Reasonable Rascal
09-24-01, 09:01
DEFINITION
Anaphylaxis is an immunological description of a type I hypersensitivity reaction mediated by IgE or IgG.
Clinically, the term is used to describe a group of symptoms (see "clinical diagnosis" for complete description) irrespective of the mechanism. Where an immunological basis for the syndrome is unproven, the term anaphylactoid" is used.
Clinical expression of anaphylaxis is variable in severity but cardiovascular collapse is the most common
life-threatening feature and bronchospasm occurs frequently.
TOXIC CAUSES
Innumerable substances may cause anaphylaxis. Common causative agents include:
Antivenoms
Blood products
Chemicals
Drugs:
Antibiotics
Antiinflammatory agents
Analgesics
Chemotherapeutic agents
Local anaesthetic agents
Neuromuscular blocking drugs
Radiocontrast agents
Foods:
Nuts
Shellfish
Insect stings
Latex
Plants
CLINICAL FEATURES
History of exposure to a substance capable of producing anaphylaxis and appropriate clinical manifestations.
These may include:
hypotension
bronchospasm
upper airways obstruction
pulmonary oedema, angioedema
generalised oedema
pruritus
rash
vomiting
diarrhoea
abdominal pain
In some cases, there may not be a clear history of exposure.
DIFFERENTIAL DIAGNOSIS
Anxiety
Asthma
Bronchospasm or laryngeal oedema due to inhalation of irritant gases
Cardiogenic shock
Foreign body in upper airway
Hypovolaemia
Pulmonary embolism
Vasovagal episode
RELEVANT INVESTIGATIONS
In such an emergency situation, no biomedical investigations are required to commence treatment.
TREATMENT
Epinephrine (Adrenaline)
Epinephrine is the preferred treatment for anaphylaxis and should be administered as soon as practicable while rectumessing and supporting vital functions. It is usually given intramuscularly but may be given
subcutaneously in mild cases. Intravenous administration is only indicated in severe cases because of the risk of ventricular dysrhythmias. In the intubated patient, endotracheal installation is possible if intravenous access is unavailable.
Doses of epinephrine:
1) Intramuscular / subcutaneous:
Adult: 0.5 to 1.0 mg
Paediatric: 0.01 mg/kg
or
Age Epinephrine 1:1000 solution
< 1 year 0.05 mL
1 year 0.1 mL
2 years 0.2 mL
3- 4 years 0.3 mL
5 years 0.4 mL
6 -12 years 0.5 mL
> 12 years 0.5 to 1 mL
The appropriate dose should be repeated every 3 to 10 minutes until an adequate response in pulse and blood pressure is observed.
2) Intravenous:
dult: 0.1 mg (1 mL of 1:10000 solution made by diluting 1 mg of epinephrine in 10 mL of normal saline) over 2 to 3 minutes.
Paediatric: 0.01 mg/kg over 2 to 3 minutes.
The appropriate dose should be repeated until an adequate response in pulse and blood pressure is observed.
Notes on epinephrine therapy:
The dosage of epinephrine is NOT one ampoule. For the intubated patient, if intravenous injection is not possible, intratracheal instillation (1 to 3 mg) is an alternative. Patients on beta-blockers may require larger doses of epinephrine.
Oxygen
Supplemental oxygen should be administered to all patients. In severe cases, especially those with airways obstruction, establishment of an adequate airway (endotracheal intubation or tracheotomy) and / or rectumisted
ventilation may be necessary.
Fluids
In patients presenting with hypotension, one to two litres of intravenous fluids should be given as soon as intravenous access is established. Colloid is preferable to crystalloid but either is acceptable. Persistent hypotension should be treated with further doses of epinephrine.
Further administration of intravenous fluids should be cautious and ideally titrated against central venous
pressure.
Corticosteroids are not life-saving and are never the primary therapy of acute anaphylaxis. They may be useful in the treatment of bronchospasm and in the prevention of relapses. An intravenous dose of 200 to 300 mg of hydrocortisone (or equivalent dose of another corticosteroid) may be given.
Nebulised salbutamol (albuterol) may be useful for refractory bronchospasm, particularly in children.
CLINICAL COURSE AND MONITORING
There is usually a rapid response to therapy and recovery is complete. Pulse, blood pressure, respiration and oxygen saturation must be monitored until full recovery.
LONG TERM COMPLICATIONS
Recurrent episodes of anaphylaxis.
The agent that caused the anaphylaxis should be identified where possible and the patient adequately advised regarding the avoidance of further reactions. A warning device or letter should be issued. Patients who suffered life-threatening anaphylaxis should be instructed in the self-use of epinephrine. The need for desensitisation to the allergen should be considered.
AUTHOR(S) / REVIEWERS
Author: Dr R. Fernando, National Poisons Information Centre, Colombo, Sri Lanka.
Reviewers: Cardiff 3/95, Berlin 10/95: A. Jaeger, R. Dowsett, J. Szajewski, V. Danel, A. Wong. Cardiff 9/96: V Afanasiev, T Della Puppa, J Huang, G. Muller, L Murray, J Szajewski, C Warden.
