Asthma and Allergy – Anaphylaxis and allergy emergencies

Anaphylaxis

Written by Dr A I Manjra

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Anaphylaxis is a life threatening condition. It is therefore essential that prevention should at all times be the basis of management in high risk patients. Evaluation of every high risk patient should include taking a detailed medical history particularly previous allergic reactions, the nature, degree, duration and severity of these reactions.

 

Common Agents involved in Anaphylaxis and their mechanisms

I. IgE-Mediated Agents

(1) Antibiotics

Penicillin

Cephalosporins

Tetracycline

Nitrofurantoin

Vancomycin

Chloramphenicol

Bacitracin

Neomycin

Kanamycin

Amphoterin B

(2) Foods

Milk
Egg
Peanut
Fish
Legumes
Bananas
Beet
Mango
Metabisulphites

(3) Foreign Proteins

Heterologous serum
ACTH
Insulin
Hymenoptera
PTH
Relaxin

(4) Therapeutic agents

Allergen extracts
Muscle Relaxants
Steroids
Vaccines
Streptokinase

II. Immune Complex or Complement Mediated

(1) Whole blood
(2) Immunoglobulins
(3) Plasma
(4) Methotrexate

III. Modulators of Arachidonic Acid Metabolism

(1) Aspirin
(2) NSAIDS
(3) Tartrazine
(4) Benzoates

IV. Direct Histamine Releasing Agents

(1) Opiates
(2) Curare
(3) Dextrate
(4) Radiocontrast media
(5) Mannitol

Management

If an agent is suspected from the history of causing a previous allergic reaction or if drugs that commonly cause allergy are to be used, it may be worthwhile to determine patient sensitivity either by RAST or skin testing. Direct skin testing does carry the risk of inducing an anaphylactic reaction and must therefore be conducted by trained personnel with resuscitation equipment available. It may be therefore preferable to do RAST testing for Hymenoptera venom allergy.

In certain situations, use of drugs to which a patient is allergic to may be life saving or medically necessary. Desensitisation may need to be carried out before use of the drug. Desensitisation is a risky, life threatening procedure and should only be carried out by highly trained doctors in an intensive care unit. The procedure involves administering gradually increasing doses of drugs initially intradermally, then subcutaneously and eventually intravenously. In penicillin or aspirin allergy oral desensitisation is not always successful and may need to be repeated for subsequent use of the same drug.

The following general rules must be followed after an anaphylactic reaction:

• (1) Avoid exposure to the allergen known to cause the reaction.
• (2) Avoid cross reacting allergens as well.
• (3) Use oral rather than intravenous or intramuscular route.
• (4) Observe patients after injections.
• (5) Patients must wear their Medic-Alert bracelets at all times.
• (6) Patients should be trained to self-administer adrenalin either subcutaneously or inhaled.
• (7) Avoid b blockers in patients with a history of anaphylaxis.
• (8) In patients undergoing immunotherapy ensure the correct allergen extract and right dose is used. Observe patient in waiting room for at least 30-45 minutes after the injection.

Treatment

The aim of treatment is to ensure oxygenation, perfusion, preventing mediator release and counteracting the effect of the mediators already in the circulation. RAPID RESUSCITATION IS LIFE SAVING. Treatment must be individualised. Initial assessment should involve assessing the extent and severity of the reaction, discontinuation of administrating the offending allergen and close monitoring of vital signs i.e. airway, breathing, blood pressure, tissue perfusion and mental status.

Drugs:

(1) Adrenalin

This is the first line treatment. Adrenalin in an aqueous solution is administered subcutaneously (0.3-0.5mls of 1:1000 dilution). If anaphylaxis is caused by an insect sting or injection, an additional dose should be administered. If shock or cardiovascular collapse persists, diluted adrenalin can be given intravenously i.e. 0.1ml in 10ml of normal saline over 10 minutes. A continuous infusion can be started if the response is poor. Add 1ml of 1:1000 dilution in 250ml of 5% dextrose water. The infusion can be started at 1mg per minute. In children however start the infusion at 0.1mg/kg per minute. Treatment should be individualised and extreme caution should be noted in the elderly, very young and those with cardiovascular disease.
One study has demonstrated that inhalation of high dose adrenalin is useful in patients with anaphylaxis. Higher doses need to be used by inhalation since the absorption that occurs is dose dependent. However, the rate of absorption was more rapid than after subcutaneous injection.

