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    ANAPHYLAXIS

    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, generalized oedema, pruritus, rash, vomiting,
    diarrhoea and 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 assessing 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:     Adult:  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
    assisted 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.

    Nebulized  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
    desensitization to the allergen should be considered. 

    AUTHOR(S)/REVIEWERS

    Author:        Dr R. Fernando, National Poison 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.