Anaphylaxis

What is anaphylaxis?

A severe, life threatening, systemic allergic reaction to a previously encountered antigen, characterised by symptoms of the airways, GIT, and CV system, resulting in CV and/or respiratory system collapse

In NSW CPGs, one or more of what symptoms may indicate anaphylaxis?

• Difficult or noisy breathing

• Swelling/tightness in the throat

• Wheeze or persistent cough

• Difficulty talking and/or hoarse voice

• Swelling of the tongue

• Persistent dizziness or collapse

• Pale and floppy (young children)

• Persistent abdominal pain and vomiting after exposure to a likely allergen (including injected medications and insect bites/stings)

What is the first line treatment in anaphylaxis, and what are the doses?

IM adrenaline (1:1000)

Adults: 500mcg @ 5/60

Paeds: 10mcg/kg max 500mcg @ 5/60

How should you position the pt in anaphylaxis?

Supine preferred.

If airway involved elevate head as needed

DO NOT STAND OR WALK THE PT

What are signs and symptoms of mild to moderate allergic reaction?

• Swelling of lips, face, eyes

• Hives or welts

• Tingling mouth

• Vomiting

• Abdominal pain

Note: Abdominal pain and vomiting are specific signs of anaphylaxis for injected medications; insect bites and stings

What is the treatment for a hypovolaemic anaphylaxis pt?

CSL - 20ml/kg as needed

What is the treatment for a wheeze in an anaphylaxis pt?

Salbutamol nebulised

5yo+ : 5mg whilst indicated

<5yo: 2.5mg whilst indicated

What is the treatment for stridor in an anaphylaxis pt?

Adrenaline nebulised

16+ : 5mg (1:1000) @ 30/60 no max

<16yo : 500mcg/kg (1:1000) max 5mg. @ 30/60 no max

When is hydrocortisone admin in anaphylaxis and what is the dose?

If wheeze persists after admin of salbutamol

Adult: IM/IV 100mg (in 2ml) nil repeat

Paeds: IM/IV 4mg/kg max 100mg nil repeat

When is glucagon administered in anaphylaxis and what is the dose?

In pts taking beta blockers if signs of hypovolaemia persist after initial bolus of CLS

16yo+: 2mg IV

When is an adrenaline infusion indicated?

In pts 16yo+ who are unresponsive to 4 IM adrenaline injections

Basic patho of anaphylaxis

Second/subsequent exposure to previously encountered antigen → reaction with IgE antibody on mast cell → mast cell degranulation → release of mediators into blood stream: histamine, bradykinins, prostaglandins → increased permeability of capillaries → mucosal oedema/plugging/rashes/angioedema/movements of fluid into interstitial space ie hypotension

How does glucagon work in anaphylaxis?

it can find a different pathway and effects positive haemodynamic changes. It exerts positive inotrope and chronotropic effects by directly activating adenyl cyclase, and bypasses B-adrenergic blockade

How does adrenaline work in anaphylaxis?

Stabilises mast cells and basophils preventing further inflammatory mediator release, and reduces capillary permeability

Adrenaline is both A and B adrenergic receptor agonist.

Alpha - peripheral vasoconstriction

B1: increased rate and force of cardiac contraction

B2: bronchodilation

A+B: relaxes gastrointestinal smooth muscle