Life-threatening emergencies
Anaphylaxis
Anaphylaxis is a generalized immunological condition of sudden onset which develops after exposure to a foreign substance in a previously sensitized person.
The mechanism may involve:
an IgE mediated reaction to a foreign protein (stings, foods, streptokinase), or to a protein-hapten conjugate (antibiotics).
complement mediated: (human proteins eg خ³-globulin, blood products)
unknown (aspirin, â€کidiopathic’)
Irrespective of the mechanism, chemical mediators (histamine, kallikreins/kinins, prostaglandins, platelet activating factors and leukotrienes) are released from mast cells and basophils, to produce clinical manifestations.
Common causes of anaphylaxis
drugs (antibiotics, especially penicillins, streptokinase, aspirin, NSAIDs)
hymenoptera (bee/wasp) stings
foods (nuts, shellfish, strawberries)
vaccines
Clinical features
The speed of onset and severity vary according to the nature and amount of the stimulus, but the onset is usually in mins/hrs. A prodromal aura, or a feeling of impending death may be present. Patients on أں-blockers or with a history of IHD or asthma may have especially severe features.
Respiratory system
Swelling of lips, tongue, pharynx and epiglottis may lead to complete upper airway occlusion. Lower airway involvement with features similar to acute severe asthma may develop—dyspnoea, wheeze, chest tightness, hypoxia and hypercapnia.
Skin
Pruritus, erythema, urticaria and angio-oedema.
Cardiovascular
Peripheral vasodilation and ↑vascular permeability cause plasma leakage from the circulation, with ↓intravascular volume, hypotension and shock. Arrhythmias, ischaemic chest pain and ECG changes may be present.
GI tract
Nausea, vomiting, diarrhoea, abdominal cramps.
Additional notes
Discontinue further administration of suspected factor (eg drug). Remove stings using forceps or by scraping the sting carefully away from skin.
Give 100% O2. Open and maintain airway (if upper airway oedema is present, emergency tracheal intubation or a surgical airway and ventilation may be required).
If bronchospasm is present, give salbutamol 5mg nebulized with O2.
Give only 50% of the usual dose of adrenaline/epinephrine to patients who are taking tricyclic antidepressants or MAOIs.
Even slow dilute IV adrenaline/epinephrine may be hazardous and so is only considered for use by an expert in the presence of life-threatening features.
Admit and observe after initial treatment: prolonged reactions/relapses may occur.
Report anaphylactic reactions related to drugs or vaccines to the Committee on Safety of Medicines. Further investigation of the cause (and in some cases, desensitisation) may be indicated. Where identified, the patient and GP must be informed and the hospital records appropriately labelled. Medic-alert bracelets may be useful.
An inhaled beta2-agonist such as salbutamol may be used as an adjunctive measure if bronchospasm is severe and does not respond rapidly to other treatment.
If profound shock judged immediately life threatening give CPR/ALS if necessary. Consider slow IV adrenaline (epinephrine) 1:10,000 solution. This is hazardous and is recommended only for an experienced practitioner who can also obtain IV access without delay.
Note the different strength of adrenaline (epinephrine) that may be required for IV use.
If adults are treated with an Epipen, the 300 micrograms will usually be sufficient. A second dose may be required. Half doses of adrenaline (epinephrine) may be safer for patients on amitriptyline, imipramine, or beta blocker.
A crystalloid may be safer than a colloid.
Written by mubushirmahmood123
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