Topics Discussed: hematology; hyperkalemia.
Excerpt:"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).
- 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).
- 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.
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