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Diagnosis & Treatment — General practitioner / health post

 

General problems

At particular risk are: children, elderly people, patients with pre-existing conditions, such as coronary heart disease, arterial hypertension, lung disease, kidney disease, allergies (sensitisation), patients with predilection sites for bleeding such as gastrointestinal ulcers, kidney stones, pulmonary cavities (tuberculous), and patients taking particular drugs, such as coumarin derivatives, platelet aggregation inhibitors and beta-blockers.

Patient presents with a tourniquet on the affected extremity

D  Diagnostics

Check venous and arterial blood supply in the extremity.

C  Comments

If a tourniquet has been applied, it should not be removed until antivenom is at hand or has already been administered and the means for treating complications, including possible complications caused by the antivenom, are available (Leviton et al. 1992).

If these requirements cannot be met within a suitable period of time, it is necessary to weigh the risk of the systemic effects of the venom that could occur after removing the tourniquet against the risk of progressive local tissue damage that may arise if the bandage is left in place.

Is it likely that a clinically relevant injection of venom has taken place?

D  Diagnostics

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.
C  Comments

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

D  Diagnostics

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.

C  Comments

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).

Who requires antivenom?

D  Diagnostics

Antivenom indications (overview)
Systemic signs of envenoming:

  • (acute) arterial hypotension,
  • (persistent) arterial hypotension,
  • haemostatic defects (clinically, laboratory parameters: clotting time or more complex tests),
  • cranial nerve deficits (ptosis, ophthalmoplegia, dysphagia, dysarthria),
  • paralysis of the limb musculature,
  • paralysis of the respiratory musculature (→ respiratory insufficiency/failure),
  • acute renal failure.

Local signs of envenoming:

  • in the case of (rapidly) progressive or already marked swelling, especially following bites by those species of snakes known to cause necrosis.

How is the appropriate antivenom chosen?

D  Diagnostics

How are antivenoms administered and complications caused by antivenoms treated?

T  Treatment
C  Comments

Symptomatic emergency medical treatment and antivenom treatment are complementary strategies.

The aim of antivenom treatment is neutralisation of the venom. The success of antivenom treatment depends on the quality of the antivenom, the specific properties of those venom components relevant to envenoming and the time point at which antivenom is administered.

Symptomatic emergency medical treatment
1. Clinical signs of shock

S  Signs & Symptoms

Very early: anaphylactic/anaphylactoid shock (uncommon).

T  Treatment
  • Treatment of the anaphylactic/anaphylactoid shock,
  • possibly antivenom.
S  Signs & Symptoms

Early (within hours): generalised fluid sequestration caused by increased capillary permeability → hypovolaemic shock. 

T  Treatment
  • Treatment of the hypovolaemia/hypovolaemic shock,
  • antivenom.
S  Signs & Symptoms

Extensive swelling, entire extremity, possibly involving the trunk (regional fluid sequestration caused by increased capillary permeability) hypovolaemic shock.

T  Treatment
  • Treatment of the hypovolaemia/hypovolaemic shock,
  • antivenom.
S  Signs & Symptoms

Usually late (hours to days after the bite): clinical signs of extensive blood loss → haemorrhagic shock.

T  Treatment
  • Treatment of the haemorrhagic shock,
  • antivenom.

Symptomatic emergency medical treatment
2. Clinical signs of progressive paralysis; paralysis of the respiratory musculature (→ dyspnoea, respiratory failure)

T  Treatment

Symptomatic emergency medical treatment
3. Clinical signs of focal neurological deficits, meningismus (intracranial bleeding!)

T  Treatment
  • Treatment of the intracranial bleeding,
  • antivenom.
C  Comments

Symptomatic emergency medical treatment and antivenom treatment are complementary strategies.

The aim of symptomatic emergency medical treatment is the rapid correction of critical parameters (fluid balance, blood pressure, oxygenation etc.) and the maintenance of vital functions (respiratory, cardiovascular).

Symptomatic measures help bridge the gap until specific treatment (antivenom) can be administered and starts being effective. If no antivenom is available or if the required effect is not achieved with antivenom, the goal is to employ symptomatic measures until such time as the venom naturally starts losing its activity.

Local treatment

1. Bite wound, including the surrounding reaction

D  Diagnostics
  • Assessment of the wound according to the usual criteria.
  • Swelling: assessment of the extent and increase in magnitude; regional signs of haemorrhage.
  • Long-term: observation for the formation of necrosis.

T  Treatment
  • Cleaning, disinfection and dressing of the wound at regular intervals.
  • Immobilisation of the extremity with a splint.
  • Padding and monitoring to prevent pressure necrosis and disturbance of the blood circulation if the oedema increases.
  • Possibly also prophylactic antibiotic treatment:
    • no interference with the bite wound: penicillin or erythromycin,
    • bite wound has been interfered with (incisions etc.): penicillin or erythromycin + aminoglycoside (Warrell 1990b).

2. Eyes, mucous membranes

D  Diagnostics
  • Inspection.
  • Eyes: split lamp, fluorescein stain.
T  Treatment

Irrigation with water.

Corneal lesions: local antibiotic (tetracycline, chloramphenicol) for the prevention of secondary infections and covering the eye (Warrell and Ormerod 1976). If a corneal lesion cannot be diagnosed because the necessary instruments are not available, the eye should be treated as if a corneal lesion were present (Warrell 1990b).

Tetanus

T  Treatment

Tetanus prophylaxis.