Potassium Flashcards
What are the reference ranges for potassium?
Ref range 3.5 – 5.3 mmol/L (serum)
- Maintained within narrow limits
- Plasma may be slightly lower
- RCPath Guidance urgent communication if < 2.5mmol/L or >6.5mmol/L
Why is membrane potential important?
Membrane potential is vital for many functions
- Propagation of action potentials – nerve, muscle , cardiac
- Hormone secretion
- Acid-base Etc.
What causes potassium to shift into cells?
- Insulin
- Beta Agonists
- Alkalosis
What causes potassium shift out of cells?
- Cell lysis
- Exercise
- Hypertonicity
- Alpha Agonists
- Acidosis
Which organs are involved in potassium control?
Renal
- Extracellular K+ balance occurs mainly in the kidney
- Predominant control is in the distal tubule ( up to 95% reabsorbed by DCT)
Extrarenal Control
- GI
- Sweat
- Skin
How does renal control of the kidneys occur?
- Hypokalaemia leads to reduced renal excretion
- Acidosis (preferential excretion of H+)
- Aldosterone porduction is stimulated high K+ which leads to excretion of potassium
What are lab investigations when there s abnormal potassium?
Sodium • Urea & Creatinine • Magnesium • Calcium & Phosphate • Glucose • Bicarbonate • Blood Gases • Urine Potassium
What are signs and symptoms of hypokalemia?
- Cardiovascular: ECG changes, Arrhythmias, Myocardial necrosis (extreme)
- Neuromuscular: Weakness, pain, tenderness, cramps, rhabdomyolysis
- Neuropsychiatric: Lethargy, apathy, depression, confusion
- Renal: Polyuria, sodium retention
- Gastrointestinal: Constipation, decreased gastric acid secretion
What are ECG changes for hypokalemia?
- Depressed ST
- Inverted T waves
- Prominent U waves
How is hypokalaemia managed?
Oral / IV (Remember 40 mmol/day will only replace obligatory losses)
- >2.5 mmol/L - Oral replacement (max 80 mmol/day)
- <2.5 mmol/L - IV K+ in normal saline
Replace slowly never with a bolus. Plan 48 hr/72 hr replacement.
Check K+ regularly
Higher rates may be given in an ITU setting with cardiac monitoring
What are fluid compartments within the body?
Intracellular Fluid (ICF) – 60-70%
Extracellular Fluid (ECF) – 30 – 40%
- Intravascular space (plasma volume ~7%)
- Interstitial space (lymph)
- Transcellular fluid (pleural, pericardal, CSF, gastrointestinal)
What is involved in the sodium potassium pump?
- 3 Sodiums are transported out of the cells and 2 Potassium is transported into the cells
- Uses ATP
What are obligatory losses of Potassium?
Obligatory Losses
- Renal = 10-20mmol/24h
- Extra renal = 20 mmol/24h
Describe RAAS
RAAS
What are categories for causes of Hypokalaemia?
- Redistribution
- True Deficits
What are resdistribution causes of hypokalemia?
In vitro (spurious)
- Uptake by WBC
- Heat
In vivo
- Alkalosis (cause / effect)
- Insulin – i.e. post infusion
- Beta adrenergic agonists – salbutamol
- Chemicals – toluene
- Hypokalaemic periodic paralysis
What are some true deficit causes of Hypokalaemia? (extrarenal)
Normal Acid:Base
- Poor intake
- Depletion
- Anorexia
- Sweating
- Cisplatin
- Cell synthesis
- Aminoglycosides
- Laxative abuse
Metabolic Acidosis
- Diarrhoea
- Fistula
- Villous Adenoma
What are some true deficit causes of Hypokalaemia? (renal)
Metabolic Acidosis
- Renal tubular acidosis (T1 & T2)
- Acetazolamide (Carbonic anhydrase inhibitor) induced RTA
- Urinary tract diversion
- DKA
Variable Acid:Base
- Hypomagnasaemia
- Antibiotics
- Amphotericin B tox
- Diuretic phase of ARF
- Leukaemia
Metabolic Alkalosis
- Diuretics
- Severe K+ depletion
- Bartter Syndrome
- Gitelman syndrome
- Liddle Syndrome
- Vomiting/gastric drainage
- Chloride loosing diarrhoea
- Cushing syndrome
- Exogenous mineralcorticoids
- Conn’s Syndrome
- Renovascular hypertension
- Malignant hypertension
- Renin-secreting tumour
What is Bartter’s syndrome?
- Hyper-reninaemic hyper-aldosteronism
- Usually presents in childhood
- Mutations of genes encoding proteins that transport ions across renal cells in the thick ascending limb of the nephron
What is Gitelman’s Syndrome?
- Hypochloremic metabolic alkalosis, hypokalaemia and hypocalciuria.
