, infections (as are common in cystic fibrosis), and certain medications (eg, anticholinergics). In addition, cystic fibrosis may predispose patients to heat-related illnesses due to higher rates of sodium and chloride lost in sweat. Heat exhaustion is characterized by hyperthermia; typically the patient's temperature is moderately elevated but is usually ≤40 C (104 F). Common manifestations of heat exhaustion include weakness, dizziness, profuse sweating, headache, and nausea/vomiting. Tachycardia and tachypnea are common, and hypotension may occur. Unlike EHS, mentation remains normal. Management includes cooling the patient (eg, air conditioning, cool water shower); oral hydration with chilled salt-containing fluids should be encouraged due to fluid and sodium losses that occur with sweating. (Choice A) This patient may have mild rhinitis (eg, rhinorrhea, congestion), which can predispose her to heat exhaustion. However, acute cystic fibrosis exacerbation typically present with increased oxygen requirement, cough, dyspnea, or sputum production. (Choice B) This patient with no CNS dysfunction and hyperthermia ≤40 C (104 F) has heat exhaustion, not EHS. (Choices C and E) Individuals with cystic fibrosis excrete excessive sodium and chloride in their sweat. As a result, they are at increased risk for dehydration, exertional hyponatremia, and hypochloremic dehydration, not hypernatremia and hyperchloremic dehydration. Infants with cystic fibrosis are particularly susceptible to hyponatremic dehydration, even without heat stress. Educational objective: Heat exhaustion is characterized by hyperthermia (typically ≤40 C [104 F]) associated with weakness, dizziness, profuse sweating, headache, and/or nausea. Mentation remains normal, unlike in exertional heat stroke. Management includes cooling (eg, cool water shower) and oral hydration with salt-containing fluids. References: Prevalence of hyponatremia at diagnosis and factors associated with the longitudinal variation in serum sodium levels in infants with cystic fibrosis. (http://www.ncbi.nlm.nih.gov/pubmed/22404954) Exertional heat illness: emerging concepts and advances in prehospital care. (http://www.ncbi.nlm.nih.gov/pubmed/25860637) Heat-related illness. (http://www.ncbi.nlm.nih.gov/pubmed/21661715) Heat-related illnesses. (http://www.ncbi.nlm.nih.gov/pubmed/30990296)

A 13-Year-Old Girl with Cystic Fibrosis Is Evaluated in the Emergency