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Author: Alexandra Croom

Suspect anaphylaxis if, after an IV or IM injection, insect sting or exposure to a potential allergen, the patient develops breathlessness and wheeze, or hypotension/shock. The potential manifestations of anaphylaxis are shown in Table 38.1; not all features will occur in every patient. Wheeze is more common in food-induced anaphylaxis, as coexistent asthma is more frequent.

Causes of anaphylactic reaction are given in Table 38.2. Symptoms usually start within minutes of exposure to a trigger, and most reactions will occur within 60 min. The route of allergen exposure influences the rapidity of symptom onset; allergens encountered parenterally and insect stings produce a more rapid clinical deterioration than ingested allergens. Delayed onset reactions (beyond 60 min) are recognized with food-dependent exercise-induced anaphylaxis (FDEIA) and meat allergy.

The management of anaphylaxis is summarized in Figure 38.1. Prompt administration of adrenaline IM is the key element of treatment.

Priorities ⬆ ⬇

Outline

Is This Anaphylaxis?!!navigator!!

The rapid onset of breathlessness and wheeze (due to upper airway obstruction or bronchospasm) or hypotension/shock, associated with itch, flushing or urticaria, suggest anaphylaxis and you should consider immediate treatment with adrenaline IM.

  • There should be a high index of suspicion if there has been exposure to a possible allergen, for example administration of IV medication, or after eating by a person known to have food allergy.
  • Skin changes are not essential to the diagnosis of anaphylaxis, and adrenaline should not be withheld in their absence if the diagnosis is suspected.
  • The differential diagnosis of anaphylaxis includes any condition that can cause the rapid onset of dyspnoea or hypotension, as well as those which cause urticaria and angioedema (Chapter 27). See Table 38.3 for a list of the most common differential diagnoses.

Suspected Severe Anaphylactic Reaction (Anaphylactic Shock)!!navigator!!

  1. Call for assistance. If there is cardiorespiratory arrest, start resuscitation.
  2. Remove the trigger allergen if possible (e.g. stop IV infusion of antibiotic; remove the stinger after a bee sting). Do not induce vomiting.
  3. Unless contraindicated because of breathlessness, lay the patient flat and raise the foot of the bed. This position should be maintained; resuming an upright position before the volume shifts in shock have improved can lead to cardiac arrest.
  4. Adrenaline is the first-line drug in anaphylaxis; absent or delayed use is associated with fatal outcome.
    • In the first instance administration should be IM in the anterolateral aspect of the thigh (where skin to muscle depth is least). A 23 G needle (blue – length 25 mm) should be used to ensure that muscle is reached; in the morbidly obese consider a 21 G (green – needle length 38 mm) or administration into the calf. Subcutaneous or deltoid muscle administration is NOT recommended. A dose of 500μgm adrenaline should be given IM. If a second dose of IM adrenaline is required it should be given at a separate site (usually the contralateral thigh).
    • Nebulized adrenaline (5 mL of 1:1000 solution) may be of some use where there is significant laryngeal obstruction due to angioedema.

  5. If there is respiratory distress, call an anaesthetist. This may be due to upper airway obstruction from oedema of the larynx or epiglottis, and may require endotracheal intubation or emergency tracheotomy.

    If there is bronchospasm, give nebulized salbutamol. IV aminophylline (Chapter 116) can be added if needed.

  6. Start an IV infusion of crystalloid, 500 mL to 1 L over 15 min (the higher rate if systolic BP is <90 mmHg). If there is heart failure, give 250 mL over 15 min. Monitor for signs of fluid overload.
  7. Give chlorphenamine 10–20 mg IV over 1 min and hydrocortisone 200 mg IV.
  8. Take timed blood samples for mast cell tryptase testing as follows: a sample as soon as possible after emergency treatment has started, a second sample ideally within 1–2h (but no later than 4h) from the onset of symptoms. A raised serum mast cell tryptase (see Table 38.4) may be used to confirm that anaphylaxis has taken place but has a poor negative predictive value.
  9. If systolic BP remains <100 mmHg:
    • Arrange transfer to the ICU.
    • Give adrenaline 0.5–1 mg (0.5–1 mL of 1in 1000 solution) IM every 10 min.
    • Continue IV crystalloid infusion, giving a further 500 mL over 30 min. When the patient's condition is stable, put in a CVP line to guide fluid management (p. 13, Table 2.7).
    • If multiple doses of adrenaline are needed, consider starting an infusion (which must be given via a central line) (p. 657).
    • If the patient has been taking a non-cardioselective beta blocker and is resistant to adrenaline, give glucagon (50μgm/kg by IV bolus followed by an infusion of 1–5 mg/h) or salbutamol by IV infusion (p. 379).

