Hypokalaemia

Hypokalaemia is a disorder of potassium homeostasis characterised by low levels of potassium (<3.5 mmol/L). It's a relatively common electrolyte abnormality.

Grading of severity

Potassium level	Severity
3.5 - 3.0	Mild
2.9 - 2.5	Moderate
< 2.5	Severe

Etiology

Hypokalaemia can occur due to increased potassium loss, redistribution of potassium into cells, or (rarely) insufficient potassium intake. Because the kidneys can reduce potassium excretion to a minimum, and the daily potassium requirement is really low, insufficient intake of potassium rarely causes hypokalaemia by itself, but it may contribute to hypokalaemia due to other causes

Increased potassium loss	Redistribution of potassium into cells
Loop diuretics	Excessive insulin (treatment of diabetic ketoacidosis or hyperglycaemic hypoerosmolar syndrom, refeeding syndrome)
Vomiting or other gastrointestinal loss	Excessive beta-adrenergic activity (severe stress (like myocardial infarction, traumatic head injury, alcohol withdrawal), administration of beta-adrenergic agonists)
Hyperaldosteronism, e.g. due to	Alkalosis

Upper gastrointestinal fluids don't contain much potassium, so loss of the fluid itself does not cause severe hypokalaemia. However, the resulting hypovolaemia can cause hyperaldosteronism, which can cause hypokalaemia.