Chapter 65: Hyperkalemia

I. PROBLEM

The serum potassium level is 7.0 mEq/L in an extremely low birthweight (ELBW) infant. Normal potassium levels are generally between 3.5 and 5.5 mEq/L, with a potassium >5.5 mEq/L indicating hyperkalemia. The exact definition varies and can be based on maturity or severity. Some reported definitions of hyperkalemia include the following:

1. Serum potassium >6 mEq/L in full-term neonates.

2. Serum potassium >6.5 mEq/L in premature infants.

3. Moderate hyperkalemia: Serum potassium 6 to 7 mEq/L

4. Severe hyperkalemia: Serum potassium >7 mEq/L

   Hyperkalemia is common in preterm and ELBW infants because of an immature tubular function and a decreased potassium excretion caused by a lower glomerular filtration rate. Plasma potassium concentration also increases in ELBW infants in the first few days after birth from the shift of potassium from the intracellular to the extracellular compartment. This is the most serious of electrolyte abnormalities because it can cause fatal arrhythmias. If electrocardiogram (ECG) changes relating to hyperkalemia are present, this is an emergency situation. Plasma potassium should be monitored in all premature infants <30 weeks postmenstrual age during the first 3 days of life because they can develop nonoliguric hyperkalemia (NOHK) and have serious complications (cardiac arrhythmias, periventricular leukomalacia, brain hemorrhage, and sudden death).

II. IMMEDIATE QUESTIONS

1. How was the specimen collected? What is the central serum potassium level? Is it a true level or factitious level? Blood obtained from a heel stick or drawn through a small-bore intravenous (IV) line or tiny needle may yield falsely elevated potassium levels secondary to hemolysis. Clot formation can also cause a 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). Note: Serum potassium level is 0.4 mEq/L higher than the plasma level. Always do a serum potassium level from a venous sample (free flowing) before treatment.

2. Does the electrocardiogram 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 of or flattened P wave, widening QRS, ST-segment depression, bradycardia, sine wave QRS-T, first-degree atrioventricular block, ventricular tachyarrhythmias, and finally cardiac arrest if the potassium levels continue to increase. Classic ECG changes include the following:

   1. Serum potassium of 5.5 to 6.5 mEq/L. Tall peaked T waves with a narrow base, shortening of PR interval, normal or decreased QT.

   2. Serum potassium of 6.5 to 8 mEq/L. Tall peaked T waves, prolonged PR interval, loss or decreased P wave, amplified R wave, widening of QRS.

   3. Serum potassium >8 mEq/L. Absent P wave, wide bizarre diphasic QRS, progressive QRS widening merging with the T wave, bundle branch blocks, ventricular fibrillation or asystole.

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

4. What are ...