Further Management ⬆ ⬇

  1. Admit to hospital. In up to 20% of cases, biphasic reactions occur between 1 and 8h after the onset of symptoms; rarely the second phase of the reaction may be more severe than the first. There are no features of anaphylaxis predictive of a biphasic reaction occurring, other than the individual having had one during a previous episode.
  2. Give hydrocortisone 200 mg 6-hourly IV for 2–4 doses and chlorphenamine 8 mg 8-hourly PO for 24–48h. Warn patients about potential sedative side effects of chlorphenamine.
  3. Inform the patient of the allergen responsible for the reaction. The advice given by non-specialists on allergen avoidance should be over-inclusive (e.g. avoid all nuts when only one type appears implicated): this can be revised in specialist care. Recommend a medical ID bracelet engraved with trigger allergens (this may be deferred until after specialist review). Put patients in contact with patient support groups (e.g. Anaphylaxis Campaign).
    • Patients at high risk of anaphylaxis should carry adrenaline for self-injection in the event of further exposure to allergen. Consult the British National Formulary for a suitable device. Adrenaline should be prescribed where an allergen is not predictably avoidable or is unknown. Prescription should not be deferred until specialist review. Prescribing and training for adrenaline autoinjectors is device specific.
    • If anaphylaxis was due to a drug, report the reaction to the Committee on Safety of Medicines (see the Adverse Reactions to Drugs section of the British National Formulary). Mark clinical notes clearly with the drug implicated; inform the patient's GP and other involved health professionals.
    • Specific allergen immunotherapy (desensitization) is indicated in the case of severe anaphylactic reaction to bee or wasp stings: seek advice from a clinical immunologist or allergist.
    • Poorly controlled asthma increases the risk of life-threatening and fatal anaphylaxis. Assess ongoing asthma control (nocturnal disturbance, frequency of use of rescue medication, oral corticosteroid use) and intensify treatment as appropriate.
    • Beta blockers will antagonize the effects of adrenaline (a beta agonist) and may make anaphylaxis difficult to treat. Risk assess their continued use and discontinue if the benefit does not outweigh that risk.
    • Refer to an allergy clinic for specialist assessment if new presentation; consider referral if previously diagnosed and taking high-risk behaviour or if a new allergen is implicated.
  4. Where there have been recurrent episodes of apparently idiopathic anaphylaxis (or reactions thought to be anaphylaxis) consider mastocytosis and carcinoid syndrome (in which asthma is associated with flushing rather than itch).

Allergic Reaction Without Anaphylaxis

Not all allergic reactions progress to anaphylaxis. Patients in whom symptoms are confined to the skin or at the point of allergen contact (e.g. oral itch with a food) should receive chlorphenamine and hydrocortisone and remain under close monitoring until their symptoms have abated.

Further Reading ⬆

Lieberman PL (2014) Recognition and first-line treatment of anaphylaxis. Am J Medicine 127, S6–S11.

National Institute for Health and Care Excellence (2016) Anaphylaxis: assessment and referral after emergency treatment. Clinical guideline (CG134). https://www.nice.org.uk/guidance/cg134?unlid = 639094620201610645435.

Simons FER, Ebisawa M, Sanchez-Borges M, et al. (2015) Update of the evidence base: World Allergy Organization anaphylaxis guidelines. World Allergy Organization Journal 8, 32 (Open access) 10.1186/s40413-015-0080-1.