These potent coagulants act as prothrombin converters, resulting in consumption of fibrinogen. This may result in rapid complete defibrination (within 30 minutes of the bite), with resulting bleeding tendency, though platelet function and numbers are usually normal, at least initially. In some species, unless adequate antivenom is given, the coagulopathy may be prolonged (eg brown snakes, taipans), while in others it may be initially severe, yet resolve spontaneously within 12 to 18 hours without antivenom treatment (eg tiger snakes). In the latter situation there may be residual raised fibrin(ogen) degradation products present up to 24 hours after the bite, giving a clue to what has occurred. Major haemorrhage associated with snakebite coagulopathy is not very common, nor is it rare, with intracranial bleeding a particular worry.
|Extensive haematoma associated with attempted insertion of jugular venous line in a patient with snake bite coagulopathy.|
Key early signs include; persistent ooze from the bite site or venepuncture sites and signs of cerebral irritation (if intracranial haemorrhage).
Key laboratory tests; prothrombin time/INR (International Normalised Ratio), APTT, complete blood picture (platelet count), fibrinogen level, fibrin(ogen) degradation products (such as XDP = d-dimer), TCT (thrombin clotting time). If in a country hospital without ready access to laboratory facilities, a whole blood clotting time is useful (see details of test).
Key species; brown snakes, tiger snakes, taipans, rough scaled snake, broad-headed snake, Stephen's banded snake, pale-headed snake.
Value of antivenom treatment: antivenom is the only effective treatment of snakebite defibrination coagulopathy and sometimes many vials of antivenom may be required. It is important to wait at least 3 hours after a dose before deciding to give further antivenom, as the key measure of effective treatment, a rise in fibrinogen (not returning to normal), will take at least this long to become apparent.