Potassium Flashcards
HYPOKALAEMIA - Features
Hypokalaemia: features
Features
- muscle weakness, hypotonia
- hypokalaemia predisposes patients to digoxin toxicity care should be taken if patients are also on diuretics
HYPOKALAEMIA - ECG Features
ECG features: U waves small or absent T waves prolonged PR interval ST depression Long QT
In Hypokalaemia U have no Pot and no T but a long PR and a long QT
The U wave is a small (0.5 mm) deflection immediately following the T wave
U wave is usually in the same direction as the T wave.
U wave is best seen in leads V2 and V3.
HYPOKALAEMIA with ACIDOSIS - Differentials
Hypokalaemia with acidosis
- Diarrhoea
- Renal tubular acidosis Types 1 and 2
- Acetazolamide
- Partially treated diabetic ketoacidosis
- Theophylline Toxicity
HYPOKALAEMIA with ALKALOSIS - Differentials
Hypokalaemia with alkalosis:
- vomiting
- diuretics
- Cushing’s syndrome
- Conn’s syndrome (primary hyperaldosteronism)
Also
- Bartter’s
- Gitelman’s
- Liddle’s
Potassium and Magnesium
Magnesium deficiency may also cause hypokalaemia. In such cases, normalizing the potassium level may be difficult until the magnesium deficiency has been corrected
Drugs causing Hyperkalaemia
Potassium sparing diuretics eg Spironolactone
ACE Inhibitors
ARBs
Ciclopsporin
Heparin
Beta-blockers (NB Beta-agonists used in emergency Mx of Hyperkalaemia)
Hypokalaemia and HTN
For exams it is useful to be able to classify the causes of hypokalaemia in to those associated with hypertension, and those which are not
Hypokalaemia with hypertension
Cushing’s syndrome (Low Renin, High Aldosterone)
Conn’s syndrome (Low Renin, High Aldosterone)
Liddle’s syndrome (Low Renin, Low Aldosterone)
11-beta hydroxylase deficiency*
Renal artery stenosis (High Renin, High Aldosterone)
Ix to differentiate = Plasma Renin and Aldosterone
Carbenoxolone, an anti-ulcer drug, and liquorice excess can potentially cause hypokalaemia associated with hypertension
*21-hydroxylase deficiency, which accounts for 90% of congenital adrenal hyperplasia cases, is not associated with hypertension
Hypokalaemia WITHOUT HTN
Hypokalaemia without hypertension
Diuretics GI loss (e.g. Diarrhoea, vomiting) renal tubular acidosis (type 1 and 2**) Bartter's syndrome Gitelman syndrome
**type 4 renal tubular acidosis is associated with hyperkalaemia
Hypokalaemic Periodic Paralysis
Hypokalaemic periodic paralysis
Hypokalaemic periodic paralysis is a rare autosomal dominant disorder characterised by episodes of paralysis, typically occur at night. The underlying defect is a mutation in muscle voltage-gated calcium channels. Attacks may be precipitated by carbohydrate meals
Management
lifelong potassium supplementation
Example Question:
A 17 year old girl is brought into A&E by her mother. The patient appears terrified after she experienced an episode on waking earlier in the morning when she could not move at all for 2 hours. This was her second episode. She reports no loss of consciousness and was aware throughout the episode. She has no other past medical history documented. She is not aware of a previous episode of epilepsy. On examination, her heart sounds and breath sounds are unremarkable. Neurological examination demonstrated no abnormalities. She normal dentition and her BMI is 19.5. A 12 lead ECG demonstrated a jerky baseline with flat T waves. What is the diagnosis?
Partial or absence seizures Guillain Barre syndrome Botulinum toxicity Myasthenia gravis > Hypokalaemia
The patient describes episode of periodic paralysis and the ECG characteristics are consistent with that of hypokaelamia. The underlying diagnosis is a rare familial condition of skeletal muscle ion channels called hypokaelamc periodic paralysis, onset most commonly in childhood and adolescents. Attacks last hours and neurological examination is normally unremarkable in between attacks. The average K+ on diagnosis is 2.4 mmol/L1. Diagnosis is often made clinically in association with low potassium but genetic testing can help if known mutations are present.
- Miller TM, Dias da Silva MR, Miller HA et al. Correlating phenotype and genotype in the periodic paralyses. Neurology. 2004;63(9):1647.
Hypokalaemic Alkalosis - Example Question
A 32 year-old man is referred by his GP after collapsing while at work. He does not remember the episode but witnesses say that there was no incontinence or fitting and the patient does not have a sore mouth or tongue. This is the first time this has happened and the patient does not have any other past medical history of note and takes no regular medication.
