8.2 Anaphylaxis & Acute Allergy

Recognising Anaphylaxis

Anaphylaxis is a severe, life-threatening, generalised or systemic hypersensitivity reaction. The Resuscitation Council UK 2021 guideline defines it clinically as sudden onset of problems in one or more of:

Skin changes alone do not constitute anaphylaxis — the life-threatening features are in the airway, breathing, and circulation.

The RCUK 2021 Anaphylaxis Algorithm

1. Diagnose anaphylaxis (ABC problems, sudden onset)
2. Call for help — resuscitation team / 999
3. Lay patient FLAT with legs raised (unless breathing difficulty favours sitting up)
4. Give IM ADRENALINE — anterolateral thigh
5. Give high-flow OXYGEN (15 L/min non-rebreather)
6. If no response at 5 min → REPEAT IM adrenaline + IV crystalloid bolus
7. If no response to TWO IM doses → REFRACTORY ALGORITHM (IV adrenaline infusion by specialists)

IM Adrenaline Doses (1 mg/mL = 1:1000 solution)

• Route: intramuscular, anterolateral aspect of the middle third of the thigh (vastus lateralis). This is the correct route and site for all responders, not IV.
• Needle: blue 23G, 25 mm; green 21G, 38 mm for obese patients.
• Repeat after 5 minutes if no improvement. Do not delay a repeat dose waiting for a response that is not occurring.
• IV adrenaline is reserved for refractory anaphylaxis and must be given by experienced specialists in a monitored setting.

Adjunctive Treatment (Not First-Line)

The 2021 RCUK guideline made important changes to adjuncts:

• Corticosteroids (hydrocortisone) are no longer recommended for the routine emergency treatment of anaphylaxis. They have no role in the acute algorithm.
• Antihistamines (chlorphenamine) are considered a third-line intervention and must not be used to treat airway, breathing, or circulation problems during initial emergency management. They may be given after stabilisation for skin symptoms.
• IV fluids: give a crystalloid bolus (adult 500-1000 mL, 10 mL/kg in children) when giving the second IM adrenaline dose or if shock persists.

Why Adrenaline Is the Only First-Line Drug

Adrenaline reverses all three pathological mechanisms of anaphylaxis: it is a potent alpha-1 agonist (vasoconstriction — reverses hypotension and mucosal oedema), beta-1 agonist (increases heart rate and contractility — reverses shock), and beta-2 agonist (bronchodilation — reverses bronchospasm). There is no alternative with this combined action, and delay in administration is associated with fatal outcomes.

Common Dental Triggers

Differentiating Anaphylaxis from Mimics

A normal pulse and rapid recovery with legs raised points to vasovagal syncope, not anaphylaxis. If there is any genuine doubt about airway, breathing, or circulation compromise, treat as anaphylaxis — the risk of giving adrenaline to a patient without anaphylaxis is far lower than the risk of withholding it from a patient who does.

After the Acute Episode

• All patients treated for anaphylaxis must be transferred to hospital by ambulance for observation (biphasic reactions can occur over hours).
• Refer to an allergy specialist for investigation and trigger identification.
• Prescribe (or advise) an adrenaline auto-injector for future use where appropriate.

Biphasic Reactions and Mandatory Observation

A biphasic anaphylactic reaction is a recurrence of symptoms after the initial episode has fully resolved, occurring 1 to 72 hours later (most commonly within 6 to 12 hours), without further exposure to the trigger. It is unpredictable and cannot be anticipated from the severity of the first reaction. This is precisely why every patient treated for anaphylaxis in the dental practice must be transported to hospital by ambulance rather than discharged home after apparent recovery: a clinically well patient can deteriorate again hours later without adrenaline on hand. Discharging a patient from the chair after they feel better is an avoidable and well-recognised cause of fatalities.

Adrenaline Auto-Injectors for Community Use

Patients at ongoing risk are prescribed a self-administered adrenaline auto-injector for community use (for example Jext, EpiPen or Emerade), which is distinct from the ampoule-based 500 micrograms IM dose drawn up in practice. The Jext weight bands are shown below:

These devices deliver a fixed dose into the anterolateral thigh and are designed for carers or the patient; they do not replace the 1:1000 ampoule in the dental kit, which allows accurate titration across the full paediatric age range.

Refractory Anaphylaxis

If there is no response after TWO IM adrenaline doses, the algorithm becomes refractory anaphylaxis: an IV adrenaline infusion is commenced by experienced specialists (anaesthetist or critical care) in a monitored setting with ECG and continuous blood pressure. The dental team does not give IV adrenaline — the priority is to keep giving IM doses at 5-minute intervals and hand over promptly.

Dental-Practice Kit and Team-Role Checklist

• Adrenaline 1:1000 (1 mg/mL) with 23G / 21G needles
• Oxygen at 15 L/min via non-rebreather mask
• Airway adjuncts (oropharyngeal airways, suction)
• IV access and crystalloid for the second-dose stage
• Call 999 early — do not wait for a second dose before summoning help
• Assign named roles: airway, drugs, 999 caller, and a timer who logs each adrenaline dose and time