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Created page with "==Introduction== Anaphylaxis generally refers to the '''systemic anaphylactic reaction''', which is a severe type 1 hypersensitivity reaction after th..."
==Introduction==
Anaphylaxis generally refers to the '''systemic anaphylactic reaction''', which is a severe [[Type I Hypersensitivity|type 1 hypersensitivity]] reaction after the animal has become sensitised to a substance.
It is '''mediated by IgE''' and characterised by the release of vasoactive substances from '''mast cells''' and basophils.
Signs occur within '''seconds to minutes''' after exposure to the allergen.
A multitude of agents can trigger anaphylaxis, including: '''foods, insect venoms from bites and stings, and any drug or blood product'''.
The primary organs affected differ between cats and dogs.
In '''dogs''', the major shock organ is the '''liver''' and mast cell degranulation in the portosystemic vasculature causes venous dilatation and pooling of blood.
In '''cats''', the major shock organs are the '''lungs''' and mast cell degranulation in the pulmonary vasculature causes constriction of bronchial airways or pulmonary veins and pooling of blood in the pulmonary vascular bed, which results in severe respiratory distress.
All other organs are affected due to the resultant hypovolaemia and hypoxaemia.
'''Disseminated intravascular coagulation''' (DIC) can lead to haemorrhages.
==Clinical Signs==
In '''dogs''', these include: restlessness, '''[[Urticaria|urticaria]], angioedema''', nausea, vomiting, diarrhoea, weakness, dyspnoae, collapse and possibly death.
In '''cats''', these include: restlessness, pruritus, vocalisation, vomiting, defecation, weakness, tachypnoea, '''bronchoconstriction, laryngeal dysfunction''', pulmonary oedema and possibly death.
==Diagnosis==
There may be a known exposure to a substance, such as the administration of a drug or envenomation by an insect or snake.
The timing of the clinical signs following exposure is often a valuable diagnostic clue.
At '''post-mortem''': dogs will show: hepatic and splanchnic congestion and gastrointestinal haemorrhage
Cats will show: laryngeal oedema, bronchoconstriction, emphysema and pulmonary haemorrage.
==Treatment==
The agent causing the anaphylaxis should be eliminated if possible, or the suspect drug should be discontinued.
For acute and severe anaphylaxis, the treatment is '''intravenous epinephrine''' to counteract bronchoconstriction and vasodilation and increase blood pressure. It can also be given intramuscularly if necessary.
'''Antihistamines''' are of no benefit in acute anaphylaxis, but may be used if there are only mild signs and urticaria. Drugs such as ranitidine or famotidine can be given.
'''Glucocorticoids''' such as prednisolone or dexamethasone can antagonise the delayed mechanisms of the allergic reaction, but take several hours to act.
'''Ancillary support''' for blood pressure include: '''fluids''' such as crystalloids or colloids to expand the intravascular volume.
Vasopressors such as '''dopamine'''
'''Bronchodilators''' for cats such as terbutaline or albuterol.
'''Oxygen''' is always indicated and can be given in a flow-by system.
The '''prognosis''' is very good if treatment is rapid and the response is immediate.
{{Learning
|flashcards = [[Small Animal Emergency and Critical Care Medicine Q&A 17]]
}}
==References==
Merck and Co (2008) '''The Merck Veterinary Manual''' ''Merial''
Wingfield, W. (2002) '''The veterinary ICU book''' ''Teton NewMedia''
Mazzaferro, E. (2011) '''Blackwell's 5-minute consult clinical companion''' ''Wiley-Blackwell''
[[Category:To Do - Helen]]
[[Category:To Do - Review]]
Anaphylaxis generally refers to the '''systemic anaphylactic reaction''', which is a severe [[Type I Hypersensitivity|type 1 hypersensitivity]] reaction after the animal has become sensitised to a substance.
It is '''mediated by IgE''' and characterised by the release of vasoactive substances from '''mast cells''' and basophils.
Signs occur within '''seconds to minutes''' after exposure to the allergen.
A multitude of agents can trigger anaphylaxis, including: '''foods, insect venoms from bites and stings, and any drug or blood product'''.
The primary organs affected differ between cats and dogs.
In '''dogs''', the major shock organ is the '''liver''' and mast cell degranulation in the portosystemic vasculature causes venous dilatation and pooling of blood.
In '''cats''', the major shock organs are the '''lungs''' and mast cell degranulation in the pulmonary vasculature causes constriction of bronchial airways or pulmonary veins and pooling of blood in the pulmonary vascular bed, which results in severe respiratory distress.
All other organs are affected due to the resultant hypovolaemia and hypoxaemia.
'''Disseminated intravascular coagulation''' (DIC) can lead to haemorrhages.
==Clinical Signs==
In '''dogs''', these include: restlessness, '''[[Urticaria|urticaria]], angioedema''', nausea, vomiting, diarrhoea, weakness, dyspnoae, collapse and possibly death.
In '''cats''', these include: restlessness, pruritus, vocalisation, vomiting, defecation, weakness, tachypnoea, '''bronchoconstriction, laryngeal dysfunction''', pulmonary oedema and possibly death.
==Diagnosis==
There may be a known exposure to a substance, such as the administration of a drug or envenomation by an insect or snake.
The timing of the clinical signs following exposure is often a valuable diagnostic clue.
At '''post-mortem''': dogs will show: hepatic and splanchnic congestion and gastrointestinal haemorrhage
Cats will show: laryngeal oedema, bronchoconstriction, emphysema and pulmonary haemorrage.
==Treatment==
The agent causing the anaphylaxis should be eliminated if possible, or the suspect drug should be discontinued.
For acute and severe anaphylaxis, the treatment is '''intravenous epinephrine''' to counteract bronchoconstriction and vasodilation and increase blood pressure. It can also be given intramuscularly if necessary.
'''Antihistamines''' are of no benefit in acute anaphylaxis, but may be used if there are only mild signs and urticaria. Drugs such as ranitidine or famotidine can be given.
'''Glucocorticoids''' such as prednisolone or dexamethasone can antagonise the delayed mechanisms of the allergic reaction, but take several hours to act.
'''Ancillary support''' for blood pressure include: '''fluids''' such as crystalloids or colloids to expand the intravascular volume.
Vasopressors such as '''dopamine'''
'''Bronchodilators''' for cats such as terbutaline or albuterol.
'''Oxygen''' is always indicated and can be given in a flow-by system.
The '''prognosis''' is very good if treatment is rapid and the response is immediate.
{{Learning
|flashcards = [[Small Animal Emergency and Critical Care Medicine Q&A 17]]
}}
==References==
Merck and Co (2008) '''The Merck Veterinary Manual''' ''Merial''
Wingfield, W. (2002) '''The veterinary ICU book''' ''Teton NewMedia''
Mazzaferro, E. (2011) '''Blackwell's 5-minute consult clinical companion''' ''Wiley-Blackwell''
[[Category:To Do - Helen]]
[[Category:To Do - Review]]