A wide range of possible presentations and clinical signs and symptoms may make it difficult to diagnose anaphylaxis. It is important to undertake a full history and examination as soon as possible. A history of previous allergies as well as the recent incident is vital. Special attention should be given to skin condition (colour, presence of rashes), pulse rate, blood pressure, respiratory rate and auscultation of the chest. A peak flow should also be measured and recorded if possible (Resuscitation Council UK 2002).
Epinephrine (adrenaline) is considered the most important drug for any severe anaphylactic reaction (see Chapter 10). It works by reversing peripheral vasodilation and reducing oedema. It also dilates the airways, increases the force of myocardial contraction and suppresses histamine release. Epi-nephrine works best when administered early after the onset of the reaction. It is safe when given intramuscularly but does have some risk when given intravenously (Resuscitation Council UK 2002).
Epinephrine injection devices are available for home use. These are currently known as the Epipen (or Anapen) and the Epipen Jr (or Anapen Junior) and can be injected as 300 mg or 150 mg respectively (Resuscitation Council UK 2002). The drug may be given before medical help is available.
1. 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.
2. 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.
3. If adults are treated with an Epipen, the 300 mg 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.
Fig. 13.1 Anaphylactic reactions. Treatment algorithm for adults by first medical responders (reprinted with permission from the Resuscitation Council UK).
Immediate treatment (see Figure 13.1)
• Position - all casualties should recline in a comfortable position. Lying flat with or without the legs elevated may be helpful if the casualty is hypotensive but unhelpful if there are breathing difficulties.
• The likely allergen should be removed if possible (i.e. stop drug infusion or blood transfusion).
• Oxygen - high-flow oxygen (10-15l/min) should be administered as soon as possible.
• Airway management - airway obstruction may develop rapidly if there is soft tissue swelling. It is important to consider early tracheal intubation and have the proper equipment readily available.
• Basic and advanced life support - if the casualty is in cardiac arrest, cardiopulmonary resuscitation should be performed according to standard basic and advanced life support guidelines (refer to Chapters 5 and 6).
• Epinephrine (adrenaline) - epinephrine should be administered intramuscularly to all patients with clinical signs of shock, airway swelling or definite breathing difficulty (Resuscitation Council UK 2002). Inspiratory stridor, wheezing, cyanosis, pronounced tachycardia and decreased capillary filling are likely signs of a severe reaction.
• For adults, a dose of 0.5 ml epinephrine 1:1000 solution (500 mg) should be administered intramuscularly. This should be repeated after about five minutes if there is no clinical improvement or if the patient deteriorates after the initial treatment, especially if hypotension causes the level of consciousness to become or remain impaired. In some cases several doses may be needed, particularly if improvement is transient.
• Intravenous administration of epinephrine should only be given in a dilution of at least 1:10000 (never 1:1000). It must be reserved for patients with profound shock that is immediately life threatening and for special indications, for example during anaesthesia. Heart rate and ECG monitoring are essential when giving an epinephrine infusion.
• Antihistamines - an antihistamine (chlorphenamine) should be administered to block the effects of histamine release
(American Heart Association (AHA) and International Liaison Committee on Resuscitation (ILCOR) 2000). The drug may cause hypotension. It must be given by either slow intravenous injection or intramuscular injection. The adult dose is 10-20 mg intramuscularly.
• Corticosteroids - hydrocortisone (as sodium succinate) should be administered after severe attacks to help avert late sequelae. The dose of hydrocortisone for adults is 100-500 mg and must be given by slow intravenous or intramuscular injection (AHA & ILCOR 2000).
• Fluid administration - a rapid infusion of 1-2 litres of fluid (such as normal saline) may be needed if severe hypotension persists after drug treatment.
• Patients with even moderately severe attacks of anaphylaxis should be warned of the possibility of an early recurrence of symptoms and in some circumstances should be kept under observation for up to 24 hours.
• If possible, the allergen should be identified and the patient should be advised to avoid future exposure.
• Patients at high risk of anaphylaxis may wish to carry their own epinephrine syringe and wear a 'Medic-alert' type bracelet.
• All patients who have suffered a severe reaction should be referred to a specialist allergy clinic for further investigation and assessment.
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