big black spider…

The Case.

A sunny Saturday morning in Sydney and your 56 year old patient was just outside doing some gardening when they feel a rather sharp bite on their right hand (on webspace between thumb and index finger).

He arrives to the ED distressed and very anxious. His vitals signs are normal and he has localised pain only.

He then hands you this saying “this is the bugger that bit me !!”  …..

  

Where do you go from here ??

BIG BLACK SPIDER

A niche post for my East-Coast Australian colleagues….

In Australia, spiders are incredibly common & their bites occur more frequently than snakebites. Luckily for us, spider-bites are usually trivial and require no treatment. There are however two groups of spiders that can cause significant envenomation;

  1. Red Back Spiders
  2. Funnel Web Spiders
A Funnel Web Spider     
A Red Back Spider        

Funnel Web Spiders are arguably the most deadly spiders worldwide, but are confined to the eastern coast of Australia. Creating a diagnostic dilemma is the fact that the potentially lethal Funnel-Web looks very similar to other ‘big black spiders’  that can inhabit the same area. These include trap-door spiders and mouse-spiders.

The following decision algorithm was created to help differentiate between these spiders, classifying them into three groups; 1. big black spiders (which includes the Funnel-Web) 2. Red Back Spiders and 3. all others (which are generally unlikely to cause significant effects).

**taken from NSW Health Guideline / adapted from Isbister & Sibbritt 2004 **

Clinical Features.

The bite is usually witnessed and very painful. Fang marks are often visible.

The Funnel Web produces a venom that contains potent neurotoxins which prevent inactivation of sodium-channels and lead to a massive increase in autonomic activity and neuromuscular excitation.

Systemic envenomation develops rapidly (30-120 mins) and features include:

        • General (agitation, irritability, vomiting, headache and abdominal pain. Decrease LOC & coma can occur)
        • Autonomic (Sweating, piloerection, lacrimation, salivation)
        • CVS (Tachycardia, hypertension [alternatively hypotension & bradycardia can occur], pulmonary oedema.
        • Neurological (muscle fasciculation [esp. tongue], oral tingling, muscle spasm & coma).

Consider the diagnosis in a young child who presents with sudden severe illness with inconsolable crying, salivation, vomiting & collapse.

It is important to note that other BBS’s do not cause significant CVS, autonomic and neurological features. An important DDx is that of Red Back envenomation, which is heralded by the triad of local pain, sweating & piloerection. Again, it does not cause coma, fascicultations or pulmonary oedema.

Evaluation & Management.

Prehospital / First Aid.

        • Application of pressure immobilisation bandage

Hospital (General).

        • Do not remove first aid until ready to treat
        • Allocation to acute/resuscitation area capable of cardiorespiratory monitoring
            • Monitor closely, IV access (x2)
            • Bloods (FBC, Electrolytes, renal function, CK, Coags)
        • Preparation for management of respiratory failure, hyper or hypotension, pulmonary oedema & coma.
        • Relevant History:
            • Was spider seen? (description of spider)
            • ?multiple bites
            • Where (geographic place) and when (elapsed time)?
            • Timing of first aid
            • Details of symptoms
        • There is no venom detection available for spider-bites.

Hospital (Specific).

        • If there are any symptoms of systemic envenomation, give 2 vials of CSL Funnel Web Spider Antivenom IV.
        • In severe envenomation with dyspnoea, APO or altered LOC, give 4 vials of CSL Funnel Web Spider Antivenom IV
        • In cardiac arrest administration of undiluted antivenom via rapid IV push may be life saving (at least 4 vials should be given).
        • Be prepared to give more !! 8 vials is a common dose.

Antivenom Therapy.

        • Two vials is minimal dose
        • Children require the same dose as adults.
        • Further doses are often required and should be given until all significant symptoms and signs have resolved.
        • TWO IV lines are recommended (one for antivenom, one for potential anaphylaxis treatment).
        • No premedication is required.
        • Start infusion very slowly & observe for reaction (aim to have dose in within 15-20mins).

The majority of cases will be less obvious, and the patient is well with no apparent envenomation. The following flow chart (taken from the NSW Health’s Snakebite  & Spiderbite Clinical Management Guidelines) demonstrates a guide to observing and evaluating the various presentations of big black spider bites !

An envenomed patient treated with antivenom can be discharged at 12 hours if clinically well, however its best to not discharge them at night.

Essentially, if the patient is asymptomatic and has no clinical evidence of envenoming, then observe them for a minimum of 6 hours after the removal of first aid.

This is exactly what happened to our avid weekend gardener. He went home at the 6 hour mark (via the store to buy some thick gardening gloves).

References.

  1. Snakebite & Spiderbite Clinical Management Guidelines 2007 – NSW Health 
  2. Isbister GK, Sibbritt D. Developing a decision tree algorithm for the diagnosis of suspected spider bites. Emerg Med Australas. 2004 Apr;16(2):161-6.
  3. Isbister GK, Fan HW. Spider bite. Lancet. 2011 Dec 10;378(9808):2039-47. Epub 2011 Jul 15.
  4. Isbister GK et al. Funnel-web spider bite: a systematic review of recorded clinical cases. Med J Aust. 2005 Apr 18;182(8):407-11.
  5. Murray L, Daly F, Little M & Cadogan M. Toxicology Handbook. 2nd Edition. Elsevier 2011.
  6. http://www.thepoisonreview.com/2010/01/22/killer-funnel-web-spiders-invade-sydney/

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