Anaesthetic Emergency - Anaphylaxis, MH, Spasms Flashcards
What is an anaphylaxis/ anaphylactic reaction?
Anaphylaxis is a life-threatening syndrome triggered by a wide range of antigens and involves multiple organ systems. An anaphylactic reaction is an example of a type I hypersensitivity reaction. It occurs after exposure to a foreign protein (antigen) that stimulates the production of IgE antibodies. After the initial exposure, antibody concentrations decease, but IgE binds to mast cells and basophils. If there is further exposure, the antigen binds with IgE antibodies and results in the release of mediators, including histamine, slow-reacting substance-A (SRS-A), leukotrienes, tryptase and prostaglandins. These substances increase mucous secretion, bronchial smooth muscle tone and vascular permeability, causing airway oedema, bronchospasm and hypotension.
What differentiates anaphylaxis from anaphylactoid?
Clinically difficult to differentiate, but the physiological process is different in that they are not mediated by sensitising IgE antibodies nor do they involve previous exposure to the antigen. The underlying mechanisms include the release of vasoactive substances (e.g. histamine), direct histamine release from mast cells or compliment activation, by either the classical or alternative pathways. Anaphylactoid reactions are most commonly seen in reactions to contrast media.
Which anaesthetic drugs can directly cause histamine release?
atracurium, mivacurium, morphine and meperidine.
What is the anaphylaxis drill?
Immediate management: Stop the administration of all agents likely to have caused the anaphylaxis. Call for help. Maintain the airway, give oxygen 100% and lie the patient flat with the legs elevated. ADRENALINE 0.5mg 1:1000, repeat in 5 mins if no improvement Alternatively, 50–100 µg i.v. (0.5–1 ml of 1:10 000) over 1 min has been recommended for patients with cardiovascular collapse, with titration of further doses as required. This should be given at a rate of 0.1 mg min−1 stopping when a response has been obtained. It is important that undiluted epinephrine 1:1000 is never given i.v. Give i.v. fluid with colloid or crystalloid (avoiding colloids that have a higher incidence of allergy). Adult patients may require 2–4 litre. Subsequent management 1. Chloraphenamine 10mg IV 2. HYDROCORTISONE 200mg Bronchodilators may be required for persistent bronchospasm. Catecholamine infusion as CVS instability may last several hours. Epinephrine 0.05–0.1 mg kg−1 min−1 (4 ml h−1 of 1:10 000 for 70 kg adult). Check ABGs for acidosis and consider bicarbonate 0.5–1.0 mmol kg−1 (8.4% solution = 1 mmol ml−1).
What are immediate investigations for anaphylaxis?
Mast cell tryptase concentration at these points: (i) immediately after the reaction has been treated (ii) about 1 h after the reaction (iii) about 6 h or up to 24 h after the reaction. It increases after both anaphylactic and anaphylactoid reactions and helps to distinguish these from other causes of an adverse event Longer term: Referal to specialist allergy centre The allergist will perform skin prick tests for general anaesthetic drugs, which show the presence of specific IgE antibodies to these drugs.
