Question Of The Day #46

This patient presents to the Emergency Department with altered mental status.  This presenting symptom can be due to a large variety of etiologies, including hypoglycemia, sepsis, toxic ingestions, electrolyte abnormalities, stroke, and more.  The management and evaluation of a patient with altered mental status depends on the primary assessment of the patient (“ABCs”, or Airway, Breathing, Circulation) to identify any acute life-threatening conditions that need to be managed emergently, the history, and the physical examination.  One mnemonic that may help in remembering the many causes of altered mental status is “AEIOUTIPS”.  The table below outlines this mnemonic.

The serum chemistry results provided show elevated BUN and Creatinine with a BUN/Cr ratio of 21.3.  A BUN/Cr ratio greater than 20 indicates decreased perfusion to the kidneys, also known as pre-renal azotemia, which can indicate dehydration, hypovolemia, or shock.  The serum chemistry also shows a severely low sodium level.  Hyponatremia can present with a variety of symptoms, including weakness, fatigue, myalgias, nausea, vomiting, headaches, altered mental status, focal neurologic deficits, seizures, or coma.  Hyponatremia can be acute or chronic, asymptomatic or symptomatic, and mild or severe.  Sodium levels below 120 mEq/L are severely low.  Neurologic symptoms, such as seizures, altered mental status, and focal neurologic deficits, are also considered severe.  Treatment should be based on patient symptoms, rather than the sodium level, as it can be difficult to assess how acute or chronic the hyponatremia state is on initial evaluation.  The presence of any severe neurologic symptoms as is seen in this scenario should prompt administration of hypertonic saline (3% NaCl).  This allows for rapid correction of serum sodium levels, which should in turn relieve the neurologic symptoms.  A 100-150mL IV bolus of 3% NaCl can be given a second time if symptoms continue after 5-10 minutes.  

Typically, hyponatremia should be corrected slowly to avoid central pontine myelinolysis.  Increases in sodium greater than 8mEq/L per 24hours should be avoided for this reason.  However, in the case of neurologic symptoms, rapid correction of sodium is opted for to prevent further damage.

Administration of “normal saline”, or 1000mL of IV 0.9% NaCl (Choice A), can increase the sodium level.  However, normal saline is not concentrated enough to rapidly increase the serum sodium to terminate neurologic symptoms.  A noncontrast CT scan of the head (Choice B) is a reasonable investigation for this altered patient, but hypertonic saline should be administered first if hyponatremia is known.  Administration of 25mg IV dextrose (Choice C), also known as “D50”, would be helpful in a patient with hypoglycemia and altered mental status. However, this patient is not hypoglycemic.

Administration of hypertonic saline (Choice D) is the best next step in this patient with severe hyponatremia and neurologic symptoms.

Correct Answer: D