Revision - Anaphylaxis & Electrolytes Flashcards
What blood test can be done to confirm anaphylaxis?
Serum tryptase within 6 hours of event (tryptase is released during mast cell degranulation)
When can discharge following anaphylaxis be considered in the following scenarios:
1) good response to single dose of adrenaline
2) needed 2x doses of adrenaline
3) previously had a biphasic reaction
4) needed >2x doses of adrenaline
5) also has severe asthma
6) present late at night
1) min 2 hours after symptom resolution
2) min 6 hours
3) min 6 hours
4) min 12 hours
5) min 12 hours
6) min 12 hours
What is ADH released in response to?
Increased serum osmolality –> leads to increased water retention in the collecting ducts in the kidneys
How does water ingestion not lead to hyponatraemia?
As water ingestion causes suppression of ADH –> water is excreted in dilute urine
How does SIADH affect sodium?
Hyponatraemia
Where is ADH released from?
Posterior pituitary
What are the 2 main way that sodium is lost through the kidneys?
1) Medications e.g. diuretics
2) Shortage of steroid hormones e.g. aldosterone, cortisol (to a lesser extent)
Which 3 medications can lead to hyponatraemia?
1) Loop diuretics
2) Thiazide diuretics
3) K+ sparing diuretics
(also SSRIs)
1st step in assessment of hyponatraemia?
Calculate serum osmolality –> is it a true hyponatraemia or not?
Serum osmolality in a true hyponatraemia?
Low
How does HHS cause low sodium and high osmolarity?
1) Blood glucose goes up very high
2) Glucose leaks into urine
3) Water & sodium follow glucose into urine
4) Concentrates glucose in blood
Which diuretic is most likely to cause renal sodium loss?
Thiazide-like diuretics
Patient is hyponatraemic and hypovolaemic.
What is cause of hyponatraemia?
DECREASED SODIUM
1) Sodium loss:
- renal loss
- loss from elsewhere e.g. GI, transdermal
2) Inadequate sodium intake (rare)
Patient is hyponatraemic and hypervolaemic.
What is cause of hyponatraemia?
In a fluid overloaded patient, fluid accumulates in the extracellular (‘third’) space. This extra fluid causes a dilutional effect on serum sodium, causing hyponatraemia.
I.e. more water than sodium, leading to a relative sodium deficiency.
What are the 4 main causes of hypervolaemic hyponatraemia?
1) CCF
2) Liver cirrhosis
3) End stage renal failure
4) Nephrotic syndrome
How can liver cirrhosis lead to hypervolaemic hyponatraemia?
Hypoalbuminaemia
How can nephrotic syndrome lead to hypervolaemic hyponatraemia?
Hypoalbuminaemia
How can hypoalbuminaemia cause hyponatraemia?
Decreases plasma oncotic pressure –> fluid accumulates in the extracellular space
Patient is hyponatraemic and euvolaemic.
What is cause of hyponatraemia?
Most commonly SIADH
Under normal conditions, what should happen to urine osmolality when serum sodium (and serum osmolality) is low?
Urine osmolality should be decreased as the body attempts to conserve sodium by producing dilute urine.
Think about when you’re really hydrated!
In euvolaemic hyponatraemia, if the urine osmolality is raised (>300mOsm/kg), what is the diagnosis?
SIADH.
A raised urine osmolality in the presence of low serum osmolality suggests SIADH, as the kidney is inappropriately producing concentrated urine despite low serum osmolality.
In euvolaemic hyponatraemia, if the urine osmolality is decreased (<300mOsm/kg), what is the diagnosis?
Water intoxication may be the cause (primary polydipsia).
Who is primary polydipsia seen in?
- psychiatric disturbances
- use of ectasy
- severe hypothyroidism
- glucocorticoid deficiency.
Managemnt of acute hyponatraemia with severe neurological symptoms (e.g. seizures, severe drowsiness)?
Medical emergency
1) IV hypertonic saline bolus (100ml 3% NaCl)
2) Close monitoring of serum sodium
Goal of sodium correction rate in hyponatraemia without severe neuro symptoms?
No more than 6 mmol/L in the first 6 hours
No more than 10 mmol/L in the first 24h
If the sodium is corrected too quickly in hyponatraemia, what is the patient at risk of?
Osmotic demyelination syndrome
Management of hypovolaemic hyponatraemia?
Rehydration with IV 0.9% normal saline, with regular monitoring of serum sodium.
Management of hypervolaemic hyponatraemia?
Fluid restriction (<1.5L/24h), with regular monitoring of serum sodium.
Management of euvolaemic hyponatraemia?
Fluid restriction (1.5L/24h), with regular monitoring of serum sodium.
When does osmotic demyelination syndrome typically present?
2-4 days after treatment
What are 3 drugs that can cause SIADH?
1) SSRIs
2) Amitriptyline
3) Carbamazepine
What hormonal abnormality can cause SIADH?
Hypothyroidism
What are the 6 features that must be present for a diagnosis of SIADH to be made?
1) hyponatraemia
2) low plasma osmolality
3) euvolaemia
4) inappropriately elevated urine osmolality (i.e. greater than plasma osmolality)
5) urine [Na+] >40 mmol/L despite normal salt intake
6) normal thyroid and adrenal function
Mx of SIADH?
Fluid restriction
ECG features of hyperkalaemia vs hypokalaemia
Hyperkalaemia:
- flattended p waves
- tall t waves
- PR prolongation
- wide QRS
Hypokalaemia:
- U waves
- T wave inversion
- ST depression
How can trauma or burns lead to hyperkalaemia?
Tissue damage sustained secondary to trauma or burns results in the release of significant volumes of potassium from damaged cells.
When is oral vs IV potassium replacement indicated in hypokalaemia?
1) If potassium is >3mmol/L, the patient is asymptomatic, and there are no ECG changes –> oral potassium replacement can be given.
2) If potassium is <3mmol/L (severe hypokalaemia) or ECG changes are present –> IV potassium replacement is indicated.
What is a ‘corrected’ calcium?
Most laboratories report a ‘corrected calcium’ alongside total calcium, in which the serum calcium level is adjusted for the serum albumin level.
What can sometimes be used in hypercalcaemia mx in patients who cannot tolerate aggressive fluid rehydration?
Loop diuretics
What 2 electrolyte disturbances can cause torsades de pointes?
1) hypokalaemia
2) hypomagnesaemia
What precipitates torsades de pointes?
Prolonged QT
Mx of mild/moderate hypocalcaemia vs severe hypocalcaemia (e.g. prolonged QT, carpopedal spasm etc)?
Mild/moderate –> oral calcium repalcement e.g. calcium carbonate
Severe –> IV calcium gluconate (10ml 10%)
What is cinacalcet?
a calcium-sensing receptor agonist that reduces PTH secretion
(used in mx of hyperparathyroidism)
What electrolyte disturbance presents similarly to hypocalcaemia?
Hypomagnesaemia
