Electrolyte disturbances - low K+

Question 1

define ↓K+?

Answer 1

mild (<3.5 mmol/L)
moderate (<3 mmol/L)
severe (<2.5 mmol/L)

Question 2

main pathological effect ↓K+?

Answer 2

muscle weakness

Question 3

pathophysiology ↓K+?

Answer 3

Pathophysiology
↓K+ in the serum (extracellular fluid, ECF)
↑chemical gradient with intracellular fluid (ICF)
↑K+ leakage from ICF
hyperpolarisation of myocyte membrane (inc. cardiac) • ↓muscle excitability.

Other effects:

↓GFR
↑NH4+ production.
↑HCO3- reabsorption.
↓Insulin secretion.
Worsens digoxin toxicity.

Question 4

causes ↓K+?

Answer 4

GI:
• Loss: diarrhoea, vomiting (inc. gastroenteritis, eating disorders, pyloric stenosis), fistula.
• ↓Intake

Kidney:
• Diuretics: thiazide, loop.
• Metabolic alkalosis.
• **DKA: hyperosmolarity and ↓insulin → K+leaves cells → lost in urine. Overall body deficit though serum levels may remain high.

Movement of K+ from ECF→ICF:
• Insulin
• β-2 agonists.
• Alkalosis
• Hypokalemic periodic paralysis: congenital, periodic, 72 hr long ↓K+.

Other causes:
↑Mineralocorticoids: ***Conn's, ***Cushing's, liquorice.
↓Mg2+, which can be due to alcoholism.
Tubular disease.
Bartter syndrome.

Question 5

Sx + Ex ↓K+?

Answer 5

HEART
• ASx/ECG changes.
• Arrhythmia: palpitations, light-headed.

NM:
• Confusion and lethargy.
• General muscular symptoms: weakness, ↓reflexes
• ↓tone, tetany, cramps, myalgia, rhabdomyolysis***

ORGAN-SPECIFIC:
• shallow breathing and respiratory failure
• constipation/ileus
• polyuria.

Other:
• Metabolic alkalosis.
• Interstitial nephritis.
↓Insulin secretion.
• Carbohydrate intolerance.
↓Growth.

Question 6

Ix ↓K+?

Answer 6

BEDSIDE:
• ECG:
- P widening.
- T flattening or inversion.
- ST depression.
- Prominent U, especially V4-6.
- QT may appear prolonged, but this is due to flattened - T merging into U (long QU).
If severe: SVT, VT, VF, Torsades de Pointes (i.e. long QU is as dangerous as long QT).
• +/- urine K+

BLOODS:
• U&E, plus Mg2+, Ca2+, and PO43-
• ↓Na+ suggests thiazides as a cause.
• Glucose
• ABG

Question 7

Tx ↓K+?

Answer 7

• K+ <3.5: no treatment, or consider K+ PO (e.g. Sando-K).
• K+ ≤3.0: K+ PO.
• K+ ≤2.5 or severe symptoms: K+ IV. Give slowly – <10 mmol/hr – and don’t give if oliguric

• replace Mg2+ if also low.