A 23-year-old man presents to the emergency department for altered mental status after a finishing a marathon. He has a medical history of obesity and anxiety and is not currently taking any medications. His temperature is 104°F (40°C), blood pressure is 147/88 mmHg, pulse is 200/min, respirations are 33/min, and oxygen saturation is 99% on room air. Physical exam reveals dry mucous membranes, hot flushed skin, and inappropriate responses to the physician's questions. Laboratory values are ordered as seen below. Hemoglobin: 15 g/dL Hematocrit: 44% Leukocyte count: 8,500/mm^3 with normal differential Platelet count: 199,000/mm^3 Serum: Na+: 165 mEq/L Cl-: 110 mEq/L K+: 4.0 mEq/L HCO3-: 20 mEq/L BUN: 30 mg/dL Glucose: 133 mg/dL Creatinine: 1.5 mg/dL Ca2+: 10.2 mg/dL AST: 12 U/L ALT: 10 U/L Which of the following is the most appropriate next step in management?
Dextrose solution
Hypotonic saline
Lactated ringer
Normal saline
Lactated ringer
This patient is presenting with hypernatremia and heat stroke for which the most appropriate next step in management is the administration of lactated ringer solution.

Heat stroke presents with hot/flushed skin, fever, altered mental status, and hypernatremia secondary to loss of free water. Patients should immediately be cooled with external measures and started on fluids. Minor cases where the patient is cognitively intact can be treated with oral replacement with an electrolyte balanced solution (though this would be heat exhaustion and not heat stroke). Patients with altered mental status should be started on normal saline or lactated ringer, and sodium levels should be corrected slowly. Rapid correction of serum sodium or administration of hypotonic fluids can cause cerebral edema and seizures; however, this is more common in hypernatremia that has persisted for days as it has led to cerebral adaptations.

Tinawi reviewed the evidence regarding the use of intravenous fluids in the hospital setting. He discusses how a large volume of normal saline can result in hypernatremia and hyperchloremia. He recommends considering the risks and benefits of colloid versus crystalloid usage.

Incorrect Answers:
Answers 1-3: 50% normal saline 50% dextrose, dextrose solution, and hypotonic saline are hypotonic solutions and would treat the hypernatremia too rapidly predisposing the patient to seizures.

Answer E: Normal saline would be a reasonable option for this patient; however, it is less desirable given that this patient is suffering from hypernatremia, hyperchloremia, and a metabolic acidosis which could be worsened by normal saline given the large sodium and chloride load of this solution.

Bullet Summary:
Hypernatremia and dehydration should be treated with lactated ringer and sodium levels should be corrected no more rapidly than 1 mEq/L/hour.