Anaphylactic shock is as a fatal condition occurring rapidly after exposure to an antigen and producing clinical features of profound generalized shock, acute respiratory distress, asphyxia, severe hypotension, and death. While occurring most frequently with intravenous or intramuscular administration in highly sensitive persons, it can also happen after ingestion or inhalation of the antigenic substance.

The common offending agents are bee or wasp stings, serum; drug therapy is highly sentisized persons, injection of penicillin or local anaesthetics, and desensitization injections with pollen extracts.

If death is suspected to be due to anaphylactic shock, history should be obtained as regards the possible cause. Autopsy should be done as soon as possible as laryngeal oedema recedes after death and may not be observed. Many of the following features will be seen. These may be grouped under:
1. External Examination
2. Internal Examination
3. Microscopic Findings

External Examination

The sight of injection or sting must be sought, photographed, and excised with 5 cm margin of skin and underlying tissue for laboratory examination of antigen. There is usually local selling of the involved tissues.

There may be oedema of face, eyelids, conjunctivae and lips, all associated with angioneurotic oedema. Asphyxial changes include subconjunctival haemorrhages and froth in the mouth and nostrils. Generalised petechial hemorrhages in the skin are usually present due to vasodilatory and increased permeability effects of histamine and the like.

Internal Examination

There may be oedema of the glottis and epiglottis spreading to the vocal cords and causing laryngeal obstruction. This oedema recedes soon after death. Roman glories together with epiglottis should be photographed from above for a permanent record.

The tracheobronchial tree contains frothy fluid and mucus. The lungs are heavier than usual, greatly distended, and show alternating areas of pink emphysema and plum coloured collapse. Visceral pleural often shows scattered petechial hemorrhages. On cut section, the lung exudes copious frothy hemorrhagic fluid. A chest x-ray, if possible, should be taken.

Petechial hemorrhages may he found on the visceral pericardium and the pericardial sac may contain moderate straw coloured transudation. The right heart is enlarged due to acute pulmonary failure. A specimen of blood should be retained for immunological study (antibody titre) and drug levels.

There is acute congestion of abdominal viscera. Oedema or haemorrhage is sometimes is found around one or both renal pelves. The lymph nodes at porta hepatis and in the mesentery may be enlarged and hyperaemic.

The brain shows diffuse congestion often with petechial hemorrhages in white matter.

Microscopic Findings

When autopsy is done quickly laryngeal oedema recedes; however, submucosal laryngeal oedema and eosinophilic infiltration can still be seen on microscopic examination.

Histology of the lungs confirms diffuse or focal pulmonary distortion (acute emphysema) alternating with collapse and bronchial constriction (histamine effect). Pulmonary arteries and capillaries show marked dilatation.

Hyperelaemia and occasional hemorrhages may be seen in the Peyer's patches 0f the small intestine, lymph nodes of the aorta hepatis, and lymph nodes of the mesentery. Spleen shows eosinophilic leukocytes in the red pulp.

Before administering the injection of penicillin or local anaesthetics and desensitization injections with pollen extracts, the Doctors must first ensure whether the patient is sensitive or allergic to penicillin or any other local anaesthetics and must exercise great care and caution as a reasonably prudent person is expected to.

As Anaphylaxis is a fatal, life-endangering, systemic reaction or generalised hypersensitivity reaction, which is characterized by the fast developing of life complicating problems involving the airway pharyngeal or laryngeal oedema, breathing bronchospasm with tachypnoea, circulation hypotension or tachycardia, or a combination of these, especially as they are associated skin and mucosal changes, yet the symptoms of anaphylaxis may be due to other causes also such as an acute cardio vascular or respiratory event.

Thus, the measurement of Tryptase serum should always be examined with an analysis of allergen – specific immunoglobulin E antibodies or, if no allergen is known, a panel of common airborne and food allergens should be measured and tested. Knowledge of the patient’s history is of vital importance while investigating suspected anaphylaxis.

Written by: Navin Kumar Jaggi and Gurmeet Singh Jaggi