Anaphylaxis and its Treatment

Anaphylaxis is a sudden onset (or rapidly progressive) severe systemic allergic reaction, affecting multiple organs. Its onset may be heralded by skin and/or mucosal changes (flushing, urticaria, angioedema) and progress to include life-threatening airway, lung and/or circulation problems. Its identification and management is based on the Resuscitation Council UK Guidelines.¹

The number of people who suffer severe systemic allergic reactions is increasing. The incidence is about 1 - 3 reactions per 10,000 population per annum, although anaphylaxis is not always recognised, so certain UK studies may underestimate the incidence.¹

An anaphylactic reaction occurs when an allergen reacts with specific IgE antibodies on mast cells and basophils (type 1 hypersensitivity reaction) triggering the rapid release of stored histamine and the rapid synthesis of newly formed mediators. These cause capillary leakage, mucosal oedema and ultimately shock and asphyxia. Anaphylactic reactions can vary in severity and rate of progression - they may progress rapidly (over a few minutes) or occasionally in a biphasic manner. Rarely manifestations may be delayed by a few hours (adding to diagnostic difficulty), or persist for more than 24 hours.
Anaphylactoid reactions are not IgE mediated but cause similar mast cell activation.

A significant number of cases of anaphylaxis are idiopathic.¹
The most common triggers of anaphylaxis:

• Foods:²
  • Peanuts
  • Pulses
  • Tree nuts (e.g. brazil nut, almond, hazelnut)
  • Fish and shellfish
  • Eggs
  • Milk
  • Sesame
• Venom, for example:
  • Bee stings
  • Wasp stings
• Drugs, including:
  • Antibiotics
  • Opioids
  • NSAI's
  • IV contrast media
  • Muscle relaxants
  • Other anaesthetic drugs

There is often (but not always) a history of previous sensitivity to an allergen, or recent history of exposure to a new drug (eg vaccination). Initially patients usually develop skin symptoms include generalised itching, urticaria and erythema, rhinitis, conjunctivitis and angio-oedema.

Signs that the airway is becoming involved include itching of the palate or external auditory meatus, dyspnoea, laryngeal oedema (stridor) and wheezing (bronchospasm). General symptoms include palpitations and tachycardia (as opposed to bradycardia in simple vasovagal at immunisation time), nausea, vomiting and abdominal pain, feeling faint - with a sense of impending doom; and ultimately collapse and loss of consciousness.

Airway swelling, stridor, breathing difficulty, wheeze, cyanosis, hypotension, tachycardia and reduced capillary filling suggest impending severe reaction.¹

If no history is available in a collapsed patient use an ABCDE advanced life-support approach to recognise and treat an anaphylactic reaction.Treat life-threatening problems as you find them. The basic principles of treatment are the same for all age groups.

Life-threatening conditions :

• Sometimes an anaphylactic reaction can present with symptoms and signs that are very similar to life-threatening asthma – this is commonest in children.
• A low blood pressure (or normal in children) with a petechial or purpuric rash can be a sign of septic shock.
• Seek help early if there are any doubts about the diagnosis and treatment.

• Faint (vasovagal episode).
• Panic attack.
• Breath-holding episode in child.
• Idiopathic (non-allergic) urticaria or angioedema.

Treatment in an emergency means following without delay a systematic assessment and treatment plan.

Monitoring

• All critically ill patients should be given oxygen.
• Maintain the PaO2 as close to normal as possible (approximately 13 kPa or 100 mm Hg).
• When/if pulse oximeter available:
  • Titrate the oxygen to maintain an oxygen saturation of 94-98%.
  • In the sickest patients this is not always possible so you may have to accept a lower value, i.e., above 8 kPa (60 mm Hg), or 90-92% oxygen saturation on a pulse oximeter.
• A normal SpO2 on oxygen does not necessarily mean ventilation is adequate (because the pulse oximeter detects oxygenation and not hypercapnoea). The patient may be breathing inadequately (with a high PaCO2).
• Use bag-mask ventilation while calling urgently for expert help. In an anaphylactic reaction upper airway obstruction or bronchospasm can make bag mask ventilation difficult or impossible.
• Consider early tracheal intubation (if equipment and expertise available). If the patient is intubated, give high concentration oxygen with a self-inflating bag.

• In adults normal BP (or a systolic BP greater than 100 mmHg).
• In children:
  • 0 to1 month: minimum 50-60 mmHg.
  • >1 to12 months: minimum 70 mmHg.
  • >1 to 10 years 70 + (age in years x 2) mmHg.
  • >10 years: minimum 90 mmHg.
• If the patient does not improve, repeat the fluid challenge.
• If there are symptoms and signs of cardiac failure (shortness of breath, increased heart rate, raised JVP, a third heart sound, and inspiratory crackles in the lungs on auscultation):
  • Decrease or stop the fluid infusion.
  • Seek expert help (inotropes or vasopressors may be needed).

When time allows.

• Immediate:
  • Take a full history from the patient (relatives, friends, and other staff).
  • Review the patient’s notes and charts. Study both absolute and trends of values relating to vital signs.
  • Check that important routine medications are prescribed and being
    given.
  • Review the results of laboratory or radiological investigations.
  • Consider what level of care is required by the patient, e.g., transport to hospital if
    in the community.
  • Make complete entries in the patient’s notes of your findings, assessment and
    treatment. Record the patient’s response to therapy.
  • Consider definitive treatment of the patient’s underlying condition.
• Long term:
  • Refer to an allergist or allergy clinic to try and identify allergen so that it may be avoided in future.
  • Organise self-use of pre-loaded pen injections for future attacks (e.g. EpiPen ®; containing 0.3 mL of 1 in 1000 strength (that is 300 μg) for adults; and for children 0.3 mL of 1 in 2000 (150 μg)). This again may be best done in allergy clinics.
  • Give a written self-management plan and arrange to teach patient and relatives how to use syringes.¹
  • Encourage patient to wear a Medic alert bracelet/necklace endorsed by doctor.