Anaphylaxis

• Anaphylaxis = serious systemic hypersensitivity reaction that is usually rapid in onset and may lead to death if not recognised and treated promptly
• Aetiology:

  • Type I hypersensitivity reaction - meaning its mediated by IgE antibodies
  • On first exposure to the allergen - IgE antibodies produced - does not cause symptoms
  • Antibodies remain attached to basophils and mast cells
  • On subsequent exposure - binding of antigens to IgE antibodies triggers basophils and mast cells to degranulate - releases histamine, tryptase, and chymase
  • These inflammatory mediators cause vasodilation, increase vascular permeability, stimulate smooth muscle contraction and increase mucus secretion
• Anaphylactoid reactions produce a similar presentation as anaphylaxis but are causes by non-IgE mediated triggering events
• Triggers:

  • Food - peanut, tree nuts and cow's milk most common in children
  • Medication - antibiotics (especially penicillin), neuromuscular blocking agents, chlorhexidine - most common in adults
  • Latex
  • Exercise - rare
  • Idiopathic
• Risk factors:

  • Previous episode
  • Known allergy of any kind
  • Concurrent allergic conditions - allergic asthma, eczema
  • Regular exposure to allergens
• Factors that can worsen reaction:

  • Advancing age
  • Asthma and other chronic lung diseases
  • Cardiovascular disease
  • Mast cell disease
  • Previous biphasic anaphylaxis
  • Taking beta-blockers or ACE inhibitors
• Biphasic anaphylaxis = recurrence of anaphylaxis after appropriate treatment, with no additional exposure to the allergen - commonly happens within 10 hours but can be 1-72 hours
• History:

  • Sudden onset and rapid progression
  • Feeling of throat closing up
  • Dyspnoea
  • Chest tightness
  • Nausea and vomiting
  • Abdominal pain (especially if caused by food allergies)
  • If patient presents late - may be confused or unresponsive because of cerebral hypoxia
• Clinical exam - airway:

  • Difficulty in breathing and/or swallowing
  • Hoarse voice
  • Stridor
  • Swollen tongue and lips +/- saliva drooling
• Clinical exam - breathing:

  • Dyspnoea and tachypnoea
  • Wheeze - widespread
  • Cyanosis
• Clinical exam - circulation:

  • Tachycardia - rapid, weak, thready pulse
  • Hypotension
  • Cold, clammy skin with prolonged CRT
• Clinical exam - skin:

  • Widespread urticarial/erythematous rash
  • Generalised pruritus
  • Angioedema
  • Flushing
• Presentation differences according to trigger:

  • Food - less rapid onset and breathing problems typically predominate
  • Medication - rapid onset and circulation problems typically predominate
  • Insect sting - rapid onset and circulation problems typically predominate
• Bedside investigations:

  • Routine observations
  • ECG
• Lab investigations:

  • Routine - FBC, U&Es, CRP, LFTs and coagulation
  • ABG if hypoxic
  • Serum mast cell tryptase (major component of mast cell secretory granules)
• Serum mast cell tryptase:

  • Recommended in all patients with suspected anaphylaxis
  • Should never delay life-saving treatment
  • At least one sample should be taken within 2 hours of symptoms onset and non longer than 4 hours later
  • An elevated serum mast cell tryptase level confirms diagnosis of anaphylaxis
  • A normal result does not rule of anaphylaxis
• The Resuscitation Council UK suggests that anaphylaxis is likely when all the following three are present:

  • Sudden onset and rapid progression of symptoms
  • Life-threatening airway and/or breathing and/or circulation problems
  • Skin and/or mucosal changes
• Management:

  • ABCDE approach
  • Call for help - critical care team and anaesthetists
  • Remove trigger if possible
  • Sitting position to help airway if possible - patient must not walk or stand
  • Immediate IM adrenaline
  • If no response after 5-10 minutes - repeat IM adrenaline and IV fluid challenge
  • If no improvement in breathing or circulation despite 2 doses of IM adrenaline = refractory anaphylaxis
• Adrenaline:

  • Non-selective alpha and beta adrenergic receptor agonist
  • Alpha receptor agonism - peripheral vasoconstriction and reduces oedema
  • Beta receptor agonism - bronchodilation, positive inotropic effects, suppresses inflammatory mediator response
  • Inject at 90 degree angle at the anterolateral aspect of the middle third thigh
  • Adrenaline dilution = 1:1000 or 1mg/mL
  • Adult and child over 12 = 500mcg (0.5ml)
  • 6-12 years = 300mcg (0.3ml)
• Adjunct therapy:

  • Antihistamines - does not form part of initial emergency management but can treat skin symptoms - use oral non-sedating antihistamine e.g. cetirizine
  • Steroids - routine use if not advised but consider after initial resuscitation for refractory reactions
  • Bronchodilators - nebulised salbutamol/ipratropium
  • Nebulised adrenaline - effective as an adjunct to treat upper airways obstruction caused by oedema - does not replace IM adrenaline
• Refractory anaphylaxis:

  • ABCDE approach
  • Early expert input early
  • Maintenance adrenaline therapy with low dose IV adrenaline infusion (only given by experienced clinician)
  • Rapid IV fluid challenge
• Anaphylaxis during pregnancy:

  • Difference in positioning of the patient to reduce compression on the inferior vena cava and abdominal aorta from the uterus
  • Should always lie on their left side
  • If >20 weeks gestation, when the patient is placed in the supine position for airway management or CPR, the uterus must be displaced manually to the left
• Cardiorespiratory arrest during anaphylaxis:

  • Adrenaline should no longer be given via the IM route due to impaired absorption
  • Attempts to give IM adrenaline may interrupt delivery of high quality CPR
  • ALS algorithm - adrenaline given via the IV or IO route
• Before discharge:

  • Consider keeping NBM for the first few hours due to risk of deterioration and requiring intubation
  • All patients require hospital admission and observation due to risk of symptom recurrence
• Discharge and follow up:

  • Referral to a specialist allergy service
  • Information about anaphylaxis - how to recognise anaphylaxis and how to avoid trigger
  • Prescription of 2 adrenaline auto-injectors with appropriate training
  • Information on risk of biphasic anaphylaxis
• Complications:

  • Anaphylactic shock - leading cause of death
  • Respiratory failure - leading cause of death
  • Refractory anaphylaxis
  • Biphasic anaphylaxis - recurrence of symptoms within 72 hours after complete recover, in absence of further exposure to the trigger
  • MI
  • Death