First aid for funnelweb spider envenomation is pressure-immobilisation.
Among the spiders, the Sydney funnelweb has the venom most dangerous to humans. Other species of funnelweb are also dangerous, and can cause a syndrome similar to the Sydney funnelweb, although probably less severe. This is also true of the related group, the mouse spiders. The following information applies to spiders in each group except where the distinction is specifically drawn.
Signs and Symptoms
The initial bite is usually painful and fang marks are generally seen. The envenomation syndrome is generally characterised by two phases: the first begins within minutes of the bite, and the second when the secretions subside – typically many hours later. Historically, deaths have occurred in either phase of envenomation. Phase 1 is characterised by:
- Pain at the bite site
- Local swelling, erythema and sweating
- Perioral numbness
- Fasciculation of the tongue
- Nausea and vomiting, abdominal pain, acute gastric dilation
- Excessive salivation, sweating, lachrymation, piloerection
- Dyspnoea, non-cardiogenic pulmonary oedema
- Lowered conscious state
- Hypertension, tachycardia, vasoconstriction
- Local and generalised fasciculation and spasm
- Hypotension
- Hypovetilation and apnoea
- Tachycardia
- Continuing non-cardiogenic pulmonary oedema
- Coma
- Irreversibe cardiac arrest
Treatment
- Ensure airway, breathing and circulation are maintained.
- Appliy pressure immobilisation bandage to the affected limb.
- Transfer to hospital, ideally where antivenom, resuscitation equipment and monitoring are available.
- Obtain intravenous access.
- Remove the bandage only in an area where appropriate resuscitation can occur and antivenom is available. (If the bandage has been removed and the patient deteriorates, it should be re-applied). Local tissue enzymes may inactivate the venom, therefore the use of a pressure immobilisation bandage may not only be helpful in delaying the onset of symptoms, but may allow for some inactivation of the venom.
- Administer antivenom as per protocol in the following section.
Until antivenom can take effect, supportive care of the envenomed patient may include:
- Supplemental oxygen
- Atropine (0.6 mg initial dose for an adult), to reduce salivation and bronchorrhoea
- Nasogastric aspiration because of gastric dilatation
- Muscle relaxants and sedatives to facilitate mechanical ventilation and control intracranial pressure
- Intubation and ventilation for respiratory failure and to reduce intracranial pressure (note: entotracheal intubation can be difficult as a result of excessive salivary secretions and violent fasciculations)
- Fluid resuscitation should be used with caution in the event of hypotension because of non-cardiogenic pulmonary oedema
Tetanus status should be assessed and prophylaxis provided if indicated.
Relapse is possible and may manifest as dyspnoea secondary to non-cardiogenic oedema, which usually responds to further antivenom (this should not be confused with iatrogenic pulmonary oedema as a result of intravenous overload, particularly in children).
If no symptoms or signs of envenomation have started 4 hours after the removal of first aid measures or post bite, the patient may be discharged (most patients presenting to hospital will not have been envenomed).
Antivenom
| The initial treatment for symptomatic funnelweb spider envenomation involves administration of two ampoules of monovalent Funnelweb Spider Antivenom. In severe cases, four ampoules should be given.
If no significant response has occurred in 15 minutes, the pressure immobilisation bandage should be reapplied if it has been removed, and a further two ampoules given. A continued poor response to antivenom should prompt reconsideration of the diagnosis. However, if funnelweb bite remains the diagnosis, further ampoules should be iven, since eight ampoules have been required on occasion. If improvement is seen in the patient's condition, the pressure immobilisation bandage can be removed. The patient should then be kept under observation, preferably in ICU, while further antivenom dosage is titrated against signs and symptoms. A case has been reported of an infant becoming critically ill after envenomation by a mouse spider. The administration of funnelweb antivenom appeared to reverse the condition and the child made a full recovery. Funnelweb spider antivenom supplied by CSL Ltd is leporine in origin. |
Photo: R. Lowe, AVRU
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Last updated: July 2005
