[10] Hypokalaemia Flashcards
What is classified as hypokalaemia?
Serum potassium concentration of <3.5mmol/L
What can the severity of hypokalaemia be classified into?
- Mild
- Moderate
- Severe
What is considered to be mild hypokalaemia?
3.1-3.5mmol/L
What is considered to be moderate hypokalaemia?
2.5-3.0mmol/L
What is considered to be severe hypokalaemia?
<2.6mmol/L
What % of cases of hypokalaemia are mild?
>95%
How can mild cases of hypokalaemia be corrected?
Simply by the use of a suitable electrolyte replacement
What is the importance of hypokalaemia?
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 on and monitored accordingly
What % of the bodies potassium is found inside cells?
About 98%
Where is the remainder of the bodies potassium found?
In the extracellular fluid, including the blood
What maintains the potassium concentration gradient between the cells and ECF?
Principally by Na/K-ATPase pump
What is the importance of potassium in the body?
It is essential for many body functions, including muscle and nerve activity
What is the electrochemical gradient of potssium between the intracellular and extracellular space essential for?
Nerve function
Why is the electrochemical gradient of potassium between the intracellular and extracellular space essential for nerve function?
As potassium is needed to repolarise the cell membrane to a resting state after an action potential has passed
What can lower potassium levels in the extracellular space lead to?
Hyperpolarisation of the resting membrane potential
What results from the hyperpolarisation of the resting membrane potential caused by lower potassium levels in the extracellular space?
A greater than normal stimulus is required for depolarisation of mmebranes to initial an action potential
What can hypokalaemia cause in the heart?
Arrhythmias
Why can hypokalaemia cause arrhythmias in the heart?
Because of a more complete recovery from sodium-channel inactivation, making the triggering of an action potential less likely.
In addition, the reduced extracellular potassium inhibits the activation of the IKr potassium current, and delays ventricular repolarisation, which may promote re-entrant arrhythmias
What are the categories of causes of hypokalaemia?
- Medication
- Excess loss
- Decreased intake
- Other
What medications can cause hypokalaemia?
- Diuretics, most commonly thiazide and loop diuretics
- Steroids
- Excessive insulin administration
- Beta-2 agonists, such as salbutamol
What can cause excess loss of potassium causing hypokalaemia?
- Diarrhoea and vomiting
- Hyperaldosteronism
- Burns or excessive sweating
Give 4 examples of causes of diarrhoea and vomiting that can lead to hypokalaemia
- Bowel obstruction
- Fistula formation
- Pyloric stenosis
- Laxative abuse
Give an example of a cause of hyperaldosteronism
Conn’s syndrome
What can cause decreased intake of potassium causing hypokalaemia?
- Inadequate replacement by IV fluids when NBM
- Malnutrition
What are the other causes of hypokalaemia?
- Chronic alcoholism
- Cushing’s syndrome
- Renal tubular acidosis
- Hypomagnesia
- Chronic peritoneal dialysis
What are the symptoms of mild cases of hypokalaemia?
Mild cases of hypokalaemia are asymptomatic
What may patients with severe cases of hypokalaemia present with?
- Muscle weakness
- Hypotonia
- Hyporeflexia
- Cramps
- Tetany
- Palpitations
- Arrhythmias
- Constipation
What investigations may be done in hypokalaemia?
- ECG
- Bloods
- VBG
When should a hypokalaemia patient be put on a cardiac monitor?
- If ECG changes are noted
- If the patient requires aggressive IV potassium treatment
What bloods should be done in hypokalemia?
- FBC
- U&Es
- PO42+
- Mg2+
When should a VBG be done in hypokalaemia?
To rapidly check potassium levels following intervention
Why is it important to do an ECG in hypokalaemia?
Hypokalaemia causes cardiac hyperexcitability, resulting in re-entrant loops and therefore giving the potential for the development of arrhythmias
What ECG changes might their be in hypokalaemia?
- Elongated PR interval
- T wave flattening or T wave inversion
- Prominent U wave
- ST segment depression
What can eventually happen to the ECG if hypokalaemia is uncorrected?
Can develop into life threatening arrhythmias such as VT and VF
What should the management of hypokalaemia involve?
Treatment of the underlying cause, alongside correction with suitable replacement
What will the specific management of hypokalaemia depend on?
The underlying cause
When should advice from a renal specialist be sought before acting in a patient with hypokalaemia?
- Patients who are fluid overloaded
- Patients on significant diuretic therapy
- Patients with complex diagnosis or managment
How can hypokalaemia be managed in mild cases without cardiac involvement, and when the patient is able to eat and drink normally?
Oral supplements such as SandoK and food high in potassium should suffice
How is hypokalaemia managed in moderate to severe cases, or with ongoing loss or inability to take supplements?
IV potassium replacement of 40mmol potassium in 1L saline
What may be required in hypokalaemia if rapid rates or higher concentrations of potassium replacement are required?
Central line and admission to be monitored may be necessary
What should be avoided when choosing fluids in hypokalaemia?
Solutions containing dextrose
Why should a dextrose free solution be used when giving fluids in hypokalaemia?
To minimise insulin stimulation which could cause worsening hypokalaemia
