History and exam
Key diagnostic factors
common
acute onset
airway swelling (angio-oedema)
Angio-oedema is a manifestation of immediate hypersensitivity with a circumscribed swelling of any part of the body, including the airway, throat, tongue, pharynx, and larynx.[32]
Assess the patient for throat and tongue swelling with difficulty breathing and swallowing. The patient may report that their throat is ‘closing up’.
Most reactions develop over several minutes.[32]
While respecting the patient’s dignity, fully expose their body to identify skin reactions.
Skin/mucosal changes are often the first presenting feature and occur in over 80% of anaphylactic reactions, but their absence does not exclude the diagnosis of anaphylaxis.[7]
Practical tip
Generalised urticaria, angio-oedema, and rhinitis do not meet criteria for anaphylaxis because life-threatening features – an airway problem, respiratory difficulty, and/or hypotension (circulatory compromise) – are absent.[32] But if in doubt, give intramuscular adrenaline and seek expert help.[32]
inspiratory stridor and hoarse voice
Look for airway obstruction and treat as an emergency if present.[32]
Stridor is a high-pitched inspiratory noise caused by upper airway obstruction.[32]
Other signs include:
No breath sounds, diminished air entry, or noisy air entry
Paradoxical chest and abdominal movements and accessory muscles of respiration.
An oxygen saturation (SpO2) <92% is considered life-threatening.
Call for expert help from an anaesthetist immediately, as airway swelling often requires early intubation, which may be technically challenging.[32]
How to insert a tracheal tube in an adult using a laryngoscope.
shortness of breath
Look for upper airway obstruction or lower airway bronchoconstriction.
Indicated by an increased respiratory rate.[32]
The patient may become tired from ‘the work of breathing’.
An oxygen saturation (SpO2) <92% is considered life-threatening.
Severe asthma may also present with wheezing, coughing, and shortness of breath. However, associated itching, urticaria, angio-oedema, abdominal pain, and hypotension is more suggestive of anaphylaxis.[51]
wheezing, chest hyperinflation, and accessory muscle use
Look for airway obstruction and treat as an emergency if present.[32]
Signs include paradoxical chest and abdominal movements, and use of accessory muscles of respiration.[32]
Wheeze, use of accessory respiratory muscles, subcostal and sternal recession in children, and abdominal breathing are signs of acute severe bronchospasm.[32]
Oxygen saturation (SpO2) <92% indicates life-threatening hypoxia.[32]
The patient may become fatigued by ‘the work of breathing’.[32]
Severe asthma may also present with wheezing, coughing, and shortness of breath. However, associated itching, urticaria, angio-oedema, abdominal pain, and hypotension is more suggestive of anaphylaxis.[51]
cyanosis
respiratory arrest
pale, clammy skin
Identify shock. Pale, clammy skin is a sign of shock.[32]
Can be present in any pathological process that causes hypovolaemia, including sepsis.
hypotension
Identify shock and check for low blood pressure:[32]
Adults and children aged 11 years or older: systolic blood pressure <90 mmHg or >30% decrease from baseline
Children aged from 1 to 10 years: <70 mmHg + [2 x age in years]
Infants aged 1 to 12 months: <70 mmHg
Neonates aged <1 month: 50 to 60 mmHg.
The patient may feel faint, dizzy, light-headed, floating, woozy, giddy, confused, helpless, or fuzzy, and may even collapse.[32]
Practical tip
Prolonged capillary refill time (>2 seconds) suggests poor peripheral perfusion, but other factors such as cold environment, poor lighting, and old age can prolong the time.[32]
Sepsis can manifest with low diastolic blood pressure. However, associated skin changes are more likely to be petechial or purpuric in sepsis, compared with the erythema (patchy, or generalised, red rash) or urticaria (also called hives, nettle rash, wheals, or welts) associated with anaphylaxis.[32]
increased pulse rate (tachycardia)
Identify shock. Raised pulse rate is often associated with hypotension and may herald cardiovascular collapse.
bradycardia
Identify shock. A low pulse rate (<40 beats per minute) often heralds cardiac arrest.
Usually a late feature.
Practical tip
Be aware that a low pulse rate may be caused by concomitant cardiac medications, such as beta-blockers.
cardiac arrest
Cardiac arrest is defined by the abrupt cessation of normal circulation or the absence of effective perfusion of vital organs. In practice, this is diagnosed by absent pulses. The patient will be unresponsive and stop breathing, and the skin will appear dusky.
confusion or disorientation
Identify disability. Airway, breathing, and circulatory problems can affect neurological status leading to confusion, agitation, and loss of consciousness.[32]
May also be triggered by administration of adrenaline (epinephrine), but tends to resolve as the other allergic symptoms abate.
urticaria (hives)
While respecting the patient’s dignity, fully expose their body to identify skin reactions.
Skin/mucosal changes are often the first presenting feature of anaphylaxis and occur in over 80% of anaphylactic reactions, but their absence does not exclude the diagnosis of anaphylaxis.[7]
Urticaria can be anywhere on the body, are usually very itchy, and are associated with anaphylaxis.[32]
Urticaria can be characterised by blanching, raised, palpable wheals, which can be linear, annular (circular), or arcuate (serpiginous).[32]
erythema
While respecting the patient’s dignity, fully expose their body to identify skin reactions.
pruritus
While respecting the patient’s dignity, fully expose their body to identify skin reactions.
rhinitis
Examine mucus membranes as rhinitis is often an early sign of progressive respiratory involvement together with bilateral conjunctivitis.
bilateral conjunctivitis
Examine mucus membranes as conjunctivitis, including redness, excessive tearing, sensitivity to light, a feeling of grittiness, swelling of the eyelids, and itchiness is often an early sign of progressive respiratory involvement together with rhinitis.
Other diagnostic factors
common
risk factors
Your history should cover risk factors including:
Exposure to a common sensitiser (see table below)
Previous anaphylaxis.
Common anaphylaxis triggers |
Food (in alphabetical order):[32][69]
Note that prevalence is greatest in children and decreases with age.[41] Anaphylaxis can also be caused by handling or inhalation of the food aerosol. |
|
Venoms (insect bites and stings):[32]
|
Latex:[32] |
Exercise:[32]
|
Hot or cold exposure: |
Idiopathic (unknown cause)[32] |
Potentiating co-factors |
Potentiating co-factors may increase the risk or severity of an allergic reaction. Examples include: |
Practical tip
Many patients are unaware of their food allergy and/or may be unaware that a particular food includes the allergen.
nausea, vomiting, diarrhoea, and incontinence
Identify symptoms that may be associated with anaphylaxis, but which do not necessarily indicate it. Nausea, vomiting, diarrhoea, and incontinence may occur together or singly and suggest allergen ingestion.
abdominal cramps and pain
Identify symptoms that may be associated with anaphylaxis, but which do not necessarily indicate it. Abdominal cramps and pain may occur alone or together with nausea, vomiting, and diarrhoea. These symptoms suggest allergen ingestion.
agitation, anxiety, and a sense of impending doom (angor animi)
Identify the emotions that may accompany anaphylaxis, including fear, apprehension, worry, and disorientation.
May be triggered by administration of adrenaline (epinephrine), but tends to resolve as the other allergic symptoms improve.
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