Electrolyte disturbance - high K+

Question 1

define ↑K+?

Answer 1

• mild: K+ ≥5.5 mmol/L (some say 5.4).
• moderate: K+ ≥6.0 mmol/L.
• severe: K+ ≥6.5 mmol/L.

↑K+ in the serum (extracellular fluid, ECF)
↓chemical gradient with intracellular fluid (ICF)
↓K+ leakage from ICF
myocyte membrane depolarisation (inc. cardiac) ↑excitability initially
later cells unable to repolarise fully
so ↓excitability.

Other physiological effects: ↓NH4+ production, ↑insulin secretion.

Question 2

causes ↑K+?

Answer 2

↓Excretion of K+:
• AKI or CKD (e.g. hypovolaemia, sepsis)
• drugs: spironolactone, amiloride, ACEi, A2RB, NSAIDs.
• Addison's
• Metabolic acidosis.
• Gordon's syndrome.

Movement of K+ from ICF→ECF:
• Acidosis
• Tissue damage: rhabdomyolysis (e.g. from trauma, intense exercise), tumour lysis syndrome.
• Drugs: digoxin, mannitol, suxamethonium, β-blockers.

↑Intake of K+:
• KCl (iatrogenic).
• Salt substitutes.
• Large blood transfusions.

A false positive test, pseudohyperkalaemia, caused by:
• Haemolysis e.g. from difficult venepuncture, wrong order of blood bottles.
• Delayed analysis of blood sample.
• ↑Platelets.

Question 3

Sx + Ex ↑K+?

Answer 3

• ASx + ECG changes.
• arrhythmias: altered HR, palpitations, light-headed.
• parasthesia
• flaccid weakness.
• ↓Reflexes

Question 4

Ix ↑K+?

Answer 4

BEDSIDE:
• get ECG if K+ >6:
- K+ >6.0: tented T, prolonged PR.
- K+ >6.5: flattened or absent P, wide QRS, bradycardia, ST elevation.
- K+ >8.0: even wider QRS, sine wave, VT.

BLOODS:
• U+E (consider repeat testing (or VBG) if haemolysed sample suspected)
• FBC to rule out pseudohyperkalaemia.
• Blood gas may show acidosis. Will also give instant K+ reading.
• Ca2+ and CK in suspected rhabdomyolysis.
• Glucose if diabetic.
• Digoxin levels if taking.

Question 5

Tx ↑K+?

Answer 5

• Stop drugs: ACEi, K+-sparing diuretics, NSAIDs.
• Mild (≥5.5 mmol/L) or moderate (≥6) and normal ECG:
• Reduce dietary intake.
• If moderate, consider insulin IV + glucose IV ± salbutamol nebs

• Severe (≥6.5 mmol/L) or ECG changes EMERGENCY
- “CIGAR”:

• Calcium gluconate IV
• Insulin IV
• Glucose IV
• Airway dilator (Salbutamol nebs)
• Remove K+ from body: furosemide or – if severe renal impairment – dialysis

Question 6

K+ physiology?

Answer 6

Major intracellular ion (98 percent of it is in ICF)
ECF level is normally 3.5-5.5.
Important for resting membrane potential, maintaining cell size, and pH regulation.

Question 7

why ↓K+ → metabolic alkalosis (↓H+)?

and vice versa

Answer 7

Renal mechanisms.
Cells in collecting duct exchange H+/K+.
↓ in one → compensation and ↓ in the other.
Synergistic with effect of cell membrane H+/K+exchange.

Question 8

what moves K+ into cells (leading to ↓K+ in ECF)?

Answer 8

• **Insulin
• β-agonists, which upregulate Na+/K+ ATPase.
• Aldosterone.
• Alkalaemia, which causes H+ to move out of cell and K+ to move in via H+/K+ exchanger.

Question 9

what moves K+ out of cells (leading to ↑K+ in ECF)?

Answer 9

• ↑Osmolality
• α-agonists and β-blockers.
• Acidaemia
• Intense exercise.