Anaphylaxis

Anaphylaxis is a severe, life-threatening, generalised hypersensitivity reaction. Adrenaline IM is the single most important treatment and should be given without delay. Position supine with legs elevated (unless breathing difficulty), and avoid…

Resuscitation Council UK Anaphylaxis Algorithm

The pathway

1 · Recognise

Sudden onset, rapid progression
Airway (stridor, angioedema)
Breathing (wheeze, SpO₂ fall)
Circulation (hypotension, tachycardia)
Skin (urticaria, erythema, flushing — absent in 20%)

2 · Call for help

Shout for help immediately. In hospital: activate cardiac arrest/emergency team.

3 · Adrenaline IM — FIRST

0.5mg (0.5ml of 1:1000) IM into anterolateral thigh. This is the only first-line treatment. Repeat after 5 minutes if no improvement.

4 · Position

Supine with legs elevated (improves venous return). Sitting up if respiratory distress. Do NOT stand them up suddenly — cardiovascular collapse risk.

5 · O₂ and airway

High-flow O₂ 15L NRB. Call anaesthetics early if stridor — may need intubation or surgical airway.

6 · IV fluid

500ml–1L crystalloid bolus rapidly. Repeat as needed.

7 · Refractory anaphylaxis

Defined as persisting respiratory or cardiovascular problems despite 2 appropriate doses of IM adrenaline
Seek critical care help early — resuscitation team in hospital, 999 in the community
Treatment is a low-dose IV adrenaline INFUSION, given by clinicians experienced in its use, plus a rapid fluid bolus and maintenance fluids
If an infusion cannot be given safely, keep repeating IM adrenaline every 5 minutes
Prolonged critical care over hours to days may be needed

8 · Antihistamines and steroids are NOT part of emergency treatment

Corticosteroids are no longer advised for routine emergency treatment (RCUK 2021). Consider only after initial resuscitation, for refractory reactions or ongoing asthma — and never in preference to adrenaline
Antihistamines are third-line and must not be used to treat Airway/Breathing/Circulation problems
After stabilisation, a non-sedating oral antihistamine (cetirizine 10–20mg PO) is preferred over chlorphenamine for persisting skin symptoms
IV chlorphenamine can itself cause hypotension when pushed rapidly

9 · Monitor

Minimum 6-hour observation after anaphylaxis. 12–24 hours if severe/refractory (biphasic risk). Prescribe self-injectable adrenaline on discharge.

Drugs

Drug	Dose	Route	Notes
Adrenaline 1:1000	0.5mg (0.5ml)	IM (anterolateral thigh)	FIRST LINE. Repeat every 5 minutes if no improvement.
IV adrenaline infusion	Low-dose infusion per local protocol	IV (specialist only)	Refractory anaphylaxis only. RCUK 2021: IV adrenaline must be used only in specialist settings by those skilled and experienced in it. It is an INFUSION, not a bolus — do not push IV adrenaline on the ward. If no infusion is possible, keep repeating IM adrenaline every 5 min.
Cetirizine	10–20mg	Oral	Third-line, after stabilisation only, for persisting urticaria or angioedema. RCUK 2021 prefers a non-sedating oral antihistamine over chlorphenamine. Never for A/B/C problems.
Hydrocortisone	200mg	IV	No longer advised routinely (RCUK 2021). Consider only after initial resuscitation in refractory reactions or where asthma contributed. Must never be given in preference to adrenaline.
0.9% NaCl	500ml–1L	IV	Fluid resuscitation for hypotension.
Salbutamol	5mg	Nebulised	For persisting bronchospasm after adrenaline.

When to escalate

Stridor or threatened airway — call anaesthetics now,No improvement after 2 doses of IM adrenaline = REFRACTORY — get critical care help now for an IV adrenaline infusion,Cardiac arrest — start ALS, give IV adrenaline,Biphasic reaction (up to 24h later) — admit all severe cases

Reference: Resuscitation Council UK Anaphylaxis Guidelines 2021

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