Examination reveals a blood pressure of 162/95 mmHg, a pulse of 74 beats per minute, a respiratory rate of 16 and a temperature of 37.4ºC. Heart sounds 1 and 2 are present with no added sounds, the lung fields are clear and his abdomen is soft and non-tender.
Blood tests performed and reveal:
Na+ 143 mmol/l K+ 3.0 mmol/l Urea 5.6 mmol/l Creatinine 76 µmol/l Bicarbonate 31 mmol/l Renin low Aldosterone low
Which of the following is the best treatment?
> Amiloride Bumetanide Spironolactone ACE inhibitor Angiotensin II receptor blocker
This man has Liddle’s syndrome, an autosomal dominant disorder characterised by hypertension associated with hypokalaemic metabolic alkalosis, low plasma renin activity, and suppressed aldosterone secretion. Amiloride is the best treatment for the hypertension and hypokalaemia as it acts on the sodium channels directly, as opposed to spironolactone, which acts on mineralocorticoid receptors.
Liddle’s syndrome is a rare autosomal dominant condition that causes hypertension and hypokalaemic alkalosis. It is thought to be caused by disordered sodium channels in the distal tubules leading to increased reabsorption of sodium.
Treatment is with either amiloride or triamterene
Hypokalaemic Periodic Paralysis - Example Question
A 19 year old gentleman with a background history of asthma presents to the Emergency Department complaining of leg weakness and the inability to walk. He had run a marathon the day before. On examination there is 3/5 weakness of the leg extensors bilaterally. Tone, reflexes and coordination are unimpaired and plantars are downgoing bilaterally. Straight leg raise and sensation to light touch and pain stimulus are unimpaired.
Blood tests show the following:
Hb 13.4g/dl WBC 6.2 x 109/l Na+ 136mmol/l K+ 2.9mmol/l Urea 6.8mmol/l Creatinine 104µmol/l
What is the most appropriate treatment in this case?
Oral potassium and encourage bed rest Hourly forced vital capacity measurements and plasma exchange > Oral potassium and encourage gentle exercise Hourly forced vital capacity measurements and IV immunoglobulin Plasma exchange and oral potassium supplementation
Hypokalaemic periodic paralysis is a rare autosomal dominant periodic paralysis but can also occur as a result of a spontaneous mutation (a third of cases have no family history). Attacks often occur in the morning with a history of strenuous exercise or a high carbohydrate meal the day before or may be provoked by stress eg. infections, lack of sleep. Weakness can range from an isolated muscle group to generalised weakness and tends to affect proximal muscles first.
Serum potassium decreases during attacks but may not necessarily fall below the normal range (3.5 -5mmol/l).
The mainstay of treatment for an acute attack is oral potassium supplementation and encouragement of gentle exercise. Intravenous potassium is reserved for those unable to swallow or with cardiac arrhythmias. Acetozolamide or dichlorphenamide are used as first line prophylactic agents.
Hypokalaemia Diagnosis - Example Question
A 27-year-old female was seen in the general medicine outpatient clinic following a referral by her GP. She had presented to her GP feeling generally tired for the last few months. Her GP organised a blood screen revealing no abnormalities except the presence of a potassium level of 2.8 mmol/l. Her GP subsequently repeated the test four weeks later revealing a level of 2.6 mmol/l, leading to the referral to the clinic. Other than the tiredness she was well in herself, denying all other symptoms. She denied specifically the presence of any cardiovascular and muscular symptoms and had never collapsed. Her past medical history was unremarkable and she was taking no prescribed medication. There was no family history of note.
Examination revealed a well 27-year-old lady. Her blood pressure was 108/78 mmHg, heart rate 82 bpm and BMI 23kg/m². Examination of her cardiovascular and respiratory systems revealed the presence of normal heart sounds, a JVP of 3cm and warm well perfused peripheries. Examination of her gastrointestinal and neurological systems was unremarkable.
Investigations conducted at the clinic revealed the following results:
Hb 122 g/l
Platelets 242 * 109/l
WBC 7.8 * 109/l
Na+ 132 mmol/l K+ 2.5 mmol/l Urea 7.2 mmol/l Creatinine 68 µmol/l Bicarbonate 37 mmol/l
Serum renin 824 (NR 100-500 pmol/l)
Serum aldosterone 82 (NR 55-250 pmol/l)
TSH 1.2 mu/l
24 hour urine result:
Na+ 28 (NR <20mmol/L if hyponatraemia)
K+ 45 (NR <10mmol/l if hypokalaemic)
Calcium 0.8 (NR <7.5 mmol/24hrs)
What is the most likely diagnosis?