- Hypomagnasaemia is present in many but not all cases
- Inactivating mutations in the SLC12A3 gene resulting in a loss of function of the encoded thiazide-sensitive sodium-chloride co-transporter (NCCT). This cell membrane protein participates in the control of ion homeostasis at the distal convoluted tubule portion of the nephron.
What is involved in attacks of Familial hypokalaemic periodic paralysis (FHPP) and Hypokalaemic periodic paralysis with thyrotoxicosis (HPP)?
- Attack involve flaccid paralysis on limbs & trunk which can last for up to 24 hrs
- Attacks can be provoked by exercise, high CHO diet, hypothermia, high sodium intake
- Cardiac arrhythmias may also be present
- Caused by mutation in the skeletal muscle voltage-gated calcium channel α-1 subunit
What are difference between HPP and FHPP?
FHPP
- AD, Caucasian, M:F 3:1
HPP
- Chinese or Japanese population, M:F 20:1
- Clinical presentation identical to FHPP but condition remits when patient becomes euthyroid
What are reference ranges for Hyperkalaemia?
- Mild (5.5 - 5.9 mmol/L)
- Moderate (6.0 - 6.4 mmol/L)
- Severe (≥6.5 mmol/L)
What are signs and symptoms of Hyperkalaemia?
Neuromuscular
- Parasthesia weakness
- Paralysis
Renal
- Natriuresis
- Decreased reabsorption of HCO3
What are ECG changes in Hyperkalaemia?
Cardiovascular
- Tall T waves
- Prolonged PR interval
- Flat P waves
- Widening of QRS complex
- VF
- Asystole
What are causes of Hyperkalaemia?
- Redistribution (Acidosis, Insulin deficiency with high glucose (DKA), Drugs (beta-blockers), Acute tissue damag, Hypoxia, Tumour lysis, Hyperkalaemic periodic paralysis)
- Increased Intake (supplement, Herbal medicines, IV Fluids
- Decreased Output (chronic renal failure, obstructive nephropathy, renal transplant, drugs, syndromes of hypoaldosteronism)
- Syndromes of Hypoaldosteronism
- Pseudohyperkalaemia (EDTA contamination, IV contamination, In vitro redistribution, haemolysis, cold, delayed centrifugation, release from WBC & platelets, Fragile cell syndrome)
Which drugs can induce hyperkalaemia?
Reduce aldosterone secretion
- ACE inhibitors,
- Angiotensin II receptor blockers
- NSAIDS, heparin
- Antifungals (ketaconazole, flucanazole)
- Cyclosporin, tacrolimus
Alter transmembrane K+ movement
- Beta blockers
- Digoxin
- Hyperosmolar solutions (mannitol, glucose & saline)
- Suxamethonium
Inhibit activity of epithelial sodium channel
- Potassium sparing diuretics (amiloride, tramterene)
- Trimethoprim
- Pentamidine
Block aldosterone binding to mineralocorticoid receptor
- Spironolactone
- Eplerenone
- Drospirenone
What is Hyperkalaemic Periodic Paralysis (HYPP)?
- Rare AD condition. Presents with muscle weakness and K+ up to 8.0 mmol/L
- Attacks variable, provoked by high K+ intake, glucocorticoids, hypothermia & recovery after exercise
- ECG show tall T waves but cardiac arrhythmias are rare
- Mutations in skeletal muscle voltage-gated sodium channel X subunit (SCN4A)
- Management salbutamol inhalers
What are laboratory investigations for Hyperkalaemia?
- Exclude spurious causes: Time / Date / Storage / WCC/ Plt /Ca/EDTA contamination
- Assess eGFR
- Assess acid-base status & glucose
- Check drug therapy
- Consider cortisol
- Check renin & aldosterone: Caution – high K+ stimulates aldosterone but suppresses renin. As eGFR falls – aldo increases & renin decreases
How is Hyperkalaemia managed?
- If plasma K>6.0mmol/l then check for EDTA contamination to ensure it is not an artefact.
- Ask for ECG to be done urgently in such patients.
- Calcium gluconate or chloride (i.e 10ml of 10% over 10mins may rpt until ECG improves) is used to stabilise the myocardium – ECG changes
- Salbutamol (10-20mg) is used for redistribution into cells – adjuvant severe & moderate. Insulin + Glucose – (10 units insulin in 25g glucose)If potassium remains high a continuous infusion of insulin and glucose may be required.
- Excretion is increased with Dialysis or Calcium resonium.
- Reduction in potassium load through medication review. Stop K+ supplement, ACE-i and K+ sparing diuretics
How is Excretion of potassium controlled?
Haemodialysis may be required in:
- Persistent hyperkalemia (>7mmol/l)
- Severe or worsening metabolic acidosis (pH <7.2)
- Uraemic pericarditis, encephalopathy, refractory pulmonary oedema.
Calcium resonium (mild/moderate)
- 15g four times daily or 30g enema in 100ml may be given in asymptomatic hyperkalemia. This takes a few days to take effect.