Anaphylaxis is an immunological description of a type I hypersensitivity reaction mediated by IgE or IgG.
Clinically, the term is used to describe a group of symptoms (see "clinical diagnosis" for complete description) irrespective of the mechanism. Where an immunological basis for the syndrome is unproven, the term anaphylactoid" is used.
Clinical expression of anaphylaxis is variable in severity but cardiovascular collapse is the most common
life-threatening feature and bronchospasm occurs frequently.
TOXIC CAUSES
Innumerable substances may cause anaphylaxis. Common causative agents include:
Antivenoms
Blood products
Chemicals
Drugs:
Antibiotics
Antiinflammatory agents
Analgesics
Chemotherapeutic agents
Local anaesthetic agents
Neuromuscular blocking drugs
Radiocontrast agents
Foods:
Nuts
Shellfish
Insect stings
Latex
Plants
CLINICAL FEATURES
History of exposure to a substance capable of producing anaphylaxis and appropriate clinical manifestations.
These may include:
hypotension
bronchospasm
upper airways obstruction
pulmonary oedema, angioedema
generalised oedema
pruritus
rash
vomiting
diarrhoea
abdominal pain
In some cases, there may not be a clear history of exposure.
DIFFERENTIAL DIAGNOSIS
Anxiety
Asthma
Bronchospasm or laryngeal oedema due to inhalation of irritant gases
Cardiogenic shock
Foreign body in upper airway
Hypovolaemia
Pulmonary embolism
Vasovagal episode
RELEVANT INVESTIGATIONS
In such an emergency situation, no biomedical investigations are required to commence treatment.
TREATMENT
Epinephrine (Adrenaline)
Epinephrine is the preferred treatment for anaphylaxis and should be administered as soon as practicable while rectumessing and supporting vital functions. It is usually given intramuscularly but may be given
subcutaneously in mild cases. Intravenous administration is only indicated in severe cases because of the risk of ventricular dysrhythmias. In the intubated patient, endotracheal installation is possible if intravenous access is unavailable.
Doses of epinephrine:
1) Intramuscular / subcutaneous:
Adult: 0.5 to 1.0 mg
Paediatric: 0.01 mg/kg
or
Age Epinephrine 1:1000 solution
< 1 year 0.05 mL
1 year 0.1 mL
2 years 0.2 mL
3- 4 years 0.3 mL
5 years 0.4 mL
6 -12 years 0.5 mL
> 12 years 0.5 to 1 mL
The appropriate dose should be repeated every 3 to 10 minutes until an adequate response in pulse and blood pressure is observed.
2) Intravenous:
dult: 0.1 mg (1 mL of 1:10000 solution made by diluting 1 mg of epinephrine in 10 mL of normal saline) over 2 to 3 minutes.
Paediatric: 0.01 mg/kg over 2 to 3 minutes.
The appropriate dose should be repeated until an adequate response in pulse and blood pressure is observed.
Notes on epinephrine therapy:
The dosage of epinephrine is NOT one ampoule. For the intubated patient, if intravenous injection is not possible, intratracheal instillation (1 to 3 mg) is an alternative. Patients on beta-blockers may require larger doses of epinephrine.
Oxygen
Supplemental oxygen should be administered to all patients. In severe cases, especially those with airways obstruction, establishment of an adequate airway (endotracheal intubation or tracheotomy) and / or rectumisted
ventilation may be necessary.
Fluids
In patients presenting with hypotension, one to two litres of intravenous fluids should be given as soon as intravenous access is established. Colloid is preferable to crystalloid but either is acceptable. Persistent hypotension should be treated with further doses of epinephrine.
Further administration of intravenous fluids should be cautious and ideally titrated against central venous
pressure.
Corticosteroids are not life-saving and are never the primary therapy of acute anaphylaxis. They may be useful in the treatment of bronchospasm and in the prevention of relapses. An intravenous dose of 200 to 300 mg of hydrocortisone (or equivalent dose of another corticosteroid) may be given.
Nebulised salbutamol (albuterol) may be useful for refractory bronchospasm, particularly in children.
CLINICAL COURSE AND MONITORING
There is usually a rapid response to therapy and recovery is complete. Pulse, blood pressure, respiration and oxygen saturation must be monitored until full recovery.
LONG TERM COMPLICATIONS
Recurrent episodes of anaphylaxis.
The agent that caused the anaphylaxis should be identified where possible and the patient adequately advised regarding the avoidance of further reactions. A warning device or letter should be issued. Patients who suffered life-threatening anaphylaxis should be instructed in the self-use of epinephrine. The need for desensitisation to the allergen should be considered.
AUTHOR(S) / REVIEWERS
Author: Dr R. Fernando, National Poisons Information Centre, Colombo, Sri Lanka.
Reviewers: Cardiff 3/95, Berlin 10/95: A. Jaeger, R. Dowsett, J. Szajewski, V. Danel, A. Wong. Cardiff 9/96: V Afanasiev, T Della Puppa, J Huang, G. Muller, L Murray, J Szajewski, C Warden.