Is the patient envenomed?
Is it likely that a clinically relevant injection of venom has taken place?
Inquire re:
- time of the bite,
- local pain,
- nausea, vomiting, abdominal pain.
Assess:
- state of consciousness.
Measure:
- blood pressure/pulse,
- respiratory rate.
Observe/investigate:
- bite marks,
- extent and intensity of local swelling,
- eyes: conjunctivitis, corneal lesions, uveitis (spitting cobras!),
- enlargement and painfulness of regional lymph nodes,
- swelling in the facial region, including the larynx/pharynx (angio-oedema),
- clinical signs of pulmonary oedema,
- clinical signs of shock,
- bleeding from bite marks and other injuries,
- subcutaneous bleeding in the region of the swelling,
- gingival bleeding,
- blood-stained sputum, vomit ("coffee ground vomitus"), stools (melaena) or urine,
- acute abdomen (intra-abdominal bleeding!),
- focal neurological deficits, meningismus (intracranial bleeding!),
- cranial nerve deficits, such as ptosis, ophthalmoplegia, dysphagia, dysarthria,
- paralysis of the skeletal musculature including the respiratory musculature (→ respiratory insufficiency/respiratory failure),
- flank pain and renal bed sensitive to percussion.
Determine:
- cause of the accident by determination of specific venom antigen and venom concentration in the serum using the ELISA method (if clinically proven and standardised test kits are commercially available),
- clotting time (bedside test),
- urinary output.
The symptoms and degree of envenoming depend not only on the amount of venom injected and numerous other variables, but also on the time that has elapsed since the bite. This variable factor must be taken into account when making the following decisions:
- exclusion of envenoming (see below),
- the time interval between clinical examinations (see Therapy phase: Hospital),
- emergency care (see below).
The fact that a patient has been bitten by a known venomous snake and the presence of bite marks do not automatically allow the conclusion that a clinically relevant injection of venom has taken place.
On the other hand, local signs, e.g. swelling at the site of the bite, following viperid bites as well as bites of some elapid species (N. nigricollis, N. nubiae, N. pallida, N. katiensis, Walterinnesia aegyptia) are generally an indication that a significant injection of venom has occurred. With bites from the Cobra species N. haje (and possibly N.arabica, N. melanleuca and N. senegalensis), however, local signs of envenoming may be absent even in cases of severe systemic envenoming (Visser and Chapman 1978, Warrell et al. 1976a).
Noticeable bleeding may be absent even if the haemostatic defect has reached such a degree that the blood is completely incoagulable (clotting time test) (e.g. with Echis sp. bites). The tendency for spontaneous systemic bleeding appears to be significantly greater with E. carinatus sochureki, however, than with E. coloratus (Leviton et al. 1992).
The simple clotting time test should always be performed if a viper bite is suspected. Haematuria (especially microhaematuria) is not a reliable sign of a venom-induced haemorrhage in those regions where urinary schistosomiasis (Schistosoma haematobium) is prevalent.
Exclusion of clinically relevant envenoming
Monitoring for signs and symptoms (see above) that would indicate systemic envenoming for at least 24 h (Warrell 1990b). For recommended examinations, see Therapy phase: Hospital.
Preparalytic phase:
Elapids: a few minutes to hours.
Preclinical phase of haemostatic defects:
Viperids: even severe haemostatic defects that can be detected on laboratory tests may not become clinically evident for a long period or even not at all (see the Biomedical database entry for Echis sp.).
Preclinical phase of autopharmacological effects (anaphylactoid and hypovolaemic shock):
In particular Vipera palaestinae and Macrovipera sp.?: minutes to hours.
The absence of signs of envenoming in the first hours after the bite does not exclude the possibility that a relevant injection of venom has taken place. There can be a delay before systemic signs of envenoming develop. Moreover, the continued absorption of venom from the region around the site of the bite can lead to renewed symptoms of systemic envenoming even after successful administration of antivenom (correction of the haemostatic defect).