Hypokalaemia Flashcards
What is the normal range of K in the serum?
3.5 - 5.5 mmol/L
At what K concentration do signs and symptoms of hypokalaemia emerge?
<3.0
What two organ systems are affected by hypokalaemia?
Muscles:
- Abdomen: cramps, ileus
- Legs: weakness (tends to start in legs then spread to arms)
- Rhabdomyolysis (widespread lysis of myocytes)
Heart:
- ECG changes
- Arrhythmia
- Atrial fibrillation most common
What’s tricky about rhabdomyolysis due to hypokalaemia?
Hypokaelaemia can trigger rhabdomyolysis, which is the widespread lysis of myocytes.
The lysis can lead to release of intracellular potassium into the serum, which masks the hypokalaemia that orginially triggered it.
What muscle signs and symptoms can result from hypokalaemia?
Weakness (starts in legs, progresses to arms)
Cramps
Ileus
Rarely, rhabdomyolysis
What cardiac signs and symtpoms are associated with hypokalaemia?
ECG changes
Arrhythmias (most common is AF; can also cause VT and torsades)
What ECG changes are associated with hypokalaemia?
ST depression
T wave inversion
Prominent U waves (comes after T wave, before P wave - might look like a double peaked T wave)
In which patients are arrhythmias due to hypokalaemia most dangerous?
- QT prolonging drugs
- Digoxin toxicity
- Hypomagnasemia
- Coronary ischaemia
In these cases, hypokaelaemia can result in VT or torsades.
What are the four main categories of causes of hypokalaemia?
Reduced GI absorption (e.g. poor PO intake)
Excess GI loss
Excess renal loss
Internal redistribution into intracellular space
What hormonal problems can cause hypokalaemia?
Excess aldosterone (primary aldoseronism), cortisol (Cushing’s), and other mineralocorticoids.
These can block renal reabsorption of filtered potassium.
What drugs can cause hypokalaemia?
Cortisol and other mineralocorticoids.
- These can block renal reabsorption of filtered potassium.
Diuretics
Insulin
How significantly must a patient be suffering from poor intake to result in hypokalaemia?
Significant.
Kidneys can usually reabsorb all potassium, so intake must be extremely low for K levels to fall.
What might cause GI loss of K?
Vomiting
Diarrhoea (inc laxative abuse)
What might cause urinary loss of K?
Diuretics
Cortisol excess (blocks reabsorption of filtered K)
Polyuria (think DKA)
Hypomagnasemia
What electrolyte imbalance can in turn lead to hypokalaemia?
Hypomagnasemia (mechanism unknown)
What can cause internal redistrubtion of K into the intracellular space?
Insulin
Catecholamines
Alkalosis
How do you work up hypokalaemia, clinically?
1: History (vomiting, diarrhoea, polyuria, drugs)
2: Check Mg
3: Measure Urine K:Creatinine ratio, and assess acid-base balance
What does a low K to Creatinine ratio suggest?
Low intake
GI losses
Internal redistribution
What does a high K to Creatinine ratio suggest?
Renal losses
Will diarrhoea lead to a metabolic acidosis or alkalosis?
Diarrhoea causes acidosis.
Diarrhoeal stool contains a higher concentration of bicarbonate than plasma, so losing it produces a net acidosis
Will vomiting lead to a metabolic acidosis or alkalosis?
Vomiting causes alkalosis.
How do you treat hypokalaemia?
Replace K.
Treat underlying aetiology.
How do you replace K?
Orally (oral KCl)
IV (IV KCl)
What is the maximum dose of PO KCl?
40mmol 4-hourly.
What is the main side effect of PO KCl?
GI upset
What is the maximum replacement rate for IV KCl?
10mmol per hour
What is the main side effect of IV KCl?
Burning pain proximal to IV site
What should you bear in mind when replacing K intravenously?
All patients receiving IV KCl should be on continuous cardiac monitoring
What do you do about a hypokalaemic patient on diuretics?
Consider stopping diuresis as it may be cause of hypokalaemia.
If patient’s diuresis cannot be stopped (essential treatment for CCF, for instance), consider switching to K-sparing diuretic.
Cutoff for:
- Mild hypokalaemia
- Moderate hypokalaemia
- Severe hypokalaemia
Mild: <3.5
Moderate: <3
Severe: <2.5
What does aldosterone do to electrolyte levels?
Aldosterone produces:
- Potassium (and H+) excretion
- Sodium resabsorption
What does a patient’s acid-base status have to do with their K levels?
In response to alkalosis, the body shifts K into the cells, in exchange for H+ ions into the blood. This regulates the alkalosis, but results in hypokalaemia.
