Anaphylaxis Flashcards
Drugs - Pharmacology
What is an allergic reaction?
Hypersensitive reaction to a stimulus, or allergen, which a person has been previously exposed to and has created antibodies.
Usual cause of allergic reaction
Inhaled, ingested or injected antigen
What is Anaphylaxis?
Severe, life-threatening generalised or systemic hypersensitivity reaction
- characterised by airway and/or breathing problems
Histamine
- neurotransmitters also found in gut
- central receptors: within brain
- peripheral histamine receptors found in smooth muscle, endothelium and sensory nerves
- potent Bronchoconstrictor
- contained and released from degranulated mast cells
- exist within WBCs (Basophils)
Signs and Symptoms of Anaphylaxis
- Sudden onset and rapid progression of symptoms
- life-threatening airway, breathing or circulatory problems
- skin and/or mucosal changes
- hypotension
- abdominal pain
- diarrhoea and vomiting
- angio-oedema
Circulation Problems
- signs of shock = pale and clammy
- increased pulse rate (tachycardia)
- Low blood pressure (hypotension) = feeling faint, collapse
- myocardial ischemia and ECH changes in individuals with normal coronary arteries.
- cardiac arrest
Gastrointestinal Symptoms
- Vomiting and diarrhoea is common particularly if allergen is ingested
Pre-hospital Management of Anaphylaxis
- Adrenaline
- Oxygen
- Fluids
- Chlorphenamine
- Hydrocortisone
What should be monitored in Pre-hospital Management of Anaphylaxis?
Pulse Oximetry
ECG
Blood Pressure
Adrenaline
- Sympathomimetic
- Stimulates alpha and beta 1 and 2 receptors (non selective)
- increases vascular resistance (vasoconstriction) tachycardia
- positive ionotrope and chronotrope
Adrenaline Dosages
500mcg/0.5mg IM injection - repeat every 3-5 minutes
1/2 doses in patients with beta blockers
Oxygenation and nebulisation
- Maintain spO2 94%-98%
- 5mg salbutamol (nebuliser)
- selective B2 agonist relieves Bronchospasm
What is Chlorphenamine
- H1 receptor antagonist
- Does not prevent histamine release
- crosses blood-brain barrier easily causes sedation/drowsiness side effects
- can be used for symptom control in milder allergic reaction
Chlorphenamine Dosage
- 10mg in 2ml
- 10mg IV/IM injection
- Slow IV injection
- No repeated doses
What is Hydrocortisone?
- Anti-inflammatory
- prevents release of histamine
- reduces activity of phospholipase and prostaglandins
- delayed mechanism of action
- reduced severity of secondary and biphasic reactions