Adrenalin has alpha, b-1 and b-2 actively. The adrenalin actively restores blood pressure and causes peripheral vasoconstriction, thereby reducing angio-oedema and urticaria. The b-2-agonist properties produce bronchodilation and a positive ionotropic effect on the heart. The b-2-agonist properties also prevent further mediator release from the mast cell.

(2) Oxygen

This should be administered as soon as possible via mask or nasal cannula. About 40-100% oxygen may be needed depending on the degree of hypoxia.

(3) Volume expansion

Intravenous access should be established early in the treatment to administer drugs and fluids. Plasma volume expanders may be necessary to maintain blood pressure. If the blood pressure does become a problem to maintain, invasive monitoring may be necessary. Dopamine can be used to restore blood pressure to normal. ½ strength Darrows Solution can be used in children whereas 5% Dextrose in half normal saline is suitable for adults. In adults, 1-2 litres in the first hour may be required whereas in children 30mls/kg in the first hour will suffice.

(4) Antihistamines

It must be remembered that large amounts of histamine are already present in the circulation occupying the receptors and that other mediators are also involved in the generation of symptoms of anaphylaxis. However by administering antihistamine further evolution of symptoms such as angio-oedema, urticaria and pruritus can be significantly reduced. Diphenhydramine (Benadryl) is given intravenously (very slowly over 5-10 minutes), intramuscularly or orally at a dose of 1mg/kg up to 50mg when the patient is haemodynamically stable. The dose should be repeated every six hours orally for about 48 hours.

(5) Steroids

The rationale for steroid use is to prevent bronchospasm progression or recurrence of symptoms. They do not play a major role in the acute management of anaphylaxis. They should however be used early in the management. The recommended drugs are either hydrocortisone intravenously at a dose of 7-10mg/kg stat followed by 5mg/kg ever six hourly until the patient is stabilised. Alternatively methylprednisolone can be administered at a dose of 2mg/kg every six hourly until the patient has stabilised.

Other Treatment

Patients with bronchospasm should preferably be treated with inhaled b-2-agonsits rather than intravenous aminophylline because of the inherent risk involved with myocardial infarction and cardiac arrhythimias. Glucagon can be used for refractory hypotension. Patients may need to be intubated early to treat hypoxaemia. This may be difficult or almost impossible once laryngeal oedema has occurred.

Treatment may need to be continued until all vital signs have returned to normal. This may continue for several days.

Prognosis is generally good but most fatalities occur within the first hour. In most patients recovery is usually complete. However patients experiencing myocardial infarction or brain damage may have significant residual morbidity.

Summary

Management of Anaphylaxis
DRUG		DOSE	INDICATION			SIDE EFFECT
General: Adrenalin (1:1000) Dilution		0.3-0.5mls Subcutaneously Repeat every 5-20 min. as needed. (max: 3 times)	Bronchospasm Urticaria Angio-oedema Laryngeal oedema			Arrhythmia Hypertension Tremor Tachycardia
Add 1ml in 250ml dextrose water for persistent hypotension Adults Infuse at 1m g/ to max 4 m g/min. Paed

Infuse at 0.1 m g/kg/min and increase by increments of 0.1 m g/kg/min till 1.5 m g/kg/min.

Oxygen

40-100%

• Hypoxia

Diphenhydramine

1mg/kg slowly IVl,imi or p.o. (max. 50mg)

• Pruritus
• Urticaria

• Drowsiness
• Dry Mouth
• Urinary Retention

 

 

RESPIRATORY MANAGEMENT
DRUG	DOSE	INDICATION	SIDE EFFECT
Nebulised Adrenalin	0.5mls to 2 ml saline via Nebuliser,	Severe upper airway obstruction oedema
Intubation or Tracheostomy		If unresponsive to above
Nebulised Salbutamol	1ml in 1ml Saline (repeat p.r.n.)	Bronchospasm	Tremor Tachycardia
Aminophylline	6mg/kg IVI Over 20 min. Thereafter 0.5-1mg/kg/hr.	Bronchospasm	Cardiac arrhythmia convulsion

 

 

Hypotension: Summary

Volume Expansion Adults: 1-2 litres of dextrose saline solution Children: 30mls/kg in the 1st hour of ½ hour of ½ dextrose Darrows. Plasma: 20mls/kg over 20 mins or Dextran or Haemacel. Adrenalin (see above). Dopamine 5-20mg/kg/min IVI. Glucagon for protracted hypotension 1mg IVI in 1 litre 5% dextrose water at 5-15mls/min. Trendelenberg position.