Hypokalemia
- causes and risk factors
- signs, symptoms and diagnosis
- pathophysiology
- treatments
- consequences and course
- the patient
- resources and references
As potassium is the most abundant intracellular cation, its deficiency can cause a range of problems.
Hypokalemia is defined as plasma [K] of less than 3.5 mM/L. Moderate hypokalemia is from 2.5-3 mM/L, with severe hypokalemia defined as less than 2.5 mM/L.
Causes and Risk Factors
Cellular redistribution:
- metabolic alkalosis
- insulin (Na/K ATPase stimulation)
- catecholamines
- beta agonists (ie ventolin)
- theophylline
- tocolytic agents
- vitamin B12
Increased loss:
- GI losses (diarrhea, laxatives, villious adenoma)
- renal losses
- hyperaldosteronism: Conn's, Cushing's, renin tumour, renovascular disease
- acidosis: DKA, RTA
- diuretics: furosemide, hydrochlorothiazide
- Barrter's
- Gittelman's
Inadequate diet
Signs, Symptoms, and Diagnosis
Obtain an ECG immediately.
- history
- physical exam
- ECG changes
- lab investigations
History
A careful history, with emphasis on diet and use of medications and laxatives, should be obtained.
Chronic hypokalemia stimulates thirst and can cause nephrogenic diabetes insipidus.
Physical Exam
The most prominent abnormalities involve the cardiovascular system, as discussed in ECG changes.
Signs of hypokalemia include:
- polyuria
- impaired muscle contraction
- peritoneal distention
- dyspnea
- paralysis
ECG changes
ECG changes are more clincially important than K levels. Changes include:
- U waves (most important; represents delayed ventricular repolarization)
- flattened or inverted T waves
- depressed ST segment
- prolonged QT interval
Hypokalemia can cause cardiacventricular or atrial arrythmias by lengthening the QT interval, prolonging action potential duration, and increasing spontaneous firing.
Lab Investigations
Serum and urine should be assayed for electrolytes and osmolality.
Acid-base status is important in renal loss.
In extrarenal hypokalemia, renal potassium excretion should be less than 20 mEq/day.
Pathophysiology
Cells will be closer to their resting potential?
cells will initially be hyperpolarized, and then the cells can't depolarize as well. pacemaker activity will decrease
Hypokalemia is going to disrupt the Na/K transporter, altering the resting potential.
Effects on the Heart
Hypokalemia can be very dangerous when combined with digoxin. Digitalis binds to the K site on the Na/K pump. less K will increase digoxin binding.
Normally, volume loss = decreased distal flow, decreasing K secretion.
Treatments
Treat the underlying cause, though carefully when urine output and renal function are impaired. Be extremely careful in
- elderly
- diabetics
- patients with decreased renal function
Hypokalemia along with hypomagnesemia is resistant to therapy unless magnesium is given alongside.
K-sparing diuretics such as spironolactone, amiloride, or triamterene can prevent renal loss
Potassium repletion
The net deficit can be difficult to determine, as can therapeutic need.
A decrease in serum K of 1 mEq is approximately 100-200 mEq total body loss.
- Oral supplementation should be used if possible: food, tablets (K-Dur) KCl liquid
- IV potassium should not exceed 10-20 mEq/hour. Avoid dextrose to prevent intracellular shift via insulin release
- do not use > 40 mmol/L via a peripheral vein or 60 mmol/L for central vein to prevent irritation
Consequences and Course
The Patient
References