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,
- breathing (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),
- conjunctival oedema,
- clinical signs of a pleural effusion, pulmonary oedema,
- clinical signs of shock,
- bleeding in the region of the swelling,
- bleeding from bite marks and other injuries,
- 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),
- myalgia with active and passive movement and upon pressure,
- dark-brown/red urine (differential diagnosis haemoglobinuria) (rhabdomyolysis!),
- flank pain and renal bed sensitive to percussion,
- severe headache, shock (refractory arterial hypotension), signs of hypoglycaemia and loss of consciousness (acute pituitary/adrenal insufficiency).
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),
- blood sugar,
- 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. Approximately 50% of confirmed Cobra bites in Malaysia and Thailand proceed with no detectable symptoms or at the most negligible local signs of envenoming (Reid 1964, Viravan et al. 1986).
Local signs, e.g. swelling at the site of the bite, following viperid and crotalid bites, as well as bites of some Cobra species, are an indication that a significant injection of venom has occurred. With Kraits, however, there are no local signs at all, and they are also unreliable following D. russelli bites.
Krait bites in particular may be completely unnoticed and unrecognised initially, as these snakes often bite humans at night while they are asleep. A Krait bite is thus an important differential diagnosis of signs of paralysis (of the cranial nerves, extremities, respiratory musculature).
Abdominal pain is recognized as a characteristic symptom of some kraits, in particular B.caeruleus (Ariaratnam et al 2008).
Clinically evident signs of a haemostatic defect may be absent. Nonetheless defibrin(ogen)ation may be present to such a degree that the blood is completely incoagulable. For this reason the simple clotting time test should always be performed if a viperid or crotalid bite is suspected.
To date, acute pituitary/adrenal insufficiency has only been reported in Myanmar, southern India and Sri Lanka. It is a complication of D. russelii siamensis and D. russelli russelli (pituitary) and D. russelii pulchella bites (adrenal) and generally does not occur during the acute phase of severe envenoming, but shortly thereafter. A simple rapid diagnostic test for blood sugar and observation of the patient's treatment-resistant hypotensive condition aid in the differential diagnosis (see the Biomedical database entry for D. russelii).
Exclusion of clinically relevant envenoming
Monitoring for signs and symptoms (see above) that would indicate systemic envenoming for at least 24 h (Warrell 1990b) (recommended examinations, see Therapy phase: Hospital).
Preparalytic phase:
- Cobras: a few minutes to 24 h.
- Kraits: 30 min –12 h.
- Daboia russelii pulchella: neurological symptoms usually precede signs of a haemostatic defect.
Preclinical phase of haemostatic defects:
Viperids, crotalids and colubrids: even severe haemostatic defects that can be detected on laboratory tests may not become clinically evident for a long period.
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 long delay before systemic signs of envenoming develop.