Addison's disease > Gitelman's syndrome Conn's disease Bartter's syndrome Laxative abuse
Gitelman’s syndrome is an autosomal recessive disorder resulting in a normotensive hypokalaemic metabolic alkalosis with hypocalciuria and is often accompanied with hypomagnesaemia. The defect is in the thiazide-sensitive sodium chloride symporter within the distal convoluted tubules, in contrast to Bartter’s syndrome which presents in the same way but with hypercalciuria owing to a defect within the ascending loop of Henle. Patients with both conditions are often asymptomatic or may complain of fatigue, cramps and weakness. Conn’s disease is associated with hypertension and in this instance the aldosterone level is normal with an elevated renin, making this diagnosis unlikely. Both Addison’s disease and laxative abuse are associated with a metabolic acidosis; in Addison’s serum potassium also tends to be elevated. The best answer is, therefore, Gitelman’s syndrome.
Hypokalaemia - Example Question
A 23 year old with known ulcerative colitis presents for the fourth time in 6 months with a severe flare. On examination, he has a distended and generally tender abdomen. He was treated with intravenous hydrocortisone, standard 0.9% saline intravenous fluids and thromboprophylaxis. Although AXR demonstrated dilated large bowel loops, no operation was deemed necessary after surgical. The same treatment continued for 3 days. On day 3 of his admission, he reports chest pain with palpations. A 12 lead ECG was taken:
SEE PASSMED PIC ECG HYPOKALAEMIA
What is the underlying diagnosis?
Hypokalaemia
Hypokaelamia is a common consequence following extensive GI losses, in addition to bicarbonate and chloride losses. In this case, lack of potassium replacement resulted in tachyarrhythmia with U waves (see extra complex after the T wave). The patient may well be intravenously dry as well but while this may result in tachycardia, it does not explain U waves.
Patient presenting with Hypokalaemia, metabolic alkalosis and a normal-high BP - Differentials?!
- Diuretic Abuse
- Gitelman’s syndrome
- Bartter’s syndrome
Diuretic abuse:
NB: Of these three, the most common cause is diuretic abuse, especially in young women, and can be ruled out with a urine diuretic assay.
Bartter’s syndrome:
Bartter’s syndrome presents early in life, with classical features of triangular facies, polyuria, polydipsia and renal failure. Serum renin and aldosterone levels are high despite a low or normal blood pressure. Urine calcium may be raised, and renal stones are a common feature.
In Gitelman’s syndrome patients may present later on in adulthood, but have a milder disease course or may be asymptomatic compared to patients with Bartter’s syndrome.
NB: Hypomagnesaemia and hypocalciuria differentiates Gitelman’s syndrome from Bartter’s syndrome.
Hypokalaemia - Example Question
A 19-year-old girl was seen in clinic with lethargy, weakness worsening over the past 4 weeks. She also complains of recurrent muscle cramps in her legs, causing her to have trouble sleeping. On further questioning she admits to urinary frequency, passing urine up to ten times a day, and feels dehydrated all the time. She also mentions that her periods which were usually irregular, have stopped 4 months ago.
On examination, she is thin, with a body mass index of 17kg/m². Her heart rate is 88 bpm and blood pressure is 108/86 mmHg.
C Reactive protein 2mg/l Haemoglobin 158 g/l White cell count 7.6 x 10^9/L Na+ 136 mmol/l K+ 2.9 mmol/l Urea 7.2 mmol/l Creatinine 108 µmol/l Corrected calcium 2.42 mmol/l
Venous blood gas result
pH 7.532
Bicarbonate 37mmol/l
What would be the next most useful investigation?
> URINE DIURETIC ASSAY
Transvaginal ultrasound (TVUS) of the ovaries Urine diuretic assay Early morning cortisol Serum renin and aldosterone levels Fasting blood glucose levels
Patients with hypokalaemia, metabolic alkalosis and a normal - low blood pressure the following differentials should be considered - diuretic abuse, Bartter’s syndrome, Gitelman’s syndrome. Of the three, the most common cause is diuretic abuse, especially in young women, and can be ruled out with a urine diuretic assay.
Bartter’s syndrome presents early in life, with classical features of triangular facies, polyuria, polydipsia and renal failure. Serum renin and aldosterone levels are high despite a low or normal blood pressure. Urine calcium may be raised, and renal stones are a common feature. In Gitelman’s syndrome patients may present later on in adulthood, but have a milder disease course or may be asymptomatic compared to patients with Bartter’s syndrome. Hypomagnesaemia and hypocalciuria differentiates Gitelman’s syndrome from Bartter’s syndrome.
This patient may need other further investigations such as a TVUS, early morning cortisol and fasting blood glucose tests to rule out other conditions, but in view of her biochemistry profile, a urine diuretic assay would be the most useful next investigation to perform.
