Funnel Web Spider Envenomation Treatment & Management

If possible and when expedient and safe, the spider should be killed and collected for identification.

A pressure immobilization bandage identical to that applied in the management of Australian snakebite should be applied immediately. ^[13] The dressing prevents migration of venom via lymphatics to the central circulation. Simultaneous immobilization (with a splint and/or sling) diminishes the muscle-pump effect on lymphatics and venous flow. Tourniquets are to be avoided.

Pressure immobilization must be maintained until the patient arrives at a hospital where antivenom is available.

Supportive care, including cardiac and respiratory life support, should be performed as necessary and according to the advanced cardiac life support (ACLS) protocol.

Most bites do not result in severe envenomation, although local pain at the site of the bite is common. When severe envenomation occurs, resuscitation measures and antivenin therapy should be instituted as necessary.

Funnel-web spider antivenom (CSL, Melbourne) is prepared by hyperimmunizing rabbits with the venom of A robustus. It has been effective in treating victims of a variety of species of Australian funnel-web spiders. Antivenom has been highly successful in the treatment of A robustus envenomation. Complete resolution of symptoms has occurred in 97% of patients treated with antivenom after confirmed funnel-web spider bites. Antivenom has been used successfully in pregnant women, breastfeeding women, and children. Anaphylaxis is a risk when giving antivenom. In a recent review, adverse effects consistent with anaphylaxis occurred in 2 patients of 75 treated with antivenom. One patient of the 75 developed serum sickness within 7 days of administration of antivenom. ^[1]

Premedication with an antihistamine and steroid to prevent anaphylaxis may be considered. However, premedication with epinephrine is contraindicated because of elevated catecholamine levels induced by the venom. Administration of epinephrine is appropriate if anaphylaxis occurs. Antivenom should be given in the ED or intensive care unit with close monitoring by medical and nursing staff. The initial dose of antivenom is 2 bottles intravenously, but most cases require 4 or more bottles.

Antivenom is indicated if any of the following are present:

• Muscle fasciculation

• Marked salivation or lacrimation

• Piloerection

• Significant tachycardia

• Hypertension in a previously normotensive patient

• Hypotension or shock

• Dyspnea

• Disorientation

• Confusion

• Depressed level of consciousness

As with any bite, ensure that tetanus immunization status is up to date.

Patients who respond to antivenom may be discharged within a day or so if no complications occur.

Management is more difficult if antivenom is unavailable; in such cases, the patient may need to spend many days in intensive care.

Important insights into management before the availability of antivenom have been provided by Fisher et al. ^[12]

Prolonged ventilation in the intensive care unit may be required for treatment of respiratory failure. Adequate sedation is essential.

Atropine has been used to provide parasympathetic blockade.

In the early stages, hypertension may be treated with alpha-blockers, but massive doses may be required.

Reversible agents are preferred because of the possible development of hypotension as envenomation progresses.

Theoretically, beta-blockade may be lethal (because of unopposed alpha-stimulation) and is not advocated.

Referral to an intensive care specialist may be necessary in cases of moderate-to-severe envenomation.

Advice from an experienced toxicologist practicing in an endemic area (eg, Sydney, Newcastle) should be sought in all funnel-web spider bites.

The New South Wales Poisons Information Centre has toxicologists available 24 hours a day.

Once successfully treated with antivenom and recovered from the acute illness, patients are unlikely to experience further complications. As with all patients receiving antivenom, the patient should be advised to seek medical care if signs of serum sickness occur.

Routine follow-up is not required; however, the theoretical risk of serum sickness caused by the foreign protein load of antivenom mandates that the patient be advised to report symptoms. Nevertheless, serum sickness has not yet been reported following treatment with funnel-web spider antivenom.