Hypokalaemia Flashcards
Potassium is the most abundant cation in the body, with more than 98% found intracellularly. Hypokalaemia is a common electrolyte abnormality found in patients within the hospital setting.
It is defined as a serum concentration of potassium < …
Potassium is the most abundant cation in the body, with more than 98% found intracellularly. Hypokalaemia is a common electrolyte abnormality found in patients within the hospital setting.
It is defined as a serum concentration of potassium < 3.5mmol/L (normal range 3.5-5.3mmol/L). Severity of hypokalaemia is further classified into
Mild = … Moderate = … Severe = …
Mild = 3.1 – 3.5mmol/L Moderate = 2.5 – 3.0mmol/L Severe = < 2.5mmol/L
Most cases of hypokalaemia (>95%) are .. and can be corrected simply by the use of suitable electrolyte replacement.
Most cases of hypokalaemia (>95%) are mild and can be corrected simply by the use of suitable electrolyte replacement.
However, even small drops in potassium levels can increase the risk of …
However, even small drops in potassium levels can increase the risk of cardiac arrhythmias, especially in post-surgical patients, so all cases of hypokalaemia should be acted upon and monitored accordingly.
Common causes for hypokalaemia can be categorised into those that arise from excess losses from the body, inadequate intake into the body, or from intracellular shifts of potassium:
What are some excess loss causes? (Hint GI, Urinary, Skin)
Gastrointestinal losses Vomiting Diarrhoea Fistulae formation Laxative abuse
Urinary losses
Diuretics (thiazide, loop diuretics, acetazolamide)
Mineralocorticoid excess (Conn’s syndrome, Cushing’s syndrome, steroid use)
Other causes: hypomagnesaemia, polyuria, renal tubular acidosis
Skin losses
Burns
Excess sweating
Gastrointestinal losses - hypokalaemia
Vomiting
Diarrhoea
Fistulae formation
Laxative abuse
Urinary losses - hypokalaemia
Diuretics (thiazide, loop diuretics, acetazolamide) Mineralocorticoid excess (Conn’s syndrome, Cushing’s syndrome, steroid use) Other causes: hypomagnesaemia, polyuria, renal tubular acidosis
Skin losses - hypokalaemia
Burns
Excess sweating
Inadequate Intake - causes of hypokalaemia
Malnutrition
Inadequate intravenous potassium replacement (in nil-by-mouth patients)
Intracellular Shifts - hypokalaemia? (3)
Alkalosis
In alkalosis, there is a shift of hydrogen ions from the intracellular to extracellular space, to minimise the rise in extracellular pH. Potassium ions then shift intracellularly to balance the flow of electrical charge across the cell membrane
Excessive insulin administration
Insulin causes increased activity of the Na-K-ATPase pump which shifts potassium intracellularly, primarily into skeletal muscle and hepatic cells
Excessive beta-adrenergic agonist activity (e.g. salbutamol)
Causes an increased activity of the Na-K-ATPase pump
Hypokalaemia is generally asymptomatic in mild cases. However, in more severe cases, patients can present with …
Hypokalaemia is generally asymptomatic in mild cases. However, in more severe cases, patients can present with muscle weakness, paraesthesia, ileus or pseudo-obstruction, hypotonia, hyporeflexia, muscle cramps, tetany, and even respiratory failure (rare), alongside potential cardiac arrhythmias (as discussed below).
Hypokalaemia causes cardiac … and can also result in functional re-entrant loops to form which can result in arrhythmias developing.
Hypokalaemia causes cardiac hyperexcitability and can also result in functional re-entrant loops to form which can result in arrhythmias developing.
There are several ECG changes that can occur in hypokalaemia:
Elongated PR interval
T wave flattening* or T wave inversion
Prominent U wave*
ST segment depression
If uncorrected, this can eventually develop into life-threatening arrhythmias such as VT or VF
*Flattening of the T wave with the presence of the U wave may appear as a prolonged QT interval, however the true QT is actually unchanged
Patients with hypokalaemia should be investigated and managed appropriately due to the associated risks, especially of cardiac arrhythmias.
The history and examination seek to not only investigate the cause, but also to evaluate the physiological manifestations of hypokalaemia. Several investigations should initially be performed, including:
ECG
If any changes relating to hypokalaemia are noted (or the patient requires aggressive IV potassium replacement), the patient may need to be put on a cardiac monitor
Bloods, especially FBC, U&Es, Ca2+ and PO42-, and Mg2+
Low magnesium levels are often associated with hypokalaemia; and low magnesium levels can often be found in patients refractory to potassium replacement therapy
A venous blood gas (VBG) can be useful for an immediate potassium check following intervention
In mild cases of hypokalaemia without ECG changes, where the patient is able to eat and drink normally, what is used to increase serum potassium?
In mild cases without ECG changes, where the patient is able to eat and drink normally, oral supplements (such as SandoK) should suffice in most circumstances.
