Spider bite

Presentation

• Local 
  • Asymptomatic through to severe local pain at bite site
    • Red back mild initial pain
    • Funnel web severe pain ++ at time of bite
  • Lymph nodes may swell/tender indicating venom movement
  • Necrotic arachnidism is an inappropriate diagnosis in Australia
• General systemic
  • Rare but may include nausea/vomiting, headache, abdo pain
• Specific systemic
  • Neuroexcitatory – Hypertension/hypotension, tachy/bradycardiac, piloerection, increased sweating, hypersalivation, muscle spasm, respiratory distress, fasciculations, severe abdominal or chest pain

Spiderbite in children

• May cause more severe and rapidly developing envenomation
• May not have clear history of spider bite and need high index of suspicion

Problem presentations

• Cryptic presentations are less common than snakebite
• Funnel web usually clear history of bite
• Red back spider commonly presents without witnessed bite but usually have clear symptoms suggesting this diagnosis
  • May have abdominal or chest pain without bite history
  • Often history of acute localised pain indicates true diagnosis

Funnel web spider

• Like taking meth and an organophosphate at the same time
• Painful bite, fang marks obvious
• Local bleeding
• Autonomic excitation
  • Diaphoresis, hypersalivation, lacrimation, piloerection, HTN, tachy/brady, miosis/mydriasis
• Neuromuscular excitation
  • Paraesthesiae, fasciculations, muscle spasm
• Non-specific systemic: 
  • Nausea/vomiting, headache, abdominal pain
• Rare
  • Pulmonary oedema, myocardial injury, drowsiness, coma
• Systemic envenoming within 4 hours but can be 10-15min

Red back spider

• Most common envenoming in Australia
• Usually feel bite but can be painless
• Local sweating, erythema/blanching or piloerection may occur
• Within minutes to an hour or more, significant local pain often with sweating
• Over hours, pain becomes more severe and spreads proximally, often with lymph node involvement
• Sweating may become regional with nausea, hypertension and malaise
• May mimic acute abdomen or cardiac chest pain
• Pain syndrome can last hours to days without treatment
• Classic presentation
  • Triad of progressive severe pain, marked sweating and hypertension
  • Triad of local bite site pain, sweating and piloerection
  • Gravitation of symptoms to lower limb i.e. burning sensation in soles of feet and lower leg pain/sweating even if bite site is elsewhere

RAVE-II

• No benefit to IV administration of antivenom over simple analgesia
• Many reported benefits in severe lactrodectism

First aid

• PBI for funnel web
  • PBI not to be removed until in resus with funnel web spider antivenom available, no clinical signs of envenomation, IV line in situ, adrenaline available
  • Can then remove PBI if not envenomed and monitor with full reassessment 1 hour later
  • If symptom free at 4 hours post-bite with first aid removed for at least 2 hours, can be discharged
• Intermittent ice for red back spider (PBI contraindicated as worsens pain)
  • If asymptomatic, do not need to monitor for any specified period of time but should advise to return if delayed symptom onset as antivenom can be effective days after bite
• Bites other than big black (i.e. possible funnel web) or red back do not need hospital assessment
• Advice all patients on risk of infection

Indications for funnel web antivenom

• Any degree of systemic envenomation (including just perioral tingling or tongue fasciculations) unless:
  • 4 hour already passed + first aid removed for at least 2 hours and symptoms have not progressed beyond mild envenoming for at least 2 hours
• Any patient with possible spider bite with excessive lacrimation, twitching of tongue, piloerection, significant tachycardia, respiratory distress, hypertension (or late hypotension), disorientation, confusion or depressed LOC
• Initial dose is 2 vials (4 vials if already severe) q15-30min until resolved
• Admit all patients overnight after antivenom delivery
• Give IV over 1-2 minutes
• Always 2 IV lines (one for resuscitation)

What if funnel web antivenom not available?

• Consider moving antivenom +- skilled clinician to patient
• Manage pulmonary oedema medically
• Alpha blockers for early hypertension
• Volume +- vasopressors for later hypotension

Indications for red back antivenom

• Severe intractable local or regional pain in a confirmed or strongly suspected red back spider bite where analgesia has proven ineffective
• Systemic envenoming
• Initial dose 2 vials
• Follow-up dosing of 2 vials with at least 2 hours in between to evaluate effectiveness of prior dose
• Do not exceed total of 4 vials without expert advice
• Dilute in N/S or Hartmann’s 100mL over 30 minutes
• Can give IM also undiluted with similar efficacy

Funnel web toxin

• 35 species at least
• South east Australia including Tasmania
• Species of proven danger to humans are limited to eastern NSW and South-East Queensland
• The only proven killer, Atrax robustus, is restricted to Sydney
• Protein toxin, Delta-hexatoxin-Ar1a is principle component

Red back toxin

• Alpha-latrotoxin is prominent

Red back vs. Funnel web

Last Updated on October 28, 2020 by Andrew Crofton