Hypokalaemia

Question 1

Definition?

Answer 1

Hypokalemia (low serum potassium) is a common electrolyte disorder that is typically caused by potassium loss (e.g., due todiarrhea, vomiting, ordiureticmedication).

Question 2

RF?

Answer 2

• Old age
• Low intake of Potassium
• Female
• Eating disorders
• Alcoholism
Bariatric surgery

Question 3

ddx?

Answer 3

pseudohypokalaemia-poor sample
congenital-hypotension or mutations
metabolic acidosis-ketoacidosis, polyuria, increased thirst and vomiting
Cushing syndrome-pituitary adenoma on imaging, signs

Question 4

Epidemiology?

Answer 4

Age: Older
Sex:
Ethnicity:
P: 1% general population

Question 5

Aetiology?

Answer 5

GI loss
Renal loss
IC shift
insufficient intake

Question 6

GI loss?

Answer 6

vomiting,
diarrhoea
adenoma
laxatives
bentonite

Question 7

renal loss?

Answer 7

primary-
RTA T1/2
Cushings
renin-secreting tumours
Fanconi syndrome
Genetic disorders-CAH, Bartter, Gitelman, Liddle

Secondary-
diuretics
B2 agonists
glucocorticoids, catecholamines, ABs,
antifungals, theophylline
endocrine causes-high aldosterone, high cortisol

Question 8

IC shift

Answer 8

alkalosis
insulin
hyposmolality
increased glycogenesis and SNS-SNS use, phaeochromocytoma, alcohol, MI, head trauma
familial periodic paralysis
thyrotoxicosis
hypothermia
intoxication

Question 9

insufficient intake

Answer 9

older
alcohol abuse
eating disorders

Question 10

CP?

Answer 10

Patients may be asymptomatic, particularly if the deficiency is mild. Symptoms usually occur if serum K+levels are< 3.0 mEq/Land/or decrease rapidly.[2]
• Cardiovascular manifestations
• Symptoms ofcardiac arrhythmias(e.g.,palpitations, irregularpulse,syncope)
• Hypotension
• Neuromuscular manifestations
• Muscle cramps and spasms[5]
• Muscle weakness, paralysis
• Respiratory failure secondary to paralysis of the respiratory muscles
• Rhabdomyolysis
• Decreaseddeep tendon reflexes
• Gastrointestinal manifestations
• Nausea, vomiting[5]
• Constipationorileus
• Fatigue
• Other manifestations
• Hyperglycemia[6]
• Polyuria[7]
• Symptoms of underlying causes, including:
○ Dehydrationingastroenteritis
○ Tachycardiaand tremors inalcohol withdrawal
○ Symptoms of thyrotoxicosis
Symptoms ofdigoxin toxicityin patients treated withdigoxin

Question 11

Patho?

Answer 11

• Too little potassium in blood
• External balance shift-increased K excretion-less in blood
• Internal balance shift-more in cells
  
  • Excess insulin-more glucose uptake-high pump-more K in cells
  • Alkalosis-H/K pump more-more k in and H out
  • Not affected in resp
  • B2 agonists and alpha-blockers-Na/K pump and Ca channels
• External balance-low intake
• Anorexia, fasting or specific diets
• Aldosterone excess-Primary hyperaldosteronism-excess use of Na/K pump-more into tubule and urine
• CHF, cirrhosis
• Diuretics-loop and thiazide-inhibit sodium absorption upstream, increased absorption downstream-more K tubule as gradient bt principle cell and tubule
• Vomiting and diarrhoea-more lost in faeces
• Sweat-exercise
• Less positive electrochemical gradient- hyperpolarised and so less reactive to stimuli
• -constipation, weakness and cramps, resp depression, arrhythmias and arrest
• Hypomagnesemia-less magnesium to bind to renal outer medullary K channels- More K + out into lumen

Question 12

Investigations-first line?

Answer 12

Laboratory studies
• Electrolytes andkidneyfunction
• Serum K+levels
• Basic metabolic panel
• Serum calcium,magnesium,phosphate
• Blood gas (venous or arterial): may showmetabolic alkalosis
• Urinary potassium: Consider measuring to narrow down underlying etiology[9][10][11]
• Methods
○ Spot urine: rapid assessment, indicated in urgent cases, less reliable than24-hourcollections
○ 24-hoururinecollection: less practical, indicated for chronic cases and uncertain diagnoses, more accurate thanspot urine
• Findings
○ Renal loss:spot urine> 15–20 mEq/L(24 hourcollection> 15 mEq/L)[10][1]
○ Extrarenal loss:spot urine< 15–20 mEq/L(24 hourcollection< 15 mEq/L)[11]
Consider confirming abnormal serum potassium levels with a repeat blood draw.
ECG

Question 13

ECG findings?

Answer 13

• Mild to moderate hypokalemia
  
  • T-waveflatteningorinversion
  • ST depression
  • ProlongedPR interval
• Moderate to severe hypokalemia
  
  • Presence ofU waves: small waveform following theT wavethat is often absent but becomes more pronounced in hypokalemia orbradycardia[2]
  • T andU wavefusion
  • QT prolongation[12]
• Dysrhythmias
  
  • Premature atrial and ventricular complexes
  • Sinusbradycardia
  • Paroxysmalatrial orjunctional tachycardia
  • Ventricular dysrhythmias, e.g.,Torsades de pointes
  • PEA/asystole

Question 14

Management?

Answer 14

• If mild:
• (>2.5mmol/L, no symptoms.) Give oral K+supplement (≥80mmol/24h, eg Sando-k® 2 tabs/8h). Review K+after 3 days. If taking a thiazide diuretic, and K+>3.0 consider repeating and/or K+-sparing diuretic.
• If severe:
• (<2.5mmol/L, and/or dangerous symptoms.) Giveivpotassium cautiously, not more than 20mmol/h, and not more concentrated than 40mmol/L. Do not give K+if oliguric.
Nevergive K+as a fast stat bolus dose.

Question 15

Prognosis?

Answer 15

• Can be life-threatening

* Need monitoring

Question 16

Complications?

Answer 16

• Cardiac arrhythmias
• Paralysis
Rebound hyperkalaemia