Acute Allergic Reactions

INTRODUCTION

• Multisystem

  • – acute anaphylaxis: the onset of hypotension, bronchospasm or upper airway obstruction (features: difficult noisy breathing, wheeze/cough, tongue swelling, tightness of throat, difficulty talking, persistent dizziness or fainting)

  • – anaphylactic reactions

• Localised

  • – angioedema

  • – urticaria

ANAPHYLAXIS AND ANAPHYLACTIC REACTIONS

Treatment (adults)

First line

• Lie person flat (must not stand or walk): call for assistance

• Oxygen 6–8 L/min (by face mask) ± airway/ventilation support

• Adrenaline using autoinjector 300 mcg or 0.3–0.5 mg (1:1000) IM, best given IM in mid anterolateral thigh (mg = mL of 1:1000 adrenaline) If no rapid improvement: repeat IM injection every 3–5 mins, then insert IV line (esp. if hypotensive)—set up an infusion 1 mg adrenaline in 1000 mL N saline (i.e. 1 mL = 1 mcg), give bolus 50 mL and then as required (best with ECG monitoring). Adrenaline rule: 0.01 mg/kg (max. 0.5 kg).

• Salbutamol aerosol inhalation (or nebulisation if severe)

• Nebulised adrenaline for bronchospasm

• Infuse crystalloid solution (esp. if hypotensive), e.g. N saline (1–2 L); consider IV glucagon and promethazine 25 mg IV

• Admit to hospital (observe at least 12 h)

• Discharge on promethazine 25 mg tds + prednisolone 50 mg/d for 2 d

If not responding

Continue adrenaline every 3–5 mins:

• hydrocortisone 500 mg IV (takes 3–4 h for effect)

• establish airway (oral airway or endotracheal intubation) if required

Treatment for children (who may be pale and floppy)

• Oxygen 6–8 L/min by mask

• Adrenaline by injector (if 10–20 kg) 125 mcg or 1:1000 (0.01 mL/kg) IM; 0.05–0.1 mL if <12 months. If poor response, repeat IM injection every 5 mins as necessary and set up infusion as for adults but lower dose of bolus.

• Admit to hospital. Observe about 4 hours (risk of biphasic reaction).

If necessary

• Hydrocortisone: 8–10 mg/kg IV

• Hypotension: colloid solutions IV (e.g. Haemaccel, stable plasma protein solution (SPPS) or Dextran 70)

• Bronchospasm: continuous nebulised salbutamol or adrenaline

• Upper airways obstruction

  • – mild to moderate: inhaled adrenaline (0.5 mL/kg) 1:1000 (max. 4 mL) dilute to 4 mL, with saline or water if nec.

  • – severe: intubation may be nec.

Peanut allergy

Diagnosis confirmed by demonstrating peanut-specific IgE by skin-prick or RAST test. Patients should avoid peanut-containing foods and carry an anaphylaxis kit.

Adrenaline antoinjector: adult and child >30 kg—300 mcg IM; child 15–30 kg (usually 1–5 years) 0.125 mcg; <10 kg not recommended.

ANGIOEDEMA AND ACUTE URTICARIA

Acute urticaria and angioedema are essentially anaphylaxis limited to the skin, subcutaneous tissues and other specific organs. They can occur together.

Treatment

Uncomplicated cutaneous swelling

• antihistamines, e.g. promethazine 25 mg (o) tds or 25 mg ...