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  1. Problem. The serum potassium level is >6 mEq/L. Normal potassium levels vary with the technique used by the laboratory and are generally between 3.5 and 5.5 mEq/L. Hyperkalemia is common in infants <1000g (~30%). If electrocardiogram (ECG) changes relating to hyperkalemia are present, this is an emergency situation (see Section V, A).

  2. Immediate questions

      1. How was the specimen collected? What is the central serum potassium level? Is it a true level or factitious? Blood obtained by heelstick or drawn through a tiny needle may yield falsely elevated potassium levels secondary to hemolysis. Clot formation can also cause falsely elevated potassium. The blood should not be obtained from a heparin-coated umbilical catheter (release of benzalkonium from a heparin-coated umbilical catheter can elevate the potassium reading).

      1. Does the ECG show cardiac changes characteristic of hyperkalemia? This may be the first indication of hyperkalemia. In neonates, serum potassium >6.7 mEq/L is associated with ECG changes. Early cardiac changes include tall, peaked, "tented" T waves, followed by loss or flattened P wave, widening QRS, ST-segment depression, bradycardia, sine wave QRS-T, first-degree atrioventricular (AV) block, ventricular tachyarrhythmias, and finally cardiac arrest if the potassium levels continue to increase.

      1. How much potassium is the infant receiving? Normal amounts of potassium given for maintenance are 1–3 mEq/kg/day.

      1. What are the blood urea nitrogen and creatinine levels? What is the urine output and body weight? Elevated blood urea nitrogen (BUN) and creatinine suggest renal insufficiency. Another indication of renal failure is decreasing or inadequate urine output with weight gain.

      1. Is there associated hyponatremia, hypoglycemia, and hypotension? With low sodium and glucose, high potassium, and hypotension, consider adrenal insufficiency.

      1. Does the infant have any of the common characteristics of premature newborns prone to hyperkalemia? These include small for gestational age, female gender, more severe respiratory distress syndrome, very low birthweight, requirement of exogenous surfactant, need for inotropic medications, and delayed feeding.

  3. Differential diagnosis

      1. Falsely elevated potassium level can be due to hemolysis or clot formation during phlebotomy or heelstick or by drawing the sample proximal to an IV site infusing potassium.

      1. Excess potassium administration from IV fluids. Potassium supplements usually are not necessary on the first day of life and often are not necessary until day 3, with the typical requirement of 1–2 mEq/kg/day.

      1. Pathologic hemolysis of red blood cells may be secondary to intraventricular hemorrhage, use of a hypotonic glucose solution (<4.7% dextrose), sepsis (most commonly, Pseudomonas), cephalohematoma, trauma, asphyxia, hypothermia, or Rh incompatibility.

      1. Renal failure can lead to hyperkalemia. Oliguria can cause decreased potassium clearance and hyperkalemia.

      1. Immaturity. Nonoliguric hyperkalemia occurs in almost half of extremely low birthweight infants and is defined as a potassium level >6.5 mmol/L in the absence of acute renal failure. This occurs without potassium intake or oliguria and can result from a shift of potassium from intracellular to extracellular space associated with decreased sodium- and potassium-activated adenosine triphosphate (Na+, K+-ATPase) activity or from immature renal tubular and glomerular functions. Hyperkalemia is often associated with hyperglycemia as ...

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