Management options

Immediate management of severe reactions consists of intravenous adrenaline 100 mg boluses and fluids, with management of the airway and administration of oxygen. Aortocaval compression must be avoided at all times. Any potential for adrenaline to cause uteroplacental vasoconstriction and uterine hypotony is outweighed by the restoration of cardiac output. Intravenous chlorphenamine 10 mg and hydrocortisone 200 mg may be given to reduce the effects of subsequent inflammatory mediator release. For less severe reactions (e.g. urticaria only), chlorphenamine alone may suffice.

In an acute reaction, blood should be taken for tryptase levels at 1 and 6-24 hours. The enzyme is normally present in mast cells and in miniscule amounts in the plasma; an increase in plasma concentration therefore represents mast cell degranulation (but does not distinguish between anaphylactic and anaphylactoid reactions). Immunoglobulin and complement levels may be suggestive, but not diagnostic, of an allergic response. If a severe reaction is suspected, the patient should be referred for testing at least 4-6 weeks later; normally this will involve skin tests (prick testing + intradermal testing). Further tests may be performed on plasma (e.g. radioallergoabsorbent test (RAST) looking for concentrations of specific antibody, e.g. to latex) or occasionally basophils or other cellular components, if skin testing is not diagnostic. The patient should be advised to obtain a 'Medi-alert' bracelet and given written details of all the drugs tested and the results, in case she should require a subsequent anaesthetic. A copy of the letter should also be sent to her general practitioner.

It is important that mothers with a previous history of severe allergic reactions are identified antenatally. Wherever possible, the previous anaesthetic record should be obtained and a plan for her care documented. Management of the known allergic case includes a general state of readiness and awareness as well as the obvious avoidance of any known allergens. Latex allergic patients may be identified from the history in most cases by asking about food allergies and skin reactions after exposure, e.g. rubber gloves, condoms, etc. If patients have had a previous severe reaction where the allergen is unknown, pretreatment with H^- and H2-antagonists + steroids should be considered, although whether this should be routinely done if the allergen is known and can be avoided is controversial. Routine screening of all women by using skin or blood testing is generally not indicated, since precautions should be taken on the basis of a strong history even if testing produces negative results.

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