Anaphylaxis

Introduction-Anaphylactic reaction

· IgE -mediated type I hypersensitivity reaction.

· Effects are due to wide spread degranulation of mast cells.

· A dose independent unpredictable adverse drug reaction

 

Mechanism:

Commonly associated with a previous exposure to a similar group of drugs or chemicals. Foreign proteins act as antigens and stimulate production of IgEantibodies. They bind to mast cells and basophils, and with subsequent exposure massive degranulation occurs due to these already formed antibodies reacting with new antigens.

There is a massive release of mediators : Eg – Histamine, leukotrienes, tryptase, protease.

They give rise to bronchoconstriction, vasodilatation and increased capillary permeability. 

Anaphylactoid reaction

· A similar clinical picture

· Mast cell degranulation is without IgE involvement and mediated via other pathways; eg complement. No need of previous exposure.

§ Eg. Contrast media

Non-immunological histamine release

Only skin reactions

Commonly seen with atracurium, morphine, pethidine

Clinical features.

Several clinical features have been observed with varying incidence.

80%		Unexplained severe hypotension
		Tachycardia
		Cyanosis, desaturation
50%		Rashes
		Flushing / pallor
		Facial oedema
36%		Bronchospasm
30%		Pharyngeal, laryngeal, generalised oedema
		Pulmonary oedema
Minority		Increased oozing
		ECG changes

Common causative agents during anaesthesia.

             · Muscle relaxants –70 %

               Suxamethoneum – 40%

               Steroid based agents ( vecuroneum, pancuroneum ) – anaphylactic

               Benzylisoquinoliniums ( atracurium, mivacurium ) – anaphylactoid

               Cross allergy with wide variety of drugs, foods, cosmetics and hair care products.

 

 

            · Latex – 12%

              Allergy may also be seen with domestic rubber products. 

              Cross reactivity with banana, avocado

 

 

            · Colloids – 5%

        Common with gelatins

 

 

            · Induction agents –4%

        TPS – 1:14 000

        Propofol – less common

              Ketamine, etomidate – least common.

 

 

            · Antibiotics – 3%

              Penicillins, cephalosporins, imipenam
 

            · Opioids – 2%

              Morphine - commonest

              Rare with synthetic opioids

 

 

            · Other – 2%

               Radiocontrast

               Protamine

               Atropine

               Bone cement

               Blood and blood products.
 

 

Anaphylaxis Drill

Consider if the patient develops stridor, wheeze, respiratory difficulty, cyanosis or clinical signs of shock.
 

1. Immediate management

♦ Stop administration of all the causative agents likely to have caused the anaphylaxis.

♦ Call for help.

♦ Maintain the airway, give 100% oxygen and lie the patient flat with legs elevated.

♦ Give Epinephrine.

                 IM: – 0.5 – 1 mg (0.5 – 1 ml of 1:1000). May repeat every 5 min until improves.

                 IV: - 50 –100 µg (0.5 – 1 ml of 1:10000) over 1 min if in CVS collapse. Repeat as required at a rate of 0.1 mg/min

• required at a rate of 0.1 mg/min.
• Never give undiluted epinephrine 1:1000  iv.

♦ Give iv fluids; Crystalloids or colloids (those with less incidence of allergy). May require 2-3 liters.

Give CPR and ALS if in cardiac arrest!

2. Subsequent management.

♦ Give antihistamines - Chlorpheniramine ( H₁)10 – 20 mg by slow iv infusion.

                                        Ranitidine ( H₂ )50 mg slow iv infusion.

♦ Give Corticosteroids – Hydrocortisone 100 –500 mg slow iv.

♦ Bronchodilators may be required for persistent bronchospasm.

♦ Catecholamine infusion as CVS instability may last longer.

     Epinephrine 0.05 – 0.1 µg/kg/min.

   ♦ Check ABG for acidosis and consider bicarbonate 0.5 – 1 mmol/kg (8.4% - 1mmol /ml)

  ♦ Consider ICU care.

Investigations.

1. Mast cell tryptase – take samples immediately, after 1 hr and between 6-24 hrs.

5 – 10 ml blood, stored in -20°C.

2. Later– Skin prick tests for each of the drugs given.

3. Specific IgE Ab.

*** It is the responsibility of the doctor who administered the drug to counsel the patient and give a diagnosis card.

Management of a patient with previous anaphylaxis

· Try to identify the causative agent with history.

· Consider regional anaesthesia or inhalational induction.

· Premedicate with: Hydrocortisone

                                    H₁ & H₂ antagonists

                                    Inhaled β agonists

· Start all necessary monitoring before induction.

· Large bore cannula.

· Make sure availability of epinephrine and full resuscitation facilities.

· Use lesser risk drugs eg. Etomidate, fentanyl, benzodiazepines.

· Minimise drugs only to essential ones.