ImmunologyTier 1Medical Sciences concept

Risk factors for severe/fatal anaphylaxis

Core concept

Delay in giving adrenaline is the single modifiable factor most strongly associated with death
- Fatal reactions have a short median time from onset to arrest: drug ~5 min, venom ~15 min, food ~30 min
- Every other intervention is secondary. Antihistamines and steroids have never been shown to prevent a fatal outcome.
Asthma is the strongest patient-level risk factor for anaphylaxis mortality, and poorly controlled asthma more so - respiratory arrest dominates food-triggered deaths

Patient factors

Asthma, especially poorly controlled or steroid-dependent
Older age; cardiovascular and respiratory comorbidity - less physiological reserve
Mast cell disease / raised baseline tryptase (hereditary alpha-tryptasaemia, systemic mastocytosis) - especially for venom anaphylaxis
Prior severe reaction (though a mild reaction does not predict a mild next one)
Adolescents and young adults - risk-taking, not carrying the device

Drug factors

Beta-blockers - blunt the adrenaline response -> refractory anaphylaxis; consider glucagon 1-2 mg IV
ACE inhibitors - block bradykinin degradation, worsen angio-oedema and hypotension
Neither is an absolute contraindication to venom immunotherapy - weigh against the risk of the sting

Cofactors (amplify a reaction that would otherwise be mild)

Exercise (food-dependent exercise-induced anaphylaxis - classically omega-5 gliadin in wheat)
NSAIDs, alcohol, acute infection, menstruation, sleep deprivation, heat

Trigger and route

Parenteral > oral; drug and venom reactions are faster and more often fatal than food
Peanut and tree nut dominate fatal food anaphylaxis
Upright posture or standing a hypotensive patient up can cause "empty ventricle" arrest - lie the patient flat, or left lateral if pregnant; never sit or stand them up

IM adrenaline into the anterolateral thigh, immediately, before anything else
- Adults and children >50 kg: 500 microg (0.5 mg) IM; devices 300 or 500 microg
- Repeat every 5 minutes if no response; >=2 doses = refractory -> adrenaline infusion, IV fluid bolus, senior help
- Give adrenaline before the reliever puffer when a known allergic asthmatic has sudden breathing difficulty
Australian devices: EpiPen, Anapen, Jext, and intranasal neffy - prescribe two, with an ASCIA Action Plan, and check technique at every visit
Observation: minimum 4 h after adrenaline; longer if severe, repeated doses, asthma, or remote from care. Biphasic reactions ~5%
Serum tryptase at presentation, 1-2 h, and a baseline sample >24 h later - a persistently raised baseline points to mast cell disease
Referral to an allergist is part of acute management, not an optional extra - trigger confirmation, immunotherapy (venom immunotherapy is highly effective), and cofactor education

3 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.