Observation time following anaphylaxis

When you have been treated for anaphylaxis, you will be kept under clinical observation for at least four hours after the last injection of adrenaline. Adrenaline has a short duration of action and wears off quickly.

Occasionally, some people have another episode of anaphylaxis without coming in contact with their allergic trigger and require further treatment with adrenaline. This is called ‘biphasic anaphylaxis’. A clinician will review your risk of recurrence of anaphylaxis and re-exposure before you are discharged.

In some cases, you may need to be admitted overnight for observation after having anaphylaxis if:

• You have received more than one dose of adrenaline to treat your anaphylaxis
• You have a history of severe asthma
• You have arrived late in the evening
• You live alone or a long way from healthcare services
• Your adrenaline injector cannot be replaced before you get home and you do not have another one.

Observe patients for at least four hours after the last injection of adrenaline following anaphylaxis. Reassess the patient after four hours. Consider the severity of the reaction, concomitant conditions and history of anaphylaxis when deciding if more time is needed.

When the initial injection of adrenaline for anaphylaxis is administered in general practice or another primary care location, where observation for four hours is not possible, arrange ambulance transfer to an appropriate facility for clinical observation.

Prolonged and biphasic reactions may occur. Biphasic reactions are estimated to occur following 3–20% of anaphylactic reactions, and cannot be predicted.

As per the ASCIA Acute Management of Anaphylaxis guidelines, a patient should be observed overnight if they:

• Had a severe reaction (hypotension or hypoxia)
• Required repeated doses of adrenaline
• Have a history of severe asthma or protracted anaphylaxis
• Have other concomitant illnesses, such as asthma, chest infection or arrhythmia
• Live alone or are remote from medical care
• Have known systemic mastocytosis
• Presented for health care late in the evening
• Cannot easily replace their adrenaline injector on discharge and have no other adrenaline injector.

Ensure protocols align with ASCIA guidelines and that systems and processes are in place for patients to undergo clinical observation for the appropriate length of time.