Anaphylactic Shock

Flashcards about Anaphylactic Shock

Anaphylactic Shock

An immediately life-threatening hypersensitive immune response to an allergen, involving 2 or more body systems.

Pathophysiology of Anaphylactic Shock

Inflammatory mediators (histamine, tryptase, leukotrienes, prostaglandins, platelet-activating factor, cytokines, chemokines) are released when cells degranulate.

Tryptase

Tryptase levels rise within minutes of an anaphylactic reaction and peak between 30 and 90 minutes. An elevated tryptase has been associated with anaphylaxis.

Haemodynamic Effects of Anaphylactic Shock

Massive vasodilation, increased vascular permeability, peripheral pooling, relative hypovolaemia which causes a drop in cardiac output which reduces organ and tissue perfusion. Constriction of extravascular smooth muscle which causes constriction of the larynx and bronchioles which reduces oxygen intake which causes hypoxaemia and hypoxia which causes organ and tissue death

Clinical Signs and Symptoms of Anaphylactic Shock

Rash (hives) (urticaria), burning/itching skin, throat swelling, anxiety, difficulty breathing, GI cramps, vomiting, hypotension, bronchospasm, oedema, decreased LOC as BP drops, death.

Treatment for Anaphylactic Shock

Remove trigger, administer high flow 100% oxygen, auscultate for bronchospasm, administer warm fluid resuscitation, blood tests including VBG/ABG, restore/maintain normothermia, and monitor urine output. Administer 0.5mg of intramuscular 1:1,000 adrenaline, repeated every 5 minutes as necessary.

Why is adrenaline the treatment for anaphylaxis?

Adrenaline has a vasodilator effect in skeletal muscle, skeletal muscle is well vascularised; after intramuscular injection into the vastus lateralis (mid-anterolateral thigh), absorption is rapid and adrenaline reaches the central circulation rapidly.

Fluid Resuscitation

Administer as much crystalloid as is required to restore/maintain MAP>65mmHg. There is no loss of haemoglobin during anaphylaxis.

Angioedema

Facial oedema, Superficial itch, Generalised rash with raised wheals, Respiratory wheeze, Abdominal pain, Hypotension. It develops more slowly, typically over a few hours, although lethal cases are reported, with a very short history. There are no systemic effects. Treatment is nebulised adrenaline.