Anaphylaxis

Question 1

Define anaphylaxis.

Answer 1

Anaphylaxis is a severe, generalised or systemic hypersensitivity reaction, characterised by rapidly developing life-threatening airway and/or breathing and/or circulation problems usually associated with skin and mucosal changes

Question 2

What is the pathophysiology of anaphylaxis?

Answer 2

Release of histamine and other agents causes: capillary leak; wheeze; cyanosis; oedema (larynx, lids, tongue, lips); urticaria.

More common in atopic individuals.

An anaphylactoid reaction results from direct release of mediators from inflammatory cells, without involving antibodies, usually in response to a drug, eg acetylcysteine

Question 3

List some precipitants of anaphylaxis.

Answer 3

• Drugs, eg penicillin, and contrast media in radiology.
• Latex.
• Stings, eggs, fish, peanuts, strawberries, semen (rare).
• Exercise, cold

Question 4

What are the signs and symptoms of anaphylaxis?

Answer 4

• Itching, sweating, diarrhoea and vomiting, erythema, urticaria, oedema.
• Wheeze, laryngeal obstruction, cyanosis.
• Tachycardia, hypotension.

Question 5

What conditions can mimic anaphylaxis?

Answer 5

• Carcinoid
• Phaemochromocytoma
• Systemic mastocytosis
• Hereditary angioedema

Question 6

How do you manage anaphylaxis?

Answer 6

• Oxygen
• Raise feet
• Adrenaline 0.5mg IM
• IV 200mg hydrocortisone and 10mg chlorphenamine(
• Saline 500mL over 15mins
• If still hypotensive/wheezy ICU then ventialtory support, adrenaline +/- aminophylline and salbutamol nebuliser

Question 7

How is adrenaline administered?

Answer 7

Adrenaline given IM

Given IV if the patient is severely ill or has no pulse AND IV dose is dofferent (100mcg/min - titrating with response - this is 0.5mL of 1:10,000 solution iv per minute.)

If on a β‎-blocker, consider salbutamol iv in place of adrenaline.

Question 8

What investigations would you do in anaphylaxis?

Answer 8

Bloods:

• Mast cell tryptase - elevated; undetectable in people who have not had anaphylactic reaction in preceding hours; but non specific
• 12 lead ECG - non specific ST changes post adrenaline
• U&E - normal unless comorbidity
• ABG - elevated lactate

Imaging:

• CXR - only after time-critical intervention administered; may show hyperinflation if bronchoconstriction; interstitial fluid

Question 9

What are the complications of anaphylaxis?

Answer 9

MI - ischaemia could be triggered by hypotension or hypertension with tachycardia after adrenaline

Recurrence of anaphylaxis - higher risk of recurrence but severity not necessarily greater

Question 10

What is the prognosis with anaphylaxis?

Answer 10

Depend on the success of immunotherapy, allergen avoidance, and compliance with carrying their adrenaline (epinephrine) auto-injectors.

Question 11

How common is anaphylaxis?

Answer 11

• Prevalence between 1-7% of US population where 0.002% die from anaphylactic reaction
• NHS anaphylaxis hospital admissions in England for all causes in children and young people under 18 has risen by around 70% in last 5 years (so have adult cases)

Question 12

What is the dose of adrenaline administered for anaphylaxis?

Answer 12

Dose of IM adrenaline is 500mcg or 0.5ml of 1 in 1000 adrenaline

Question 13

How common are side-effects of non-ionic contrast agents? Name some side-effects.

Answer 13

Rare

Most side effects of these contrast agents are mild and self-limiting and even these are unusual e.g headache, vomiting, rash.

Non-ionic contrast agents are excreted by the kidneys and are nephrotoxic – the elderly, patients with myeloma and known renal impairment are all at risk. They may also exacerbate asthma. They may precipitate lactic acidosis in diabetic patients taking metformin.