Almost all of potassium ingested through diet is absorbed. The kidneys excrete more than 90% of daily intake and are the organs primarily responsible for the elimination of potassium. Under normal conditions, potassium excretion via the gastrointestinal route is negligible.(9)
Practice points
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General
Hypokalaemia is defined as serum potassium < 3.5 mmol/L.
Mild hypokalaemia: serum potassium of 2.5 to 3.5 mmol/L
Moderate hypokalaemia: serum potassium < 2.5 mmol/L with no ECG changes.
Severe hypokalaemia: serum potassium < 1.5 mmol/L or with ECG changes.(2)
A decrease of 1 mmol/L in serum potassium concentration refers to a 10% to 30% decrease in body potassium. (9, 10) In the absence of an independent factor causing transcellular potassium shifts, the magnitude of the deficit in body stores of potassium correlates with the degree of hypokalaemia. On average, serum potassium decreases by 0.3 mmol per litre for each 100 mmol reduction in total body stores, but the response is extremely variable. Because potassium repletion is rarely an urgent undertaking, err on the low end of this estimate to avoid inducing hyperkalaemia (11)
Hypokalaemia can cause functional changes in striated muscle, smooth muscle, and the heart. Severe hypokalaemia can lead to electrocardiography (ECG) changes including increase in the amplitude of P-waves, prolongation in PR and QT intervals, decrease in the amplitude of T-waves, inversion in T-waves, depression in ST segments, and the appearance of U-waves. Paralytic ileus and gastric dilatation develop when the smooth muscles are affected. Rhabdomyolysis, myoglobinuria, severe muscle weakness, paralysis, respiratory distress and respiratory arrest are observed. Fasciculation and tetany are observed in muscles. Persistent metabolic alkalosis develops with hypokalaemia.(9)
Dose
Dosing for daily parenteral potassium supplementation is based on ESPGHAN 2018 recommendations:(4)
Potassium administration should regard initial phase of oliguria and the risk of non-oliguric hyperkalaemia in VLBW infants. A deferment of parenteral potassium supply might be required to avoid hyperkalaemia.
Parenteral potassium requirement during Phase I (Transition phase) – from birth until maximal weight loss (e.g. until Day 5 of life): 0 to 3 mmol/kg/day
Parenteral potassium requirement during Phase II (Intermediate phase) – period from maximal weight loss to regaining birthweight: 1 to 3 mmol/kg/day
Parenteral potassium requirement during Phase III (Stable phase) – regular weight gain phase
Preterm neonates <1500 g: 2 to 5 mmol/kg/day and
Infants≥1500 g: 1.5 to 3.0 mmol/kg/day.
Treatment of mild to moderate hypokalaemia is based on expert opinion. (5)
Treatment of severe or symptomatic hypokalaemia with correction dose of 0.3-0.5 mmol/kg/dose over 1 hour is based on expert opinion. (5)
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